Reactions of quadruply chelated silyl- and germyl-molybdenum hydrido complexes with isocyanides: observation of the trans-influence on the silyl ligand

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.