Versatile Coordination Modes of Multidentate Neutral Amine Ligands with Group 1 Metal Cations

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CCDC 2120222–2120225 and 2125503 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

This article references 60 other publications.

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   King, David M.; Tuna, Floriana; McInnes, Eric J. L.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Liddle, Stephen T.

   Science (Washington, DC, United States) (2012), 337 (6095), 717-720CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)

   The terminal U nitride linkage is a fundamental target in the study of f-orbital participation in metal-ligand multiple bonding but has previously eluded characterization in an isolable mol. Here, the authors report the prepn. of the terminal U(V) nitride complex [UN(TrenTIPS)][Na(12-crown-4)2] {in which TrenTIPS = [N(CH2CH2NSiPri3)3]3- and Pri = CHMe2} by reaction of the U(III) complex [U(TrenTIPS)] with sodium azide followed by abstraction and encapsulation of the Na cation by the polydentate crown ether 12-crown-4. Single-crystal x-ray diffraction reveals a U-terminal nitride bond length of 1.825(15) angstroms (15 is the std. uncertainty). The structural assignment is supported by 15N-isotopic labeling, electronic absorption spectroscopy, magnetometry, electronic structure calcns., elemental analyses, and liberation of NH3 after treatment with H2O.

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   Science (Washington, DC, United States) (2018), 359 (6378), 896-900CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)

   Currently, the only compds. known to support fixation and functionalization of dinitrogen (N2) under nonmatrix conditions are based on metals. Here we present the observation of N2 binding and redn. by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N2 binding to two borylene units results in either neutral (B2N2) or dianionic ([B2N2]2-) products that can be interconverted by resp. exposure to further reductant or to air. The 15N isotopologues of the neutral and dianionic mols. were prepd. with 15N-labeled dinitrogen, allowing observation of the nitrogen nuclei by 15N NMR spectroscopy. Protonation of the dianionic compd. with distd. water furnishes a diradical product with a central hydrazido B2N2H2 unit. All three products were characterized spectroscopically and crystallog.

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   Auerhammer, D.; Arrowsmith, M.; Dewhurst, R. D.; Kupfer, T.; Böhnke, J.; Braunschweig, H. Closely related yet different: a borylene and its dimer are non-interconvertible but connected through reactivity. Chem. Sci. 2018, 9, 2252– 2260,  DOI: 10.1039/C7SC04789D

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   Closely related yet different: a borylene and its dimer are non-interconvertible but connected through reactivity

   Auerhammer, Dominic; Arrowsmith, Merle; Dewhurst, Rian D.; Kupfer, Thomas; Boehnke, Julian; Braunschweig, Holger

   Chemical Science (2018), 9 (8), 2252-2260CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)

   The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)]4 (I, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B:B(CN)(cAAC)] (II), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Also, reactions of I or II with elemental S and Se in various stoichiometries provided access to a variety of cAAC-stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena-2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addn. reactions and soln. stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity obsd. between I and II.

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   Arrowsmith, M.; Braunschweig, H.; Celik, M. A.; Dellermann, T.; Dewhurst, R. D.; Ewing, W. C.; Hammond, K.; Kramer, T.; Krummenacher, I.; Mies, J.; Radacki, K.; Schuster, J. K. Neutral zero-valent s-block complexes with strong multiple bonding. Nat. Chem. 2016, 8, 890– 894,  DOI: 10.1038/nchem.2542

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   Neutral zero-valent s-block complexes with strong multiple bonding

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   Nature Chemistry (2016), 8 (9), 890-894CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)

   The metals of the s block of the periodic table are well known to be exceptional electron donors, and the vast majority of their mol. complexes therefore contain these metals in their fully oxidized form. Low-valent main-group compds. have recently become desirable synthetic targets owing to their interesting reactivities, sometimes on a par with those of transition-metal complexes. In this work, we used stabilizing cyclic (alkyl)(amino)carbene ligands to isolate and characterize the first neutral compds. that contain a zero-valent s-block metal, beryllium. These brightly colored complexes ,e.g, I and II, display very short beryllium-carbon bond lengths and linear beryllium coordination geometries, indicative of strong multiple Be-C bonding. Structural, spectroscopic and theor. results show that the complexes adopt a closed-shell singlet configuration with a Be(0) metal center. The surprising stability of the mol. can be ascribed to an unusually strong three-center two-electron π bond across the C-Be-C unit.

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   Wang, G. – C.; Walley, J. E.; Dickie, D. A.; Pan, S.; Frenking, G.; Gilliard, R. J., Jr A Stable, Crystalline Beryllium Radical Cation. J. Am. Chem. Soc. 2020, 142 (10), 4560– 4564,  DOI: 10.1021/jacs.9b13777

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   A Stable, Crystalline Beryllium Radical Cation

   Wang, Guocang; Walley, Jacob E.; Dickie, Diane A.; Pan, Sudip; Frenking, Gernot; Gilliard, Robert J.

   Journal of the American Chemical Society (2020), 142 (10), 4560-4564CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Beryllium(I) complex with cyclic alkylaminocarbene, 2-pyrrolidinylidene, ligands were prepd. and characterized. The alk.-earth elements (Be, Mg, Ca, Sr, and Ba) strongly favor the formation of diamagnetic compds. in the +2 oxidn. state. Herein we report a paramagnetic beryllium radical cation, [(cAAC)2Be]+• [2, cAAC = 1-(2,6-diisopropylphenyl)-3,3-diethyl-5,5,-dimethyl-2-pyrrolidinylidene] cyclic (alkyl)(amino)carbene, prepd. by oxidn. of a zero-valent beryllium complex [(cAAC)2Be] (1) with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Compd. 2 was characterized by EPR spectroscopy, elemental anal., X-ray crystallog., and DFT calcns. Notably, the isolation of 2 represents the first s-block charged radical and the first cryst. beryllium radical.

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   Klett, J. Structural Motifs of Alkali Metal Superbases in Non-coordinating Solvents. Chem.─Eur. J. 2021, 27, 888– 904,  DOI: 10.1002/chem.202002812

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   Structural Motifs of Alkali Metal Superbases in Non-coordinating Solvents

   Klett, Jan

   Chemistry - A European Journal (2021), 27 (3), 888-904CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A review. Lochmann-Schlosser superbases (LSB) are a std. reagent in synthetic chem. to achieve an exchange of a proton on an org. framework with an alkali metal cation, which in turn can be replaced by a wide range of electrophilic groups. In std. examples, the deprotonating reagent consists of an equimolar mixt. of n-butyllithium and potassium t-butoxide. However, the nature of the reactive species could not be pinned down either for this compn. or for similar mixts. with comparable high reactivity. Despite the poor soly. and the fierce reactivity, some insights into this mixt. were achieved by some indirect results, comparison with chem. related systems, or skillful deductions. Recent results, mainly based on new sol. compds., delivered structural evidence. These new insights lead to advanced and more detailed conclusions about the interplay of the involved components.

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   A review. A no. of additives that can be used to make asym. reactions perfect were highlighted. Without changing other reaction conditions, simply adding additives led to improved asym. catalysis, such as reduced reaction time, improved yield, or/and increased selectivity.

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   Lithium chloride: An active and simple catalyst for cyanosilylation of aldehydes and ketones

   Kurono, Nobuhito; Yamaguchi, Masayo; Suzuki, Ken; Ohkuma, Takeshi

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   LiCl acted as a highly effective catalyst for cyanosilylation of various aldehydes and ketones to the corresponding silylated cyanohydrins. The reaction proceeded smoothly with a substrate/catalyst molar ratio of 100-100 000 at 20-25 °C under solvent-free conditions. α,β-Unsatd. aldehydes were completely converted to the 1,2-adducts. The cyanation products can be isolated by direct distn. of the reaction mixt.

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    An overview of N-heterocyclic carbenes

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    Nature (London, United Kingdom) (2014), 510 (7506), 485-496CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)

    A review. The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of org. compds. for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in org. chem., with numerous applications in com. important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chem., summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

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    Cyclic (Alkyl)(Amino)Carbenes (CAACs): Stable Carbenes on the Rise

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    A review. Carbenes are compds. that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the prepn. by group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electroneg. and π-donor amino substituents of diaminocarbenes is replaced by a σ-donating but not π-donating alkyl group are discussed. As a consequence, CAACs are more nucleophilic (σ-donating) but also more electrophilic (π-accepting) than diaminocarbenes. Addnl., the presence of a quaternary carbon in the position α to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. The peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, the authors describe the prepn. of room temp. stable phosphorus derivs. in which the heteroatom is in the zero oxidn. state, nucleophilic boron compds., and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidn. state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc were isolated. Depending on the metal, the majority of spin d. can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small mols. at room temp., such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results were obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their use in harsh conditions. This property was used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts.

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    Reich, H. J. Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms. Chem. Rev. 2013, 113, 7130– 7178,  DOI: 10.1021/cr400187u

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    Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms

    Reich, Hans J.

