Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

The preparation and
characterization of a series of isostructural cobalt complexes [Co­(t-Bu)2PEPyEP­(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)2PEPyEP­(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.