Organic Syntheses via Transition Metal Complexes, 74 [1] Novel Phosphonium Allenide and 2‐Phosphanylethenyl Carbene Chromium and Tungsten Complexes

Alkynylcarbene complexes (CO) 5 MC(OEt)‐C≡CR 1 (M = Cr, W; R = Ph, t Bu, SiMe 3 ) readily add tertiary phosphanes PPhR 2 ′ 4 (R′ = Ph, Me) to form stable zwitterionic phosphonium allenide complexes (CO) 5 M ‐ ‐C(OEt) = CC(R)‐P+PhR 2 ′ 5 . Complex 5a (M = Cr, R = R′ = Ph) was characterized by X‐ray diffraction. The addition of secondary phosphanes PHR 2 6 to 1 affords red (2‐phosphanyl ethenyl)‐carbene complexes (CO) 5 MC(OEt)‐CHC(R)‐PR 2 ( E )‐ 8 (R = t Bu, c C 6 H 11 , Ph) in 34–89% isolated yields. Dinuclear complexes (CO) 5 MC(OEt)‐CHC(R)‐P(R 2 )M(CO) 5 ( E )‐ 9 are obtained as byproducts. Compounds ( E )‐ 8b (M = Cr, R = c C 6 H 11 ) and ( E )‐ 9i (M = Cr, R = Ph) were characterized by X‐ray analyses.