    Chemical Reviews (Washington, DC, United States) (2013), 113 (9), 7130-7178CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    In this review a summary is first presented, in a comprehensive but not exhaustive way, regarding common structure types found in the solid state by single-crystal X-ray crystallog. A brief account is the offered with respect to the methods for detg. soln. structures and a summary of what is known about soln. structures of the principal classes of organolithium reagents. The main part of the review is a summary and discussion of organolithium reactions where significant exptl. studies have provided mechanistic insights.

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    Harrison-Marchand, A.; Mongin, F. Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 1. Structural Data. Chem. Rev. 2013, 113, 7470– 7562,  DOI: 10.1021/cr300295w

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    Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 1. Structural Data

    Harrison-Marchand, Anne; Mongin, Florence

    Chemical Reviews (Washington, DC, United States) (2013), 113 (10), 7470-7562CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. This review will focus on structures of organo(bi)metallic species for which the ligands mainly realize nucleophilic transfers for addn. or deprotonation purposes.

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    Mongin, F.; Harrison-Marchand, A. Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs. Chem. Rev. 2013, 113, 7563,  DOI: 10.1021/cr3002966

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    Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

    Mongin, Florence; Harrison-Marchand, Anne

    Chemical Reviews (Washington, DC, United States) (2013), 113 (10), 7563-7727CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. Mixing two organometallic reagents leads to synergic mixed aggregates or ate complexes for which we suggest (as well as for oligomers) the name "Mixed AggregAte" or MAA. Generalities concerning the formation and main features of the MAAs are presented. The aim was to present the main reactions using bimetallic combinations.

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    Gentner, T. X.; Mulvey, R. E. Alkali-Metal Mediation: Diversity of Applications in Main-Group Organometallic Chemistry. Angew. Chem., Int. Ed. 2021, 60, 9247– 9262,  DOI: 10.1002/anie.202010963

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    Alkali-Metal Mediation: Diversity of Applications in Main-Group Organometallic Chemistry

    Gentner, Thomas X.; Mulvey, Robert E.

    Angewandte Chemie, International Edition (2021), 60 (17), 9247-9262CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. Organolithium compds. have been at the forefront of synthetic chem. for over a century, as they mediate the synthesis of myriads of compds. that are utilized worldwide in academic and industrial settings. For that reason, lithium has always been the most important alkali metal in organometallic chem. Today, that importance is being seriously challenged by sodium and potassium, as the alkali-metal mediation of org. reactions in general has started branching off in several new directions. Recent examples covering main-group homogeneous catalysis, stoichiometric org. synthesis, low-valent main-group metal chem., polymn., and green chem. are showcased in this Review. Since alkali-metal compds. are often not the end products of these applications, their roles are rarely given top billing. Thus, this Review has been written to alert the community to this rising unifying phenomenon of "alkali-metal mediation".

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    Collum, D. B. Is N,N,N’,N’-tetramethylethylenediamine a good ligand for lithium?. Acc. Chem. Res. 1992, 25, 448– 454,  DOI: 10.1021/ar00022a003

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    Is N,N,N',N'-tetramethylethylenediamine a good ligand for lithium?

    Collum, David B.

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    A review with >88 refs. The title ligand TMEDA has proven to be invaluable as a modifier of organolithium reactivity. Voluminous results have dramatically influenced notions of solvation, aggregation, and reactivity. A more confused view is present in the literature of the mechanism by which TMEDA modifies organolithium structure and reactivity. The following guidelines are given for consideration: (1) TMEDA appears to manifest a highly substrate-dependent affinity for lithium; (2) TMEDA should have the most pronounced effects on organolithium structure and reactivity in the absence of strong donor solvents, e.g., THF; and (3) the affinity of TMEDA for lithium and the resulting influence on reactivity may have an inordinate temp. sensitivity.

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    Strohmann, C.; Seibel, T.; Strohfeldt, K. [tBuLi·(−)-Sparteine]: Molecular Structure of the First Monomeric Butyllithium Compound. Angew. Chem., Int. Ed. 2003, 42, 4531– 4533,  DOI: 10.1002/anie.200351308

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    [tBuLi·(-)-sparteine]: Molecular structure of the first monomeric butyllithium compound

    Strohmann, Carsten; Seibel, Timo; Strohfeldt, Katja

    Angewandte Chemie, International Edition (2003), 42 (37), 4531-4533CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Reaction of (-)-sparteine with tBuLi in n-pentane at -78° subsequently warmed to -50° gave light brown platelets of (I) in 71% yield; I was characterized by x-ray crystallog. and B3LYP/6-31+G(d) DFT calcns.

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    Knauer, L.; Wattenberg, J.; Kroesen, U.; Strohmann, C. The smaller, the better? How the aggregate size affects the reactivity of (trimethylsilyl)methyllithium. Dalton Trans 2019, 48, 11285– 11291,  DOI: 10.1039/C9DT02182E

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    The smaller, the better? How the aggregate size affects the reactivity of (trimethylsilyl)methyllithium

    Knauer, Lena; Wattenberg, Jonathan; Kroesen, Ulrike; Strohmann, Carsten

    Dalton Transactions (2019), 48 (30), 11285-11291CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)

    Weighting both the basicity and nucleophilicity of an organolithium compd. is crucial for an effective use of these reagents in syntheses. To achieve this, an aggregate of optimal size and reactivity has to be formed by adding suitable donating agents. Against usual expectations, this is not inevitably the smallest possible aggregate. In this work, we show that the monomeric complex of (trimethylsilyl)methyllithium stabilized by the bidentate diamine ligand, (R,R)-N,N,N',N'-tetramethyl-1,2-cyclohexanediamine, [(R,R)-TMCDA] shows no significant reactivity. In contrast, two dimeric aggregates stabilized by monodentate quinuclidine were obtained, exhibiting enhanced reactivity compared to the parent compd. and to the monomeric complex.

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20. 20

    Reich, H. J.; Green, D. P.; Medina, M. A.; Goldenberg, W. S.; Gudmundsson, B. Ö.; Dykstra, R. R.; Phillips, N. H. Aggregation and Reactivity of Phenyllithium Solutions. J. Am. Chem. Soc. 1998, 120, 7201– 7210,  DOI: 10.1021/ja980684z

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    20

    Aggregation and Reactivity of Phenyllithium Solutions

    Reich, Hans J.; Green, D. Patrick; Medina, Marco A.; Goldenberg, Wayne S.; Gudmundsson, Birgir Oe.; Dykstra, Robert R.; Phillips, Nancy H.

    Journal of the American Chemical Society (1998), 120 (29), 7201-7210CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Phenyllithium forms a mixt. of tetramer and dimer in ether. Complete conversion to dimeric solvates is achieved by the addn. of THF, dioxolane, DME, or TMEDA in near stoichiometric amts. The addn. of 2,5-dimethyltetrahydrofuran favors dimer, but tetramer is still detectable at 14 equiv of cosolvent. PMDTA converts PhLi to monomer in ether. In THF, PhLi is a mixt. of dimer and monomer. Addn. of TMEDA forms complexes, but the dimer/monomer ratio is essentially unaffected. PMDTA and HMPA form monomeric PhLi stoichiometrically. HMTTA (hexamethyltriethylenetetramine) and DMPU also result in monomer formation but several equiv. are required. 12-Crown-4 shows no spectroscopically detectable complexation of PhLi in THF. All of the cosolvents tested increase the reactivity of PhLi in THF in a test metalation reaction: HMPA and 12-crown-4 show the largest effects, PMDTA is intermediate, and HMTTA and TMEDA result in the least activation. In two selectivity tests, HMPA and 12-crown-4 show a substantially lower selectivity than the other cosolvents. The authors postulate that a contribution from a highly reactive sepd. ion pair (SIP) intermediate is responsible for the lower selectivity.

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21. 21

    Raston, C. L.; Whitaker, C. R.; White, A. H. Lewis-Base Adducts of Main Group Metal(I) Compounds. XI. Di-μ-iodo-bis(N,N,N′N′′,N′′-pentamethyldiethylenetriamine-N,N′,N′′-sodium). Aust. J. Chem. 1989, 42, 1393– 1396,  DOI: 10.1071/CH9891393

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    21

    Lewis-base adducts of main group metal(I) compounds. XI. Di-μ-iodo-bis(N,N,N',N'',N''-pentamethyldiethylenetriamine-N,N',N''-sodium)

    Raston, Colin L.; Whitaker, Claire R.; White, Allan H.

    Australian Journal of Chemistry (1989), 42 (8), 1393-6CODEN: AJCHAS; ISSN:0004-9425.

    The synthesis and structural characterization of Na2(μ-I)2L (L = N,N,N',N'',N''-pentamethyldiethylenetriamine) is recorded. Single-crystal x-ray structure detn. shows the compd. to be a μ,μ'-diiodo-bridged dimer, with the tridentate base making up the five-coordinate environment of Na. Crystals are triclinic, P‾1, a 10.113(2), b 9.470(2), c 8.793(4) Å, α 114.48(2), β 92.09(2), γ 96.65(1)°, Z = 1 dimer; R 0.037 for 1837 obsd. reflections.

