Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO_2, CO, and H^+

Abstract

The preparation and characterization of a series of isostructural cobalt complexes Co(t-Bu)_2(P^EPy^EP)(t-Bu)_2(CH_3CN)_2]-[BF_4]_2 (Py = pyridine, E = CH_2, NH, O, and X = BF_4 (1a-c)) and the corresponding one-electron reduced analogues Co(t-Bu)_2P^EPy^EP(t-Bu)_2(CH_3CN)_2][BF_4]_2 (2a-c) are reported. The reactivity of the reduced cobalt complexes with CO_2, CO, and H^+ to generate intermediates in a CO_2 to CO and H_2O reduction cycle are described. The reduction of 1a-c and subsequent reactivity with CO_2 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 CO_2. By investigating a series of isostructural complexes, correlations in reactivity with ligand electron withdrawing effects are made.