Iodanyl Radical Catalysis

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1. 1

   Maity, A.; Hyun, S.-M.; Powers, D. C. Oxidase Catalysis via Aerobically Generated Hypervalent Iodine Intermediates. Nat. Chem. 2018, 10, 200– 204,  DOI: 10.1038/nchem.2873

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   Oxidase catalysis via aerobically generated hypervalent iodine intermediates

   Maity, Asim; Hyun, Sung-Min; Powers, David C.

   Nature Chemistry (2018), 10 (2), 200-204CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)

   The development of sustainable oxidn. chem. demands strategies to harness O2 as a terminal oxidant. Oxidase catalysis, in which O2 serves as a chem. oxidant without necessitating incorporation of oxygen into reaction products, would allow diverse substrate functionalization chem. to be coupled to O2 redn. Direct O2 utilization suffers from intrinsic challenges imposed by the triplet ground state of O2 and the disparate electron inventories of four-electron O2 redn. and two-electron substrate oxidn. Here, we generate hypervalent iodine reagents-a broadly useful class of selective two-electron oxidants-from O2. This is achieved by intercepting reactive intermediates of aldehyde autoxidn. to aerobically generate hypervalent iodine reagents for a broad array of substrate oxidn. reactions. The use of aryl iodides as mediators of aerobic oxidn. underpins an oxidase catalysis platform that couples substrate oxidn. directly to O2 redn. We anticipate that aerobically generated hypervalent iodine reagents will expand the scope of aerobic oxidn. chem. in chem. synthesis.
2. 2

   Hyun, S.-M.; Yuan, M.; Maity, A.; Gutierrez, O.; Powers, D. C. The Role of Iodanyl Radicals as Critical Chain Carriers in Aerobic Hypervalent Iodine Chemistry. Chem. 2019, 5, 2388– 2404,  DOI: 10.1016/j.chempr.2019.06.006

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   The Role of Iodanyl Radicals as Critical Chain Carriers in Aerobic Hypervalent Iodine Chemistry

   Hyun, Sung-Min; Yuan, Mingbin; Maity, Asim; Gutierrez, Osvaldo; Powers, David C.

   Chem (2019), 5 (9), 2388-2404CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)

   Selective O2 utilization remains a substantial challenge in synthetic chem. Biol. small-mol. oxidn. reactions often utilize aerobically generated high-valent catalyst intermediates to effect substrate oxidn. Available synthetic methods for aerobic oxidn. catalysis are largely limited to substrate functionalization chem. by low-valent catalyst intermediates (i.e., aerobically generated Pd(II) intermediates). Motivated by the need for new chem. platforms for aerobic oxidn. catalysis, we recently developed aerobic hypervalent iodine chem. Here, we report that in contrast to the canonical two-electron oxidn. mechanisms for the oxidn. of organoiodides, the developed aerobic hypervalent iodine chem. proceeds via a radical chain mechanism initiated by the addn. of aerobically generated acetoxy radicals to aryl iodides. Despite the radical chain mechanism, aerobic hypervalent iodine chem. displays substrate tolerance similar to that obsd. with traditional terminal oxidants, such as peracids. We anticipate that these insights will enable new sustainable oxidn. chem. via hypervalent iodine intermediates.
3. 3

   Maity, A.; Frey, B. L.; Hoskinson, N. D.; Powers, D. C. Electrocatalytic C–N Coupling via Anodically Generated Hypervalent Iodine Intermediates. J. Am. Chem. Soc. 2020, 142, 4990– 4995,  DOI: 10.1021/jacs.9b13918

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   Electrocatalytic C-N Coupling via Anodically Generated Hypervalent Iodine Intermediates

   Maity, Asim; Frey, Brandon L.; Hoskinson, Nathanael D.; Powers, David C.

   Journal of the American Chemical Society (2020), 142 (11), 4990-4995CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Development of new electrosynthetic chem. promises to impact the efficiency and sustainability of org. synthesis. Anodically generated hypervalent I intermediates effectively couple interfacial electron transfer with oxidative C-H/N-H coupling chem. The developed hypervalent I electrocatalysis is applicable in both intra- and intermol. C-N bond-forming reactions. Available mechanistic data indicate that anodic oxidn. of aryl iodides generates a transient I(II) intermediate that is critically stabilized by added acetate ions. This report represents the 1st example of metal-free hypervalent I electrocatalysis for C-H functionalization and provides mechanistic insight that the authors anticipate will contribute to the development of hypervalent I mediators for synthetic electrochem.
4. 4

   Frey, B. L.; Figgins, M. T.; Van Trieste, G. P.; Carmieli, R.; Powers, D. C. Iodine–Iodine Cooperation Enables Metal-Free C–N Bond-Forming Electrocatalysis via Isolable Iodanyl Radicals. J. Am. Chem. Soc. 2022, 144, 13913– 13919,  DOI: 10.1021/jacs.2c05562

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   Iodine-Iodine Cooperation Enables Metal-Free C-N Bond-Forming Electrocatalysis via Isolable Iodanyl Radicals

   Frey, Brandon L.; Figgins, Matthew T.; Van Trieste III, Gerard P.; Carmieli, Raanan; Powers, David C.

   Journal of the American Chemical Society (2022), 144 (30), 13913-13919CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Small mol. redox mediators convey interfacial electron transfer events into bulk soln. and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here, the authors report that 1,2-diiodo-4,5-dimethoxybenzene is an efficient electrocatalyst for C-H/E-H coupling that operates at ≥0.5 mol % catalyst loading. Spectroscopic, crystallog., and computational results indicate a crit. role for a three-electron I-I bonding interaction in stabilizing an iodanyl radical intermediate (i.e., formally I(II) species). As a result, the optimized catalyst operates at >100 mV lower potential than the related monoiodide catalyst 4-iodoanisole, which results in improved product yield, higher faradaic efficiency, and expanded substrate scope. The isolated iodanyl radical is chem. competent in C-N bond formation. These results represent the 1st examples of substrate functionalization at a well-defined I(II) deriv. and bona fide iodanyl radical catalysis and demonstrate 1-electron pathways as a mechanistic alternative to canonical two-electron hypervalent I mechanisms. The observation establishes I-I redox cooperation as a new design concept for the development of metal-free redox mediators.
5. 5

   Wendlandt, A. E.; Stahl, S. S. Quinone-Catalyzed Selective Oxidation of Organic Molecules. Angew. Chem., Int. Ed. 2015, 54, 14638– 14658,  DOI: 10.1002/anie.201505017

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   Quinone-Catalyzed Selective Oxidation of Organic Molecules

   Wendlandt, Alison E.; Stahl, Shannon S.

   Angewandte Chemie, International Edition (2015), 54 (49), 14638-14658CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A review. Quinones are common stoichiometric reagents in org. chem. Para-quinones with high redn. potentials, such as DDQ and chloranil, are widely used and typically promote hydride abstraction. In recent years, many catalytic applications of these methods were achieved by using transition metals, electrochem., or O2 to regenerate the oxidized quinone in situ. Complementary studies led to the development of a different class of quinones that resemble the ortho-quinone cofactors in copper amine oxidases and mediate the efficient and selective aerobic and/or electrochem. dehydrogenation of amines. The latter reactions typically proceed by electrophilic transamination and/or addn.-elimination reaction mechanisms, rather than hydride abstraction pathways. The collective observations show that the quinone structure has a significant influence on the reaction mechanism and has important implications for the development of new quinone reagents and quinone-catalyzed transformations.
6. 6

   Basch, H.; Mogi, K.; Musaev, D. G.; Morokuma, K. Mechanism of the Methane → Methanol Conversion Reaction Catalyzed by Methane Monooxygenase: A Density Functional Study. J. Am. Chem. Soc. 1999, 121, 7249– 7256,  DOI: 10.1021/ja9906296

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   Mechanism of the Methane → Methanol Conversion Reaction Catalyzed by Methane Monooxygenase: A Density Functional Study

   Basch, Harold; Mogi, Koichi; Musaev, Djamaladdin G.; Morokuma, Keiji

   Journal of the American Chemical Society (1999), 121 (31), 7249-7256CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   The hybrid d. functional (DFT) method B3LYP was used to study the mechanism of the methane hydroxylation reaction catalyzed by a non-heme diiron enzyme, methane monooxygenase (MMO). The key reactive compd. Q of MMO was modeled by (NH2)(H2O)Fe(μ-O)2(η2-HCOO)2Fe(NH2)(H2O), I. The reaction is shown to take place via a bound-radical mechanism and an intricate change of the electronic structure of the Fe core is assocd. with the reaction process. Starting with I, which has a diamond-core structure with two FeIV atoms, L4FeIV(μ-O)2FeIVL4, the reaction with methane goes over the rate-detg. H-abstraction transition state III to reach a bound-radical intermediate IV, L4FeIV(μ-O)(μ-OH(···CH3))FeIIIL4, which has a bridged hydroxyl ligand interacting weakly with a Me radical and is in an FeIII-FeIV mixed valence state. This short-lived intermediate IV easily rearranges intramolecularly through a low barrier at transition state V for addn. of the Me radical to the hydroxyl ligand to give the methanol complex VI, L4FeIII(OHCH3)(μ-O)FeIIIL4, which has an FeIII-FeIII core. The barrier of the rate-detg. step, methane H-abstraction, was calcd. to be 19 kcal/mol. The overall CH4 oxidn. reaction to form the methanol complex, I + CH4 → VI, was found to be exothermic by 39 kcal/mol.
7. 7

   Liu, K. E.; Valentine, A. M.; Qiu, D.; Edmondson, D. E.; Appelman, E. H.; Spiro, T. G.; Lippard, S. J. Characterization of a Diiron(III) Peroxo Intermediate in the Reaction Cycle of Methane Monooxygenase Hydroxylase from Methylococcus capsulatus (Bath). J. Am. Chem. Soc. 1995, 117, 4997– 4998,  DOI: 10.1021/ja00122a032

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   Characterization of a diiron(III) peroxide intermediate in the reaction cycle of methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath)

   Liu, Katherine E.; Valentine, Ann M.; Qiu, Di; Edmondson, Dale E.; Appelman, Evan H.; Spiro, Thomas G.; Lippard, Stephen J.

   Journal of the American Chemical Society (1995), 117 (17), 4997-8CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   The spectroscopic properties of the first intermediate formed in the reaction of the reduced hydroxylase (Hred) enzyme of MMO from Methylococcus capsulatus (Bath) with dioxygen were studied by optical and resonance Raman spectroscopy. Kinetic traces measured at single wavelengths revealed a broad absorption ≈ 600-650 nm (ε625 ≈ 1500 M-1 cm-1 per Fe2 site) for this intermediate, which grows in with a rate const. of ≈ 20 s-1 under pseudo-first order conditions (excess dioxygen). Resonance Raman spectra were recorded of rapid freeze quench samples frozen 10 ms, 155 ms, and 60 s after mixing Hred with dioxygen. For the 155-ms sample, at which time the concn. of the intermediate is maximized, excitation at 647 nm revealed an isotopically sensitive spectral feature at 905 cm-1. This signal, absent in the other two samples, was assigned as the O-O stretching frequency of a diiron(III) peroxo unit present in this intermediate. Excitation at 413 nm did not enhance this feature, indicating that the absorption at 625 nm arises from peroxo-to-iron charge transfer. Upon 18O2 substitution, the 905-cm-1 band shifted by 25 cm-1 to 880 cm-1, a value less than the theor. expected shift of 52 cm-1. Upon 16O-18O substitution, the signal was obsd. at 893 cm-1. The smaller than expected shifts could arise from coupling of ν(O-O) with other modes present in the peroxo species.
8. 8

   Power, P. P. Main-Group Elements as Transition Metals. Nature 2010, 463, 171– 177,  DOI: 10.1038/nature08634

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   Main-group elements as transition metals

   Power, Philip P.

   Nature (London, United Kingdom) (2010), 463 (7278), 171-177CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)

   A review. The last quarter of the twentieth century and the beginning decade of the twenty-first witnessed spectacular discoveries in the chem. of the heavier main-group elements. The discoveries that led to this change originated from a simple desire to synthesize main-group compds. that were unknown as stable species. These featured one or more of the following: (1) multiple bonds between heavier main-group elements such as Al, Si, P or their heavier congeners; (2) stable low-valent derivs. with open coordination sites; (3) mols. with quasi-open coordination sites as a result of frustrated Lewis pairs; (4) stable paramagnetic electron configurations (that is radicals) with unpaired electrons centered on heavier main-group elements; or (5) stable singlet diradicaloid electron configurations. The new compds. that were synthesized highlighted the fundamental differences between their electronic properties and those of the lighter elements to a degree that was not previously apparent. This led to new structural and bonding insights as well as a gradually increasing realization that the chem. of the heavier main-group elements more resembles that of transition-metal complexes than that of their lighter main-group congeners. The similarity is underlined by recent work, which showed that many of the new compds. react with small mols. such as H2, NH3, C2H4 or CO under mild conditions and display potential for applications in catalysis.
9. 9

   Vogiatzis, K. D.; Polynski, M. V.; Kirkland, J. K.; Townsend, J.; Hashemi, A.; Liu, C.; Pidko, E. A. Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities. Chem. Rev. 2019, 119, 2453– 2523,  DOI: 10.1021/acs.chemrev.8b00361

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   Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities

   Vogiatzis, Konstantinos D.; Polynski, Mikhail V.; Kirkland, Justin K.; Townsend, Jacob; Hashemi, Ali; Liu, Chong; Pidko, Evgeny A.

