An octahedral cobalt(iii) complex based on cheap 1,2-phenylenediamine as a bifunctional metal-templated hydrogen bond donor catalyst for fixation of CO2 with epoxides under ambient conditions

Hydrogen bond donors (HBDs) are a sustainable privileged class of catalysts which are broadly used for the activation of compounds in synthetic chemistry. Among them, the metal-templated HBD complexes present perspective systems with high catalytic potential. In this respect, here we report the design of the next-generation octahedral Co(iii) complexes based on cheap commercially available 1,2-phenylenediamine and 3,5-di-tert-butyl-salicylaldehyde. It was shown that the obtained Co(iii) complex with an iodide counter-anion operates as a bifunctional one-component hydrogen bond donor/nucleophilic catalyst for the fixation of carbon dioxide with epoxides into valuable cyclic carbonates under ambient conditions (RT and 1 bar CO2) and solvent- and co-catalyst-free conditions. The TON and TOF values of 38 and 1.6, respectively, were achieved at a low catalyst loading (2 mol%) under ambient conditions. Furthermore, the obtained Co(iii) complex catalyzed the reaction with a diluted air/CO2 mixture (15 vol% of CO2) producing the desired cyclic carbonate in a 92% yield. A plausible catalytic cycle consistent with all experimental observations was proposed based on DFT calculations. The epoxide-opening step was found to be the rate-determining step. Besides, the influence of different additives on the catalysis was investigated and explained computationally.

Automated summary

A next-generation octahedral Co(III) complex was designed based on cheap commercially available materials, which efficiently catalyzed the reaction of epoxides with carbon dioxide to produce valuable cyclic carbonates under ambient conditions. The catalyst showed high catalytic activity and selectivity, achieving TON and TOF values of 38 and 1.6, respectively, at a low catalyst loading under solvent- and co-catalyst-free conditions.