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

Abstract

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.