   Chemical Reviews (Washington, DC, United States) (2019), 119 (4), 2453-2523CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

   Computational chem. provides a versatile toolbox for studying mechanistic details of catalytic reactions and holds promise to deliver practical strategies to enable the rational in silico catalyst design. The versatile reactivity and nontrivial electronic structure effects, common for systems based on 3d transition metals, introduce addnl. complexity that may represent a particular challenge to the std. computational strategies. In this review, we discuss the challenges and capabilities of modern electronic structure methods for studying the reaction mechanisms promoted by 3d transition metal mol. catalysts. Particular focus will be placed on the ways of addressing the multiconfigurational problem in electronic structure calcns. and the role of expert bias in the practical utilization of the available methods. The development of d. functionals designed to address transition metals is also discussed. Special emphasis is placed on the methods that account for solvation effects and the multicomponent nature of practical catalytic systems. This is followed by an overview of recent computational studies addressing the mechanistic complexity of catalytic processes by mol. catalysts based on 3d metals. Cases that involve noninnocent ligands, multicomponent reaction systems, metal-ligand and metal-metal cooperativity, as well as modeling complex catalytic systems such as metal-org. frameworks are presented. Conventionally, computational studies on catalytic mechanisms are heavily dependent on the chem. intuition and expert input of the researcher. Recent developments in advanced automated methods for reaction path anal. hold promise for eliminating such human-bias from computational catalysis studies. A brief overview of these approaches is presented in the final section of the review. The paper is closed with general concluding remarks.
10. 10

    Xie, W.-W.; Liu, Y.; Yuan, R.; Zhao, D.; Yu, T.-Z.; Zhang, J.; Da, C.-S. Transition Metal-Free Homocoupling of Unactivated Electron-Deficient Azaarenes. Adv. Synth. Catal. 2016, 358, 994– 1002,  DOI: 10.1002/adsc.201500445

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    Transition Metal-Free Homocoupling of Unactivated Electron-Deficient Azaarenes

    Xie, Wen-Wen; Liu, Yue; Yuan, Rui; Zhao, Dan; Yu, Tian-Zhi; Zhang, Jian; Da, Chao-Shan

    Advanced Synthesis & Catalysis (2016), 358 (6), 994-1002CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)

    This work has established the first direct homocoupling of unactivated electron-deficient azaarenes in the presence of TMPMgCl (2,2,6,6-tetramethylpiperidinylmagnesium chloride) and TMEDA (tetramethylethylenediamine). In this process, no transition metal was used while freely available air was employed as the oxidant. The investigated successful substrates included quinolines, isoquinoline, 3-phenylated pyridines, and 2-phenylated quinoxalines, giving moderate to high yields. The homocoupling of quinolines was effectively scaled up to one gram in high yield. Addnl., an iridium complex of 6,6'-dimethyl-2,2'-biquinoline was prepd. and characterized as an efficient red-emitting material.
11. 11

    Chu, T.; Boyko, Y.; Korobkov, I.; Nikonov, G. I. Transition Metal-like Oxidative Addition of C–F and C–O Bonds to an Aluminum(I) Center. Organometallics 2015, 34, 5363– 5365,  DOI: 10.1021/acs.organomet.5b00793

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    Transition Metal-like Oxidative Addition of C-F and C-O Bonds to an Aluminum(I) Center

    Chu, Terry; Boyko, Yaroslav; Korobkov, Ilia; Nikonov, Georgii I.

    Organometallics (2015), 34 (22), 5363-5365CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)

    Oxidative addn. of very robust C-F and C-O bonds was accomplished in reactions of the Al(I) compd. NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr]- and Ar = 2,6-Pri2C6H3) with fluoroarenes, fluoroalkanes, and ethers. Similar to the transition metals, the ease of aryl C-F oxidative addn. decreases as the degree of fluorination diminishes on the arom. substrate. As well, kinetic studies on the addn. of 1,2,3,4-tetrafluorobenzene to compd. 1 revealed a 2nd-order reaction characterized by a very neg. entropy of activation (ΔS⧧ = -113.6(3) J/K·mol), consistent with a transition metal-like oxidative addn. process.
12. 12

    Protchenko, A. V.; Birjkumar, K. H.; Dange, D.; Schwarz, A. D.; Vidovic, D.; Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. A Stable Two-Coordinate Acyclic Silylene. J. Am. Chem. Soc. 2012, 134, 6500– 6503,  DOI: 10.1021/ja301042u

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    A Stable Two-Coordinate Acyclic Silylene

    Protchenko, Andrey V.; Birjkumar, Krishna Hassomal; Dange, Deepak; Schwarz, Andrew D.; Vidovic, Dragoslav; Jones, Cameron; Kaltsoyannis, Nikolas; Mountford, Philip; Aldridge, Simon

    Journal of the American Chemical Society (2012), 134 (15), 6500-6503CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Simple two-coordinate acyclic silylenes, SiR2, have hitherto been identified only as transient intermediates or thermally labile species. By making use of the strong σ-donor properties and high steric loading of the B(NDippCH)2 substituent (Dipp = 2,6-iPr2C6H3), an isolable monomeric species, Si{B(NDippCH)2}{N(SiMe3)Dipp}, can be synthesized which is stable in the solid state up to 130°. This silylene species undergoes facile oxidative addn. reactions with dihydrogen (at sub-ambient temps.) and with alkyl C-H bonds, consistent with a low singlet-triplet gap (103.9 kJ mol-1), thus demonstrating fundamental modes of reactivity more characteristic of transition metal systems.
13. 13

    Lappert, M. F.; Miles, S. J.; Atwood, J. L.; Zaworotko, M. J.; Carty, A. J. Oxidative Addition of An Alcohol to the Alkylgermanium(II) Compound Ge[CH(SiMe₃)₂]₂; Molecular Structure of Ge[CH(SiMe₃)₂]₂(H)OEt. J. Organomet. Chem. 1981, 212, C4– C6,  DOI: 10.1016/S0022-328X(00)85535-7

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    Oxidative addition of an alcohol to the alkylgermanium(II) compound Ge[CH(SiMe3)2]2; molecular structure of Ge[CH(SiMe3)2]2(H)OEt

    Lappert, Michael F.; Miles, Stuart J.; Atwood, Jerry L.; Zaworotko, Michael J.; Carty, Arthur J.

    Journal of Organometallic Chemistry (1981), 212 (1), C4-C6CODEN: JORCAI; ISSN:0022-328X.

    The alkylgermanium(II) compd. GeR2 [R = CH(SiMe3)2] readily reacts with an alc. R'OH (R' = Me, Et) to yield the oxidative adduct GeR2 R'OH, one of which (R' = Et) has been characterized by single crystal x-ray diffraction as Ge(H)R2(OR').
14. 14

    Gynane, M. J.; Lappert, M. F.; Miles, S. J.; Power, P. P. Ready Oxidative Addition of an Alkyl or Aryl Halide to a Tin(II) Alkyl or Amide; Evidence for a Free-Radical Pathway. J. Chem. Soc. Chem. Commun. 1976, 256– 257,  DOI: 10.1039/c39760000256

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    Ready oxidative addition of an alkyl or aryl halide to a tin(II) alkyl or amide; evidence for a free-radical path

    Gynane, Michael J. S.; Lappert, Michael F.; Miles, Stuart J.; Power, Philip P.

    Journal of the Chemical Society, Chemical Communications (1976), (7), 256-7CODEN: JCCCAT; ISSN:0022-4936.

    Alkyl or phenyl halides RX with Sn[CH(SiMe3)2]2 (X = Cl, Br, I) or Sn[N(SiMe3)2]2 (X = Br, I) in hexane at 20° readily gave the 1:1 adduct (or 1:2 adduct for RX = CH2Br2, CH2I2) which shows 2 sets of diastereotopically distinct Me3Si groups for Sn[CH(SiMe3)2]2(X)R but not the N analog. Optical activity and ESR data suggest a radical mechanism.
15. 15

    Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Patel, D.; Smith, J. D.; Zhang, S. Oxidative Addition to a Monomeric Stannylene To Give Four-Coordinate Tin Compounds Containing the Bulky Bidentate Ligand C(SiMe₃)₂SiMe₂CH₂CH₂Me₂Si(Me₃Si)₂C. Crystal Structures of CH₂Me₂Si (Me₃Si)₂CSnC (SiMe₃)₂SiMe₂CH₂, CH₂Me₂Si(Me₃Si)₂CSnMe(OCOCF₃)C(SiMe₃)₂SiMe₂CH₂, and (CF₃COO)₂MeSnC(SiMe₃)₂SiMe₂CH₂CH₂M₂Si-(Me₃Si)₂CSnMe(OCOCF₃)₂. Organometallics 2000, 19, 49– 53,  DOI: 10.1021/om990779p

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    15

    Oxidative Addition to a Monomeric Stannylene To Give Four-Coordinate Tin Compounds Containing the Bulky Bidentate Ligand C(SiMe3)2SiMe2CH2CH2Me2Si(Me3Si)2C. Crystal Structures of [cyclic] CH2Me2Si(Me3Si)2CSnC(SiMe3)2SiMe2CH2, [cyclic] CH2Me2Si(Me3Si)2CSnMe(OCOCF3)C(SiMe3)2SiMe2CH2, and (CF3COO)2MeSnC(SiMe3)2SiMe2CH2CH2Me2Si(Me3Si)2CSnMe(OCOCF3)2

    Eaborn, Colin; Hill, Michael S.; Hitchcock, Peter B.; Patel, Deepa; Smith, J. David; Zhang, Suobo

    Organometallics (2000), 19 (1), 49-53CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)

    Reaction of (THF)2KRRK(THF)2 (RR = C(SiMe3)2SiMe2CH2CH2Me2Si(Me3Si)2C) with SnCl2 in Et2O gave a mixt. of the cyclic and linear SnII compds. [cyclic] RSnR, and ClSnRRSnCl. This mixt. was treated with MeI to give the corresponding SnIV compds. [cyclic] RSnMeIR and IClMeSnRRSnMeClI. Treatment of the later with AgO2CCF3 gave the corresponding stannadisilacycloheptane I and trifluoroacetate II, which were structurally characterized.
16. 16

    Peng, Y.; Guo, J.-D.; Ellis, B. D.; Zhu, Z.; Fettinger, J. C.; Nagase, S.; Power, P. P. Reaction of Hydrogen or Ammonia with Unsaturated Germanium or Tin Molecules Under Ambient Conditions: Oxidative Addition versus Arene Elimination. J. Am. Chem. Soc. 2009, 131, 16272– 16282,  DOI: 10.1021/ja9068408

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    Reaction of Hydrogen or Ammonia with Unsaturated Germanium or Tin Molecules under Ambient Conditions: Oxidative Addition versus Arene Elimination

    Peng, Yang; Guo, Jing-Dong; Ellis, Bobby D.; Zhu, Zhongliang; Fettinger, James C.; Nagase, Shigeru; Power, Philip P.

