Rhodium-Catalyzed Carbon–Silicon Bond Activation for Synthesis of Benzosilole Derivatives

Abstract

A rhodium-catalyzed coupling reaction of 2-trimethylsilylphenylboronic acid with internal alkynes is developed for the synthesis of 2,3-disubstituted benzosilole derivatives. A range of functional groups, encompassing ketones, esters, amines, aryl bromides, and heteroarenes, are compatible, which provides rapid access to diverse benzosiloles. Sequential 2-fold coupling enables modular synthesis of asymmetrically substituted 1,5-dihydro-1,5-disila-s-indacene, a π-extended molecule of interest in organic electronics. In terms of the mechanism, the reaction involves cleavage of a C(alkyl)-Si bond in a trialkylsilyl group, which normally requires extremely harsh conditions for activation. Mechanistic studies, including effects of substituents, reveal that C-Si bond cleavage does not proceed through a hypercoordinated silicon species, but rather through a rhodium-mediated activation process. The potential use of the reaction in catalytic asymmetric synthesis of Si-chiral benzosiloles is also demonstrated.

Intramolecular Chain Hydrosilylation of Alkynylphenylsilanes Using a Silyl Cation as a Chain Carrier

“…These features are associated with the low-lying LUMOs of the siloles, which originate from orbital interaction between the σ* orbital of the silylene moiety and the π* orbital of the butadiene moiety [5]. The popular synthetic routes to benzo-and dibenzosiloles involve intra-and intermolecular cyclization reactions with transition metal catalysts [6][7][8][9], and the use of a chiral supporting ligand enables the synthesis of siloles with a chiral silicon center [10,11]. In particular, direct Si-C or C-H activation is a powerful method that does not require an activated functional group on the aromatic ring [12][13][14][15][16][17].…”

Direct Conversion of a Si–C(aryl) Bond to Si–Heteroatom Bonds in the Reactions of η3-α-Silabenzyl Molybdenum and Tungsten Complexes with 2-Substituted Pyridines

“…1 Many catalytic and stoichiometric reactions via Si−C(aryl) bond activation have been developed using late-transition-metal complexes. 1,2 In these reactions, oxidative addition of Si−C(aryl) bonds to low-valent metal centers plays a crucial role. 2 In contrast, the counterparts using early-transition-metal complexes have received less attention.…”

“…The crystals were washed with hexane (0.2 mL × 2) and then dried under vacuum to give 2-Mo (18 mg, 0.030 mmol) in 58% yield as orange crystals. 1 were dissolved in toluene (5 mL) in a Schlenk tube. After the mixture was stirred at room temperature for 10 min, the resulting orange solution was evaporated under vacuum.…”

“…2-W (12 mg, 0.018 mmol) was obtained as orange crystals in 24% yield. 1 were dissolved in toluene (3 mL) in a Schlenk tube. After the solution was stirred at 40°C for 48 h, the resulting orange reaction mixture was evaporated under vacuum.…”

Efficient Access to Substituted Silafluorenes by Nickel‐Catalyzed Reactions of Biphenylenes with Et2SiH2

“…Silafluorenes 8 and 9 were separated by column chromatography. Keywords: CÀC activation · density functional calculations · nickel · SiÀ H activation · silanes ion formed in the reaction of HSi-functionalized 2-silylbiphenyl derivatives 2A C H T U N G T R E N N U N G (R 2 HSi) and the trityl cation [18] or by Rh-catalyzed H 2 elimination from 2A C H T U N G T R E N N U N G (R 2 HSi) and subsequent CÀC coupling; [19][20][21] iii) by Ir-catalyzed [2+2+2] cycloaddition of silicon-bridged 1,6-diynes with alkynes; [22] and iv) by metathesis reactions of 2,2'-dimetalated biphenyls and R 2 SiX 2 [8,[23][24][25][26] or triorganyl silanes R 3 SiX. [27][28][29] Furthermore, a Pd-catalyzed reaction starting from 2,2-dihalogenated biphenyls and Et 2 SiH 2 has also been reported.…”