Facile Arylation of Four-Coordinate Boron Halides by Borenium Cation Mediated Boro-desilylation and -destannylation

The addition of AlCl3 to four-coordinate boranes of the general formula (C–N-chelate)BCl2 results in halide abstraction and formation of three-coordinate borenium cations of the general formula [(C–N-chelate)BCl]+. The latter react with both arylstannanes and arylsilanes by boro-destannylation and -desilylation, respectively, to form arylated boranes. Catalytic quantities of AlCl3 were sufficient to effect high-yielding arylation of (C–N-chelate)BCl2. Boro-destannylation is more rapid than boro-desilylation and leads to double arylation at the boron center, whereas in reactions with arylsilanes either single or double arylation occurs dependent on the nucleophilicity of the arylsilane and on the electrophilicity of the borenium cation. The electrophilicity of the borenium cation derived from 2-phenylpyridine was greater than that of the benzothiadiazole analogues, enabling the boro-desilyation of less nucleophilic silanes and the direct electrophilic borylation of 2-methylthiophene.


■ INTRODUCTION
Four-coordinate boron compounds containing a chelating πconjugated C/N donor and two exocyclic aromatic moieties, termed (C−N-chelate)BAr 2 (e.g., 1-BAr 2 right Scheme 1), have been extensively studied for application in optoelectronic devices. 1,2 Changing the exocyclic aryl groups in 1-BAr 2 significantly modulates the key optoelectronic properties including the frontier orbital energies and the photoluminescence quantum yield. 2,3 Therefore, efficient and versatile routes to libraries of these compounds are important to optimize the materials properties and deliver improved device performance. A particularly attractive approach is the arylation of (C−Nchelate)BX 2 (e.g., 1-BX 2 , X = Cl or Br) to form a wide range of (C−N-chelate)BAr 2 compounds, as the starting compounds are readily accessed by electrophilic C−H borylation (Scheme 1). 3,4 Installation of aromatic moieties at three-coordinate boron species is generally achieved by reaction with either arylithium or aryl Grignard reagents. 5 However, reaction of these reagents with Lewis base adducts of boranes often gives the desired product in poor yield. 4 Instead functionalization of borane-Lewis adducts such as (2-phenylpyridyl)BBr 2 (1-BBr 2 , Scheme 1) requires organozinc or organoaluminum reagents to achieve high-yielding transmetalation. 3,4 Unfortunately these nucleo-philes are highly sensitive to protic species (ROH), and the synthesis of organozinc reagents often results in mixtures containing ionic species (termed zincates) and coordinated etherate solvent, which can complicate transmetalation. 6 Alternative nucleophiles are required that are readily synthesized, are well-defined, can be handled in air, and enable the boron-containing products to be easily isolated, preferably without column chromatography. Arylsilanes and arylstannanes meet these criteria; however, while three-coordinate boranes (e.g., ArBBr 2 ) undergo transmetalation with arylsilanes and arylstannanes, four-coordinate boranes do not due to the Lewis acidity at boron being effectively quenched by the dative bond. 4 We hypothesized that conversion of (C−N-chelate)BX 2 into borenium cations, 7 [(C−N-chelate)BX] + , using a halophilic Lewis acid (e.g., AlCl 3 ) will enable transmetalation using arylstannanes and arylsilanes. The process is potentially catalytic in the halophile, as the byproduct from transmetalation will react as a functional equivalent of [R 3 Si] + or [R 3 Sn] + , abstracting halide to generate further equivalents of borenium cations for subsequent transmetalation (Scheme 2). Related, albeit stoichiometric in halophile, approaches have been reported for activating chloro-boron subphthalocyanine and F 2 B-dipyrromethenes toward substitution of B−X with chalcogen-based nucleophiles. 8 In contrast, the use of borenium cations in boro-desilylation has extremely limited precedence, 9 while their use in boro-destannylation has not been reported to date to the best of our knowledge. Herein is reported catalytic (in AlCl 3 activator) borenium cation mediated borylation as a simple method to functionalize (C−N-chelate)BCl 2 species based on benzothiadiazole (BT) and pyridyl with aryl and heteroaryl groups.

