[NiX2(NHC)2] Complexes in the Hydrosilylation of Internal Alkynes

A number of nickel(II) dihalide complexes with small monodentate N-heterocyclic carbene ligands was synthesized and tested for their catalytic activity in the hydrosilylation of internal alkynes. The nickel(0) active species was obtained from the starting nickel(II) complex by reduction with diethylzinc. In all cases the catalytic reaction yielded the syn product selectively. The fastest catalysts reached full conversion of the symmetric alkyne 3-hexyne in 60 min at 50 degrees C, with 5 mol-% catalyst loading. The asymmetrically substituted internal alkyne 1-phenyl-1-propyne gave full conversion within 30 min. The major product (83%) was shown to be the expected (E)-1-phenyl-1-(triethylsilyl) propene. The active catalyst was demonstrated to be a homogeneous species.