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)(eta(2) - H2C--CHSiR3)] (1a-e) and trans-[W(CO)(4)(eta(2)-H2C=CHSiR3)(2)] (2a-e) (R = Me, OMe, OCH2CH2OMe, and Cl) have been synthesized photochemically and characterized by IR and H-1, C-13 and Si-29 NMR spectroscopy. The values of the coordination shifts of the vinylic protons and carbons, Ab = 6 (free vinylsilane,) - 5 (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 d pi-pi* interaction takes place between the carbonyltungsten moiety and trichlorovinylsilane. Analysis of C-13 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 eta(2)-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 H-1 NMR studies. (c) 2005 Elsevier B.V. All rights reserved.