    Journal of the American Chemical Society (2009), 131 (44), 16272-16282CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The reactions of H or NH3 with germylenes and stannylenes were studied exptl. and theor. Treatment of the germylene GeAr#2 (Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2) with H2 or NH3 afforded the tetravalent products Ar#2GeH2 (1) or Ar#2Ge(H)NH2 (2) in high yield. The reaction of the more crowded GeAr'2 (Ar' = C6H3-2,6-(C6H3-2,6-iPr2)2) with NH3 also afforded a tetravalent amide Ar'2Ge(H)NH2 (3), whereas with H2 the tetravalent hydride Ar'GeH3 (4) was obtained with Ar'H elimination. In contrast, the reactions with the divalent Sn(II) aryls did not lead to Sn(IV) products. Instead, arene eliminated Sn(II) species were obtained. SnAr#2 reacted with NH3 to give the Sn(II) amide {Ar#Sn(μ-NH2)}2 (5) and Ar#H elimination, whereas no reaction with H2 could be obsd. up to 70°. The more crowded SnAr'2 reacted readily with H2, D2, or NH3 to give {Ar'Sn(μ-H)}2 (6), {Ar'Sn(μ-D)}2 (7), or {Ar'Sn(μ-NH2)}2 (8) all with arene elimination. The compds. were characterized by 1H, 13C, and 119Sn NMR spectroscopy and by x-ray crystallog. DFT calcns. revealed that the reactions of H2 with EAr2 (E = Ge or Sn; Ar = Ar# or Ar') initially proceed via interaction of the σ orbital of H2 with the 4p(Ge) or 5p(Sn) orbital, with back-donation from the Ge or Sn lone pair to the H2 σ* orbital. The subsequent reaction proceeds by either an oxidative addn. or a concerted pathway. The exptl. and computational results showed that bond strength differences between Ge and Sn, as well as greater nonbonded electron pair stabilization for Sn, are more important than steric factors in detg. the product obtained. In the reactions of NH3 with EAr2 (E = Ge or Sn; Ar = Ar# or Ar'), the divalent ArENH2 products are the most stable for both Ge and Sn. However the tetravalent amido species Ar2Ge(H)NH2 were obtained for kinetic reasons. The reactions with NH3 proceed by a different pathway from the hydrogenation process and involve two NH3 mols. in which the lone pair of one NH3 becomes assocd. with the empty 4p(Ge) or 5p(Sn) orbital while a 2nd NH3 solvates the complexed NH3 via intermol. N-H···N interactions.
17. 17

    Protchenko, A. V.; Bates, J. I.; Saleh, L. M.; Blake, M. P.; Schwarz, A. D.; Kolychev, E. L.; Thompson, A. L.; Jones, C.; Mountford, P.; Aldridge, S. Enabling and Probing Oxidative Addition and Reductive Elimination at a Group 14 Metal Center: Cleavage and Functionalization of E–H Bonds by a Bis(boryl)stannylene. J. Am. Chem. Soc. 2016, 138, 4555– 4564,  DOI: 10.1021/jacs.6b00710

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    Enabling and Probing Oxidative Addition and Reductive Elimination at a Group 14 Metal Center: Cleavage and Functionalization of E-H Bonds by a Bis(boryl)stannylene

    Protchenko, Andrey V.; Bates, Joshua I.; Saleh, Liban M. A.; Blake, Matthew P.; Schwarz, Andrew D.; Kolychev, Eugene L.; Thompson, Amber L.; Jones, Cameron; Mountford, Philip; Aldridge, Simon

    Journal of the American Chemical Society (2016), 138 (13), 4555-4564CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    By employing strongly σ-donating boryl ancillary ligands, the oxidative addn. of H2 to a single site SnII system was achieved for the first time, generating (boryl)2SnH2. Similar chem. can also be achieved for protic and hydridic E-H bonds (N-H/O-H, Si-H/B-H, resp.). In the case of NH3 (and H2O, albeit more slowly), E-H oxidative addn. can be shown to be followed by reductive elimination to give an N- (or O-)borylated product. Thus, in stoichiometric fashion, redox-based bond cleavage/formation is demonstrated for a single main group metal center at room temp. From a mechanistic viewpoint, a two-step coordination/proton transfer process for N-H activation is viable through the isolation of species Sn(boryl)2·NH3 and [Sn(boryl)2(NH2)]- and their onward conversion to the formal oxidative addn. product Sn(boryl)2(H)(NH2).
18. 18

    Oae, S. Ligand Coupling Reactions Through Hypervalent and Similar Valence-Shell Expanded Intermediates. Croat. Chem. Acta 1986, 59, 129– 151

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    Ligand coupling reactions through hypervalent and similar valence-shell expanded intermediates

    Oae, Shigeru

    Croatica Chemica Acta (1986), 59 (1), 129-51CODEN: CCACAA; ISSN:0011-1643.

    A review with 68 refs. Ligand coupling reactions through hypervalent and valent-shell expanded intermediates were discussed. Included were ligand coupling reactions on tricoordinated S, on P and I compds., and ligand coupling reactions on transition metal atoms.
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    Oae, S. Ligand Coupling Rreactions of Hypervalent Species. Pure Appl. Chem. 1996, 68, 805– 812,  DOI: 10.1351/pac199668040805

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    Ligand coupling reactions of hypervalent species

    Oae, Shigeru

    Pure and Applied Chemistry (1996), 68 (4), 805-812CODEN: PACHAS; ISSN:0033-4545. (Blackwell)

    The concept of ligand coupling is explained and the actual examples of many important reactions in which not only sulfur and phosporus centered hypervalent species, but iodine, silicon and copper centered hypervalent ones are presented. Many other reactions in which the central metal atoms in the nickel triad elements are considered to behave as the catalytic site for ligand coupling reaction, such as the Waeker process and the Heck reaction. A review with 70 refs.
20. 20

    Sagae, T.; Ogawa, S.; Furukawa, N. Stereochemical Proof for Front Side Deuteride Attack via σ-Sulfurane in the Reductive Desulfinylation of Sulfoxides with Lithium Aluminum Deuteride. Tetrahedron Lett. 1993, 34, 4043– 4046,  DOI: 10.1016/S0040-4039(00)60611-1

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    Stereochemical proof for front side deuteride attack via σ-sulfurane in the reductive desulfinylation of sulfoxides with lithium aluminum deuteride

    Sagae, Takahiro; Ogawa, Satoshi; Furukawa, Naomichi

    Tetrahedron Letters (1993), 34 (25), 4043-6CODEN: TELEAY; ISSN:0040-4039.

    Stereochem. results obtained from the concomitant redn. and desulfinylation of 1-phenyl-2-pyridyl-2-(p-tolylsulfinyl)- and 1,2-diphenyl-2-phenylsulfinylethanols with lithium aluminum deuteride reveal that the reactions proceed stereospecifically via σ-sulfurane as a common intermediate.
21. 21

    Crivello, J. V. Redox Initiated Cationic Polymerization: Reduction of Diaryliodonium Salts by 9-BBN. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 5639– 5651,  DOI: 10.1002/pola.23605

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    Redox initiated cationic polymerization: Reduction of diaryliodonium salts by 9-BBN

    Crivello, James V.

    Journal of Polymer Science, Part A: Polymer Chemistry (2009), 47 (21), 5639-5651CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)

    Diaryliodonium salts undergo facile redn. by the dialkylborane, 9-BBN. The combination of these two reagents constitutes a redox couple that can be employed as a convenient and versatile initiator system for the cationic polymns. of styrenic monomers, vinyl ethers and the ring-opening polymns. of cyclic ethers and acetals including; epoxides, oxetanes, THF, and 1,3,5-trioxane. The polymns. of these monomers can be carried out in either neat monomer or under soln. conditions. Typically, the redox cationic polymns. of the above monomers are rapid and exothermic. Optical pyrometry (IR thermog.) was employed as a convenient method with which to monitor and optimize the aforementioned redox initiated cationic polymns. Studies of the effects of variations in the structure and concns. of the diaryliodonium salt and 9-BBN on the polymns. of various monomers were carried out. A mechanism for the redox cationic initiation of the polymns. was proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5639-5651, 2009.
22. 22

    Barton, D. H.; Finet, J.-P. Bismuth(V) reagents in organic synthesis. Pure Appl. Chem. 1987, 59, 937– 946,  DOI: 10.1351/pac198759080937

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    Bismuth(V) reagents in organic synthesis

    Barton, Derek H. R.; Finet, Jean Pierre

    Pure and Applied Chemistry (1987), 59 (8), 937-46CODEN: PACHAS; ISSN:0033-4545.

    A review with 30 ref., mainly of the authors' work, on the efficiency of bismuth(V) reagents in carrying out arylations at oxygen, carbon, and nitrogen.
23. 23

    Bothwell, J. M.; Krabbe, S. W.; Mohan, R. S. Applications of Bismuth(III) Compounds in Organic Synthesis. Chem. Soc. Rev. 2011, 40, 4649– 4707,  DOI: 10.1039/c0cs00206b

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    Applications of bismuth(III) compounds in organic synthesis

    Bothwell, Jason M.; Krabbe, Scott W.; Mohan, Ram S.

    Chemical Society Reviews (2011), 40 (9), 4649-4707CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)

    A review. This review article summarized the applications of bismuth(III) compds. in org. synthesis since 2002. Although there are an increasing no. of reports on applications of bismuth(III) salts in polymn. reactions, and their importance is acknowledged, they are not included in this review. This review was largely organized by the reaction type although some reactions can clearly be placed in multiple sections. While every effort was made to include all relevant reports in this field, any omission is inadvertent and the authors apologize in advance for the same (358 refs.).
24. 24

    Xu, S.; He, Z. Recent Advances in Stoichiometric Phosphine-Mediated Organic Synthetic Reactions. RSC Adv. 2013, 3, 16885– 16904,  DOI: 10.1039/c3ra42088d

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    Recent advances in stoichiometric phosphine-mediated organic synthetic reactions

    Xu, Silong; He, Zhengjie

    RSC Advances (2013), 3 (38), 16885-16904CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)

    A review. Org. synthetic reactions mediated by tertiary phosphines have attracted much attention in the org. chem. community in the past two decades. These reactions can be divided into two categories: phosphine-catalyzed and stoichiometric phosphine-mediated transformations. While the phosphine-catalyzed reactions mechanistically rely on the unique properties of tertiary phosphines such as excellent nucleophilicity and good leaving group ability, the stoichiometric transformations are usually driven by nucleophilicity and strong oxyphilicity of tertiary phosphines. Since tertiary phosphines represent an important class of versatile chem. reagents in org. synthesis, stoichiometric phosphine-mediated reactions have recently demonstrated their uniqueness and high efficiency in org. synthesis, particularly with respect to the construction of carbon-carbon and carbon-heteroatom bonds, and therefore have stimulated much research interest. In this review, recent advances in stoichiometric phosphine-mediated reactions primarily including olefinations and annulations are summarized.
25. 25

    Moon, H. W.; Cornella, J. Bismuth Redox Catalysis: An Emerging Main-Group Platform for Organic Synthesis. ACS Catal. 2022, 12, 1382– 1393,  DOI: 10.1021/acscatal.1c04897

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    Bismuth Redox Catalysis: an Emerging Main-group Platform for Organic Synthesis

    Moon, Hye Won; Cornella, Josep

    ACS Catalysis (2022), 12 (2), 1382-1393CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    A review. Bismuth has recently been shown to be able to maneuver between different oxidn. states, enabling access to unique redox cycles that can be harnessed in the context of org. synthesis. Indeed, various catalytic Bi redox platforms have been discovered and revealed emerging opportunities in the field of main group redox catalysis. The goal of this perspective is to provide an overview of the synthetic methodologies that have been developed to date, which capitalize on the Bi redox cycling. Recent catalytic methods via low-valent Bi(II)/Bi(III), Bi(I)/Bi(III), and high-valent Bi(III)/Bi(V) redox couples are covered as well as their underlying mechanisms and key intermediates. In addn., different design strategies stabilizing low-valent and high-valent bismuth species has been illustrated and also highlighted the characteristic reactivity of bismuth complexes compared to the lighter p-block and d-block elements. Thr opportunities and future directions in this emerging field of catalysis is discussed. This perspective will provide synthetic chemists with guiding principles for the future development of catalytic transformations employing bismuth.
26. 26

    Xie, C.; Smaligo, A. J.; Song, X.-R.; Kwon, O. Phosphorus-Based Catalysis. ACS Cent. Sci. 2021, 7, 536– 558,  DOI: 10.1021/acscentsci.0c01493

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    Phosphorus-Based Catalysis

    Xie, Changmin; Smaligo, Andrew J.; Song, Xian-Rong; Kwon, Ohyun

    ACS Central Science (2021), 7 (4), 536-558CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)

    Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compd.-mediated single electron transfer processes. We briefly summarize five addnl. topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.
27. 27

    Yoshimura, A.; Yusubov, M. S.; Zhdankin, V. V. Synthetic Applications of Pseudocyclic Hypervalent iodine compounds. Org. Biomol. Chem. 2016, 14, 4771– 4781,  DOI: 10.1039/C6OB00773B

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    Synthetic applications of pseudocyclic hypervalent iodine compounds

    Yoshimura, Akira; Yusubov, Mekhman S.; Zhdankin, Viktor V.

    Organic & Biomolecular Chemistry (2016), 14 (21), 4771-4781CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)

    A review. In the present review, the prepn. and structural features of pseudocyclic iodine(III) and iodine(V) derivs. are discussed, and recent developments in their synthetic applications are summarized.
28. 28

    Yusubov, M. S.; Yoshimura, A.; Zhdankin, V. V. Iodonium Ylides in Organic Syntthesis. Arkivoc 2017, 2016, 342– 374,  DOI: 10.3998/ark.5550190.p009.732

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    Zhdankin, V. V. Hypervalent Iodine Chemistry: Preparation, Structure and Synthetic Applications of Polyvalent Iodine Compounds; John Wiley and Sons Ltd.: New York, 2014.

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    Zhdankin, V. V. Organoiodine(V) Reagents in Organic Synthesis. J. Org. Chem. 2011, 76, 1185– 1197,  DOI: 10.1021/jo1024738

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    Organoiodine(V) reagents in organic synthesis

    Zhdankin, Viktor V.

    Journal of Organic Chemistry (2011), 76 (5), 1185-1197CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)

    A review. Organohypervalent iodine reagents have attracted significant recent interest as versatile and environmentally benign oxidants with numerous applications in org. synthesis. This Perspective summarizes synthetic applications of hypervalent iodine(V) reagents: 2-iodoxybenzoic acid (IBX), Dess-Martin periodinane (DMP), pseudocyclic iodylarenes, and their recyclable polymer-supported analogs. Recent advances in the development of new catalytic systems based on the generation of hypervalent iodine species in situ are also overviewed.
31. 31

    Yoshimura, A.; Zhdankin, V. V. Advances in Synthetic Applications of Hypervalent Iodine Compounds. Chem. Rev. 2016, 116, 3328– 3435,  DOI: 10.1021/acs.chemrev.5b00547

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    Advances in Synthetic Applications of Hypervalent Iodine Compounds

    Yoshimura, Akira; Zhdankin, Viktor V.

