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

Abstract

Photolysis of the norbornadiene (nbd) complex [W(CO) 4(η 4-nbd)] ( 1) creates a coordinatively unsaturated d 6 species which interacts with the Si–H bond of tertiary and secondary silanes (Cl 3SiH, Et 3SiH, Et 2SiH 2, Ph 2SiH 2) to yield hydride complexes of varying stability. In reaction of complex 1 with Cl 3SiH, oxidative addition of the Si–H bond to the tungsten(0) center gives the seven-coordinate tungsten(II) complex [WH(SiCl 3)(CO) 3(η 4-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 Et 3SiH leads to the hydrosilylation of the η 4-nbd ligand to selectively yield endo-2-triethylsilylnorbornene (nbeSiEt 3). The latter silicon-substituted norbornene gives the unstable pentacarbonyl complex [W(CO) 5(η 2-nbeSiEt 3)], whose conversion leads to the initiation of ring-opening metathesis polymerization (ROMP). Reaction of secondary silanes (Et 2SiH 2 and Ph 2SiH 2) 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 Et 2SiH 2, the intermediate dihydride complex [WH(μ-H–SiEt 2)(CO) x (η 4-nbd)] was detected by 1H and 13C NMR spectroscopy. As one of the products formed in photochemical reaction of W(CO) 6 with Ph 2SiH 2, the dinuclear complex [{W(μ-η 2-H–SiPh 2)(CO) 4} 2] was identified by NMR spectroscopic methods.