■ RESULTS AND DISCUSSION
Our initial attempts to access new 2-BAr 2 compounds used an isolated organozinc reagent synthesized from ZnBr 2 and p-tolylMgBr in THF, but this led to low yields of the desired arylated product. The low conversion was attributed to the "Zn(p-tolyl) 2 " formed under these conditions actually being the zincate [Mg(THF) 4 (μ-Br) 2 (Zn(p-tol) 2 ) 2 ] n . 10 Due to the significant challenge presented in forming etherate-free arylzinc reagents, 10 ArylSiMe 3 and ArylSnBu 3 nucleophiles were investigated for expanding the exocyclic boron substituents.
Mixing 2-BCl 2 (readily formed from the unborylated precursor 2 (F8-BT-F8) and BCl 3 ) 3 with 2 equiv of PhSnBu 3 in CH 2 Cl 2 at room temperature led to no reaction until catalytic (ca. 5 mol %) AlCl 3 was added to the reaction mixture. Compound 2-BCl 2 then slowly transformed into diphenylated 2-BPh 2 at 20°C (Scheme 3). Heating of the reaction resulted in a more rapid reaction and good conversion to 2-BPh 2 (89% isolated yield after 16 h at 60°C in CH 2 Cl 2 in a sealed tube). The addition of AlCl 3 results in chloride abstraction from 2-BCl 2 and borenium cation formation (indicated by downfield shifts in the 1 H NMR spectrum and formation of [AlCl 4 ] − in the 27 Al NMR spectrum), consistent with previous studies on related compounds. 3 The borenium cation [2-BCl] + is then sufficiently electrophilic to boro-destannylate PhSnBu 3 . An alternative mechanism where AlCl 3 and PhSnBu 3 react to form Al-Ph species (which have been previously reported to transmetalate to four-coordinate boron halides) 4 is precluded based on previous work where the combination of these reagents (in the absence of 2-BCl 2 ) in haloalkane solvents (such as CH 2 Cl 2 ) leads to solvent activation via C−Cl···AlCl 3 interactions (Friedel−Crafts-type reactivity) and carbodestannylation to form R 3 C-Ph. 11 Friedel−Crafts products are not observed in the reaction with 2-BCl 2 , which is attributed to AlCl 3 reacting rapidly to form the borenium cation, thus disfavoring solvent activation. The ability to form 2-BPh 2 in high conversion using catalytic AlCl 3 confirmed that the electrophilic [Bu 3 Sn] + (or a functional equivalent thereof) byproduct can react with further 2-BCl 2 , directly or via initial reaction with [AlCl 4 ] − , to provide access to additional equivalents of borenium cations.
The boro-destannylation reaction was extended to 2-Bu 3 Sn-9,9-dioctylfluorene (6), synthesized by standard procedures. The reaction of 5-BCl 2 with 2.2 equiv of 6 and catalytic AlCl 3 (ca. 5 mol %) proceeded at room temperature, but required 18 h for formation of 5-(F8) 2 in high conversion. The longer reaction time compared to transmetalation with 3 is attributable to the variation in arene nucleophilicity. Attempts to selectively form the monoarylated product by addition of 1 equiv of 6 to 5-BCl 2 (with catalytic AlCl 3 ) led to a mixture of 5-BCl 2 /5-BCl(F8) and 5-B(F8) 2 . 5-(F8) 2 also can be synthesized from 5 in a two-step, one-pot reaction without the use of a glovebox in 88% yield. Compound 5-BCl 2 is prepared by reaction of 5 with BCl 3 , followed by degassing (removing excess BCl 3 and the HCl byproduct from C−H borylation) and subsequent addition of catalytic AlCl 3 and 2.2 equiv of 6 (both weighed and handled under ambient atmosphere). The product, 5-(F8) 2 , is then simply isolated by filtering through silica.