    Chemical Reviews (Washington, DC, United States) (2016), 116 (5), 3328-3435CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. The prepn., structure, and chem. of hypervalent iodine compds. are reviewed with emphasis on their synthetic application. Compds. of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compds. are widely used in org. synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidns., rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compds. represent a particularly important achievement in the field of hypervalent iodine chem. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compds. as an environmentally sustainable alternative to heavy metals.
32. 32

    Hach, R. J.; Rundle, R. E. The Structure of Tetramethylammonium Pentaiodide. J. Am. Chem. Soc. 1951, 73, 4321– 4324,  DOI: 10.1021/ja01153a086

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    The structure of tetramethylammonium pentaiodide

    Hach, Ralph J.; Rundle, R. E.

    Journal of the American Chemical Society (1951), 73 (), 4321-4CODEN: JACSAT; ISSN:0002-7863.

    Me4NI5 is end-centered monoclinic with a0 = 13.34, b0 = 13.59, c0 = 8.90 A., β = 107°50', ρcalcd. = 3.06, Ζ = 4. The structure, based on space group C2/c, consists of nearly square iodine nets within which V-shaped I5- ions can be distinguished. I-I distances within the ion are 2.93 A. and 3.14 A., compared to 2.67 A. for the distance in I2. Other I-I distances within one net are 3.55 A. or greater, while the nets are 4.3 A. apart. The structure of the I5- ion bears no relation to the square ICl4- ion, where the I-Cl distance is close to the sum of the covalent radii. It is suggested that I- does not tend to use its d-orbitals above the valence shell for covalent bonds with I and the complex ions result from the interaction of I- with polarizable I2 mols. Resonating structures result in enough covalent character of the I-I bond to weaken the I-I bond. The relation between polyhalide ions and "polyiodine" polymer complexes is discussed briefly.
33. 33

    Pimentel, G. C. The Bonding of Trihalide and Bifluoride Ions by the Molecular Orbital Method. J. Chem. Phys. 1951, 19, 446– 448,  DOI: 10.1063/1.1748245

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    The bonding of trihalide and bifluoride ions by the molecular-orbital method

    Pimentel, George C.

    Journal of Chemical Physics (1951), 19 (), 446-8CODEN: JCPSA6; ISSN:0021-9606.

    A simple mol. orbital treatment is presented to explain the bonding in trihalide ions, X3-, XY2-, and XYZ-, and bifluoride ion. HF2-. The mol. orbitals are formed from linear combinations of ηρσ halogen orbitals, and the 1s H orbital and stable bonding mol. orbitals are obtained without the introduction of higher at. orbitals. Applications are suggested in prediction of other stable species and low-energy reaction intermediates.
34. 34

    Cardenal, A. D.; Maity, A.; Gao, W.-Y.; Ashirov, R.; Hyun, S.-M.; Powers, D. C. Iodosylbenzene Coordination Chemistry Relevant to Metal–Organic Framework Catalysis. Inorg. Chem. 2019, 58, 10543– 10553,  DOI: 10.1021/acs.inorgchem.9b01191

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    Iodosylbenzene Coordination Chemistry Relevant to Metal-Organic Framework Catalysis

    Cardenal, Ashley D.; Maity, Asim; Gao, Wen-Yang; Ashirov, Rahym; Hyun, Sung-Min; Powers, David C.

    Inorganic Chemistry (2019), 58 (16), 10543-10553CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)

    Hypervalent iodine compds. formally feature expanded valence shells at iodine. These reagents are broadly used in synthetic chem. due to the ability to participate in well-defined oxidn.-redn. processes and because the ligand-exchange chem. intrinsic to the hypervalent center allows hypervalent iodine compds. to be applied to a broad array of oxidative substrate functionalization reactions. The authors recently developed methods to generate these compds. from O2 that are predicated on diverting reactive intermediates of aldehyde autoxidn. toward the oxidn. of aryl iodides. Coupling the aerobic oxidn. of aryl iodides with catalysts that effect C-H bond oxidn. would provide a strategy to achieve aerobic C-H oxidn. chem. In this Forum Article, the aspects of hypervalent iodine chem. and bonding that render this class of reagents attractive lynchpins for aerobic oxidn. chem. are discussed. The authors then discuss the oxidn. processes relevant to the aerobic prepn. of 2-(tert-butylsulfonyl)iodosylbenzene, which is a popular hypervalent iodine reagent for use with porous metal-org. framework (MOF)-based catalysts because it displays significantly enhanced soly. as compared with unsubstituted iodosylbenzene. Popular synthetic methods to this reagent often provide material that displays unpredictable disproportionation behavior due to the presence of trace impurities. The authors provide a revised synthetic route that avoids impurities common in the reported methods and provides access to material that displays predictable stability. Finally, the authors describe the coordination chem. of hypervalent iodine compds. with metal clusters relevant to MOF chem. and discuss the potential implications of this coordination chem. to catalysis in MOF scaffolds.
35. 35

    Ochiai, M.; Takeuchi, Y.; Katayama, T.; Sueda, T.; Miyamoto, K. Iodobenzene-Catalyzed α-Acetoxylation of Ketones. In Situ Generation of Hypervalent (Diacyloxyiodo)benzenes Using m-Chloroperbenzoic Acid. J. Am. Chem. Soc. 2005, 127, 12244– 12245,  DOI: 10.1021/ja0542800

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    Iodobenzene-Catalyzed α-Acetoxylation of Ketones. In Situ Generation of Hypervalent (Diacyloxyiodo)benzenes Using m-Chloroperbenzoic Acid

    Ochiai, Masahito; Takeuchi, Yasunori; Katayama, Tomoko; Sueda, Takuya; Miyamoto, Kazunori

    Journal of the American Chemical Society (2005), 127 (35), 12244-12245CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The iodobenzene-catalyzed α-oxidn. of ketones, in which diacyloxy(phenyl)-λ3-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid serves as a terminal oxidant, is reported. Oxidn. of a ketone with m-chloroperbenzoic acid in acetic acid in the presence of a catalytic amt. of iodobenzene, BF3·Et2O, and water at room temp. under argon affords an α-acetoxy ketone in good yield. P-Methyl- and p-chloroiodobenzene also serve as efficient catalysts in this direct oxidn. When the reaction was carried out in the absence of a catalytic amt. of iodobenzene, Baeyer-Villiger oxidn. of the ketone took place. It is noted that use of water and BF3·Et2O is crucial to the success of this α-acetoxylation.
36. 36

    Frey, B.; Maity, A.; Tan, H.; Roychowdhury, P.; Powers, D. C. Sustainable Methods in Hypervalent Iodine Chemistry. In Iodine Catalysis in Organic Synthesis; Wiley, 2022; pp 335– 386.

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    Wang, X.; Studer, A. Iodine(III) Reagents in Radical Chemistry. Acc. Chem. Res. 2017, 50, 1712– 1724,  DOI: 10.1021/acs.accounts.7b00148

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    Iodine(III) Reagents in Radical Chemistry

    Wang, Xi; Studer, Armido

    Accounts of Chemical Research (2017), 50 (7), 1712-1724CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)

    A review. The chem. of hypervalent iodine(III) compds. has gained great interest over the past 30 years. Hypervalent iodine(III) compds. show valuable ionic reactivity due to their high electrophilicity but also express radical reactivity as single electron oxidants for carbon and heteroatom radical generation. Looking at ionic chem., these iodine(III) reagents can act as electrophiles to efficiently construct C-CF3, X-CF3 (X = heteroatom), C-Rf (Rf = perfluoroalkyl), X-Rf, C-N3, C-CN, S-CN, and C-X bonds. In some cases, a Lewis or a Bronsted acid is necessary to increase their electrophilicity. In these transformations, the iodine(III) compds. react as formal "CF3+", "Rf+", "N3+", "Ar+", "CN+", and "X+" equiv. On the other hand, one electron redn. of the I(III) reagents opens the door to the radical world, which is the topic of this Account that focuses on radical reactivity of hypervalent iodine(III) compds. such as the Togni reagent, Zhdankin reagent, diaryliodonium salts, aryliodonium ylides, aryl(cyano)iodonium triflates, and aryl(perfluoroalkyl)iodonium triflates. Radical generation starting with I(III) reagents can also occur via thermal or light mediated homolysis of the weak hypervalent bond in such reagents. This reactivity can be used for alkane C-H functionalization. We will address important pioneering work in the area but will mainly focus on studies that have been conducted by our group over the last 5 years. We entered the field by investigating transition metal free single electron redn. of Togni type reagents using the readily available sodium 2,2,6,6-tetramethylpiperidine-1-oxyl salt (TEMPONa) as an org. one electron reductant for clean generation of the trifluoromethyl radical and perfluoroalkyl radicals. That valuable approach was later successfully also applied to the generation of azidyl and aryl radicals starting with the corresponding benziodoxole (Zhdankin reagent) and iodonium salts. In the presence of alkenes as radical acceptors, vicinal trifluoromethyl-, azido-, and arylaminoxylation products result via a sequence comprising radical addn. to the alkene and subsequent TEMPO trapping. Electron-rich arenes also react with I(III) reagents via single electron transfer (SET) to give arene radical cations, which can then engage in arylation reactions. We also recognized that the isonitrile functionality in aryl isonitriles is a highly efficient perfluoroalkyl radical acceptor, and reaction of Rf-benziodoxoles (Togni type reagents) in the presence of a radical initiator provides various perfluoroalkylated N-heterocycles (indoles, phenanthridines, quinolines, etc.). We further found that aryliodonium ylides, previously used as carbene precursors in metal-mediated cyclopropanation reactions, react via SET redn. with TEMPONa to the corresponding aryl radicals. As a drawback of all these transformations, we realized that only one ligand of the iodine(III) reagent gets transferred to the substrate. To further increase atom-economy of such conversions, we identified cyano or perfluoroalkyl iodonium triflate salts as valuable reagents for stereoselective vicinal alkyne difunctionalization, where two ligands from the I(III) reagent are sequentially transferred to an alkyne acceptor. Finally, we will discuss alkynyl-benziodoxoles as radical acceptors for alkynylation reactions. Similar reactivity was found for the Zhdankin reagent that has been successfully applied to azidation of C-radicals, and also cyanation is possible with a cyano I(III) reagent. To summarize, this Account focuses on the design, development, mechanistic understanding, and synthetic application of hypervalent iodine(III) reagents in radical chem.
38. 38

    Borden, W. T.; Hoffmann, R.; Stuyver, T.; Chen, B. Dioxygen: What Makes this Triplet Diradical Kinetically Persistent?. J. Am. Chem. Soc. 2017, 139, 9010– 9018,  DOI: 10.1021/jacs.7b04232

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    Dioxygen: What Makes This Triplet Diradical Kinetically Persistent?

    Borden, Weston Thatcher; Hoffmann, Roald; Stuyver, Thijs; Chen, Bo

    Journal of the American Chemical Society (2017), 139 (26), 9010-9018CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Exptl. heats of formation and enthalpies obtained from G4 calcns. both find that the resonance stabilization of the two unpaired electrons in triplet O2, relative to the unpaired electrons in two hydroxyl radicals, amts. to 100 kcal/mol. The origin of this huge stabilization energy is described within the contexts of both MO and valence-bond (VB) theory. Although O2 is a triplet diradical, the thermodn. unfavorability of both its hydrogen atom abstraction and oligomerization reactions can be attributed to its very large resonance stabilization energy. The unreactivity of O2 toward both these modes of self-destruction maintains its abundance in the ecosphere and thus its availability to support aerobic life. However, despite the resonance stabilization of the π system of triplet O2, the weakness of the O-O σ bond makes reactions of O2, which eventually lead to cleavage of this bond, very favorable thermodynamically.
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    Bawn, C. E. H.; Jolley, J. E. The Cobalt-Salt-Catalyzed Autoxidation of Benzaldehyde. Proc. R. Soc. London Ser. A 1956, 237, 297– 312,  DOI: 10.1098/rspa.1956.0178

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    The cobalt-salt-catalyzed autoxidation of benzaldehyde

    Bawn, C. E. H.; Jolley, J. E.

    Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1956), 237 (), 297-312CODEN: PRLAAZ; ISSN:1364-5021.

    The autoxidation of benzaldehyde in glacial AcOH catalyzed by Co salts was studied by kinetic and analytical methods. In the initial phase O reacts quantitatively with aldehyde to form perbenzoic acid, but as the reaction proceeds, the peracid concn. falls. The initiating reaction is the interaction of the cobaltic ion with the aldehyde. The over-all rate of oxidation can be fully explained by the following kinetic scheme: PhCO. + O2 → PhCOOO.; PhCOOO. + PhCHO → PhCOOOH + PhCO. (propagation). 2C6H5 COOO → inert products (termination). Oxidation was inhibited by hydroquinone, diphenylamine, and 2-naphthol and retarded by benzoquinone.
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    Bilgrien, C.; Davis, S.; Drago, R. S. The Selective Oxidation of Primary Alcohols to Aldehydes by O₂ Employing a Trinuclear Ruthenium Carboxylate Catalyst. J. Am. Chem. Soc. 1987, 109, 3786– 3787,  DOI: 10.1021/ja00246a049

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    The selective oxidation of primary alcohols to aldehydes by oxygen employing a trinuclear ruthenium carboxylate catalyst

    Bilgrien, Carl; Davis, Shannon; Drago, Russell S.

