A Flexible Bis-Co(Iii) Porphyrin Cage As A Bimetallic Catalyst For The Conversion Of Co(2)And Epoxides Into Cyclic Carbonates

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)-1was studied for the formation of cyclic carbonates from CO(2)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 CO(2)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)Clmeso-tetraphenylporphyrin (CoCl-TPP) model. When quantitative conversion of PO into propylene carbonate (PC) was reached (0.1 mol% catalyst, 1.2 mol% pyridine, 120 degrees C, 30 bar of CO2) only 23 % of PC was obtained withCoCl-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.