Titanocene-Catalyzed Hydrosilylation of Imines: Experimental and Computational Investigations of the Catalytically Active Species

Abstract

In this paper we communicate mechanistic investigations of the asymmetric catalytic hydrosilylation of imines using (R,R)-ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium (R)-1,1′-binaphth-2-olate (1) and (S,S)-ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium dichloride (2) as catalyst precursors. After activation with RLi (R = alkyl, aryl) and a silane, these complexes are well-known catalysts for hydrosilylation reactions. However, the exact nature of the catalytic active species is still a subject of debate and was therefore investigated by us using experimental (IR, NMR, EPR, GC/MS) and computational methods. Our results indicate an EBTHITiRSiH2Ph compound (EBTHI = ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl), R = alkyl, aryl) as the catalytically active species. This Ti(IV) species is postulated to be responsible for the lower activities of 1 and 2 in contrast to hydrosilylations with ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium difluoride (3), for which a Ti(III)-H compound was postulated to be the active species.