    Journal of the American Chemical Society (1987), 109 (12), 3786-7CODEN: JACSAT; ISSN:0002-7863.

    Primary and secondary alcs. were oxidized by O to carbonyl compds. in the presence of Ru3O(O2CR)6 L3 and Ru3O(O2CR)6L3+ (R = Me, Et; L = H2O, PPh2) catalysts. The mechanism of the oxidn. is discussed, although the active catalyst species could not be identified.
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    Mukaiyama, T.; Yamada, T. Recent Advances in Aerobic Oxygenation. Bull. Chem. Soc. Jpn. 1995, 68, 17– 35,  DOI: 10.1246/bcsj.68.17

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    Recent advances in aerobic oxygenation

    Mukaiyama, Teruaki; Yamada, Tohru

    Bulletin of the Chemical Society of Japan (1995), 68 (1), 17-35CODEN: BCSJA8; ISSN:0009-2673. (Nippon Kagakkai)

    A review with 138 refs. Recent advances in the aerobic oxygenations of olefins, using transition-metal complex catalysts, are reviewed. The main topics focused on are the cobalt(II)-complex-catalyzed oxygenation of olefins, nickel(II)-complex-catalyzed aerobic epoxidn., enantioselective, aerobic epoxidn. using chiral manganese(III) complex catalysts, aerobic Baeyer-Villiger oxidn. and direct oxygenation of arom. compds.
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    Yamada, T.; Takai, T.; Rhode, O.; Mukaiyama, T. Highly Efficient Method for Epoxidation of Olefms with Molecular Oxygen and Aldehydes Catalyzed by Nickel(II) Complexes. Chem. Lett. 1991, 20, 1– 4,  DOI: 10.1246/cl.1991.1

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43. 43

    Das, P.; Saha, D.; Saha, D.; Guin, J. Aerobic Direct C(sp²)–H Hydroxylation of 2-Arylpyridines by Palladium Catalysis Induced with Aldehyde Auto-oxidation. ACS Catal. 2016, 6, 6050– 6054,  DOI: 10.1021/acscatal.6b01539

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    Aerobic Direct C(sp2)-H Hydroxylation of 2-Arylpyridines by Palladium Catalysis Induced with Aldehyde Auto-Oxidation

    Das, Prasenjit; Saha, Debajyoti; Saha, Dibyajyoti; Guin, Joyram

    ACS Catalysis (2016), 6 (9), 6050-6054CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    Herein we present a Pd-catalyzed direct C-H hydroxylation of 2-arylpyridines using mol. oxygen (O2) as the sole oxidant. The key aspects of the method include: (a) the activation of mol. oxygen with a nontoxic and inexpensive aldehyde; (b) an efficient assocn. of the in situ-generated acyl peroxo radical with palladium catalysis; and (c) convenient operating conditions. On the basis of the results obtained in a series of control expts., a PdII/PdIV catalytic cycle is implicated for the transformations. Furthermore, the method offers an easy access to a broad range of substituted 2-(pyridin-2-yl)phenols in good isolated yields.
44. 44

    Weinstein, A. B.; Stahl, S. S. Palladium Catalyzed Aryl C–H Amination with O₂ via in situ Formation of Peroxide-Based Oxidant(s) from Dioxane. Catalysis Sci. Technol. 2014, 4, 4301– 4307,  DOI: 10.1039/C4CY00764F

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    Palladium catalyzed aryl C-H amination with O2 via in situ formation of peroxide-based oxidant(s) from dioxane

    Weinstein, Adam B.; Stahl, Shannon S.

    Catalysis Science & Technology (2014), 4 (12), 4301-4307CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)

    (DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramol. aryl C-H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decompn. product of dioxane. An induction period obsd. for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidn. of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for palladium-catalyzed aerobic oxidn. reactions conducted in ethereal solvents.
45. 45

    Jorissen, W.; Dekking, A. On the Induced Oxidation of Iodobenzene During the Oxidation of Acetaldehyde in an Atmosphere of Oxygen. Recl. Trav. Chim. Pays-Bas 1938, 57, 1125– 1126,  DOI: 10.1002/recl.19380571010

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    The induced oxidation of iodobenzene during the oxidation of acetaldehyde in an atmosphere of oxygen

    Jorissen, W. P.; Dekking, A. C. B.

    Recueil des Travaux Chimiques des Pays-Bas et de la Belgique (1938), 57 (), 1125-6CODEN: RTCPB4; ISSN:0370-7539.

    A soln. of iodobenzene in acetaldehyde exposed for several weeks to O2 gave crystals of iodoxybenzene.
46. 46

    Jain, S. L.; Sain, B. An Unconventional Cobalt-Catalyzed Aerobic Oxidation of Tertiary Nitrogen Compounds to N-Oxides. Angew. Chem., Int. Ed. 2003, 42, 1265– 1267,  DOI: 10.1002/anie.200390324

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    An unconventional cobalt-catalyzed aerobic oxidation of tertiary nitrogen compounds to N-oxides

    Jain, Suman L.; Sain, Bir

    Angewandte Chemie, International Edition (2003), 42 (11), 1265-1267CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Tertiary nitrogen compds., e.g., pyridine, Et2NPh, were oxidized to the N-oxides in nearly quant. yields by bubbling mol. oxygen into a soln. of the N compd. in the presence of mol. sieves and cobalt Schiff base complex I as catalyst.
47. 47

    Maity, A.; Powers, D. C. Hypervalent Iodine Chemistry as a Platform for Aerobic Oxidation Catalysis. Synlett 2019, 30, 257– 262,  DOI: 10.1055/s-0037-1610338

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    Hypervalent Iodine Chemistry as a Platform for Aerobic Oxidation Catalysis

    Maity, Asim; Powers, David C.

    Synlett (2019), 30 (3), 257-262CODEN: SYNLES; ISSN:0936-5214. (Georg Thieme Verlag)

    A review. Here, we highlight the recent development of aerobic oxidn. catalysis via hypervalent I(III) and I(V) intermediates. The described chem. intercepts reactive intermediates generated during aldehyde autoxidn. to accomplish the oxidn. of aryl iodides. The aerobically generated hypervalent iodine intermediates are utilized to couple an array of substrate functionalization chem. to the redn. of O 2. 1. Introduction 2. Chem. of Aerobically Generated I(III) Intermediates 3. Chem. of Aerobically Generated I(V) Intermediates 4. Conclusions.
48. 48

    Buckler, S. A. Autoxidation of Trialkylphosphines. J. Am. Chem. Soc. 1962, 84, 3093– 3097,  DOI: 10.1021/ja00875a011

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    Autoxidation of trialkylphosphines

    Buckler, Sheldon A.

    Journal of the American Chemical Society (1962), 84 (), 3093-7CODEN: JACSAT; ISSN:0002-7863.

    The major products formed in the autoxidn. of trialkylphosphines were the corresponding phosphine oxides and phosphinate esters: phosphonates and phosphates were formed in lesser amts. Air (100 ml./min.) was passed through 12.4 g. (C4H9)3P (I) in 135 ml. hexane 2.5 hrs. at 26°; the products were 42% (CH9)3PO, 49% (CH9)2PO2C4H9 (II), 6% C4H9P(O)(OC4H9)2, and 3% OP-(OC4H9)3, which were sepd. by gas chromatography: with Me2CO as solvent the relative amts. of the products were not greatly changed. Autoxidn. of 5.6 g. tricyclohexylphosphine (III) in 135 ml. hexane with air (100 ml./min. 2.5 hrs.) at 26° gave 50% tricyclohexylphosphine oxide, 40% cyclohexyl dicyclohexylphosphinate (IV), and 10% mixt. of dicyclohexyl cyclohexylphosphonate (V) and phosphate esters. The major products in the oxidns. were sepd. by distn., fractional crystn., or chromatography. In other oxidns., when the original exothermic reaction had subsided, the air or O flow was continued until a spot test made by addn. of 1 drop soln. to I ml. CS2 gave no red color. Ph3PO (5.9 g.) was obtained from 10.5 g. Ph3P and 0.13 g. 2,2'-azobis(2-methylpropionitrile) in 95 ml. C6H6 which was blown 3 hrs. with O at 78°. The rate of autoxidn. of I in hexane by air was fast at room temp. and independent of I concn. up to 98% completion; the time required for reaction with pure O was about 1/5 that with air. The total amt. of O consumed agreed with that required by the observed products. An induction period was noted at -20° but not at 26°. Changes in flow rate, O concn. in the gas stream, initial I concn., and temp. (-20 to 80°) did not have a significant bearing on the relative amts. of major products. The amt. of (C4H9)3PO increased steadily as the solvent became more polar. I reacted very slowly with O in C6H6, PhMe, or PhCl below 60°; at 60° a spontaneous reaction took place, giving normal products. In tert-BuPh a moderate reaction took place at room temp. The presence of 2 molar equivs. of C6H6 in CoH14 did not inhibit the autoxidn. (C4H9)3PO was one of the major products of I oxidn. in EtOH and in aq. EtOH. Et dibutylphosphinate (VI) was formed in a large excess of dry EtOH almost to the exclusion of the Bu ester. That VI was not formed at the expense of H was shown by oxidn. of a mixt. of II and I in abs. EtOH; the amt. of II present after oxidn. was equal to that added initially. When I was oxidized in the presence of a modest excess of dry EtOH, both esters were produced along with BuOH in an amt. equiv. to the Et ester. In aq. alc., the products were BuOH, (C4H9)PO, and (C4H9)2P(O)H. Ph2NH and hydroquinone (0.02-0.10 mole-%) effectively inhibited the oxidn. of tertiary phosphines, and had some effect in suppressing air oxidn. of primary and secondary phosphines, but it was of shorter duration. Autoxidn. of I was inhibited by less than molar amts. of diphenyl disulfide, PhSH, NaOEt, and NaOH; Ph3P was an inhibitor in equimolar amts. or somewhat less; metal salts, BzH, or styrene had no important effect. Cooxidn. of equimolar amts. of I and III in hexane gave, in addn. to the usual amts. of tertiary phosphine oxides, 4 other major products: II. IV, cyclohexyl dibutyhphosphinate (VII), and butyl dicyclohexylphosphinate (VIII). That the mixed esters were not produced by exchange reactions after oxidn. was shown by combining the crude oxidn. mixts. from the individual phosphines and subjecting this mixt. to the conditions of the cooxidn. expt. A radical chain mechanism was proposed for the autoxidn. in which O reacted with an intermediate hydrocarbon radical rather than directly with P. Evidence in support of this mechanism was obtained by a study of tert-butoxy radicals with I. I (5.55 g.) and 3.65 g. di-tert-butyl peroxide heated 8 hrs. under N at 130° gave a major product and minor amts. of (C4H9)3PO. The former was indirectly identified on the basis of nuclear magnetic resonance and infrared spectra as tert-butyl dibutylphosphinite. Further evidence favoring the mechanism came from a study of autoxidn. of neat samples of I with limited O. Significant amts. of the intermediate lower phosphinite ester were detected. The formation of the phosphinate ester lagged behind that of the oxide in the early stages, although approx. equal amts. were present when autoxidn. was complete. Authentic samples of compds. required for comparison with the isolated products were prepd. Dibutylphosphinic acid (20.0 g.) and 100 ml. SOCl2 refluxed 0.5 hr., the mixt. evapd. in vacuo, 18 ml. BuOH and 15 ml. pyridine added to the residue with cooling, and the mixt. heated 1 hr. at 100° gave 56% II, b0.05 105°, n27D 1.4422. VI, b1-2, 96° (67% yield), and VII, b0.7 139°, n25D 1.4650, were similarly prepd., using abs. EtOH and cyclohexanol, resp., in place of BuOH. A soln. of 3.7 g. dicyclohexylphosphinyl chloride (IX) in 20 ml. hot diglyme added to 0.4 g. Na in 15 ml. cyclohexanol, and the mixt. heated 3.5 hrs. at 115° and 0.5 hr. at 165° gave 19% IV, m. 85-6° (petr. ether). Cyclohexylphosphonyl dichloride (9.0 g.) added to a hot soln. of 2.3 g. Na in 100 ml. cyclohexanol and the mixt. stirred 4 hrs. at 110° gave V. IX (15 g.) in 30 ml. C6H6 added to 1.4 g. Na in 60 ml. BuOH and the mixt. heated 3 hrs. at 100° gave 80% VIII, b0.3 134°, n24D 1.4900. A mixt. of 6.7 g. BuOH and 6.6 g. pyridine added to 15 g. dibutylchlorophosphine in 100 ml. hexane, the mixt. stirred 0.5 hr., and filtered under N gave 78% Bu dibutylphosphinite (X), b0.5 80°, n26D 1.4453. I reacted with atm. O, underwent rapid transesterification with EtOH, and reacted with aq. EtOH to give (C4H9)2POH.
49. 49

    Floyd, M.; Boozer, C. Kinetics of Autoxidation of Trialkylphosphines. J. Am. Chem. Soc. 1963, 85, 984– 986,  DOI: 10.1021/ja00890a034

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    Kinetics of autoxidation of trialkylphosphines

    Floyd, M. B.; Boozer, C. E.

