Cyclic Voltammetric Studies of Arylisocyanidecobalt(I) Complexes with Tertiary Phosphine Ligands

Abstract

50 Arylisocyanide-Co(I) complexes with tertiary phosphine ligands, both monosubstituted [Co(CNR)₄PR'₃]X and disubstituted [Co(CNR)₃(PR'₃)₂]X, X = ClO₄, BF₄, have been investigated by cyclic voltammetry in acetonitrile solution. Behaviour ranges from reversible to irreversible. Several distinct trends emerge. The E_ox values systematically increase as substituents in the arylisocyanide ligand progress from electron- donating to electron-withdrawing. Sometimes this trend is reversed, possibly attributable to steric hindrance. The E_ox values also systematically increase as the tertiary phosphine ligand becomes weaker σ-donating/stronger π*-accepting due to substituents. Trialkylphosphines show weaker π-acidity than triarylphosphines, except with electron-withdrawing substituents, like P(CH₂Ph)₃ and P(CH₂CH₂CN)₃. Cobalt(I) complexes of 4:1 arylisocyanide: tertiary phosphine ligand composition tend to have substantially higher E_ox values than 3:2 complexes with identical arylisocyanide and tertiary phosphine ligands.