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

Piano-stool Mn(I) cationic carbyne complexes react with bis(diphenylphosphino)methane to afford selectively either cyclic λ5-1,3-diphosphetium semi-ylides or Mn(I) complexes featuring unprecedented phosphonioketene ligands, depending on the nature of the carbyne substituent, aryl or alkyl, respectively.135