Co(II) benzimidazoles complexes: Synthesis, characterization and catalytic studies to chemical fixation of CO2 in cyclic carbonates

One of the most challenging environment problem is the control emissions of greenhouse gases; carbon dioxide levels in atmosphere are the highest since records began; the concentration of CO2 in atmosphere has risen up from 280 ppm to 400 ppm during the last century and, the average global temperature has increased between 0.6 °C and 1 °C in the same period. New routes to transform CO2 into desirable and economically competitive products are the main goal for chemists.1 In this sense, we developed five cobalt(II) benzimidazole complexes (Figure 1) which were characterized by 1H and 13C NMR, elemental analysis, IR, electronic spectra (diffuse reflectance and methylene chloride solution), ESI-HRMS, Raman and crystalline structure. The complexes had their catalytic performance studied in the CO2 fixation reaction with an epoxide forming cyclic carbonates. The catalytic performance is showed in Table 1. In summary, we have synthesized five tetracoordinate cobalt complexes, calculated their field parameters, studied magnetic and structural behavior and a complete catalytic study was performed. All complexes were able to catalyze the cycloaddition reaction. Different types of bases were tested and TBAB was the best. An equilibrium between nucleophilic/leaving group ability of anion is responsible to the better conversion using TBAB. Temperature has a high impact in catalytic activities arising TON e TOF when increasing this variable. Reactions with different epoxides was performed in optimal conditions and the systems were active with all epoxides tested.