Hydrosilylation Catalysis by <i>C</i>₂-Symmetric Bis(silylamido) Complexes of Yttrium

The yttrium hydride {[DADMB]YH(THF)}2 (2; DADMB = 2,2'-bis(tert-butyldimethylsilylamido)-6,6'-dimethylbiphenyl), conveniently generated in situ from [DADMB]YMe(THF)2 (1), is an active olefin hydrosilylation catalyst. This system represents the first use of a d0 metal complex with non-Cp ligands in the catalytic hydrosilylation of olefins. Studies of the reactivity and regio- and enantioselectivity for various olefins and silanes are presented. High preference for terminal addition in the case of aliphatic olefins is observed, while aromatic olefins exhibit preference for 2,1-addition. Both primary and secondary silanes have been employed. Preliminary studies of the enantioselectivity of the chiral catalyst show that 90% ee can be achieved in the hydrosilylation of norbornene with PhSiH3. Kinetic studies support a mechanism consistent with the generally accepted one for hydrosilylation catalyzed by early transition metal species, involving rapid olefin insertion into a Y−H bond followed by a Si−C bond-forming σ-bond metathesis of the resulting yttrium alkyl with silane.