Formation of Zn-Zn and Zn-Pd Bonded Complexes by Reactions of Terminal Zinc Hydrides with Pd(II) Species.

Abstract

Divalent palladium-induced homocoupling of terminal zinc hydrides to zinc-zinc bonded complexes was achieved herein. Reactions of zinc hydrides [LZnH] (L = CH3C(2,6-iPr2C6H3N)CHC(CH3)(N(CH2)nCH2PPh2); 1a: n = 1; 1b: n = 2) with 0.5 equiv of allyl(cyclopentadienyl)palladium(II) afforded heterotrinuclear [Zn2Pd] complexes 3 containing direct Zn-Zn and Zn-Pd bonds, with concomitant elimination of propylene and cyclopentadiene. Complexes 3 were also accessed by the reactions of zinc hydrides 1 with allylpalladium(II) chloride with release of propylene and hydrogen chloride. Treatment of zinc hydrides 1 with 1 equiv of allyl(cyclopentadienyl)palladium(II) gave Zn-Pd bonded complex 5 by elimination of propylene, which can be transformed into heterotrinuclear complex 3 by further reaction with one additional molar equivalent of zinc hydrides. Heterobimetallic Zn-Pd complex 5b was found to be an effective catalyst in the hydrosilylation of benzaldehyde and its derivatives. Reaction of 5b with silane reagent Ph2SiH2 produced [Pd2Si2H2] complex 8 with cleavage of the Pd-Zn bond, which served as an initiating species in the catalytic reaction. Complexes 4b, 5, and 8 in this study were characterized by X-ray diffraction.