Design And Synthesis Of Binuclear Cobalt Complexes For The Copolymerization Of CO₂and Cyclohexane Oxide

Carbon dioxide (CO2) is an abundant, non-toxic, cheap and readily available C1resource,which is used in several important industrial processes. Efficient conversion of carbon dioxide is of great significance both in theoretical research and practical industrial production. The production of polycarbonates by the alternating copolymerization of Carbon dioxide and epoxides having typical green polymerization characteristics. As polycarbonate has important applications in medicine, optical devices, electronic instruments and other fields, the copolymerization received increasing attention. The polymerization process involves much interesting information, such as the catalytic conversion rate, polymer/cyclic product selectivity, the carbonate units and ether units selectivity in the polymerization product. Therefore, to find out a catalyst system which can efficiently and selectively transform carbon dioxide into polymers with high molecular weight and high carbonate linkages is one of the key issues in this research area. Currently, many systems can achieve the goal of copolymerization with carbon dioxide and epoxides, among those systems tetradentate Schiff base (salen) cobalt system gives the best performance.A series of binuclear Cobalt-Salen complexes was designed and successfully synthesized, according to the theory of "bimetallic cooperation mechanism", with2-tert-butylbenzene-1,4-diol, cyclohexane-1,2-diamine hydrochloride,9,9-dimethylxanthene and cobalt acetate as start stuff materials. The prepared ligands were characterized by1H-NMR、13C-NMR and TOF-MS and the prepared Cobalt-Salen complexes were characterized by1H-NMR and MS. The synthesized binuclear Cobalt-Salen complexes joined by flexible or rigid group were used for the alternating coupling of carbon dioxide and cyclohexane oxide under mild conditions. The results showed that the binuclear cobalt system connected through flexible chain gives almost no improvement in activity compared with mononuclear Cobalt-Salen system, this may be due to the flexible group could not limit the two cobalt ions at a suitable distance, so the bimetallic cooperation do not exist; among the binuclear cobalt systems connected through rigid groups only complex Ⅴ improves the catalytic activity significantly, speculated that the characteristics of rigid structure of Ⅴ is benefit for the two cobalt ions keeping at a suitable distance of cobalt in order to achieve a bimetallic cooperation process. Activity of the other two rigid groups connected complexes do not improve significantly, but polymers’stereoselective changes greatly which means a synergistic effect exist between the binuclear cobalt, but the synergistic effect is negative effect due to the inappropriate distance between the binuclear cobalt ions.