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22. 22

    Cousins, D. M.; Davidson, M. G.; Frankis, C. J.; García-Vivó, D.; Mahon, M. F. Tris(2-dimethylaminoethyl)amine: A simple new tripodal polyamine ligand for Group 1 metals. Dalton Trans 2010, 39, 8278– 8280,  DOI: 10.1039/c0dt00567c

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    22

    Tris(2-dimethylaminoethyl)amine: a simple new tripodal polyamine ligand for Group 1 metals

    Cousins, David M.; Davidson, Matthew G.; Frankis, Catherine J.; Garcia-Vivo, Daniel; Mahon, Mary F.

    Dalton Transactions (2010), 39 (35), 8278-8280CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)

    The first examples of Group 1 metal complexes of tris(2-dimethylaminoethyl)amine (Me6TREN) are reported including monomeric Na complexes contg. η4-bound ligands, suggesting their potential use in alkali-metal-mediated synthetic applications.

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23. 23

    Davidson, M. G.; García-Vivó, D.; Kennedy, A. R.; Mulvey, R. E.; Robertson, S. D. Exploiting σ/π Coordination Isomerism to Prepare Homologous Organoalkali Metal (Li, Na, K) Monomers with Identical Ligand Sets. Chem.─Eur. J. 2011, 17, 3364– 3369,  DOI: 10.1002/chem.201003493

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    23

    Exploiting σ/π coordination isomerism to prepare homologous organoalkali metal (Li, Na, K) monomers with identical ligand sets

    Davidson, Matthew G.; Garcia-Vivo, Daniel; Kennedy, Alan R.; Mulvey, Robert E.; Robertson, Stuart D.

    Chemistry - A European Journal (2011), 17 (12), 3364-3369, S3364/1-S3364/6CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Tetraamine tris(N,N-dimethyl-2-aminoethyl)amine (Me6TREN) was used as a scaffold support to provide coordinative satn. in the complexes PhCH2M·Me6TREN (M = Li, Na, K). The Li deriv. displays a Li-C σ interaction with a pyramidalized CH2 both in the solid state and in soln., and represents the first example of η4 coordination of Me6TREN to Li. In the Na deriv., the metal cation slips slightly towards the delocalized π electrons while maintaining a partial σ interaction with the CH2 group. For the K case, coordinative satn. successfully yields the first monomeric benzylpotassium complex, in which the anion binds to the metal cation exclusively through its delocalized π system resulting in a planar CH2 group.

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24. 24

    Armstrong, D. R.; Davidson, M. G.; García-Vivó, D.; Kennedy, A. R.; Mulvey, R. E.; Robertson, S. D. Monomerizing Alkali-Metal 3,5-Dimethylbenzyl Salts with Tris(N, N-dimethyl-2-aminoethyl)amine (Me₆TREN): Structural and Bonding Implications. Inorg. Chem. 2013, 52, 12023– 12032,  DOI: 10.1021/ic401777x

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    24

    Monomerizing Alkali-Metal 3,5-Dimethylbenzyl Salts with Tris(N,N-dimethyl-2-aminoethyl)amine (Me6TREN): Structural and Bonding Implications

    Armstrong, David R.; Davidson, Matthew G.; Garcia-Vivo, Daniel; Kennedy, Alan R.; Mulvey, Robert E.; Robertson, Stuart D.

    Inorganic Chemistry (2013), 52 (20), 12023-12032CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)

    Alkali-metal (Li, Na, K) complexes of the substituted benzyl anion 3,5-dimethylbenzyl (Me2C6H3CH2-) derived from 1,3,5-trimethylbenzene (mesitylene) were coerced into monomeric forms by supporting them with the tripodal tetradentate Lewis donor tris(N,N-dimethyl-2-aminoethyl)amine, [N(CH2CH2NMe2)3, Me6TREN]. Mol. structure anal. by x-ray crystallog. establishes that the cation-anion interaction varies as a function of the alkali-metal, with the carbanion binding to Li mainly in a σ fashion, to K mainly in a π fashion, with the interaction toward Na being intermediate between these two extremes. This distinction is due to the heavier alkali-metal forcing and using the delocalization of neg. charge into the arom. ring to gain a higher coordination no. in accordance with its size. Me6TREN binds the metal in a η4 mode at all times. This coordination isomerism is shown by multinuclear NMR spectroscopy to also extend to the structures in soln. and is further supported by d. functional theory (DFT) calcns. on model systems. A Me6TREN stabilized benzyl K complex was used to prep. a mixed-metal ate complex by a cocomplexation reaction with tBu2Zn, with the benzyl ligand acting as an unusual ditopic σ/π bridging ligand between the two metals, and with the small Zn atom relocalizing the neg. charge back on to the lateral CH2 arm to give a complex best described as a contacted ion pair K zincate.

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25. 25

    Kennedy, A. R.; Mulvey, R. E.; Urquhart, R. I.; Robertson, S. D. Lithium, sodium and potassium picolyl complexes: syntheses, structures and bonding. Dalton Trans 2014, 43, 14265– 14274,  DOI: 10.1039/C4DT00808A

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    25

    Lithium, sodium and potassium picolyl complexes: syntheses, structures and bonding

    Kennedy, Alan R.; Mulvey, Robert E.; Urquhart, Robert I.; Robertson, Stuart D.

    Dalton Transactions (2014), 43 (38), 14265-14274CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)

    Synthetically important for introducing a picolyl scaffold into a mol. construction, alkali metalated picoline (methylpyridine) complexes are also interesting in their own right for the diversity of their ligand-metal bonding possibilities. Here the syntheses of seven new such complexes are reported: namely three 4-picoline derivs. 4-picLi·Me6TREN, 1, 4-picNa·Me6TREN, 2, and [4-picK·2(4-picH)]∞, 3; and four 2-picoline derivs., 2-picLi·Me6TREN, 4, 2-picLi·PMDETA, 4', 2-picNa·Me6TREN, 5, and [2-picK·PMDETA]2, 6' [where pic = NC5H4(CH2); Me6TREN = tris(N,N-dimethyl-2-aminoethyl)amine, (Me2NCH2CH2)3N; PMDETA = N,N,N',N'',N''-pentamethyldiethylenetriamine, (Me2NCH2CH2)2NMe]. X-ray crystallog. studies establish that the lighter alkali metal complexes 1, 2, 4' and 5 adopt monomeric structures in contrast to the polymeric and dimeric arrangements adopted by potassium complexes 3 and 6', resp. All complexes also were characterized by soln. NMR spectroscopy (1H, 13C, and where relevant 7Li). This study represents the first example of sodium and potassium picolyl complexes to be isolated and characterized. DOSY (Diffusion-Ordered Spectroscopy) expts. performed on 4 and 4' suggest both compds. retain their monomeric constitutions in C6D6 soln. Discussion focuses on the influence of the metal and neutral donor mol. on the structures and the nature of the ligand-metal (enamido vs. aza-allylic) interactions.

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26. 26

    Robertson, S. D.; Kennedy, A. R.; Liggat, J. J.; Mulvey, R. E. Facile synthesis of a genuinely alkane-soluble but isolable lithium hydride transfer reagent. Chem. Commun. 2015, 51, 5452– 5455,  DOI: 10.1039/C4CC06421F

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    26

    Facile synthesis of a genuinely alkane-soluble but isolable lithium hydride transfer reagent

    Robertson, Stuart D.; Kennedy, Alan R.; Liggat, John J.; Mulvey, Robert E.

    Chemical Communications (Cambridge, United Kingdom) (2015), 51 (25), 5452-5455CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    2-Tert-Butyl-1,2-dihydropyridinyllithium was prepd. and isolated in cryst. monomeric form by addn. of tBuLi to pyridine and the crystal structure of its triamine adduct, [2-tBuC5H5NLi·(Me2NCH2CH2)3N] (3·Me6TREN) was detd. The complex 3 reacts with benzophenone with hydride transfer and formation of the alcoholate Ph2CHOLi. 1-Lithio-2-butyl-1,2-dihydropyridines, typically formed as intermediates in the nucleophilic substitution (addn./elimination) of pyridine with (n- or t-)butyl lithium, have been isolated and comprehensively characterized. The linear substituted isomer is polymeric while the branched substituted isomer is a cyclotrimer. The lower oligomerization of the latter complex confers exceptional hexane soly. making it an excellent lithium hydride source in non-polar, aliph. media. A Me6TREN stabilized monomer of the tBu complex represents the first 1,2-dihydropyridyllithium complex to be characterized crystallog.

