Redox potential–structure relationships in metal complexes. Part 3. The electrochemical activation of co-ordinated hydrazido(2–)-ligands

Abstract

The complexes [Mo(N₂RR′)(S₂CNMe₂)₃]⁺, R,R′= alkyl or aryl, undergo two successive reversible one-electron reductions in non-aqueous electrolytes at platinum or vitreous carbon electrodes. The initial electron-transfer product [Mo(N₂RR′)(S₂CNMe₂)₃]⁰ disproportionates to [Mo(N₂RR′)(S₂CNMe₂)₃]⁺ and to the product of the second electron transfer, [Mo(N₂RR′)(S₂CNMe₂)₃]^–. Two-electron reduction of the cation leads to electroactivation of the N₂RR′ ligand towards attack by electrophiles and reduction/protonation is shown to liberate the free hydrazine, NH₂NMe(Ph), in ca. 57% yield. A plausible mechanism for this electroactivation is discussed, and, from studies of related complexes, it is suggested that the redox orbitals of the [Mo(N₂R₂)(S₂CNMe₂)₃]⁺ complex are associated with the MoN–N function.