    Journal of the American Chemical Society (1963), 85 (), 984-6CODEN: JACSAT; ISSN:0002-7863.

    The kinetics of the autoxidn. of tributylphosphines in o-dichlorobenzene have been studied by O consumption measurements. The data indicate that the reaction involves the concurrent autoxidn. of intermediate phosphinite esters. Tributyl phosphite was found to undergo autoxidn. at a rate slower than that of tributylphosphine by a factor of at least 1.5. The data reveal that the reaction requires free radical initiation, which in this study was supplied by azo-bis(isobutyronitrile). The autoxidation is a relatively long chain process with a very small activation energy.
50. 50

    Boisvert, L.; Denney, M. C.; Hanson, S. K.; Goldberg, K. I. Insertion of Molecular Oxygen into a Palladium(II) Methyl Bond: A Radical Chain Mechanism Involving Palladium(III) Intermediates. J. Am. Chem. Soc. 2009, 131, 15802– 15814,  DOI: 10.1021/ja9061932

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    50

    Insertion of Molecular Oxygen into a Palladium(II) Methyl Bond: A Radical Chain Mechanism Involving Palladium(III) Intermediates

    Boisvert, Luc; Denney, Melanie C.; Kloek Hanson, Susan; Goldberg, Karen I.

    Journal of the American Chemical Society (2009), 131 (43), 15802-15814CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The reaction of (bipy)PdMe2 (1) (bipy = 2,2'-bipyridine) with mol. oxygen results in the formation of the palladium(II) methylperoxide complex (bipy)PdMe(OOMe) (2). The identity of the product 2 has been confirmed by independent synthesis. Results of kinetic studies of this unprecedented oxygen insertion reaction into a palladium alkyl bond support the involvement of a radical chain mechanism. Reproducible rates, attained in the presence of the radical initiator 2,2'-azobis(2-methylpropionitrile) (AIBN), reveal that the reaction is overall first-order (one-half-order in both [1] and [AIBN], and zero-order in [O2]). The unusual rate law (half-order in [1]) implies that the reaction proceeds by a mechanism that differs significantly from those for org. autoxidns. and for the recently reported examples of insertion of O2 into Pd(II) hydride bonds. The mechanism for the autoxidn. of 1 is more closely related to that found for the autoxidn. of main group and early transition metal alkyl complexes. Notably, the chain propagation is proposed to proceed via a stepwise associative homolytic substitution at the Pd center of 1 with formation of a pentacoordinate Pd(III) intermediate.
51. 51

    Le Vaillant, F.; Wodrich, M. D.; Waser, J. Room Temperature Decarboxylative Cyanation of Carboxylic Acids Using Photoredox Catalysis and Cyanobenziodoxolones: A Divergent Mechanism Compared to Alkynylation. Chem. Sci. 2017, 8, 1790– 1800,  DOI: 10.1039/C6SC04907A

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    Room temperature decarboxylative cyanation of carboxylic acids using photoredox catalysis and cyanobenziodoxolones: a divergent mechanism compared to alkynylation

    Le Vaillant, Franck; Wodrich, Matthew D.; Waser, Jerome

    Chemical Science (2017), 8 (3), 1790-1800CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)

    The one-step conversion of aliph. carboxylic acids to the corresponding nitriles was accomplished via the merger of visible light mediated photoredox and s (CBX) reagents. The reaction proceeded in high yields with natural and non-natural α-amino and α-oxy acids, affording a broad scope of nitriles with excellent tolerance of the substituents in the α position. The direct cyanation of dipeptides and drug precursors was also achieved. The mechanism of the decarboxylative cyanation was investigated both computationally and exptl. and compared with the previously developed alkynylation reaction. Alkynylation was found to favor direct radical addn., whereas further oxidn. by CBX to a carbocation and cyanide addn. appeared more favorable for cyanation. A concerted mechanism was proposed for the reaction of radicals with EBX reagents, in contrast to the usually assumed addn. elimination process.
52. 52

    Galicia, M.; González, F. Electrochemical Oxidation of Tetrabutylammonium Salts of Aliphatic Carboxylic Acids in Acetonitrile. J. Electrochem. Soc. 2002, 149, D46– D50,  DOI: 10.1149/1.1450616

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    Electrochemical oxidation of tetrabutylammonium salts of aliphatic carboxylic acids in acetonitrile

    Galicia, M.; Gonzalez, F. J.

    Journal of the Electrochemical Society (2002), 149 (3), D46-D50CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)

    The anodic oxidn. of a series of tetrabutylammonium aliph. carboxylates has been performed in acetonitrile on glassy carbon electrodes. The electrochem. behavior was studied without the interference of the anodic oxidn. of the solvent. The cyclic voltammetry anal. shows that the electron transfer and the decarboxylation are stepwise. The coulometric anal. shows that the overall mechanism is monoelectronic. However preparative scale electrolysis shows the intervention of two electron-transfer steps leading to carbocations, which then react with the acetonitrile and the carboxylate itself to form N-acylamides as principal products. Two types of adsorption of the carboxylate ions and the alkyl carbocations were proposed to occur selectively, namely, on a small fraction of active sites or on the functional groups existing on the glassy carbon surfaces.
53. 53

    Wirth, T. Iodine(III) Mediators in Electrochemical Batch and Flow Reactions. Curr. Opin. Electrochem. 2021, 28, 100701,  DOI: 10.1016/j.coelec.2021.100701

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    Iodine(III) mediators in electrochemical batch and flow reactions

    Wirth, Thomas

    Current Opinion in Electrochemistry (2021), 28 (), 100701CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    A review. The anodic oxidn. of aryl iodides is a powerful method for synthesis of hypervalent iodine compds., which have matured to frequently used reagents in org. synthesis. The electrochem. route eliminates the use of expensive or hazardous oxidants for their synthesis. Hypervalent iodine reagents generated at the anode are successfully used as either in-cell or ex-cell mediators for many valuable chem. transformations including fluorinations and oxidative cyclisations. The recent advances in the area of flow electrochem. are providing addnl. benefits and allow new synthetic applications. Mechanistic insights and novel technologies enable the development of new concepts for sustainable chem.
54. 54

    Fuchigami, T.; Fujita, T. Electrolytic Partial Fluorination of Organic Compounds. 14. The First Electrosynthesis of Hypervalent Iodobenzene Difluoride Derivatives and Its Application to Indirect Anodic gem-Difluorination. J. Org. Chem. 1994, 59, 7190– 7192,  DOI: 10.1021/jo00103a003

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    Electrolytic Partial Fluorination of Organic Compounds. 14. The First Electrosynthesis of Hypervalent Iodobenzene Difluoride Derivatives and Its Application to Indirect Anodic gem-Difluorination

    Fuchigami, Toshio; Fujita, Toshiyasu

    Journal of Organic Chemistry (1994), 59 (24), 7190-2CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)

    The electrosynthesis of hypervalent iodobenzene difluorides was accomplished by anodic oxidn. of p-nitro- and p-methoxyiodobenzenes with Et3N·3HF in anhyd. acetonitrile, and p-methoxyiodobenzene difluoride was used as a mediator for indirect anodic gem-difluorination of dithioketals.
55. 55

    Doobary, S.; Sedikides, A. T.; Caldora, H. P.; Poole, D. L.; Lennox, A. J. J. Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron-Rich Substrates. Angew. Chem., Int. Ed. 2020, 59, 1155– 1160,  DOI: 10.1002/anie.201912119

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    Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron-rich Substrates

    Doobary, Sayad; Sedikides, Alexi T.; Caldora, Henry P.; Poole, Darren L.; Lennox, Alastair J. J.

    Angewandte Chemie, International Edition (2020), 59 (3), 1155-1160CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Fluorinated alkyl groups are important motifs in bioactive compds., pos. influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their prepn., yet current methods are limited in their alkene-types and tolerance of electron-rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a no. of unactivated alkene-types that is tolerant of electron-rich functionality, giving products that are otherwise unattainable. Key to success is the electrochem. generation of a hypervalent iodine mediator using an "ex-cell" approach, which avoids oxidative substrate decompn. The more sustainable conditions give good to excellent yields in up to decagram scales. Of note, when handling HF reagents, personal protection is of utmost importance.
56. 56

    Elsherbini, M.; Winterson, B.; Alharbi, H.; Folgueiras-Amador, A. A.; Génot, C.; Wirth, T. Continuous-Flow Electrochemical Generator of Hypervalent Iodine Reagents: Synthetic Applications. Angew. Chem., Int. Ed. 2019, 58, 9811– 9815,  DOI: 10.1002/anie.201904379

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    Continuous-Flow Electrochemical Generator of Hypervalent Iodine Reagents: Synthetic Applications

    Elsherbini, Mohamed; Winterson, Bethan; Alharbi, Haifa; Folgueiras-Amador, Ana A.; Genot, Celina; Wirth, Thomas

    Angewandte Chemie, International Edition (2019), 58 (29), 9811-9815CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    An efficient and reliable electrochem. generator of hypervalent iodine reagents has been developed. In the anodic oxidn. of iodoarenes to hypervalent iodine reagents under flow conditions, the use of electricity replaces hazardous and costly chem. oxidants. Unstable hypervalent iodine reagents can be prepd. easily and coupled with different substrates to achieve oxidative transformations in high yields. The unstable, electrochem. generated reagents can also easily be transformed into classic bench-stable hypervalent iodine reagents through ligand exchange. The combination of electrochem. and flow-chem. advantages largely improves the ecol. footprint of the overall process compared to conventional approaches.
57. 57

    Francke, R. Recent Progress in the Electrochemistry of Hypervalent Iodine Compounds. Curr. Opin. Electrochem. 2021, 28, 100719,  DOI: 10.1016/j.coelec.2021.100719

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    Recent progress in the electrochemistry of hypervalent iodine compounds

    Francke, Robert

    Current Opinion in Electrochemistry (2021), 28 (), 100719CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    A review. Hypervalent iodine compds. constitute a well-established and broadly used reagent family in org. synthesis. As they are usually either used in stoichiometric quantities or generated in situ from an aryl iodide precursor using a terminal oxidant, the assocd. waste and sepn. problems pose major challenges en route to sustainable and scalable processes. In this regard, the use of inexpensive elec. current as a traceless oxidant for the in-situ generation of hypervalent iodine has emerged as a promising alternative. This review summarizes the advances over the past 2 years, including improved electrolysis protocols, new synthetic applications, and concepts for enhancing the sustainability of the reactions.
58. 58

    Antonchick, A. P.; Samanta, R.; Kulikov, K.; Lategahn, J. Organocatalytic, Oxidative, Intramolecular C–H Bond Amination and Metal-free Cross-Amination of Unactivated Arenes at Ambient Temperature. Angew. Chem., Int. Ed. 2011, 50, 8605– 8608,  DOI: 10.1002/anie.201102984

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    Organocatalytic, Oxidative, Intramolecular C-H Bond Amination and Metal-free Cross-Amination of Unactivated Arenes at Ambient Temperature

    Antonchick, Andrey P.; Samanta, Rajarshi; Kulikov, Katharina; Lategahn, Jonas

    Angewandte Chemie, International Edition (2011), 50 (37), 8605-8608, S8605/1-S8605/70CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    An atom-economical, environmentally friendly organocatalytic method for the prepn. of carbazoles through C-N bond formation and unprecedented first cross-amination of non-prefunctionalized arenes under metal-free conditions are reported. 2,2'-Diiodo-4,4',6,6'-tetramethylbiphenyl catalyzes the intramol. amination. The best results were obtained in hexafluoro-2-propanol. E.g., in presence of 2,2'-diiodo-4,4',6,6'-tetramethylbiphenyl and AcOOH in hexafluoro-2-propanol/CH2Cl2, reaction of 2-AcNHC6H4Ph gave 77% carbazole (I). The intermol. version of this reaction was also studied. E.g., 2H-1,4-benzoxazin-3(4H)-one reacts smoothly with mesitylene in presence of stoichiometric amts. of (diacetoxy)iodobenzene to give the cross-amination product at room temp.
59. 59

    Frey, B. L.; Thai, P.; Patel, L.; Powers, D. C. Structure–Activity Relationships for Hypervalent Iodine Electrocatalysis. Synthesis 2023, DOI: 10.1055/a-2029-0617 .

