ELECTROOXIDATION OF METAL CARBONYL ANIONS. FORMATION AND REACTIVITY OF 17-ELECTRON MANGANESE(0) RADICALS

Article abstract of DOI:10.1016/S0022-328X(00)99774-2

The series of carbonylmanganese anions Mn(CO)3P2^-, with P = phosphites and phosphines, undergo reversible anodic oxidation to the 17-electron radicals Mn(CO)3P2^. in tetrahydrofuran solutions.The reactivity of the carbonyl-manganese radicals of Mn(CO)3P2^. is evaluated in the context of hydrogen atom transfer from tributyltin hydride.The donor properties of the carbonylmanganates are strongly modulated by the ligands - the reversible oxidation potentials E_1/2 of phosphine-substituted anions being significantly more negative than those of the phosphite analogs.By contrast the reactivity of the phosphine- and phosphite-substituted radicals are not differentiated by electronic factors.However steric effects (as indicated by the cone angle of the phosphite or phosphine ligand play a strong role in determining the reactivity of these 17-electron radicals.The combination of cyclic voltammetry, chronoamperometry, coulometry, and product analysis is used to establish the mechanism of hydrogen transfer from tribultyn hydride to Mn(CO)3P2^. in THF solutions.The measurement of the second-order rate constants k₂ for hydrogen transfer by double potential step chronoamperometry (DPSC) is described.