Dehydrogenative silylation of vinylarenes with Et3SiH catalyzed by mixed valent CCC-NHC Rh(III)/Rh(I) pincer complex

• Selective dehydrogenative silylation of vinylarenes with tertiary silanes was achieved using well defined CCC-NHC pincer Rh complexes. • The novel mixed-valent Rh(III)/Rh(I) complex exhibited the highest catalytic activity. • The transformation proceeded efficiently under solvent-free conditions, enhancing its environmental and economic appeal. • Both electron-rich and electron-deficient vinylarenes were well tolerated, affording (E)-alkenylsilanes in good yields (65-86%) Selective dehydrogenative silylation of vinylarenes with tertiary silanes catalyzed by well-defined CCC-NHC pincer Rh complexes has been developed. The CCC-NHC pincer Rh precatalysts [( Bu C i C i C Bu )RhCl(µ-Cl) 2 Rh(COD)] ( 7 ), [( Bu C i C i C Bu )RhCl(µ-Cl)] 2 ( 8 ), [( Bu C i C i C Bu )RhCl 2 (NHMe 2 )] ( 9 ), and [( Bu C i C i C Bu )RhCl 2 Py] ( 10 ), ( Bu C i C i C Bu = 2-((1,3-bis(N-butylimidazol-2-ylidene)phenylene) that were evaluated were all found to promote the dehydrogenative silylation of vinylarenes with Et 3 SiH to selectively form the corresponding ( E )-alkenylsilane under solvent-free conditions. The most active precatalyst was the novel mixed valent Rh(III)/Rh(I) complex, [( Bu C i C i C Bu )RhCl(µ-Cl) 2 Rh(COD)] ( 7 ). The catalytic system displays wide substrate scope. Electron rich and electron deficient vinylarenes were well tolerated affording the corresponding alkenylsilanes in good yields (65-86%). Preliminary mechanistic investigations indicated that the Rh(III) center was responsible for the catalytic performance.