Formation of a tungsten vinylvinylidene complex from addition of alkyne to (dppe)(OC)3W=C=CHPh

Article abstract of DOI:10.1021/om00095a006

Reaction of mer-(dppe)(OC)₃W=C=CHPh with dimethyl acetylenedicarboxylate (DMAC) results in formation of Z and E isomers of a vinylvinylidene product, (dppe)(OC)₃W=C=C(COOCH₃)C-(COOCH₃)=CHPh. The reaction presumably proceeds through an η¹-cyclobutenyl complex prior to forming the final product which reflects net insertion of the added alkyne into the C_α-C_β bond of the vinylidene reagent. The kinetically formed Z isomer is rapidly converted to the E isomer by light, with a photostationary state ratio of 1:8 Z/E. Infrared and ¹H and ¹³C NMR data are reported for both isomers. The X-ray crystal structure of the Z isomer shows an octahedral tungsten environment and an approximate cisoid geometry for the vinylvinylidene fragment. The compound crystallizes in space group P2₁/c with four molecules per unit cell (a = 11.140 (4) A?, b = 18.047 (6) A?, c = 19.850 (7) A?; β = 94.87 (3)°; V = 3976.3 A?³; ρ(calcd) = 1.521 g/cm³). Full-matrix least-squares refinement of 358 variables using 4146 data with I ≥ 3σ(I) converged with unweighted and weighted residuals of 4.1% and 3.1%, respectively.