The use of arylsilanes in place of arylstannanes is preferable from a toxicity perspective. However, reacting PhSiMe 3 and 2-BCl 2 with a range of AlCl 3 loadings and reaction conditions (at 20 and 60°C) consistently resulted in minimal transmetalation. It is well documented that silicon−boron exchange only proceeds with highly electrophilic boranes, in contrast with tin−boron exchange. 14 This suggests that the borenium cation [2-BCl] + is insufficiently electrophilic to effect boro-desilylation of PhSiMe 3 . A more nucleophilic silane, 2-Me-5-Me 3 Sithiophene, 7, was therefore utilized. Compound 2-BCl 2 was combined with an excess (2.2 equiv) of 7, resulting in no reaction. Addition of AlCl 3 (ca. 5 mol %) to the reaction mixture initiated transmetalation, leading to only one transmetalation per boron, producing 2-BCl(MeT) (Scheme 6), even after long reaction times. As the borenium cation [2-B(MeT)] + formed after the first transmetalation and subsequent halide abstraction contains a thienyl π donor, its Lewis acidity is presumably reduced relative to [2-BCl] + , disfavoring boro-desilylation of 7. Analogous trends have been previously observed when comparing the Lewis acidity of [PhBCl(amine)] + and [Cl 2 B(amine)] + borocations. 15 Compound 2-BCl(MeT) then can be further arylated using other organometallic reagents; for example reaction with Zn(C 6 F 5 ) 2 gave the mixed arylated complex 2-B(MeT)(C 6 F 5 ) (in 81% isolated yield). This provides a simple route to mixed arylated compounds, (C−N-chelate)BAr 1 (Ar 2 ). It is notable that current routes to unsymmetrically substituted borane derivatives are challenging and require multiple steps and purifications. This is due to the formation of Ar 1 Ar 2 BX (for reaction with lithiated C−N-precursors), often leading to mixtures generally necessitating purification by fractional distillation. 16 (C−N-chelate)BAr 2 compounds based on 2-arylpyridyls and derivatives have been more extensively studied than the benzothiadiazole systems for a range of optoelectronic applications. 2,6a,17 Therefore, the borenium cation mediated boro-destannylation/boro-desilylation reactions of these species were explored. 2-Phenylpyridine, 1, was readily borylated by a modification of a literature method 4 using BCl 3 , 2,4,6-tri-tBu-pyridine (TBP), and AlCl 3 to form 1-BCl 2 . Compound 1-BCl 2 was stable to ambient conditions and could be readily isolated in air simply by sequential washing with H 2 O/MeOH and pentane. In contrast BT derivatives (e.g., 2-BCl 2 ) are sensitive to water and column chromatography. The enhanced stability of 1-BCl 2 is attributed to a stronger N→B dative bond in the pyridyl congener. The addition of an equivalent of AlCl 3 to 1-BCl 2 led to formation of the borenium salt [1-BCl][AlCl 4 ], as indicated by a signal at +39.0 ppm in the 11 B NMR spectrum and further confirmed by X-ray diffraction studies (crystallized by cooling a saturated CH 2 Cl 2 solution to 4°C , Figure 1). The solid-state structure of [1-BCl][AlCl 4 ] reveals a planarized tricyclic structure and a trigonal planar environment at boron (∑ = 359.8°). Although two [AlCl 4 ] − anions are proximal, the four Al−Cl (two participating in Al−Cl−B bridges and two not) distances are all identical (within 3σ), suggesting that these close contacts are principally due to electrostatic forces and packing effects. The ability of the borenium cation [1-BCl] + to mediate boro-destannylation was investigated. Addition of 2.2 equiv of PhSnBu 3 to 1-BCl 2 resulted in no reaction until addition of ca. 5 mol % of AlCl 3 , which resulted in rapid boro-destannylation at 20°C to form 1-BPh 2 . This compound has been previously synthesized by Murakami and co-workers via 1-BBr 2 and AlPh 3 . 