Photochemical reactions of [W(CO)4(η4-nbd)] with hydrosilanes: Generation of new hydrido complexes of tungsten and their reactivity

Photolysis of the norbornadiene (nbd) complex [W(CO)4(η4-nbd)] (1) creates a coordinatively unsaturated d6 species which interacts with the Si–H bond of tertiary and secondary silanes (Cl3SiH, Et3SiH, Et2SiH2, Ph2SiH2) to yield hydride complexes of varying stability. In reaction of complex 1 with Cl3SiH, oxidative addition of the Si–H bond to the tungsten(0) center gives the seven-coordinate tungsten(II) complex [WH(SiCl3)(CO)3(η4-nbd)], which has been fully characterized by NMR spectroscopic methods (1H, 13C{1H}, 2D 1H–1H COSY, 2D 13C–1H HMQC and 29Si{1H}). Reaction of 1 with Et3SiH leads to the hydrosilylation of the η4-nbd ligand to selectively yield endo-2-triethylsilylnorbornene (nbeSiEt3). The latter silicon-substituted norbornene gives the unstable pentacarbonyl complex [W(CO)5(η2-nbeSiEt3)], whose conversion leads to the initiation of ring-opening metathesis polymerization (ROMP). Reaction of secondary silanes (Et2SiH2 and Ph2SiH2) with 1 leads to the hydrosilylation and hydrogenation of nbd and the formation of bis(silyl)norbornane and silylnorbornane as the major products. In reaction of 1 and Et2SiH2, the intermediate dihydride complex [WH(μ-H–SiEt2)(CO)x(η4-nbd)] was detected by 1H and 13C NMR spectroscopy. As one of the products formed in photochemical reaction of W(CO)6 with Ph2SiH2, the dinuclear complex [{W(μ-η2-H–SiPh2)(CO)4}2] was identified by NMR spectroscopic methods.