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    Yang, W.; Zhang, L.; Xiao, D.; Feng, R.; Wang, W.; Pan, S.; Zhao, Y.; Zhao, L.; Frenking, G.; Wang, X. A Diradical Based on Odd-Electron σ-Bonds. Nat. Commun. 2020, 11, 3441,  DOI: 10.1038/s41467-020-17303-4

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    A diradical based on odd-electron σ-bonds

    Yang, Wenbang; Zhang, Li; Xiao, Dengmengfei; Feng, Rui; Wang, Wenqing; Pan, Sudip; Zhao, Yue; Zhao, Lili; Frenking, Gernot; Wang, Xinping

    Nature Communications (2020), 11 (1), 3441CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)

    The concept of odd-electron σ-bond was first proposed by Linus Pauling. Species contg. such a bond have been recognized as important intermediates encountered in many fields. A no. of radicals with a one-electron or three-electron σ-bond have been isolated, however, no example of a diradical based odd-electron σ-bonds has been reported. So far all stable diradicals are based on two s/p-localized or π-delocalized unpaired electrons (radicals). Here, we report a dication diradical that is based on two Se:Se three-electron σ-bonds. In contrast, the dication of sulfur analog does not display diradical character but exhibits a closed-shell singlet.
61. 61

    Zhang, S.; Wang, X.; Su, Y.; Qiu, Y.; Zhang, Z.; Wang, X. Isolation and Reversible Dimerization of a Selenium–Selenium Three-Electron σ-Bond. Nat. Commun. 2014, 5, 4127,  DOI: 10.1038/ncomms5127

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    Isolation and reversible dimerization of a selenium-selenium three-electron σ-bond

    Zhang, Senwang; Wang, Xingyong; Su, Yuanting; Qiu, Yunfan; Zhang, Zaichao; Wang, Xinping

    Nature Communications (2014), 5 (), 4127CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)

    Three-electron σ-bonding that was proposed by Linus Pauling in 1931 has been recognized as important in intermediates encountered in many areas. A no. of three-electron bonding systems have been spectroscopically investigated in the gas phase, soln. and solid matrix. However, X-ray diffraction studies have only been possible on simple noble gas dimer Xe:Xe and cyclic framework-constrained N:N radical cations. Here, we show that a diselena species modified with a naphthalene scaffold can undergo one-electron oxidn. using a large and weakly coordinating anion, to afford a room-temp.-stable radical cation contg. a Se:Se three-electron σ-bond. When a small anion is used, a reversible dimerization with phase and marked color changes is obsd.: radical cation in soln. (blue) but diamagnetic dimer in the solid state (brown). These findings suggest that more examples of three-electron σ-bonds may be stabilized and isolated by using naphthalene scaffolds together with large and weakly coordinating anions.
62. 62

    Sagl, D. J.; Martin, J. C. The Stable Singlet Ground State Dication of Hexaiodobenzene: Possibly σ-Delocalized Dication. J. Am. Chem. Soc. 1988, 110, 5827– 5833,  DOI: 10.1021/ja00225a038

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    The stable singlet ground state dication of hexaiodobenzene: possibly a σ-delocalized dication

    Sagl, D. J.; Martin, J. C.

    Journal of the American Chemical Society (1988), 110 (17), 5827-33CODEN: JACSAT; ISSN:0002-7863.

    Two-electron oxidn. of hexaiodobenzene (I), with Cl2 or H2O2 in CF3SO2OH, contg. trifluoroacetyl triflate, provides a stable, isolable salt of the singlet ground state dication C6I62+ (II), which is easily reduced to regenerate neutral I. The singlet ground state is evidenced by the diamagnetic character of pure II (magnetic susceptibility, χ = -2.59 × 10-4 emu G-1 mol-1 at 300 K) and by the observation of a sharp singlet in its 13C NMR (79.1 ppm). I shows a 13C NMR singlet (121.7 ppm), which moves upfield by 42.6 ppm upon oxidn. to dication II. This is interpreted in terms of removal of two electrons from the HOMO of I, an antibonding σ-delocalized MO made up primarily of the filled iodine p orbitals in the plane of the arom. ring, as designated by an extended Hueckel calcn. This suggests a stable, closed-shell, 10-electron σ-delocalization dication, which may be viewed as a Hueckel σ-arom. species, providing a ring current responsible for the upfield shift of the 13C NMR singlet. Replacement of one iodine in II by a much smaller fluorine destroys the stabilization attributed to the σ-delocalized orbital system of II.
63. 63

    Zhang, S.; Wang, X.; Sui, Y.; Wang, X. Odd-Electron-Bonded Sulfur Radical Cations: X-ray Structural Evidence of a Sulfur–Sulfur Three-Electron σ-Bond. J. Am. Chem. Soc. 2014, 136, 14666– 14669,  DOI: 10.1021/ja507918c

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    Odd-Electron-Bonded Sulfur Radical Cations: X-ray Structural Evidence of a Sulfur-Sulfur Three-Electron σ-Bond

    Zhang, Senwang; Wang, Xingyong; Sui, Yunxia; Wang, Xinping

    Journal of the American Chemical Society (2014), 136 (42), 14666-14669CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The one-electron oxidns. of 1,8-chalcogen naphthalenes Nap(SPh)2 (1) and Nap(SPh)(SePh) (2) lead to the formation of persistent radical cations 1•+ and 2•+ in soln. EPR spectra, UV-vis absorptions, and DFT calcns. show a three-electron σ-bond in both cations. The former cation remains stable in the solid state, while the latter dimerizes upon crystn. and returns to being radical cations upon dissoln. This work provides conclusive structural evidence of a sulfur-sulfur three-electron σ-bond (in 1•+) and a rare example of a persistent heteroat. three-electron σ-bond (in 2•+).
64. 64

    Kita, Y.; Tohma, H.; Hatanaka, K.; Takada, T.; Fujita, S.; Mitoh, S.; Sakurai, H.; Oka, S. Hypervalent Iodine-induced Nucleophilic Substitution of para-Substituted Phenol Ethers. Generation of Cation Radicals as Reactive Intermediates. J. Am. Chem. Soc. 1994, 116, 3684– 3691,  DOI: 10.1021/ja00088a003

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    Hypervalent Iodine-Induced Nucleophilic Substitution of para-Substituted Phenol Ethers. Generation of Cation Radicals as Reactive Intermediates

    Kita, Yasuyuki; Tohma, Hirofumi; Hatanaka, Kenji; Takada, Takeshi; Fujita, Shigekazu; Mitoh, Shizue; Sakurai, Hiromu; Oka, Shigenori

    Journal of the American Chemical Society (1994), 116 (9), 3684-91CODEN: JACSAT; ISSN:0002-7863.

    A novel hypervalent iodine-induced nucleophilic substitution of para-substituted phenol ethers in the presence of a variety of nucleophiles is described. UV and ESR spectroscopic studies indicate that this reaction proceeds via cation radicals, [ArH•+], as reactive intermediates generated by single-electron transfer from a charge-transfer complex of the phenol ether with phenyliodine(III) bis(trifluoroacetate). This is the first case that involves a radical intermediate in hypervalent iodine oxidns. of arom. compds.
65. 65

    Moteki, S. A.; Usui, A.; Zhang, T.; Solorio Alvarado, C. R.; Maruoka, K. Site-Selective Oxidation of Unactivated C–H Bonds with Hypervalent Iodine(III) Reagents. Angew. Chem. 2013, 125, 8819– 8822,  DOI: 10.1002/ange.201304359

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    Amey, R. L.; Martin, J. C. Identity of the Chain-Carrying Species in Halogenations with Bromo- and Chloroarylalkoxyiodinanes: Selectivities of Iodinanyl Radicals. J. Am. Chem. Soc. 1979, 101, 3060– 3065,  DOI: 10.1021/ja00505a038

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    Identity of the chain-carrying species in halogenations with bromo- and chloroarylalkoxyiodinanes: selectivities of iodinanyl radicals

    Amey, Ronald L.; Martin, J. C.

    Journal of the American Chemical Society (1979), 101 (11), 3060-5CODEN: JACSAT; ISSN:0002-7863.

    Free-radical halogenation of substituted toluenes with I and II (X = Br, Cl) in C6H6 is highly selective for benzylic H atoms. The process involves cyclic iodinanyl radicals, except in the case of II (X = Br), which appears to react via a Br-atom chain. The essentially identical values of ρ+ for both I are consistent with a common chain-carrying species for both bromination and chlorination. Identical ρ+ values were not obsd. for PhICl2. Such iodinanyl radicals, unlike those derived from I and II (X = Cl) are constrained to a C-I-O angle far smaller than 180°, allowing an opportunity to study the effects of bending on radical selectivities. The intermediacy of iodinanyl radicals in free-radical chlorinations is further supported by evidence from photoinitiated reactions of I and II (X = Cl) with Me2CHCHMe2, in which Cl atoms are not involved. Allylic chlorinations of cis- and trans-2-butenes with I and II (X = Cl) were selective, high-yield reactions which give little or no addn. to the C:C double bond.
67. 67

    Bloomfield, G.; Rubber, F. Polyisoprenes, and Allied Compounds. Part VI. The Mechanism of Halogen-Substitution Reactions, and the Additive Halogenation of Rubber and of Dihydromyrcene. J. Chem. Soc. 1944, 114– 120,  DOI: 10.1039/jr9440000114

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    Rubber, polyisoprenes and allied compounds. VI. The mechanism of halogen-substitution reactions and the additive halogenation of rubber and dihydromyrcene

    Bloomfield, Geo. F.

    Journal of the Chemical Society (1944), (), 114-20CODEN: JCSOA9; ISSN:0368-1769.

    cf. C. A. 37, 6491.4. The chlorination of cyclohexene (I) by Cl or SO2Cl2 (in the absence of a peroxide catalyst) yields substituted and additive chlorination products; the former retain in full the original olefinic unsatn. as indicated by I-value detn. Whereas SO2Cl2 forms only the additive dichloride and a monochloro.ovrddot.olefin which is substituted exclusively in the 3-position, Cl yields a mixt. of satd. tri-Cl deriv. (Cl-substituted addn. product) and isomeric monochloro.ovrddot.olefins (3- and 4-substituted), with some additive dichloride. No evidence of substitution on a doubly bound C atom has been obtained in the chlorination of I, dihydromyrcene (II) and rubber (III) by Cl. The diminished unsatn. of the Cl-substitution products of II and III is attributed to cyclization-a process which is complete with III but affects only a minor proportion of the mols. of II. The same cyclizing tendency appears in the substitutive bromination of III by N-bromosuccinimide (IV), but not to any appreciable extent in the similar bromination of II. Additive chlorination products are formed when III is brought into reaction with Cl liberated by the thermal dissocn. of PhICl2 or of SO2Cl2 in the presence of a peroxide. The mode of reaction of Br with III, about which many contradictory statements have been made, is found to be entirely additive if the solvent contains a trace of EtOH and the temp. is 0°. A method based on Br addn. can be used for estg. III hydrocarbon. Additive Br and Cl derivs. of III are comparatively stable, and give no indication of the spontaneous elimination of HCl or HBr either through cyclization reactions or the reformation of double bonds at temps. up to 80°. The provision of Cl in free-radical form appears to be an essential for obtaining the wholly additive chlorination of III and allied olefins. The reaction of mol. Br or Cl, on the other hand, follows a course which can be adequately explained by the initial formation of an activated dihalide, the fate of which is detd. by the nature of the olefinic system and the exptl. conditions. Peroxide-free I (20 cc.), treated with 14.4 g. Cl at 80° in the absence of O and in very subdued light, gives 4.33 g. HCl, corresponding to 59% substitutive reaction; the main products are 4.3 g. monochlorocyclohexene (V), 8.4 g. dichlorocyclohexane (VI) and 4.2 g. trichlorocyclohexane. V is probably a mixt. of 80% of the 3- and 20% of the 4-Cl deriv. but contains no 1-Cl deriv. The 1-Cl deriv., b13 35°, was prepd. from cyclohexanone and PCl5. The mono-Cl deriv. of II was prepd. by the action of Cl on an excess of II, but was purified with great difficulty. III hydrocarbon (15 g.) in 300 cc. CCl4 and 19.2. g. PhICl2, on heating to boiling, give 10 g. of polyisoprene dichloride (VII), a fibrous mass with a probable mol. wt. of 127,000; there was less than 4% substitutive reaction. An additive reaction to the extent of 98% was observed when Me2CO-extd. crepe III reacted similarly (4% of Bz2O2 present); with quinol only 86% of the reagent was utilized in 30 min. at the b. p., and 27% of the reacting PhICl2 chlorinated the III substitutively. The action of Cl on VII in CCl4 in bright light gives a product with 53% Cl. Reaction of SO2Cl2 and I in the presence of quinol gives VI; other products were the chloride of 2-chlorocyclohexyl sulfite, b0.002 74°, and a compd., m. 92°, believed to be bis(2-chlorocyclohexyl) sulfite. I and SO2Cl2 in the presence of I give a mixt. of VI and the 3-Cl isomer of V. A Cl-substituted III (Cl 35.95%) and SO2Cl2 in CCl4 (in presence of Bz2O2) at 80° in N in the dark does not react completely in 2 hrs.; the reaction of 7.7 g. SO2Cl2 corresponds to 3.75 g. of additive and 4.15 g. substitutive reaction. II (44 cc.) and 16.7 g. SO2Cl2 in the presence of Bz2O2 yield 14.5 g. of II dichloride, b0.2 55-6°; 13.4 g. II and 26.2 g. SO2Cl2 give 18.6 g. of II tetrachloride, b0.002 82-90°, m. 50°. III and SO2Cl2 in CCl4 at 80° give VII, with a mol. wt. of 120,000, which is stable in air and at 80°. II and IV in CCl4 at 77° in a N atm. yield a mono-Br deriv., b0.1 54°. III and IV in C6H6 give a product with 37.4% Br (reactive Br 35%). A sol III (obtained by diffusion of rubber into light petroleum) in CHCl3 and Br at -30° to -40° give a pale-brown resinous product with 69% Br; it does not evolve HBr up to 80°. The behavior of III and Br in other solvents is discussed. Br addn. is satisfactory for estg. III hydrocarbon. The mechanism of additive halogenation reactions is considered.
68. 68