4 The synthesis of 1-BPh 2 in one pot in two steps from 2- The rapid room-temperature double boro-destannylation observed on combination of 1-BCl 2 , catalytic AlCl 3 , and PhSnBu 3 is in contrast to the BT congener 2-BCl 2 (which requires heating to 60°C). This suggests an enhanced electrophilicity of the boron center in [1-BY] + (Y = Cl and Ph) relative to that in [2-BY] + . This was confirmed by the observation that addition of 2.2 equiv of PhSiMe 3 to 1-BCl 2 in the presence of catalytic (ca. 5 mol %) AlCl 3 rapidly led to monoarylation (<10 min) and complete double arylation of boron within 10 h at 20°C to form 1-BPh 2 . Thus, with 1-BCl 2 double transmetalation is possible using the less toxic arylsilane reagent. This methodology can also be performed without the aid of a glovebox with no significant loss in yield, and the doubly arylated products can be isolated simply by filtration through a short plug of silica followed by drying in vacuo. The electronically deactivated silane (meta-Br-C 6 H 4 )SiMe 3 was also a viable reagent for transmetalation to boron; however, at 20°C this led only to a single arylation of 1-BCl 2 (using ca. 5 mol % AlCl 3 ), with no further arylation proceeding at 20°C (Scheme 7). Double arylation of 1-BCl 2 can be realized with (meta-Br-C 6 H 4 )SiMe 3 by heating 1-BCl 2 /catalytic AlCl 3 in 1,2-Cl 2 C 6 H 4 . The change in solvent is essential, as in this case heating a mixture of AlCl 3 , CH 2 Cl 2 , and an arylsilane for prolonged periods of time led to Friedel−Crafts alkyation reactions. 11 Analogous conditions enabled the synthesis of the spiro complex 1-B(biphenyl) (Scheme 7, bottom) in good yield (82%) from the commercially available 9,9-dimethyl-9H-9silafluorene. Spiro complexes such as 1-B(biphenyl) have been extensively explored as electron transport materials in electroluminescent devices. 18 It is notable that attempts to make the analogous spiro compound from 2-BCl 2 using catalytic AlCl 3 failed with no reaction observed at 20 or 60°C, again indicating the lower electrophilicity of the [    methylthiophene (presumably due to insufficient Lewis acidity) and is less chlorophilic than [1-BCl] + , resulting in the consumption of 0.5 equiv of the latter by rapid halide transfer from the expected initial product 1-B(MeT)Cl. 19 The addition of a second equivalent of AlCl 3 to this reaction mixture led to consumption of all 1-BCl 2 and full conversion to

■ CONCLUSIONS
The catalytic (in AlCl 3 ) borenium cation mediated arylation of four-coordinate boron compounds using aryl stannanes and aryl silanes represents a simple route to (C−N-chelate)B(aryl) 2 species, which are useful for optoelectronic applications. The methodology proceeds with a range of arylstannanes and arylsilanes without the requirement for a glovebox or isolation of the (C−N-chelate)BCl 2 . Single and double arylation of each boron center can be selected by appropriate choice of reagents, thus enabling facile access to unsymmetrically substituted fourcoordinate boron compounds that are challenging to access via other methodologies.

