Reaction of pentacarbonyl(η2-bis(trimethylsilyl)ethyne)tungsten(0) with tricyclohexylphosphine: X-ray structure of pentacarbonyltricyclohexylphosphinetungsten(0)

The pentacarbonyl(?2-bis(trimethylsilyl)ethyne)tungsten(0), W(CO)5(?2-btmse), reacts with tricyclohexylphosphine, PCy3, to yield two stable endproducts which could be isolated and fully characterized by using the single crystal X-ray diffractometry and the MS, IR, and NMR spectroscopy: W(CO)5(PCy3) and trans-W(CO)4(PCy3)2. The former complex is the alkyne substitution product, while the latter one is formed from the conversion of its labile cis-isomer, which is generated by further reaction of the CO substitution product, cis-W(CO)4(?2-btmse)(PCy3), with a second PCy3 molecule. The intermediate cis-W(CO)4(?2-btmse)(PCy3) complex could not be detected even in the solution. The cis-W(CO)4(PCy3)2 complex was observable, however, found to be instable and rapidly isomerizes to trans-W(CO)4(PCy3)2. The crystal and molecular structure of W(CO)5(PCy3) was determined and compared with those of trans-W(CO)4(PCy3)2. The coordination sphere around the W atom is a slightly distorted octahedron, involving five carbonyls and one phosphine. The W-C distances have values between 1.986(6) and 2.042(6) Å. The W-P distance is 2.5794(12) Å. Maximum deviation from an ideal octahedral coordination angle is observed to be 95.68(17)°. All three cyclohexyl rings are in chair configuration.