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27. 27

    Leich, V.; Spaniol, T. P.; Okuda, J. Formation of α-[KSiH₃] by hydrogenolysis of potassium triphenylsilyl. Chem. Commun. 2015, 51, 14772– 14774,  DOI: 10.1039/C5CC06187C

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    Formation of α-[KSiH3] by hydrogenolysis of potassium triphenylsilyl

    Leich, V.; Spaniol, T. P.; Okuda, J.

    Chemical Communications (Cambridge, United Kingdom) (2015), 51 (79), 14772-14774CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    Hydrogenation of easily accessible potassium triphenylsilyl [K(Me6TREN)SiPh3] gave the hydrogen storage material α-[KSiH3] in high yields by an unusual hydrogenolytic cleavage of silicon-Ph bonds.

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28. 28

    Mukherjee, D.; Osseili, H.; Spaniol, T. P.; Okuda, J. Alkali Metal Hydridotriphenylborates [(L)M][HBPh₃] (M = Li, Na, K): Chemoselective Catalysts for Carbonyl and O₂ Hydroboration. J. Am. Chem. Soc. 2016, 138, 10790– 10793,  DOI: 10.1021/jacs.6b06319

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    28

    Alkali metal hydridotriphenylborates [(L)M][HBPh3] (M = Li, Na, K): chemoselective catalysts for carbonyl and CO2 hydroboration

    Mukherjee, Debabrata; Osseili, Hassan; Spaniol, Thomas P.; Okuda, Jun

    Journal of the American Chemical Society (2016), 138 (34), 10790-10793CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Light alkali metal hydridotriphenylborates M[HBPh3] (M = Li, Na, K), characterized as tris{2-(dimethylamino)ethyl}amine (L) complexes [(L)M][HBPh3], act as efficient catalysts for the chemoselective hydroboration of a wide range of aldehydes and ketones using pinacolborane HBpin. The lithium deriv. showed a remarkably high TOF of ≥17 s-1. These compds. also catalyze the hydroborative redn. of CO2 to give formoxyborane HCO2Bpin without any over-redn.

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29. 29

    Kennedy, A. R.; McLellan, R.; McNeil, G. J.; Mulvey, R. E.; Robertson, S. D. Tetraamine Me₆Tren induced monomerization of alkali metal borohydrides and aluminohydrides. Ployhedron 2016, 103, 94– 99,  DOI: 10.1016/j.poly.2015.08.046

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30. 30

    Osseili, H.; Mukherjee, D.; Beckerle, K.; Spaniol, T. P.; Okuda, J. Me₆TREN-Supported Alkali Metal Hydridotriphenylborates [(L)M][HBPh₃] (M = Li, Na, K): Synthesis, Structure, and Reactivity. Organometallics 2017, 36, 3029– 3034,  DOI: 10.1021/acs.organomet.7b00308

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    30

    Me6TREN-Supported Alkali Metal Hydridotriphenylborates [(L)M][HBPh3] (M = Li, Na, K): Synthesis, Structure, and Reactivity

    Osseili, Hassan; Mukherjee, Debabrata; Beckerle, Klaus; Spaniol, Thomas P.; Okuda, Jun

    Organometallics (2017), 36 (16), 3029-3034CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)

    Triphenylborane (BPh3) abstracted the β-SiH in [(L)M{N(SiHMe2)2}] (L = Me6TREN; M = Li, Na, K) in THF to give the hydridotriphenylborates [(L)M][HBPh3]. Reactions in benzene favored silazide instead of hydride abstraction to give [(L)M][Ph3B-N(SiHMe2)2]. The hydridotriphenylborates [(L)M][HBPh3] catalyzed the chemoselective hydroboration of benzophenone by pinacolborane (HBpin), with the Li deriv. being the most active. The soln. structure of [(L)Li][HBPh3] was qual. studied in the context of its superior catalytic activity. Fluxional coordination of L in [(L)Li(THF)]+ in tandem with a THF solvent mol. was revealed by NMR spectroscopy. para-Substituents in [HB(C6H4-p-X)3]- influenced the rate which is apparently detd. by the addn. of the B-H function to the isolable alkoxy borate intermediate [(L)Li][Ph2CHOBPh3].

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31. 31

    Davison, N.; Waddell, P. G.; Dixon, C.; Wills, C.; Penfold, T. J.; Lu, E. A monomeric (trimethylsilyl)methyl lithium complex: synthesis, structure, decomposition and preliminary reactivity studies. Dalton Trans. 2022,  DOI: 10.1039/D1DT03532K

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    Standfuss, S.; Spaniol, T. P.; Okuda, J. Lithiation of a Cyclen-Derived (NNNN) Macrocycle and Its Reaction with n-Butyllithium. Eur. J. Inorg. Chem. 2010, 2010, 2987– 2991,  DOI: 10.1002/ejic.201000199

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    Redko, M. Y.; Jackson, J. E.; Huang, R. H.; Dye, J. L. Design and Synthesis of a Thermally Stable Organic Electride. J. Am. Chem. Soc. 2005, 127, 12416– 12422,  DOI: 10.1021/ja053216f

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    Design and Synthesis of a Thermally Stable Organic Electride

    Redko, Mikhail Y.; Jackson, James E.; Huang, Rui H.; Dye, James L.

    Journal of the American Chemical Society (2005), 127 (35), 12416-12422CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    An electride was synthesized that is stable to auto-decompn. at room temp. The key was the theor. directed synthesis of a per-aza analog of cryptand[2.2.2] in which each of the linking arms contains a piperazine ring I. This complexant was designed to provide strong complexation of Na+ via pre-organization of a crypt that contains eight non-reducible tertiary amine nitrogens. The structure and properties indicate that, as with other electrides, the anions are electrons trapped in the cavities formed by close-packing of the complexed cations. The isostructural sodide, with Na- anions in the cavities, is also stable at and above room temp.

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34. 34

    Davison, N.; Falbo, E.; Waddell, P. G.; Penfold, T. J.; Lu, E. A monomeric methyllithium complex: synthesis and structure. Chem. Commun. 2021, 57, 6205– 6208,  DOI: 10.1039/D1CC01420J

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    34

    A monomeric methyllithium complex: synthesis and structure

    Davison, Nathan; Falbo, Emanuele; Waddell, Paul G.; Penfold, Thomas J.; Lu, Erli

    Chemical Communications (Cambridge, United Kingdom) (2021), 57 (50), 6205-6208CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    Methyllithium (MeLi) is the parent archetypal organolithium complex. MeLi exists as aggregates in solns. and solid states. Monomeric MeLi is postulated as a highly reactive intermediate and plays a vital role in understanding MeLi-mediated reactions but has not been isolated. Herein, we report the synthesis and structure of the first monomeric MeLi complex enabled by a new hexadentate neutral amine ligand.

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35. 35

    Fohlmeister, L.; Stasch, A. Alkali Metal Hydride Complexes: Well-Defined Molecular Species of Saline Hydrides. Aust. J. Chem. 2015, 68, 1190– 1201,  DOI: 10.1071/CH15206

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    Alkali Metal Hydride Complexes: Well-Defined Molecular Species of Saline Hydrides*

    Fohlmeister, Lea; Stasch, Andreas

    Australian Journal of Chemistry (2015), 68 (8), 1190-1201CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)

    A review is presented on synthesis, crystal structure, and properties of well-defined alkali metal hydride complexes. The first examples of well-defined alkali metal hydride complexes were synthesized and characterized in recent years, and their properties and underlying principles for their generation and stabilization are emerging. This article gives an account of the hydrides of the alkali metals (Group 1 metals) and selected '-ate' complexes contg. hydrides and alkali metals, and reviews the chem. of well-defined alkali metal hydride complexes including their syntheses, structures, and characteristics. The properties of the alkali metal hydrides LiH, NaH, KH, RbH, and CsH are dominated by their ionic NaCl structure. Stable, sol., and well-defined LiH and NaH complexes were obtained by metathesis and β-hydride elimination reactions that require suitable ligands with some steric bulk and the ability to coordinate to several metal ions. These novel hydride complexes reward with higher reactivity and different properties compared with their parent ionic solids.

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36. 36

    Wolf, B. M.; Anwander, R. Chasing Multiple Bonding Interactions between Alkaline-Earth Metals and Main-Group Fragments. Chem.─Eur. J. 2019, 25, 8190– 8202,  DOI: 10.1002/chem.201901169

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    36

    Chasing Multiple Bonding Interactions between Alkaline-Earth Metals and Main-Group Fragments

    Wolf, Benjamin M.; Anwander, Reiner

    Chemistry - A European Journal (2019), 25 (35), 8190-8202CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. Formally dianionic ligands such as alkylidenes or organoimidos play a major role in the organometallic chem. of transition metals and are an emerging topical area of f-element chem. The pursuit and development of main-group-metal congeners has been tackled sporadically but is clearly lacking behind. The pronounced ionic bonding in particular, prevailing in alkali and alk.-earth (Ae) metal derivs., proved cumbersome. Recent substantial progress in the resp. field of divalent Ae chem. has been triggered by the implementation of new synthesis strategies involving new AeII precursors and tailor-made ligands. The main emphasis of this Minireview will be on the synthesis and reactivity of well-defined Group 2 alkylidenes, organoimides, silylenes, and phosphandiides.