■ EXPERIMENTAL SECTION
Unless otherwise stated, all manipulations were carried out using standard Schlenk techniques under argon or in an MBraun UniLab glovebox, under an atmosphere of argon (<0.1 ppm of O 2 /H 2 O). Unless otherwise indicated, solvents were distilled from appropriate drying agents: tetrahydrofuran (potassium); toluene (potassium); nhexane (NaK); and dichloromethane (CaH 2 ). Tetrahydrofuran and dichloromethane were stored over activated 3 Å molecular sieves, while toluene and n-hexane were stored over potassium mirrors. 2, 2-BCl 2 , 4, 5, 2-methyl-5-tributylstannylthiophene, trimethyl(5-methylthiophen-2-yl)silane, tributyl(9,9-dioctyl-9H-fluoren-2-yl)stannane, and [Mg(THF) 4 (μ-Br) 2 (Zn(p-tol) 2 ) 2 ] n were prepared according to previously published procedures. 3,10 All other compounds were purchased from commercial sources and used as received. NMR spectra were recorded on Bruker AvanceIII-400 or Bruker Ascend-400 spectrometers. Chemical shifts are reported as dimensionless δ values and are referenced relative to residual protio-impurities in the NMR solvents for 1 H and 13 C{ 1 H}, respectively, while 11 B and 19 F{ 1 H} shifts are referenced relative to external BF 3 -etherate and hexafluorobenzene, respectively. Coupling constants J are given in hertz (Hz) as positive values regardless of their real individual signs. The multiplicities of the signals are indicated as "s", "d", "t", "pent", "sept", or "m" for singlet, doublet, triplet, pentet, septet, or multiplet, respectively. Carbon atoms directly bonded to boron are not always observed in the 13 C{ 1 H} NMR spectra due to quadrupolar relaxation leading to considerable signal broadening. In a number of compounds individual carbon resonances are not observed for all inequivalent protons (particularly in the octyl chains) due to resonance coincidence. High-resolution mass spectra (HRMS) were recorded on a Waters QTOF mass spectrometer. Microanalysis was performed by Stephen Boyer at the London Metropolitan University microanalytical service. For the arylated compounds accurate combustion data were not obtainable with consistently low %C content observed. This is attributed to boron carbide formation and persisted even when V 2 O 5 was used as an oxidant. For these compounds NMR spectra are included in the SI to support compound purity, Synthesis of 2-B(MeT) 2 . BCl 3 , 1 M in DCM (0.3 mL, 0.3 mmol), was added to a solution of 2 (95 mg, 0.10 mmol) in DCM (3 mL), and the solution was stirred overnight under the dynamic flow of nitrogen. The solvent was then removed under reduced pressure. The resulting residue was dissolved in DCM (3 mL), and AlCl 3 (1 mg) was added to the solution. 2-Methyl-5-tributylstannylthiophene (90 mg, 0.22 mmol) was added to the reaction mixture, which was then stirred overnight. The solvent was then removed under reduced pressure, and the purification was performed under ambient atmosphere using nonpurified solvents thereon. The residue was dissolved in hexane and was passed through (using hexane initially and then 10% DCM/90% hexane as eluent) a short plug of base-treated silica gel (pretreated with 5% NEt 3 /hexane), and only the purple-colored solution was retained. The solvent was removed to afford a purple residue. Yield: 78 mg, 67%. 