Reactivity of a series of isostructural cobalt pincer complexes with CO2, CO, and H(+).

Abstract

The preparation and characterization of a series of isostructural cobalt complexes [Co(t-Bu)2P(E)Py(E)P(t-Bu)2(CH3CN)2][BF4]2 (Py = pyridine, E = CH2, NH, O, and X = BF4 (1a-c)) and the corresponding one-electron reduced analogues [Co(t-Bu)2P(E)Py(E)P(t-Bu)2(CH3CN)2][BF4]2 (2a-c) are reported. The reactivity of the reduced cobalt complexes with CO2, CO, and H(+) to generate intermediates in a CO2 to CO and H2O reduction cycle are described. The reduction of 1a-c and subsequent reactivity with CO2 was investigated by cyclic voltammetry, and for 1a also by infrared spectroelectrochemistry. The corresponding CO complexes of (2a-c) were prepared, and the Co-CO bond strengths were characterized by IR spectroscopy. Quantum mechanical methods (B3LYP-d3 with solvation) were used to characterize the competitive reactivity of the reduced cobalt centers with H(+) versus CO2. By investigating a series of isostructural complexes, correlations in reactivity with ligand electron withdrawing effects are made.