Protonation of manganese phosphonioallenyl complexes

► The nucleophilic addition of tertiary phosphines to the manganese allenylidene complexes [Mn]CCC(R)Ph proceeds at the Cα atom rather than the Cγ atom to afford the manganese α-phosphonioallenyl adducts [Mn]−-C(+PR3)CC(R)Ph. ► The protonation of the latter results in the η2-1,2-phosphonoioallenes [Mn](HC(+PR3)CC(R)Ph rather than the corresponding (phosphonio)vinylcarbenes [Mn]C(+PR3)(CHC(R)Ph). ► The protonation of the mononuclear dppm adduct [Mn]−-C(+PPh2CH2PPh2)CCPh2 proceed as a intramolecular substitution of the η2-allene moiety to give the corresponding manganese phosphine complex [Mn](PPh2CH2+PPh2-CHCCPh2) bearing the tethered phosphonioallenyl group. ► The manganese η2-1,2-phosphonoioallenes [Mn](HC(+PR3)CC(R)Ph do not isomerize into the corresponding η2-2,3-isomers.