Synthesis and characterization of metal (M = Al or Ga) 2-phosphino (phenolate/benzenethiolate) complexes and their electrochemical behavior in the presence of CO2

A series of Group 13 complexes MLX2 (M=Al or Ga, L=SC6H4-2-(PBu2)-Bu-t or OC6H4-2-(PBu2)-Bu-t, X=Me or C6F5) have been synthesized and characterized by multinuclearNMRspectroscopy and single crystal X-ray diffraction. Reactions of Me3Al or Me3Ga with an equivalent of either 2-(Bu2P)-Bu-t(C6H4) OH (1) or 2-(Bu2P)-Bu-t(C6H4) SH (5) resulted in the formation of four new(2,3,6, and 7), 4-coordinate dimethyl chelate (S, P or O, P) complexes via methane elimination. The dimethyl gallium complexes (3 and 7) underwent a further reaction with excess B(C6F5) 3, and through ligand exchange (methyl/pentafluorophenyl), resulted in the disubstituted bis(pentafluorophenyl) analogs (4 and 8). Cyclic voltammetry (CV) experiments for all compounds in the presence of and the absence of (1-8) CO2 were performed. For compounds showing cathodic reduction waves under CO2 (2,3,4, and 6), bulk electrolysis experiments were performed. Electrochemical studies indicate that, for several compounds, a transient CO2 adduct is formed which undergoes a one-electron, irreversible (or partially irreversible) reduction to form an unstable radical anion.