Macrocyclic Dizinc(II) Alkyl and Alkoxide Complexes: Reversible CO2 Uptake and Polymerization Catalysis Testing

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• 作者：Charles Romain ; Michael S. Bennington ; Andrew J. P. White ; Charlotte K. Williams ; Sally Brooker
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：December 21, 2015
• 年：2015
• 卷：54
• 期：24
• 页码：11842-11851
• 全文大小：581K
• ISSN：1520-510X

文摘

The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [L^EtZn₂Et₂] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [L^EtZn₂(ⁱPrO)₂] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 脳 10^鈥? min^鈥?, with [LA] = 1 M and [initiator] = 5 mM at 25 掳C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO₂) and cyclohexene oxide at 80 掳C and 1 bar of CO₂ pressure. However, stoichiometric reactions between complex 2 and CO₂, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [L^EtZn₂(ⁱPrO)(ⁱPrOCO₂)] (3a) and [L^EtZn₂(ⁱPrOCO₂)₂] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1鈥?b>3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.