    Moteki, S. A.; Usui, A.; Selvakumar, S.; Zhang, T.; Maruoka, K. Metal-Free C–H Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible-Light Photolysis: Successful Trapping with Electron-Deficient Olefins. Angew. Chem., Int. Ed. 2014, 53, 11060– 11064,  DOI: 10.1002/anie.201406513

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    Metal-Free C-H Bond Activation of Branched Aldehydes with Hypervalent Iodine(III) Catalyst under Visible-Light Photolysis: Successful Trapping with Electron-Deficient Olefins

    Moteki, Shin A.; Usui, Asuka; Selvakumar, Sermadurai; Zhang, Tiexin; Maruoka, Keiji

    Angewandte Chemie, International Edition (2014), 53 (41), 11060-11064CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Direct acyl radical formation of linear aldehydes (RCH2-CHO) and subsequent hydroacylation with electron-deficient olefins can be effected with various types of metal and nonmetal catalysts/reagents. In marked contrast, however, no successful reports on the use of branched aldehydes have been made thus far because of their strong tendency of generating alkyl radicals through the facile decarbonylation of acyl radicals. Here, use of a hypervalent iodine(III) catalyst under visible light photolysis allows a mild way of generating acyl radicals from various branched aldehydes, thereby giving the corresponding hydroacylated products almost exclusively. Another characteristic feature of this approach is the catalytic use of hypervalent iodine(III) reagent, which is a rare example on the generation of radicals in hypervalent iodine chem.
69. 69

    Wang, X.; Studer, A. Regio- and Stereoselective Cyanotriflation of Alkynes Using Aryl(cyano)iodonium Triflates. J. Am. Chem. Soc. 2016, 138, 2977– 2980,  DOI: 10.1021/jacs.6b00869

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    Regio- and Stereoselective Cyanotriflation of Alkynes Using Aryl(cyano)iodonium Triflates

    Wang, Xi; Studer, Armido

    Journal of the American Chemical Society (2016), 138 (9), 2977-2980CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    A novel, mild, and versatile approach for regioselective syn-addn. of both the CN and OTf groups of aryl(cyano)iodonium triflates to alkynes is described. The reaction uses Fe-catalysis and can be conducted in gram scale. Products of the vicinal cyanotriflation can be stereospecifically further functionalized, rendering the method highly valuable.
70. 70

    Macikenas, D.; Skrzypczak-Jankun, E.; Protasiewicz, J. D. A New Class of Iodonium Ylides Engineered as Soluble Primary Oxo and Nitrene Sources. J. Am. Chem. Soc. 1999, 121, 7164– 7165,  DOI: 10.1021/ja991094j

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    A New Class of Iodonium Ylides Engineered as Soluble Primary Oxo and Nitrene Sources

    Macikenas, Dainius; Skrzypczak-Jankun, Ewa; Protasiewicz, John D.

    Journal of the American Chemical Society (1999), 121 (30), 7164-7165CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The ability of (tosyliminoiodo)arene 2-Me3CSO2C6H4I:NTs (I)and iodosylarene 2-Me3CSO2C6H4IO (II), both of which were prepd. from 2-Me3CSO2C6H4I, as primary sources of O atoms and tosylimino groups was investigated. E.g., reaction of I with Ph3P gave 83% Ph3P:NTs. E.g., reaction of II with Me2S gave 95% Me2SO. The soly. of I and II in org. media are high.
71. 71

    Thai, P.; Frey, B. L.; Figgins, M. T.; Thompson, R. R.; Carmieli, R.; Powers, D. C. Selective Multi-electron Aggregation at a Hypervalent Iodine Center by Sequential Disproportionation. Chem. Commun. 2023, 59, 4308– 4311,  DOI: 10.1039/D3CC00549F

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    Selective multi-electron aggregation at a hypervalent iodine center by sequential disproportionation

    Thai, Phong; Frey, Brandon L.; Figgins, Matthew T.; Thompson, Richard R.; Carmieli, Raanan; Powers, David C.

    Chemical Communications (Cambridge, United Kingdom) (2023), 59 (29), 4308-4311CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    The sequential disproportionation reactions was enable selective aggregation of two- or four electron-holes at a hypervalent iodine center was reported. Disproportionation of an anodically generated iodanyl radical affords an iodosylbenzene deriv. Subsequent iodosylbenzene disproportionation was triggered to provide access to an iodoxybenzene. These results demonstrated that multielectron oxidn. at the one-electron potential by selective and sequential disproportionation chem.
72. 72

    Lucas, H. J. K. E. R. Iodoxybenzene (Benzene, iodoxy-) (A) Disproportionation of Iodosobenzene. Org. Synth. 1942, 22, 72– 75

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    Iodoxybenzene

    Lucas, H. J.; Kennedy, E. R.; Formo, M. W.; Johnson, John R.

    Organic Syntheses (1942), 22 (), 72-5CODEN: ORSYAT; ISSN:0078-6209.

    Rapid steam distn. of PhIO gives 92-5% of PhIO2. The soly. of PhIO2 in 1 l. of H2O is 2.8 g. at 12° and 12 g. at 100°.
73. 73

    Richter, H. W.; Cherry, B. R.; Zook, T. D.; Koser, G. F. Characterization of Species Present in Aqueous Solutions of [Hydroxy(mesyloxy)iodo]benzene and [Hydroxy(tosyloxy)iodo]benzene. J. Am. Chem. Soc. 1997, 119, 9614– 9623,  DOI: 10.1021/ja971751c

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    Characterization of species present in aqueous solutions of [hydroxy(mesyloxy)iodo]benzene and [hydroxy(tosyloxy)iodo]benzene

    Richter, Helen Wilkinson; Cherry, Brian R.; Zook, Teresa D.; Koser, Gerald F.

    Journal of the American Chemical Society (1997), 119 (41), 9614-9623CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Upon dissoln. in H2O, both HOIPhO3SR (R = Me, Ph) undergo complete ionization to give PhI+OH cation (I) and the corresponding RSO3- anion as fully solvated species, i.e., free ions, which do not form ion pairs with each other. I is presumed to be ligated with ≥1 H2O mol. at an apical site of the I(III) originally occupied by the sulfonate group. In view of the relative basicities of HO- and H2O, the OH ligand of the I.H2O cation is expected to be strongly bound, and the H2O ligand should be weakly bound to the I(III) center. This species has pKA 4.30 ± 0.05. I.H2O and its conjugate base are present in equil. with the cation [Ph(HO)I-O-I+(OH2)Ph]. This μ-oxo dimer is present at significant levels even in relatively dil. solns., as the combination equil. const. is 540 ± 50. This dimer can be protonated, and the pKA of the conjugate acid is ≈2.5. The equil. const. for dimerization of PhI+(OH2)O-, the most important monomer in acidic solns., is ≈8.6.
74. 74

    Maity, A.; Hyun, S. M.; Wortman, A. K.; Powers, D. C. Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue. Angew. Chem., Int. Ed. 2018, 57, 7205– 7209,  DOI: 10.1002/anie.201804159

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    Oxidation Catalysis by an Aerobically Generated Dess-Martin Periodinane Analogue

    Maity, Asim; Hyun, Sung-Min; Wortman, Alan K.; Powers, David C.

    Angewandte Chemie, International Edition (2018), 57 (24), 7205-7209CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Hypervalent iodine(V) reagents, such as Dess-Martin periodinane (DMP) and 2-iodoxybenzoic acid (IBX), are broadly useful oxidants in chem. synthesis. Development of strategies to generate these reagents from dioxygen (O2) would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidn. reactions. Recently the authors disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidn. Aerobic oxidn. of iodobenzenes is coupled with disproportionation of the initially generated I(III) compds. to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidn. chem. analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidn. catalysis.
75. 75

    Dess, D. B.; Martin, J. C. Readily Accessible 12-I-5 Oxidant for the Conversion of Primary and Secondary Alcohols to Aldehydes and Ketones. J. Org. Chem. 1983, 48, 4155– 4156,  DOI: 10.1021/jo00170a070

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    Readily accessible 12-I-5 oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones

    Dess, D. B.; Martin, J. C.

    Journal of Organic Chemistry (1983), 48 (22), 4155-6CODEN: JOCEAH; ISSN:0022-3263.

    Oxidn. of 2-IC6H4CO2H with KBrO3 in aq. H2SO4, followed by treatment of the oxidn. product with Ac2O gave 87% periodinane I, a 10-I-5 species (i.e., 10 valence electrons are formally involved in binding 5 ligands to the central iodine atom). I reacted rapidly with primary or secondary alcs. at room temp. to give the corresponding aldehydes or ketones in high yield. Excess I does not further oxidize the aldehyde or ketone under the reaction conditions. The reaction is strongly catalyzed by excess alc. or strong acid, but is unaffected by pyridine. I oxidizes benzylic alcs. selectively in the presence of satd. alcs. Procedures for sepg. the carbonyl product from the reaction mixt. are mild and simple. Cryst. I is stable at room temp. in the absence of moisture.
76. 76

    Dess, D. B.; Martin, J. C. A Useful 12-I-5 Triacetoxyperiodinane (the Dess-Martin Periodinane) for the Selective Oxidation of Primary or Secondary Alcohols and a Variety of Related 12-I-5 Species. J. Am. Chem. Soc. 1991, 113, 7277– 7287,  DOI: 10.1021/ja00019a027

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    A useful 12-I-5 triacetoxyperiodinane (the Dess-Martin periodinane) for the selective oxidation of primary or secondary alcohols and a variety of related 12-I-5 species

    Dess, Daniel B.; Martin, J. C.

    Journal of the American Chemical Society (1991), 113 (19), 7277-87CODEN: JACSAT; ISSN:0002-7863.

    The stable 10-I-4 species 1-hydroxy-1,3-dihydro-3,3-bis(trifluoromethyl)-1,2-benziodoxole 1-oxide (I) is the ring-closed form of o-iodoxyhexafluorocumyl alc. It is prepd. by the oxidn. of chloroiodinane II with KBrO3 in aq. H2SO4. The x-ray crystal structure of the tetrabutylammonium salt of I showed the unusual feature of an apical, neg. charged oxide ligand. 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one (III) (Dess-Martin Periodinane), derived from the 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide by treatment with Ac2O, is an extremely useful reagent for the conversion of primary and secondary alcs. to aldehydes and ketones at 25 °C. It does not oxidize aldehydes to carboxylic acids under these conditions. It selectively oxidizes alcs. in the presence of furan rings or sulfides and does not react with vinyl ethers. Geraniol is oxidized to geranial without isomerization to nerol. Benzylic or allylic alcs. are selectively oxidized in the presence of satd. alkanols. The alc. oxidn. mechanism is discussed.
77. 77

    Chinn, A. J.; Sedillo, K.; Doyle, A. G. Phosphine/Photoredox Catalyzed Anti-Markovnikov Hydroamination of Olefins with Primary Sulfonamides via α-Scission from Phosphoranyl Radicals. J. Am. Chem. Soc. 2021, 143, 18331– 18338,  DOI: 10.1021/jacs.1c09484

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    Phosphine/Photoredox Catalyzed Anti-Markovnikov Hydroamination of Olefins with Primary Sulfonamides via α-Scission from Phosphoranyl Radicals

    Chinn, Alex J.; Sedillo, Kassandra; Doyle, Abigail G.

    Journal of the American Chemical Society (2021), 143 (43), 18331-18338CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    A dual phosphine and photoredox catalytic system that enables direct formation of sulfonamidyl radicals from primary sulfonamides RSO2NH2 (R = 4-tert-butylphenyl, Me, cyclopropyl, thiophen-2-yl, etc.) was reported. Mechanistic investigations support that the N-centered radical is generated via α-scission of the P-N bond of a phosphoranyl radical intermediate, formed by sulfonamide nucleophilic addn. to a phosphine radical cation. As compared to the recently well-explored β-scission chem. of phosphoranyl radicals, this strategy is applicable to activation of N-based nucleophiles and is catalytic in phosphine. The application of this activation strategy to an intermol. anti-Markovnikov hydroamination of unactivated olefins (such as cyclohexene, hex-1-ene, styrene, etc.) with primary sulfonamides RSO2NH2 is highlighted. A range of structurally diverse secondary sulfonamides [such as 4-(tert-butyl)-N-hexylbenzenesulfonamide, 4-(tert-butyl)-N-(3-phenylpropyl)benzenesulfonamide, 2-chloro-N-cyclohexylbenzenesulfonamide, etc.] can be prepd. in good to excellent yields under mild conditions.