14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh( iii ) devoid of agostic interactions. The complexes [X-Rh(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], where X = Cl ( Rh-1 ), Br ( Rh-2 ), I ( Rh-3 ), OTf ( Rh-4 ), Cl·GaCl 3 ( Rh-5 ); derive from a bis(silyl)- o -tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl-Ir(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], Ir-1 , in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et 3 SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et 3 SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M( iii ) complexes. 14-electron Rh and Ir species as robust catalysts for silicon functionalization.