Reactions of quadruply chelated silyl- and germyl-molybdenumhydrido complexes with isocyanides: observation of the trans-influence on the silylligand

Abstract

The reactions of a series of silyl- and germyl-molybdenum hydrido complexes, [MoH₃{E(Ar)[Ph₂PCH₂CH₂P(Ph)C₆H₄–o]₂}] (E = Si, Ge; Ar = Ph, C₆F₅, 4-Me₂NC₆H₄), with various isocyanides result in the liberation of hydrogen and formation of the molybdenum isocyanide complexes, [MoH(CNR){E(Ar)[Ph₂PCH₂CH₂P(Ph)C₆H₄–o]₂}] (R = t-Bu, cyclo-C₆H₁₁, PhCH₂, Ph, 2,6-Me₂C₆H₃), in which the isocyanide ligand ligates at the site opposite to the E atom. The new complexes show in their solid-state IR spectra an intense band assignable to CN stretching, which is found to be considerably lower than that of the corresponding free isocyanide (more than 100 cm⁻¹), demonstrating the existence of π-back-bonding from the electron-rich metal centre to the isocyanide ligand. Both X-ray crystallographic analyses and spectroscopic evidence confirm the strong trans-influence of the Si group.