Synthesis and Reactions of Tungsten Oxo Vinylalkylidene Complexes:  Reactions of WCl_2(O)(PX_3) (X = OMe, R) Precursors with 3,3-Diphenylcyclopropene

Complexes of the type WCl_2(O)[PX_3]_3 (PX_3 = P(OMe)_3 (1); PMePh_2 (2)) were synthesized according to procedures previously described in the literature. Upon treatment with 3,3-diphenylcyclopropene, complexes 1 and 2 afforded the corresponding η^2-cyclopropene complexes. Spectroscopic data of W(η^2-diphenylcyclopropene)Cl_2(O)[PX_3]_2 (PX_3 = P(OMe)_3 (4); PMePh_2 (5)) were consistent with an octahedral geometry in which the two mutually trans PX_3 ligands and the cyclopropene ligand occupy equatorial positions cis to the apical oxo ligand. The thermal rearrangement of the η^2-cyclopropene complexes leads to the dimerization product of 3,3-diphenylcyclopropene: 1,1,6,6-tetraphenyl-1,3,5-hexatriene. The presence of carbene species before the dimerization occurs has been demonstrated. Upon treatment with 2 equiv of lithium hexafluoro-tert-butoxide, complexes 4 and 5 give the vinyl alkylidene complexes W(=CHCH=CPh_2)(O)[OC(CH_3)(CF_3)_2]_2[PX_3] (PX_3 = P(OMe)_3 (10); PMePh_2 (7)). The spectroscopic data of 10 and 7 indicated a distorted trigonal bipyramid, where the oxo and alkylidene ligands are cis to each other and placed in the equatorial plane