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37. 37

    Wolf, B. M.; Stuhl, C.; Anwander, R. Synthesis of homometallic divalent lanthanide organoimides from benzyl complexes. Chem. Commun. 2018, 54, 8826– 8829,  DOI: 10.1039/C8CC05234D

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    37

    Synthesis of homometallic divalent lanthanide organoimides from benzyl complexes

    Wolf, Benjamin M.; Stuhl, Christoph; Anwander, Reiner

    Chemical Communications (Cambridge, United Kingdom) (2018), 54 (64), 8826-8829CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    The reaction of LnI2(thf)2 with benzyl potassium affords the homoleptic benzyl complexes [Ln(CH2Ph)2]n of samarium, europium, and ytterbium. In the cases of Eu and Yb, the treatment of [Ln(CH2Ph)2]n with one equiv of 2,6-diisopropylaniline gives access to tetrameric organoimide complexes [(thf)Ln(μ3-NDipp)]4, representing the first examples of homometallic Ln(II) imides. This study revealed that the Yb(II) organoimide chem. is significantly different from that of calcium.

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38. 38

    Wolf, B. M.; Stuhl, C.; Maichle-Mössmer, C.; Anwander, R. Lewis-Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium. Chem.─Eur. J. 2018, 24, 15921– 15929,  DOI: 10.1002/chem.201803619

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    38

    Lewis-Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium

    Wolf, Benjamin M.; Stuhl, Christoph; Maichle-Moessmer, Caecilia; Anwander, Reiner

    Chemistry - A European Journal (2018), 24 (59), 15921-15929CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Discrete organoimide complexes of the divalent rare-earth metals samarium, europium, and ytterbium are reported. Tandem salt metathesis-protonolysis reactions using LnII bis(tetramethylaluminate) precursors [Ln(AlMe4)2]n and monopotassium salts of 2,6-diisopropylaniline (H2NDipp) and triphenylsilylamine prove viable and efficient protocols. Depending on the ionic radius of the LnII metal centers and the steric demand of the imido carbon backbone, mono- and dilanthanide arrangements of general compn. [(thf)xLn(NR)(AlMe3)]y (Ln = Sm, Eu, Yb; R = Dipp, SiPh3) are found in the solid state. Complex formation and stabilization is achieved by coordination of the Lewis acid AlMe3, which also prevents formation of higher aggregated species. The feasibility of redox chem. is shown with the plumbocene deriv. Cp*2Pb, providing access to the corresponding monomeric LnIII half-sandwich complexes [Cp*Ln(NR)(AlMe3)(thf)2] (Ln = Sm, Yb).

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39. 39

    Lu, E.; Chu, J. – X.; Chen, Y. – F. Scandium Terminal Imido Chemistry. Acc. Chem. Res. 2018, 51, 557– 566,  DOI: 10.1021/acs.accounts.7b00605

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    Scandium Terminal Imido Chemistry

    Lu, Erli; Chu, Jiaxiang; Chen, Yaofeng

    Accounts of Chemical Research (2018), 51 (2), 557-566CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)

    A review. Research into transition metal complexes bearing multiply bonded main-group ligands has developed into a thriving and fruitful field over the past half century. These complexes, featuring terminal M=E/M≡E (M = transition metal; E = main-group element) multiple bonds, exhibit unique structural properties as well as rich reactivity, which render them attractive targets for inorg./organometallic chemists as well as indispensable tools for org./catalytic chemists. This fact has been highlighted by their widespread applications in org. synthesis, for example, as olefin metathesis catalysts. In the ongoing renaissance of transition metal-ligand multiple-bonding chem., there have been reports of M=E/M≡E interactions for the majority of the metallic elements of the periodic table, even some actinide metals. In stark contrast, the largest subgroup of the periodic table, rare-earth metals (Ln = Sc, Y, and lanthanides), have been excluded from this upsurge. Indeed, the synthesis of terminal Ln=E/Ln≡E multiple-bonding species lagged behind that of the transition metal and actinide congeners for decades. Although these species had been pursued since the discovery of a rare-earth metal bridging imide in 1991, such a terminal (nonpincer/bridging hapticities) Ln=E/Ln≡E bond species was not obtained until 2010. The scarcity is mainly attributed to the energy mismatch between the frontier orbitals of the metal and the ligand atoms. This renders the putative terminal Ln=E/Ln≡E bonds extremely reactive, thus resulting in the formation of aggregates and/or reaction with the ligand/environment, quenching the multiple-bond character. In 2010, the stalemate was broken by the isolation and structural characterization of the first rare-earth metal terminal imide - a scandium terminal imide - by our group. The double-bond character of the Sc=N bond was unequivocally confirmed by single-crystal X-ray diffraction. Theor. investigations revealed the presence of two p-d π bonds between the scandium ion and the nitrogen atom of the imido ligand and showed that the dianionic [NR]2- imido ligand acts as a 2σ,4π electron donor. Subsequent studies of the scandium terminal imides revealed highly versatile and intriguing reactivity of the Sc=N bond. This included cycloaddn. toward various unsatd. bonds, C-H/Si-H/B-H bond activations and catalytic hydrosilylation, dehydrofluorination of fluoro-substituted benzenes/alkanes, CO2 and H2 activations, activation of elemental selenium, coordination with other transition metal halides, etc. Since our initial success in 2010, and with contributions from us and across the community, this young, vibrant research field has rapidly flourished into one of the most active frontiers of rare-earth metal chem. The prospect of extending Ln=N chem. to other rare-earth metals and/or different metal oxidn. states, as well as exploiting their stoichiometric and catalytic reactivities, continues to attract research effort. Herein we present an account of our investigations into scandium terminal imido chem. as a timely summary, in the hope that our studies will be of interest to this readership.

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40. 40

    Raston, C. L.; Skelton, B. W.; Whitaker, C. R.; White, A. H. Lewis-Base Adducts of Main Group 1 Metal Compounds. IV. Synthesis and Structure of the XLiL₃ System (X = Cl, Br, I, L = 4-t-Butylpyridine, and X = I, L = Quinoline). Aust. J. Chem. 1988, 41, 341,  DOI: 10.1071/CH9880341

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    Lewis-base adducts of main Group 1 metal compounds. IV. Synthesis and structure of the XLiL3 system (X = Cl, Br, I, L = 4-tert-butylpyridine, and X = I, L = quinoline)

    Raston, Colin L.; Skelton, Brian W.; Whitaker, Claire R.; White, Allan H.

    Australian Journal of Chemistry (1988), 41 (3), 341-9CODEN: AJCHAS; ISSN:0004-9425.

    [LiL3X] (X = Cl, Br, I; L = 4-t-butylpyridine) were prepd. by recrystn. of the anhyd. LiX from the parent base, and characterized structurally by single-crystal x-ray structure detn. [LiL3Cl] and [LiL3Br] are isomorphous (monoclinic, P21); [LiL3I] is orthorhombic, Pbca. These complexes are all pseudo-trigonal and contain 4-coordinate XLiN3 arrays [Li-X, 2.33(1); 2.53(1); 2.76(4) Å; Li-N, 2.03(1)-2.11(1); 2.04(1)-2.09(2); 2.03(4)-2.07(4) Å]. Similar data are also recorded for LiL13I.L1( L1 = quinoline) (monoclinic, P21/c). While a close parallel may be drawn between the chem. of Li(I) and Cu(I) in respect of [LiL3X], LiL13I is unusual in being the first MXL3 deriv. for a quinoline-type ligand; it is a monoquinoline solvate.

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41. 41

    Raston, C. L.; Skelton, B. W.; Whitaker, C. R.; White, A. H. Lewis-base adducts of main Group 1 metal compounds. Part 2. Syntheses and structures of [Li₄Cl₄(pmdien)₃] and LiI(pmdien)]. J. Chem. Soc., Dalton Trans. 1988, 987– 990,  DOI: 10.1039/dt9880000987

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    Lewis-base adducts of main group 1 metal compounds. Part 2. Syntheses and structures of μ3-chloro-tri-μ-chloro-μ-[pentamethyldiethylenetriamine]bis(pentamethyldiethylenetriamine)tetralithium(I) and iodo(pentamethyldiethylenetriamine)lithium(I)

    Raston, Colin L.; Skelton, Brian W.; Whitaker, Claire R.; White, Allan H.

    Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1988), (4), 987-90CODEN: JCDTBI; ISSN:0300-9246.

    Crystn. of LiCl from its soln. in excess N,N,N',N',N''-pentamethyldiethylenetriamine (pmdien) in hydrocarbon yields [Li4Cl4(pmdien)3], crystals of which are monoclinic, space group P21/n. LiI yields [LiI(pmdien)], crystals of which are orthorhombic, space group Pbam. In the iodide, there are 2 independent mols., each with m symmetry and 4-coordinate Li [Li-12.75(3), 2.67(3) Å], whereas the chloride contains both 4- and 5-coordinate Li atoms.

