Co(III)/Alkali-Metal(I) Heterodinuclear Catalysts for the Ring-Opening Copolymerization of CO(2) and Propylene Oxide.
Co(III)/Alkali-Metal(I) Heterodinuclear Catalysts for the Ring-Opening Copolymerization of CO(2) and Propylene Oxide.
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DOI：
10.1021/jacs.0c07980
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发表时间：
2020-11-11
影响因子：
15
通讯作者：
Williams CK
中科院分区：
文献类型：
--
作者：
Deacy AC;Moreby E;Phanopoulos A;Williams CK
二氧化碳和环氧丙烷的开环共聚是将废物增值为具有商业吸引力的聚（碳酸亚丙酯）（PPC）多元醇的有用手段。该反应受限于低催化活性、对大量过量链转移剂的耐受性差以及形成副产物的倾向。在此，报道了一系列包含异双核Co（III）/M（I）大环络合物（其中M（I）=第1族金属）的新催化剂。这些催化剂显示出PPC多元醇的高效生产、出色的产率（转换数）、定量二氧化碳吸收（>99%）和多元醇形成的高选择性（>95%）。最具活性的Co（III）/K（I）络合物在低催化剂负载（0.025 mol %，70 °C，30 bar CO2）下显示出800 h-1的转换频率。共聚反应得到很好的控制，并产生具有可预测摩尔质量和窄分散度（Di < 1.15）的羟基遥爪PPC。聚合反应动力学符合二级速率定律，环氧丙烷和催化剂浓度均为一级，CO2压力为零级。Eyring分析，检查温度对传播速率系数（kp）的影响，揭示了聚碳酸酯形成的过渡态势垒：ΔG = +92.6 ± 2.5 kJ mol-1。Co（III）/K（I）催化剂在其它环氧化物与二氧化碳的共聚中也具有高活性和选择性。
The ring-opening copolymerization of carbon dioxide and propene oxide is a useful means to valorize waste into commercially attractive poly(propylene carbonate) (PPC) polyols. The reaction is limited by low catalytic activities, poor tolerance to a large excess of chain transfer agent, and tendency to form byproducts. Here, a series of new catalysts are reported that comprise heterodinuclear Co(III)/M(I) macrocyclic complexes (where M(I) = Group 1 metal). These catalysts show highly efficient production of PPC polyols, outstanding yields (turnover numbers), quantitative carbon dioxide uptake (>99%), and high selectivity for polyol formation (>95%). The most active, a Co(III)/K(I) complex, shows a turnover frequency of 800 h–1 at low catalyst loading (0.025 mol %, 70 °C, 30 bar CO2). The copolymerizations are well controlled and produce hydroxyl telechelic PPC with predictable molar masses and narrow dispersity (Đ < 1.15). The polymerization kinetics show a second order rate law, first order in both propylene oxide and catalyst concentrations, and zeroth order in CO2 pressure. An Eyring analysis, examining the effect of temperature on the propagation rate coefficient (kp), reveals the transition state barrier for polycarbonate formation: ΔG‡ = +92.6 ± 2.5 kJ mol–1. The Co(III)/K(I) catalyst is also highly active and selective in copolymerizations of other epoxides with carbon dioxide.
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