Protonation of manganese phosphonioallenyl complexes

The addition of phosphines to the manganese allenylidene complexes Cp(CO)2Mndouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(Ph)R (R = H, Ph) proceeds selectively at the Cα atom to result in the α-phosphonioallenyl complexes Cp(CO)2Mn−–C(+PR31)double bond; length as m-dashCdouble bond; length as m-dashC(Ph)R. The protonation of the latter affords the η2-(1,2)-phosphonioallenes Cp(CO)2Mn{η2-(1,2)-HC(+PR31)double bond; length as m-dashCdouble bond; length as m-dashC(Ph)R}, rather than the phosphoniovinylcarbenes Cp(CO)2Mndouble bond; length as m-dashC(+PR31)–HCdouble bond; length as m-dashC(Ph)R. All complexes obtained are stereochemically rigid and do not isomerize into the η2-(2,3)-phosphonioallene isomers.