Direct Hydrogenation of Sterically Hindered, Unactivated Alkenes Catalyzed by Phosphino(silyl)-Nickel Complexes

Readily accessible (PSi)Ni(II)-benzyl complexes supported by bidentate phosphino(silyl) ligation were found to be effective pre-catalysts for the direct hydrogenation of a variety of highly sterically hindered, unfunctionalized alkenes under relatively mild conditions (2.5-5 mol% Ni, 10 atm H2, 50 degrees C) and without the need for additional additives or activator species. A range of substrates, including di-, tri-, and tetra-substituted alkenes were evaluated in this regard and afforded good to moderate yields. Substrates featuring alpha,beta-unsaturated carbonyl functionality were also readily hydrogenated with no evidence for reduction of carbonyl or ester C-O functionalities. Deuteration experiments highlight the occurrence of chain walking which occurs in the background of the reported catalytic chemistry. Readily accessible (PSi)Ni(II)-benzyl complexes were found to be effective pre-catalysts for the hydrogenation of a variety of highly sterically hindered, unfunctionalized alkenes without the need for additional additives or activator species. A range of substrates, including di-, tri-, and tetra-substituted alkenes were evaluated in this regard, with good to moderate yields obtained. image