1 1 (br), 154.4, 152.0, 151.9,  150.8 (br), 150.1, 148.0, 142.5, 142.5, 142.2, 141.4, 140.9, 134.7, 133.2 1 mL, 0.1 mmol), was added to a solution of 2 (50 mg, 0.055 mmol) in DCM (3 mL), and the solution was stirred overnight under the dynamic flow of nitrogen. The solvent was then removed under reduced pressure. The resulting residue was dissolved in DCM (3 mL), and AlCl 3 (1 mg) was added to the solution. Tributylphenylstannane (40 mg, 0.121 mmol) was added to the solution, and the reaction mixture was stirred and heated overnight at 60°C. The solvent was then removed under reduced pressure, and the purification was performed under ambient atmosphere using nonpurified solvents thereon. The residue was dissolved in hexane and was passed through (using hexane initially and then 10% DCM/90% hexane as eluent) a short plug of base-treated silica gel (pretreated with 5% NEt 3 /hexane), and only the purplecolored solution was retained. The solvent was removed to afford a purple residue. Yield: 53 mg, 89%. The spectra agree with that previously reported. 3 Synthesis of 4-(BPh 2 ) 2 . BCl 3 , 1 M solution in DCM (0.30 mL, 0.3 mmol), was added to a bright yellow solution of 4 (50 mg, 0.076 mmol) and 2,4,6-tritbutylpyridine (38 mg, 0.154 mmol) in DCM (3 mL). The solution rapidly changed color to a dark red. AlCl 3 (20 mg, 0.15 mmol) was then added to the reaction mixture. After rotating for 16 h, an additional portion of AlCl 3 (20 mg, 0.15 mmol) was added to the reaction mixture. The solution was rotated for a further 16 h, whereupon the solution turned dark green. The DCM was removed under reduced pressure, and the reaction mixture was dissolved in o-DCB (4 mL). Tributylphenylstannane (0.15 mL, 0.456 mmol) was added to the reaction mixture, which was then stirred at 20°C for 48 h and heated at 40°C for 16 h. NMe 4 Cl (50 mg, 0.456 mmol) was added to the reaction mixture, and after 1 h the solvent was removed under reduced pressure. The purification was performed under ambient atmosphere using nonpurified solvents thereon. The residue was purified via column chromatography on base-treated silica gel (5% NEt 3 /hexane) [eluent chloroform/hexane (2:8)] to afford a purple residue. Yield: 24 mg, 32%. The spectra agree with that previously reported. 3 Synthesis of 5-B(MeT) 2 . BCl 3 , 1 M in DCM (0.2 mL, 0.20 mmol), was added to a solution of 5 (95 mg, 0.18 mmol) in DCM (3 mL), and the solution was stirred overnight under the dynamic flow of nitrogen. The solvent was then removed under reduced pressure. The resulting residue was dissolved in DCM (3 mL), and AlCl 3 (1 mg) was added to the solution. 2-Methyl-5-tributylstannylthiophene (154 mg, 0.40 mmol) was added to the reaction mixture, which was then stirred overnight. The solvent was then removed under reduced pressure, and the purification was performed under ambient atmosphere using nonpurified solvents thereon. The residue was purified via column chromatography on base-treated silica gel (5% NEt 3 /hexane) [eluent DCM/hexane (1:9)] to afford a dark blue residue. Yield: 67 mg, 51%. 1 1 mL, 0.1 mmol), was added to a solution of 5 (30 mg, 0.057 mmol) in DCM (3 mL), and the solution was stirred overnight under the dynamic flow of nitrogen. The solvent was then removed under reduced pressure. The resulting residue was dissolved in DCM (3 mL), and AlCl 3 (1 mg) was added to the solution. Tributyl(9,9-dioctyl-9H-fluoren-2-yl)stannane (85 mg, 0.125 mmol) was added to the reaction mixture, which was then stirred overnight. The solvent was then removed under reduced pressure, and the purification was performed under ambient atmosphere using nonpurified solvents thereon. The residue was dissolved in hexane and was passed through a short plug of basetreated silica gel (5% NEt 3 /hexane), and only the dark blue colored solution was retained. The solvent was removed to afford a purple residue. Yield: 66 mg, 88%. 