The G SRC="/images/gifchars/eta.gif" BORDER=0 >2(3e)-vinyl complex [Mo{=C(Ph)CHPh}{P(OMe)3}2Cp] is oxidized by [FeCp2]+, [CPh3]+, orB(C6F5)3 to form the 17-electron cation [Mo{=C(Ph)CHPh}{P(OMe)3}2Cp]+, which on warming loses H toform the cationic ges/gifchars/eta.gif" BORDER=0 >2(4e)-alkyne complex [Mo(ges/gifchars/eta.gif" BORDER=0 >2-PhCges/entities/tbd1.gif">CPh){P(OMe)3}2Cp]+. In the case of the borane there isevidence for a competing reaction between the ges/gifchars/eta.gif" BORDER=0 >2-vinylcomplex and the acid (H2O)B(C6F5)3, resulting in theformation of a labile trans-stilbene complex.