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42. 42

    Berthet, J. – C.; Siffredi, G.; Thuéry, P.; Ephritikhine, M. Synthesis and crystal structure of pentavalent uranyl complexes. The remarkable stability of UO₂X (X = I, SO₃CF₃) in non-aqueous solutions. Dalton Trans. 2009, 3478,  DOI: 10.1039/b820659g

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    Synthesis and crystal structure of pentavalent uranyl complexes. The remarkable stability of UO2X (X = I, SO3CF3) in non-aqueous solutions

    Berthet, Jean-Claude; Siffredi, Gerald; Thuery, Pierre; Ephritikhine, Michel

    Dalton Transactions (2009), (18), 3478-3494CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)

    The reaction of [UO2I2(THF)3] with KC5R5 (R = H, Me) or K2C8H8 in pyridine gave crystals of [{UO2(py)5}{KI2(py)2}]∞ (1), which were desolvated under vacuum into pulverulent [UO2(py)2.2KI2] (2). Similar reactions with [UO2(OTf)2] afforded [UO2(py)2.3K(OTf)2] (3) as a powder and crystals of [{UO2(py)5}2{K3(OTf)5}·py]∞ (4·py), which were also obtained together with crystals of [{UO2(py)5}2{K(OTf)2(py)2}][OTf]·py (5·py) by treating [UO2(OTf)2] with KC4Me4P. Crystals of 6·py, the Tl analog of 5·py, were isolated from the reaction of [UO2(OTf)2] and TlC5H5. Treatment of [UO2I2(THF)3] with LiCH2SiMe3 in pyridine afforded crystals of [{UO2(py)5}{LiI(py)2}][I] (7) while [UO2(OTf)2] reacted with the alkyllithium reagent in MeCN to give crystals of [{UO2(py)5}{Li2(OTf)3}]∞ (8) in pyridine. The crystal structures of 1, 4·py, 5·py, 6·py, 7 and 8 revealed U:O M interactions (M = Li, K, Tl), and the rich diversity of these structures, from dinuclear (7) to 3-dimensional polymeric (4), is related to the distinct coordination nos. of the M+ ion and ligation modes of the bridging iodide and triflate ligands as well as the presence of U:O M interactions. Mononuclear [UO2(OTf)(THF)n] (9) and [UO2(OTf)(Et2O)0.5] (10) were resp. obtained by reaction of [UO2(OTf)2] with KC5R5 in THF or LiCH2SiMe3 in Et2O and were transformed into [UO2(OTf)(py)2] (11) in pyridine. Treatment of [UO2I2(THF)3] with TlC5H5 in pyridine afforded crystals of [UO2(py)5][I]·py (12·py) which were desolvated under vacuum into the powder of [UO2I(py)2.5] (14). The same reaction in THF gave [UO2I(THF)2.7] (13) in powder form. Crystals of [UO2(CyMe4BTBP)(py)][OTf]·1.5py (15·1.5py) (CyMe4BTBP = 6,6'-bis(3,3,6,6-tetramethylcyclohexano-1,2,4-triazin-3-yl)-2,2'-bipyridine) and the powder of [UO2I(CyMe4BTBP)] (16) were obtained by treating [UO2(CyMeBTBP)X2] (X = OTf, I) with KC5Me5 or TlC5H5, resp. The uranyl(V) chloride and nitrate compds. [UO2Cl(py)3] (17) and [UO2(NO3)(py)3] (18) were prepd. by reaction of the uranyl(VI) precursors with TlC5H5 in pyridine; complex 18 was also obtained by treating 13 with TlNO3. Crystals of the neutral mononuclear complex [UO2(OTf)(py)4] (19) were isolated from reaction of [UO2(OTf)2] with Me3SiC5H5 in MeCN. Similar reaction with [UO2Cl2(THF)2]2 in pyridine gave crystals of [UO2Cl2(py)3]. The crystal structures of 12·py, 15·1.5py and 19 were detd.; the structure of 15 was compared with that of the uranyl(VI) counterpart. All the uranyl(V) compds. are remarkably stable in pyridine soln.; the IR absorption at 816 cm-1 is attributed to the νasym(U:O) of the ubiquitous [UO2(py)5]+ species.

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43. 43

    Liu, F. – C.; Shadike, Z.; Wang, X. – F.; Shi, S.-Q.; Zhou, Y. – N.; Chen, G. – Y.; Yang, X. – Q.; Weng, L. – H.; Zhao, J. – T.; Fu, Z. – W. A Novel Small-Molecule Compound of Lithium Iodine and 3-Hydroxypropionitride as a Solid-State Electrolyte for Lithium–Air Batteries. Inorg. Chem. 2016, 55, 6504– 6510,  DOI: 10.1021/acs.inorgchem.6b00564

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    A Novel Small-Molecule Compound of Lithium Iodine and 3-Hydroxypropionitride as a Solid-State Electrolyte for Lithium-Air Batteries

    Liu, Fang-Chao; Shadike, Zulipiya; Wang, Xiao-Fang; Shi, Si-Qi; Zhou, Yong-Ning; Chen, Guo-Ying; Yang, Xiao-Qing; Weng, Lin-Hong; Zhao, Jing-Tai; Fu, Zheng-Wen

    Inorganic Chemistry (2016), 55 (13), 6504-6510CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)

    A novel small-mol. compd. of lithium iodine and 3-hydroxypropionitrile (HPN) has been successfully synthesized. Our combined exptl. and theor. studies indicated that LiIHPN is a Li-ion conductor, which is utterly different from the I--anion conductor of LiI(HPN)2 reported previously. Solid-state lithium-air batteries based on LiIHPN as the electrolyte exhibit a reversible discharge capacity of more than 2100 mAh g-1 with a cyclic performance over 10 cycles. Our findings provide a new way to design solid-state electrolytes toward high-performance lithium-air batteries.

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44. 44

    Thirumoorthi, R.; Chivers, T. Structural Comparison of Lithium Iodide Complexes of Symmetrical and Unsymmetrical [CH₂(PPh₂NSiMe₃)(PPh₂NR)] (R = SiMe₃, H) Ligands. J. Struct. Chem. 2018, 59, 1221– 1227,  DOI: 10.1134/S002247661805030X

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    Structural Comparison of Lithium Iodide Complexes of Symmetrical and Unsymmetrical [CH2(PPh2NSiMe3)(PPh2NR)](R = SiMe3, H) Ligands

    Thirumoorthi, R.; Chivers, T.

    Journal of Structural Chemistry (2018), 59 (5), 1221-1227CODEN: JSTCAM; ISSN:0022-4766. (Springer)

    Compds. [(LiI)1] and [(LiI)2]2 crystallize in the centrosym. space group P21/n. They are made up of neutral ligands [H2C(PPh2NSiMe3)2] (1) and [H2C(PPh2NSiMe3)(PPh2NH)] (2) and a LiI mol. In both cases, N,N chelation with lithium is obsd. Ligand 2 contains two different nitrogen centers viz., P=N(SiMe3) and P=N(H), which are coordinated unsym. to lithium (Li-N = 2.055(8) and 2.072(8) Å) to form [{LiI}{CH2(PPh2NSiMe3)×(PPh2NH)}] as monomer units that are linked via intermol. coordination between NH and Li (2.097(8) Å) to form a central four-membered ring, Li2N2 with four-coordinate lithium atoms. In contrast, [(LiI)1] is monomeric with a three-coordinate lithium center. This disparity is reflected in the Li-I bond distances (2.699(11) Å for [(LiI)1] and 2.824(7) Å) for [(LiI)2]2). The dimer [(LiI)2]2 displays intramol. Csp3H-π and intermol. Csp2H-π interactions (between phosphorus-substituted Ph groups).

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45. 45

    Ivanova, I. S.; Ilyukhin, A. B.; Tsebrikova, G. S.; Polyakova, I. N.; Pyatova, E. N.; Solov’ev, V. P.; Baulin, V. E.; Tsivadze, A. Y. 2,4,6-Tris[2-(diphenylphosphoryl)-4-ethylphenoxy]-1,3,5-triazine: A new ligand for lithium binding. Inorg. Chim. Acta 2019, 497, 119095,  DOI: 10.1016/j.ica.2019.119095

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    2,4,6-Tris[2-(diphenylphosphoryl)-4-ethylphenoxy]-1,3,5-triazine: A new ligand for lithium binding

    Ivanova, Irina S.; Ilyukhin, Andrey B.; Tsebrikova, Galina S.; Polyakova, Irina N.; Pyatova, Elena N.; Solov'ev, Vitaly P.; Baulin, Vladimir E.; Yu. Tsivadze, Aslan

    Inorganica Chimica Acta (2019), 497 (), 119095CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)

    The synthesis, IR, UV-visible spectra, the stability consts. of the Li+L, Na+L and K+L complexes in MeCN and ion-selective properties of new phosphoryl-contg. tripodand 2,4,6-tris[2-(diphenylphosphoryl)-4-ethylphenoxy]-1,3,5-triazine (L) and crystal structures L·H2O (1), [LiL(ClO4)...(H2O)LLi](ClO4)·11H2O (2), [LiLI...(H2O)LLi]I·18H2O (3) and [K2L2I]I·7.2H2O (4) were described. The podand L exhibits Li+ and good Li+/Na+ selectivity.

