Mechanistic Study on the Insertion of Phenylacetylene into cis-Bis(silyl)platinum(II) Complexes

Abstract

Four bis(silyl)platinum complexes cis-Pt(SiR3)2(PMe2Ph)2 (SiR3 = SiMe2Ph (1a), SiMePh2 (1b), SiPh3 (1c), SiFPh2 (1d)) have been prepared and their reactions with alkynes and alkenes examined. The X-ray structures of 1a−c exhibit significant distortion from the square planar geometry in the order 1b > 1c > 1a. Complexes 1a−d react with phenylacetylene in solution to give the corresponding insertion complexes cis-Pt{C(Ph)CH(SiR3)}(SiR3)(PMe2Ph)2 (2a−d). Complex 1c reacts also with acetylene to afford the insertion complex cis-Pt(CHCHSiPh3)(SiPh3)(PMe2Ph)2 (2e), whose structure has been determined by X-ray diffraction study. Kinetic studies indicate the insertion process involving prior dissociation of PMe2Ph ligand from 1, followed by insertion of phenylacetylene into the Pt−SiR3 bond. The reactivity toward insertion decreases in the order 1c > 1a > 1b ≫ 1d. Factors responsible for the reactivity order are discussed on the basis of kinetic data and X-ray structures.