Abstract
Based on the ligand H4Salen-8tBu (salen-4), a new dinuclear cobalt complex (salen-4)[Co(III)TFA]2 (salen-4 = 3,5-di-tert-butylsalicylaldehyde-3,3′-diaminobiphenylamine; TFA = trifluoroacetic acid) has been firstly synthesized and characterized. It shows high catalytic activity for the copolymerization of propylene oxide (PO) and carbon dioxide (CO2), yielding regioregular poly(propylene carbonate) (PPC) with little generation of propylene carbonate (PC) by-product. It has been found that (salen-4)[Co(III)TFA]2 shows higher activity at milder conditions, generating a polymer with maximum Mn of 293 kg/mol and a narrow molecular weight distribution PDI of 1.35. The influences of reaction time, CO2 pressure, reaction temperature, nature of the cocatalyst, catalyst dosage and substrate concentration on the molecular weight, yield and selectivity of the polymer were explored in detail. The results showed that the (salen-4)[Co(III)TFA]2/[PPN]TFA catalyst system demonstrated a remarkable TOF as high as 735 h–1. In addition, a hypothetical catalytic reaction mechanism was proposed based on density functional theory (DFT) calculations and the catalytic reaction results of the (salen-4)[Co(III)TFA]2.
Highlights
IntroductionWith the development of social industrialization, the concentration of CO2 in the atmosphere keeps rising, resulting in the greenhouse effect and a series of associated environmental disasters [1]
With the development of social industrialization, the concentration of CO2 in the atmosphere keeps rising, resulting in the greenhouse effect and a series of associated environmental disasters [1].CO2 is an inexpensive, a nontoxic, rich and special renewable C1 building block [2,3,4].So far, wide attention has been paid to the chemical conversion of CO2 into high value-added energy, materials and chemical products
The possible reason is that when the reaction time is too long, the polymer will adhere to the surface of the catalyst and reduces the contact area between the active center and propylene oxide (PO), resulting in a slower catalytic rate
Summary
With the development of social industrialization, the concentration of CO2 in the atmosphere keeps rising, resulting in the greenhouse effect and a series of associated environmental disasters [1]. Inspired by Inoue’s pioneering work, researchers have developed many catalysts [13,14,15,16,17,18,19,20,21,22,23] It is still a big challenge for scientists to develop low-cost, prepared and highly efficient catalysts for fixation and conversion of CO2 under mild conditions. Klaus and coworkers developed a dinuclear salen-Cr complex They found that with a suitable distance, the two metal centers showed a perfect synergy in high dilution, but a low selectivity of carbonate linkages [39]. When (salen-4)[Co(III)TFA]2 was used as a catalyst for PO and CO2 copolymerization under mild conditions, it displayed excellent catalytic performance with high activity and selectivity.
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