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    Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr. 1976, A32, 751– 767,  DOI: 10.1107/S0567739476001551

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    Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides

    Shannon, R. D.

    Acta Crystallographica, Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography (1976), A32 (5), 751-67CODEN: ACACBN; ISSN:0567-7394.

    The effective ionic radii of R. Shannon and R. Prewitt (1969) were revised to include more unusual oxidn. states and coordinations. Revisions were based on new structural data, empirical bond strength-bond length relations, and plots of (1) radii vs. vol., (2) radii vs. coordination no., and (3) radii vs. oxidn. state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In3+-X, Pb2+-X, and Tl+-X. Bonds with delocalized electrons and therefore metallic character, such as Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.

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    Perdew, J. P.; Ernzerhof, M.; Burke, K. Rationale for mixing exact exchange with density functional approximations. J. Chem. Phys. 1996, 105, 9982– 9985,  DOI: 10.1063/1.472933

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    Rationale for mixing exact exchange with density functional approximations

    Perdew, John P.; Ernzerhof, Matthias; Burke, Kieron

    Journal of Chemical Physics (1996), 105 (22), 9982-9985CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)

    D. functional approxns. for the exchange-correlation energy ExcDFA of an electronic system are often improved by admixing some exact exchange Ex: Exc ≈ ExcDFA + (1/n)(Ex - ExDFA). This procedure is justified when the error in ExcDFA arises from the λ = 0 or exchange end of the coupling-const. integral ∫01dλ Exc,λDFA. We argue that the optimum integer n is approx. the lowest order of Goerling-Levy perturbation theory which provides a realistic description of the coupling-const. dependence Exc,λ in the range 0 ≤ λ ≤ 1, whence n ≈ 4 for atomization energies of typical mols. We also propose a continuous generalization of n as an index of correlation strength, and a possible mixing of second-order perturbation theory with the generalized gradient approxn.

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    Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648– 5652,  DOI: 10.1063/1.464913

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    Density-functional thermochemistry. III. The role of exact exchange

    Becke, Axel D.

    Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.

    Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.

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    Lee, C. T.; Yang, W. T.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785– 789,  DOI: 10.1103/PhysRevB.37.785

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    Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density

    Lee, Chengteh; Yang, Weitao; Parr, Robert G.

    Physical Review B: Condensed Matter and Materials Physics (1988), 37 (2), 785-9CODEN: PRBMDO; ISSN:0163-1829.

    A correlation-energy formula due to R. Colle and D. Salvetti (1975), in which the correlation energy d. is expressed in terms of the electron d. and a Laplacian of the 2nd-order Hartree-Fock d. matrix, is restated as a formula involving the d. and local kinetic-energy d. On insertion of gradient expansions for the local kinetic-energy d., d.-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calcns. on a no. of atoms, pos. ions, and mols., of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.

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    Dill, J. D.; Pople, J. A. Self-consistent molecular orbital methods. XV. Extended Gaussian-type basis sets for lithium, beryllium, and boron. J. Chem. Phys. 1975, 62, 2921– 2923,  DOI: 10.1063/1.430801

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    Self-consistent molecular orbital methods. XV. Extended Gaussian-type basis sets for lithium, beryllium, and boron

    Dill, James D.; Pople, John A.

    Journal of Chemical Physics (1975), 62 (7), 2921-3CODEN: JCPSA6; ISSN:0021-9606.

    Self-consistent Gaussian type basis sets are given: 5-21G for Be and Li and 6-31G for B. All s and p coeffs. and exponents were varied for the B at. ground state until an energy min. was reached. For Li and Be, an initial set of Gaussian exponents and s coeffs. was obtained similarly for the at. ground state (Li 2S, Be 1S). The optimum p coeffs. were obtained by repeating the procedure on the excited states of Li(2P) and Be(3P).

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    Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297– 3305,  DOI: 10.1039/b508541a

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    Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy

    Weigend, Florian; Ahlrichs, Reinhart

    Physical Chemistry Chemical Physics (2005), 7 (18), 3297-3305CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

    Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 mols. representing (nearly) all elements-except lanthanides-in their common oxidn. states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, d. functional theory and correlated methods, for which we had chosen Moller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.

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52. 52

    Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. Consistent van der Waals Radii for the Whole Main Group. J. Phys. Chem. A 2009, 113, 5806– 5812,  DOI: 10.1021/jp8111556

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    52

    Consistent van der Waals Radii for the Whole Main Group

    Mantina, Manjeera; Chamberlin, Adam C.; Valero, Rosendo; Cramer, Christopher J.; Truhlar, Donald G.

    Journal of Physical Chemistry A (2009), 113 (19), 5806-5812CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)

    At. radii are not precisely defined but are nevertheless widely used parameters in modeling and understanding mol. structure and interactions. The van der Waals radii detd. by Bondi from mol. crystals and data for gases are the most widely used values, but Bondi recommended radius values for only 28 of the 44 main-group elements in the periodic table. In the present Article, we present at. radii for the other 16; these new radii were detd. in a way designed to be compatible with Bondi's scale. The method chosen is a set of two-parameter correlations of Bondi's radii with repulsive-wall distances calcd. by relativistic coupled-cluster electronic structure calcns. The newly detd. radii (in Å) are Be, 1.53; B, 1.92; Al, 1.84; Ca, 2.31; Ge, 2.11; Rb, 3.03; Sr, 2.49; Sb, 2.06; Cs, 3.43; Ba, 2.68; Bi, 2.07; Po, 1.97; At, 2.02; Rn, 2.20; Fr, 3.48; and Ra, 2.83.

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53. 53

    Pollard, V. A.; Orr, S. A.; McLellan, R.; Kennedy, A. R.; Hevia, E.; Mulvey, R. E. Lithium diamidodihydridoaluminates: bimetallic cooperativity in catalytic hydroboration and metalation applications. Chem. Commun. 2018, 54, 1233– 1236,  DOI: 10.1039/C7CC08214B

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    53

    Lithium diamidodihydridoaluminates: bimetallic cooperativity in catalytic hydroboration and metallation applications

    Pollard, Victoria A.; Orr, Samantha A.; McLellan, Ross; Kennedy, Alan R.; Hevia, Eva; Mulvey, Robert E.

    Chemical Communications (Cambridge, United Kingdom) (2018), 54 (10), 1233-1236CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    Aluminum-lithium binuclear heterometallic amide hydride-bridged complexes were prepd. and examd. by single-crystal x-ray structure anal.; the complexes catalyze hydroboration of carbonyl compds. with pinacolborane, giving aralkyl pinacolborate esters. Cooperativity between the Li and Al centers is implicated in catalytic hydroboration reactions of aldehydes and ketones with pinacolborane via heteroleptic lithium diamidodihydridoaluminates. In addn. to implementing hydroalumination, these versatile heteroleptic ates can also perform as amido bases as illustrated with an acidic triazole.

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54. 54

    Barjat, H.; Morris, G. A.; Smart, S.; Swanson, A. G.; Williams, S. C. R. High-Resolution Diffusion-Ordered 2D Spectroscopy (HR-DOSY) – A New Tool for the Analysis of Complex-Mixtures. J. Magn. Reson. Ser. B 1995, 108, 170– 172,  DOI: 10.1006/jmrb.1995.1118

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    54

    High-resolution diffusion-ordered 2D spectroscopy (HR-DOSY) - A new tool for the analysis of complex mixtures

    Barjat, Herve; Morris, Gareth A.; Smart, Sean; Swanson, Alistair G.; Williams, Steven C. R.

    Journal of Magnetic Resonance, Series B (1995), 108 (2), 170-2CODEN: JMRBE5; ISSN:1064-1866. (Academic)

    The title method allows the sepn. of the NMR spectra of complex mixts. of small mols. into their component contributions with a resoln. comparable to that of liq. chromatog.-NMR methods, rapidly and simply. When the method was applied to the anal. of a HClO4 ext. of gerbil brain, excellent resoln. was achieved and many individual metabolites were identified from the chem. shifts and multiplet patterns of their sepd. high-resoln. spectra.

