UNUSUAL ACTIVITY AND SELECTIVITY IN ALKYNE HYDROSILYLATION WITH AN IRIDIUM CATALYST STABILIZED BY AN O-DONOR LIGAND

Catalytic alkyne hydrosilylation has been found for iridium in the O-donor ligand environment of Grim's triso ligand (=tris(diphenyloxophosphoranyl)methanide). The reaction is selective for 1-alkynes and regioselective for β-products and gives the thermodynamically less favored cis-vinylsilane products by an unexpected anti addition of Si-H to the triple bond. Mechanistic studies suggest that the alkyne first inserts into the M-Si, not the M-H, bond and that a trans to cis rearrangement occurs via an η2-vinyl intermediate before reductive elimination. A number of Rh and Ir complexes of the type [(triso)ML2] are prepared. IR studies on the CO complexes show that the donor power of triso compares with that of other related ligands in an unexpected order: Tp < P3O93- < triso < Cp. © 1990, American Chemical Society. All rights reserved.