1   . AlCl 3 (1 mg) was added to a solution of 2-BCl 2 (50 mg, 0.5 mmol) and trimethyl(5-methylthiophen-2-yl)silane (20 μL, 0.1 mmol) in DCM (0.7 mL). After inverting for 14 h at room temperature NMR investigation showed only one arylation had occurred. The reaction mixture was then evaporated to dryness, and the residue was dissolved in DCM (0.7 mL). Zn(C 6 F 5 ) 2 (24 mg, 0.6 mmol) was added to the reaction mixture. After stirring for 3 h the reaction mixture was filtered through a plug of base-treated silica gel (5% NEt 3 /hexane). The reaction mixture was then purified via column chromatography on base-treated silica gel (5% NEt 3 / hexane) [eluent DCM/hexane (1:9)] to afford a dark purple residue. Yield: 48 mg, 81%. 1  tri-tert-butylpyridine (0.8 g, 3.2 mmol), and 2-phenylpyridine (0.5 g, 3.2 mmol) were dissolved in DCM (40 mL). AlCl 3 (0.854 mg, 6.4 mmol) was added to the reaction mixture, whereupon a color change from colorless to yellow was observed. After stirring for 4 h the reaction mixture was degassed under vacuum and NMe 4 Cl (0.351 g, 3.2 mmol) was added, whereupon the reaction mixture changed color from yellow to colorless. The reaction mixture was evaporated to dryness and washed with water (3 × 100 mL) and hexane (100 mL). The resulting white powder was dried under reduced pressure. Yield: 0.584 g, 77%. 1  Synthesis of 1-BPh 2 via Tributylphenylstannane. AlCl 3 (2 mg) was added to a suspension of 1-BCl 2 (31 mg, 0.13 mmol) and tributylphenylstannane (106 mg, 0.286 mmol) in DCM (4 mL). 1-BCl 2 dissolved almost instantly upon the addition of AlCl 3 . The reaction mixture was stirred overnight, and the solution was passed through a short plug of silica gel. The purification was performed under ambient atmosphere using nonpurified solvents thereon. The reaction mixture was evaporated to dryness under reduced pressure, and the resulting white residue was washed with hexane to yield the desired product as a white crystalline solid. Yield: 30 mg, 72%.
Synthesis of 1-BPh 2 via Trimethylphenylsilane. In a J.Young's NMR tube AlCl 3 (1 mg) was added to a suspension of 1-BCl 2 (23 mg, 0.10 mmol) and trimethylphenylsilane (33 mg, 0.21 mmol) in DCM (0.7 mL). The reaction mixture was inverted for 10 h, whereupon NMR investigation showed the reaction had gone to completion. The purification was performed under ambient atmosphere using nonpurified solvents thereon The reaction mixture was then evaporated to dryness and dissolved in DCM (5 mL), and the solution was passed through a short plug of silica gel. The resulting solution was evaporated to dryness under reduced pressure to yield the desired product as a white crystalline solid. Yield: 29 mg, 92%.
The spectra agree with that previously reported. 4 Synthesis of 1-B(m-BrPh) 2 . AlCl 3 (15 mg, 0.11 mmol) was added to a suspension of 1-BCl 2 (31 mg, 0.13 mmol) and trimethyl(3bromophenyl)silane (55 μL, 0.29 mmol) in o-DCB (0.7 mL). The reaction mixture was heated at 60°C for 16 h. NMe 4 Cl (15 mg, 0.14 mmol) was added to the reaction mixture, and the solvent was removed under reduced pressure. The resulting residue was purified via column chromatography on silica gel [eluent DCM/hexane (5:5)] to afford the desired product as a white crystalline solid. Yield: 38 mg, 62%. 1  Synthesis of 1-B(biphenyl). AlCl 3 (2 mg) was added to a suspension of 1-BCl 2 (30 mg, 0.13 mmol) and 9,9-dimethyl-9H-9silafluorene (30 mg, 0.14 mmol) in o-DCB (0.7 mL). The reaction mixture was then heated overnight at 60°C. The solvent was then removed under reduced pressure, and the purification was performed under ambient atmosphere using nonpurified solvents thereon. The resulting residue was dissolved in hexane and was filtered through a short plug of silica gel; hexane (100 mL) and then DCM (100 mL) were then passed through the silica gel, and the DCM fraction was collected and evaporated to dryness under reduced pressure to give the desired product as a white crystalline solid. Yield: 33 mg, 82%. 1 150.8, 143.1, 140.5, 137.5, 131.0, 130.7, 130.1, 127.2