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 -back-bonding from the electron-rich metal centre to the isocyanide ligand. Both X-ray crystallographic analyses and spectroscopic evidence confirm the strong transinfluence of the Si group.