Steric and Electronic Factors That Control Two-Electron Processes between Metal Carbonyl Cations and Anions

Reactions of metal carbonyl cations (Mn(CO)₆⁺, Re(CO)₆⁺, Mn(CO)₄PPh₃⁺, Mn(CO)₄(PPh₃)₂⁺, Mn(CO)₅PEt₃⁺, Mn(CO)₅PPh₂Me⁺, Re(CO)₅PPh₃⁺, and CpFe(CO)₃⁺) with metal carbonyl anions (Co(CO)₃PPh₃, Co(CO)₄, Mn(CO)₅⁻, Mn(CO)₄PPh₃⁻, Mn(CO)₄PEt₃⁻, Mn(CO)₄PPh₂Me⁻, Mn(CO)₃(PPh₃)₂⁻, CpFe(CO)₂⁻, Re(CO)₅⁻, and Re(CO)₄PPh₃⁻) are reported. Peak potentials are reported for all ions, and nucleophilicities (as measured by reaction with Mel) are reported for the anions. Reaction of any metal carbonyl cation with any metal carbonyl anion leads ultimately to binuclear products, which are the thermodynamic products. The binuclear products are formed by a single-electron transfer. In over half of the reactions between metal carbonyl cations and anions, a two-electron change results in a new metal carbonyl cation and anion. The two-electron change may be considered mechanistically as a CO²⁺ transfer with the more nucleophilic of the two anions retaining the CO²⁺. The kinetic and thermodynamic driving forces and the suggested mechanism are examined.