Stepwise Formation of σ-Alkynyl, Vinylidene, and Vinylphosphonium Complexes of Manganese(I)

Reaction of methyl propiolate with the diphosphinomethanide complex [Mn(CO)4{(PPh2)2CH}] (1) produces simultaneously the insertion of the alkyne into the
C−H bond, giving [Mn(CO)4{(PPh2)2C−C(H)C(CO2Me)H}] (2), and the deprotonation of the alkyne mediated
by the diphosphinomethanide ligand, affording the
σ-alkynyl derivative fac-[Mn(C⋮C−CO2Me)(CO)3(dppm)]
(3). Protonation of 3 with HBF4 at 200 K affords the
corresponding vinylidene compound fac-[Mn(CC(H)CO2Me)(CO)3(dppm)]BF4 (5), which, on raising the temperature to 243 K, undergoes the spontaneous insertion
of the vinylidene ligand into a Mn−P bond.