Photochemical synthesis and spectroscopic characteristic of the first vinylsilane carbonyl complexes of tungsten(0)

A series of new vinylsilane complexes of the type [W(CO)5(η2-H2Cdouble bond; length as m-dashCHSiR3)] (1a–e) and trans-[W(CO)4(η2-H2Cdouble bond; length as m-dashCHSiR3)2] (2a–e) (R = Me, OMe, OCH2CH2OMe, and Cl) have been synthesized photochemically and characterized by IR and 1H, 13C and 29Si NMR spectroscopy. The values of the coordination shifts of the vinylic protons and carbons, Δδ = δ (free vinylsilane) − δ (coordinated vinylsilane), strongly suggest that trimethylvinylsilane (a) is coordinated more loosely to the tungsten atom in compounds of type 1 and 2 than other vinylsilanes (b–e). The strongest dπ–π* interaction takes place between the carbonyltungsten moiety and trichlorovinylsilane. Analysis of 13C NMR data of vinylsilane compounds revealed that the electron-donating methyl substituents and the electron-withdrawing chlorine substituents at the silicon atom cause opposite deviations from the ideal symmetrical η2-coordination of vinylsilane to the tungsten atom. The bis(vinylsilane) complexes 2a–e are shown to exist in several isomeric forms, whose solution dynamics were investigated by variable-temperature 1H NMR studies.