A flexible bis‐Co(III) porphyrin cage as a bimetallic catalyst for the conversion of CO2 and epoxides into cyclic carbonates. Issue 22 (16th September 2020) - Schoepff, Laetitia
Abstract: A molecular cage consisting of two free‐base porphyrins connected by four flexible linkers was metalated with Co(III) to afford in good yield a bimetallic catalyst. The catalytic activity of the bis‐Co(III) porphyrin molecular cage (CoCl)2 ‐1 was studied for the formation of cyclic carbonates from CO2 and propylene oxide (PO) or styrene oxide (SO) with pyridine as cocatalyst. Various reaction parameters such as the molar ratio of the catalyst and the co‐catalyst, the time of reaction, the temperature and CO2 pressure were investigated. The molecular cage was shown to be a catalyst of high selectivity for the studied reactions and much more efficient to convert the epoxides to the corresponding cyclic carbonates than the monomeric Co(III)Cl meso ‐tetraphenylporphyrin (CoCl‐TPP ) model. When quantitative conversion of PO into propylene carbonate (PC) was reached (0.1 mol% catalyst, 1.2 mol% pyridine, 120 °C, 30 bar of CO2 ) only 23 % of PC was obtained with CoCl‐TPP (0.2 mol%). This enhanced catalytic activity is attributed to the synergistic effect of the two metal sites incorporated in the framework of the molecular cage. Abstract : Synergistic action in a bimetallic nanosized catalyst : A bimetallic catalyst consisting of a flexible molecular cage with two Co(III) porphyrins is investigated to convert CO2 and epoxides into cyclic carbonates. The preorganisation of the two metal centres in the hollow framework favours their intramolecular cooperative action leading to superior catalytic performance than for a Co(III) meso ‐tetraphenylporphyrin.