Dual reactivity pattern of Mn(I) carbyne complexes Cp(CO)2Mn+≡C–R (R = Ar, Alk) vs. dppm: Subtle balance between double intramolecular nucleophilic addition and nucleophilic addition followed by migratory CO insertion

Abstract The Mn(I) cationic carbyne complexes [Cp(CO) 2 Mn + ≡C–R]BX 4 (R = Ph, Tol, Me, Bn; X = F, Cl, Ph) react with bis(diphenylphosphino)methane to afford selectively either cyclic λ 5 -1,3-diphosphetium semi-ylides [RC–P + Ph 2 CH 2 P + Ph 2 )]BPh 4 ([ R 4 ]BPh 4 ; R = Ph, Tol), or Mn(I) complexes [Cp(CO)Mn(η 3 -(P,C,C)-Ph 2 PCH 2 P + Ph 2 C(R)=C=O)]BX 4 ([ R 5 ]BX 4 ; R = Me, X = Ph; R = Bn, X = F) featuring unprecedented phosphonioketene ligands depending on the nature of the carbyne substituent, aryl or alkyl, respectively. The selective formation of these products is tentatively rationalized through the key formation of a transient cationic Mn(I) phosphoniocarbene complexes [Cp(CO) 2 Mn=C(R)PPh 2 + CH 2 PPh 2 ]BX 4 bearing a pendent phosphine moiety. The molecular structures of semi-ylide [ Ph 4 ]BPh 4 and complex [ Bn 5 ]BF 4 were elucidated by single-crystal X-ray diffraction.