A New Catalytic Route for the Activation of sp‐Hybridized Carbon–Hydrogen Bonds

Abstract

In the last two decades we have developed a new type of transition-metal (TM)-catalyzed reaction of vinyl-substituted organosilicon compounds with olefins, known as a silylative coupling (SC, or trans-silylation; Scheme 1), that is complementary to metathesis. This reaction occurs by cleavage of the = C À H bond of an olefin and the = C À Si bond of a vinylsilane, in contrast to cross-metathesis, which uses the same substrates and also gives the same products (except the gem-isomer), by cleavage of the C=C bond. Various TM complexes (i.e. Ru, Rh, Ir, and Co) containing an MÀH and MÀSi bond initially, or one generated in situ, catalyze this process. [1,2] ) The mechanism for SC catalyzed by ruthenium complexes elucidated by Wakatsuki [3] and by us [4] involves insertion of a vinylsilane into the MÀH bond and b-Si transfer to the metal, with elimination of ethylene, to generate MÀSi species, then insertion of the alkene into the MÀSi bond and b-H transfer to the metal, with elimination of a substituted vinylsilane as product, and regeneration of the catalyst.The SC process under optimum conditions has become an excellent synthetic tool for the regio-and stereoselective synthesis of functionalized vinylsilicon compounds such as (E)-N-(silyl)vinylcarbazole, [5a] amides, [5b] 1-silyl-1-(boryl)-ethenes, [5c] functionalized cyclosiloxanes, cyclosilazanes, [5d] and silsesquioxanes [5e] as well as macromolecular organosilicon compounds containing (E)-1,2-bis(silyl)fragments. [6] These compounds can be used as synthetic reagents for organic synthesis and as materials precursors and are difficult to prepare by other TM-catalyzed reactions such as crossmetathesis. The trans-silylation reaction has recently been extended to other metalloids such as boron [7] and germanium.

Facile Catalytic Hydrosilylation of Pyridines

“…To the best of our knowledge, these reactions are the first examples of a reversible hydrosilylation. [16] Compound 2 also underwent dehydrosilylation in benzene upon the addition of B(C 6 F 5 ) 3 , which abstracted hydride from the 4-position with the precipitation of the pyridinium salt [C 5 H 5 N·SiMe 2 Ph]HB(C 6 F 5 ) 3 . This salt decomposed slowly (in 24 h) in dichloromethane with the formation of C 5 H 5 N·B-(C 6 F 5 ) 3 and HSiMe 2 Ph.…”

New catalytic route to borasiloxanes

“…The mechanistic aspects of b-boryl and b-silyl elimination occuring in these processes based on DFT calculations have been recently reported. 3a,b The reaction, well-recognized as a new catalytic route for activation of QC-H bond of olefins and QC-E bond of vinylmetalloid derivatives (where E = Si, B, Ge and others) with ethylene evolution has been recently extended to the activation of RC-H 4,5 (for E = Si, Ge), QC aryl -H (E = Si) 6 as well as -OH bonds of alcohols 7 and silanols, 8 particularly by vinylsilanes (for review see ref. 9).…”

Mechanism of co-dimerization of vinylboronates with terminal alkynes catalyzed by ruthenium-hydride complex

“…This mode of reactivity is general for olefins when vinylsilanes, vinylgermanes [10,11] or vinylboranes [12,13] are used, while with alkynes the reaction occurs only with vinylmetalloids from the 14th group of the periodic table [14].…”