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55. 55

    Neufeld, R.; Stalke, D. Accurate molecular weight determination of small molecules via DOSY-NMR by using external calibration curves with normalized diffusion coefficients. Chem. Sci. 2015, 6, 3354– 3364,  DOI: 10.1039/C5SC00670H

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    55

    Accurate molecular weight determination of small molecules via DOSY-NMR by using external calibration curves with normalized diffusion coefficients

    Neufeld, Roman; Stalke, Dietmar

    Chemical Science (2015), 6 (6), 3354-3364CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)

    Detn. of the aggregation and solvation nos. of organometallic complexes in soln. is an important task to increase insight in reaction mechanisms. Thus knowing which aggregates are formed during a reaction is of high interest to develop better selectivity and higher yields. Diffusion-ordered spectroscopy (DOSY), which separates NMR signals according to the diffusion coeff., finds increasing use to identify species in soln. However, there still is no simple relationship between diffusion coeff. and mol. wt. (MW). Some methods have been developed to est. the MW but still with a significant error of ±30%. Here authors describe a novel development of MW-detn. by using an external calibration curve (ECC) approach with normalized diffusion coeffs. Taking the shape of the mols. into account enables accurate MW-predictions with a max. error of smaller than ±9%. Moreover we show that the addn. of multiple internal refs. is dispensable. One internal ref. (that also can be the solvent) is sufficient. If the solvent signal is not accessible, 16 other internal stds. (aliphatics and aroms.) are available to avoid signal overlapping problems and provide flexible choice of analytes. This method is independent of NMR-device properties and diversities in temp. or viscosity and offers an easy and robust method to det. accurate MWs in soln.

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    Du, J.; Douair, I.; Lu, E.; Seed, J. A.; Tuna, F.; Wooles, A. J.; Maron, L.; Liddle, S. T. Evidence for ligand- and solvent-induced disproporationation of uranium(IV). Nat. Commun. 2021, 12, 4832,  DOI: 10.1038/s41467-021-25151-z

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    56

    Evidence for ligand- and solvent-induced disproportionation of uranium(IV)

    Du, Jingzhen; Douair, Iskander; Lu, Erli; Seed, John A.; Tuna, Floriana; Wooles, Ashley J.; Maron, Laurent; Liddle, Stephen T.

    Nature Communications (2021), 12 (1), 4832CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)

    Abstr.: Disproportionation, where a chem. element converts its oxidn. state to two different ones, one higher and one lower, underpins the fundamental chem. of metal ions. The overwhelming majority of uranium disproportionations involve uranium(III) and (V), with a singular example of uranium(IV) to uranium(V/III) disproportionation known, involving a nitride to imido/triflate transformation. Here, we report a conceptually opposite disproportionation of uranium(IV)-imido complexes to uranium(V)-nitride/uranium(III)-amide mixts. This is facilitated by benzene, but not toluene, since benzene engages in a redox reaction with the uranium(III)-amide product to give uranium(IV)-amide and reduced arene. These disproportionations occur with potassium, rubidium, and cesium counter cations, but not lithium or sodium, reflecting the stability of the corresponding alkali metal-arene byproducts. This reveals an exceptional level of ligand- and solvent-control over a key thermodn. property of uranium, and is complementary to isolobal uranium(V)-oxo disproportionations, suggesting a potentially wider prevalence possibly with broad implications for the chem. of uranium.

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    Ojeda-Amador, A. I.; Martínez-Martínez, A. J.; Kennedy, A. R.; O’Hara, C. T. Structural Studies of Cesium, Lithium/Cesium, and Sodium/Cesium Bid(trimethylsilyl)amide (HMDS) Complexes. Inorg. Chem. 2016, 55, 5719– 5728,  DOI: 10.1021/acs.inorgchem.6b00839

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    57

    Structural Studies of Cesium, Lithium/Cesium, and Sodium/Cesium Bis(trimethylsilyl)amide (HMDS) Complexes

    Ojeda-Amador, Ana I.; Martinez-Martinez, Antonio J.; Kennedy, Alan R.; O'Hara, Charles T.

    Inorganic Chemistry (2016), 55 (11), 5719-5728CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)

    Reacting cesium fluoride with an equimolar n-hexane soln. of lithium bis(trimethylsilyl)amide (LiHMDS) gave CsHMDS (1) in 80% yield (after sublimation). This preparative route to 1 negates the need for pyrophoric Cs metal or organocesium reagents in its synthesis. If a 2:1 LiHMDS:CsF ratio is employed, the heterobimetallic polymer [LiCs(HMDS)2]∞ (2) was isolated (57% yield). By combining equimolar quantities of NaHMDS and CsHMDS in hexane/toluene [toluene·NaCs(HMDS)]∞ (3) was isolated (62% yield). Attempts to prep. the corresponding potassium-cesium amide failed and instead yielded the known monometallic polymer [toluene·Cs(HMDS)]∞ (4). With the aim of expanding the structural diversity of Cs(HMDS) species, 1 was reacted with several different Lewis basic donor mols. of varying denticity, namely, (R,R)-N,N,N',N'-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA] and N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), tris[2-(dimethylamino)ethyl]amine (Me6-TREN) and tris[2-(2-methoxyethoxy)ethyl]amine (TMEEA). These reactions yielded dimeric [donor·NaCs(HMDS)2]2 (5-7) [where donor is (R,R)-TMCDA, TMEDA and PMDETA, resp.], the tetranuclear open-dimer [{Me6-TREN·Cs(HMDS)}2{Cs(HMDS)}2] (8) and the monomeric [TMEEA·Cs(HMDS)] (9). Complexes 2, 3, and 5-9 were characterized by x-ray crystallog. and in soln. by multinuclear NMR spectroscopy.

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    Woltornist, R. A.; Collum, D. B. Aggregation and Solvation of Sodium Hexamethyldisilazide: Across the Solvent Spectrum. J. Org. Chem. 2021, 86, 2406– 2422,  DOI: 10.1021/acs.joc.0c02546

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    58

    Aggregation and Solvation of Sodium Hexamethyldisilazide: Across the Solvent Spectrum

    Woltornist, Ryan A.; Collum, David B.

    Journal of Organic Chemistry (2021), 86 (3), 2406-2422CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)

    We report soln. structures of sodium hexamethyldisilazide (NaHMDS) solvated by >30 std. solvents (ligands). These include: toluene, benzene, and styrene; triethylamine and related trialkylamines; pyrrolidine as a representative dialkylamine; dialkylethers including THF, tert-butylmethyl ether, and di-Et ether; dipolar ligands such as DMF, HMPA, DMSO, and DMPU; a bifunctional dipolar ligand nonamethylimidodiphosphoramide (NIPA); polyamines N,N,N',N'-tetramethylenediamine (TMEDA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDTA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and 2,2'-bipyridine; polyethers 12-crown-4, 15-crown-5, 18-crown-6, and diglyme, [2.2.2]cryptand and tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1). Combinations of 1H, 13C, 15N, and 29Si NMR spectroscopies, the method of continuous variations, x-ray crystallog., and d. functional theory (DFT) computations reveal ligand-modulated aggregation to give mixts. of dimers, monomers, triple ions, and ion pairs. 15N-29Si Coupling consts. distinguish dimers and monomers. Solvation nos. are detd. by a combination of solvent titrns., obsd. free and bound solvent in the slow exchange limit, and DFT computations. The relative abilities of solvents to compete in binary mixts. often match that predicted by conventional wisdom but with some exceptions and evidence of both competitive and cooperative (mixed) solvation. Crystal structures of a NaHMDS cryptate ion pair and a 15-crown-5-solvated monomer are included. Results are compared with those for lithium hexamethyldisilazide, lithium diisopropylamide, and sodium diisopropylamide.

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    Neufeld, R.; Stalke, D. Solution Structure of Turbo-Hauser Base TMPMgCl·LiCl in d₈-THF. Chem.─Eur. J. 2016, 22, 12624– 12628,  DOI: 10.1002/chem.201601494

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    Solution Structure of Turbo-Hauser Base TMPMgCl·LiCl in [D8]THF

    Neufeld, Roman; Stalke, Dietmar

    Chemistry - A European Journal (2016), 22 (36), 12624-12628CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Turbo-Hauser bases are very useful and highly reactive organometallic reagents in synthesis. Esp. TMPMgCl·LiCl 1 (TMP = 2,2,6,6-tetramethylpiperidide) is an excellent base for converting a wide range of (hetero)arom. substrates into highly functionalized compds. with a broad application in org. synthesis. The knowledge of its structure in soln. is of essential importance to understand the extraordinary reactivity and selectivity. However, very little is known about the aggregation of this prominent reagent in soln. Herein, we present the THF-soln. structure of 1 by employing our newly elaborated DOSY NMR method based on external calibration curves (ECC) with normalized diffusion coeffs.

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60. 60

    Feng, B.; Zhang, H.-Y.; Qin, H.; Peng, Q.; Leng, X.; Chen, Y. Hydrogenation of Alkenes Catalyzed by Rare-Earth Metal Phosphinophosphinidene Complexes: 1,2-Addition/Elimination Versus σ-Bond Metathesis Mechanism. CCS Chem. 2021, 3, 3585– 3594,  DOI: 10.31635/ccschem.021.202101468

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