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

The Mn(I) cationic carbyne complexes [Cp(CO)2Mn+≡C–R]BX4 (R = Ph, Tol, Me, Bn; X = F, Cl, Ph) react with bis(diphenylphosphino)methane to afford selectively either cyclic λ5-1,3-diphosphetium semi-ylides [RC–P+Ph2CH2P+Ph2)]BPh4 ([R4]BPh4; R = Ph, Tol), or Mn(I) complexes [Cp(CO)Mn(η3-(P,C,C)-Ph2PCH2P+Ph2C(R)=C=O)]BX4 ([R5]BX4; 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)2Mn=C(R)PPh2+CH2PPh2]BX4 bearing a pendent phosphine moiety. The molecular structures of semi-ylide [Ph4]BPh4 and complex [Bn5]BF4 were elucidated by single-crystal X-ray diffraction. 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. [Display omitted] •Synthesis of λ5-1,3-diphosphetium semi-ylides by a formal carbyne transfer to dppm.•Formation of unprecedented phosphonioketene ligands in Mn coordination sphere.•Dual reactivity pattern of cationic Mn(I) carbyne complexes vs. dppm as a function of carbyne substituent.