Synergic Heterodinuclear Catalysts for the Ring-Opening Copolymerization (ROCOP) of Epoxides, Carbon Dioxide, and Anhydrides.
Synergic Heterodinuclear Catalysts for the Ring-Opening Copolymerization (ROCOP) of Epoxides, Carbon Dioxide, and Anhydrides.
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用于环氧化合物、二氧化碳和苯胺开环共聚的协同异双核催化剂。
DOI：
10.1021/acs.accounts.2c00197
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发表时间：
2022-08-02
影响因子：
18.3
通讯作者：
Williams, Charlotte K.
中科院分区：
文献类型：
--
作者：
Diment, Wilfred T.;Lindeboom, Wouter;Fiorentini, Francesca;Deacy, Arron C.;Williams, Charlotte K.
开发可持续塑料材料是21世纪化学的重要目标。实现这一目标的关键目标包括利用可持续单体和开发可化学回收/降解的聚合物。由环氧化物和CO2的开环共聚（ROCOP）合成的聚碳酸酯和由环氧化物和酸酐的ROCOP合成的聚酯满足这些标准。尽管如此，为这些过程设计有效的催化剂仍然具有挑战性。典型的问题包括需要高催化剂负载量;与其它商业化聚合相比催化活性低;以及需要昂贵、有毒的助催化剂。非常需要开发用于这两种类型的ROCOP的有效催化剂。该帐户详细介绍了我们在这两种相关聚合反应的催化剂开发方面的工作，特别关注双核配合物，这些配合物通常在没有任何助催化剂的情况下应用。我们已经开发了与我们的催化剂串联的机理假设，并在整个帐户中，我们描述了动力学，计算和结构活性研究，这些催化剂的性能的基础。我们对同双核M（II）M（II）配合物催化环氧环己烷（CHO）/CO2 ROCOP的初步研究提供了支持链穿梭催化机理的数据，这意味着两种金属在催化中的不同作用。这一机理假说激发了混合金属、异双核催化剂的发展。这类催化剂中的第一种是异双核Zn（II）Mg（II）络合物，其对于CHO/CO2 ROCOP表现出比同双核[Zn（II）Zn（II）和Mg（II）Mg（II）]类似物更高的速率。扩大这一发现，我们随后开发了一种Co（II）Mg（II）复合物，显示了CHO/CO2 ROCOP的现场领先率，并允许独特的洞察这两种金属在这个复合物中的作用，其中它被确定为Mg（II）中心减少过渡态熵和Co（II）中心减少过渡态焓。根据这些发现，我们随后开发了一系列异双核M（III）M（I）催化剂，其能够催化宽范围的共聚，包括CHO/CO2、环氧丙烷（PO）/CO2和CHO/邻苯二甲酸酐（PA）的开环共聚。发现具有Co（III）K（I）和Al（III）K（I）的催化剂分别对PO/CO2和CHO/PA ROCOP特别有效。这样的M（III）M（I）络合物通过双核金属化物机制起作用，其中M（III）结合并活化单体，而M（I）物质紧密结合聚合物变化以允许插入活化的单体中。我们的研究说明了如何仔细的催化剂设计可以产生高效的系统，以及如何机械理解的发展，这一过程的援助。还讨论了未来研究的途径，包括这些异双核催化剂在可持续材料合成中的适用性。
The development of sustainable plastic materials is an essential target of chemistry in the 21st century. Key objectives toward this goal include utilizing sustainable monomers and the development of polymers that can be chemically recycled/degraded. Polycarbonates synthesized from the ring-opening copolymerization (ROCOP) of epoxides and CO2, and polyesters synthesized from the ROCOP of epoxides and anhydrides, meet these criteria. Despite this, designing efficient catalysts for these processes remains challenging. Typical issues include the requirement for high catalyst loading; low catalytic activities in comparison with other commercialized polymerizations; and the requirement of costly, toxic cocatalysts. The development of efficient catalysts for both types of ROCOP is highly desirable. This Account details our work on the development of catalysts for these two related polymerizations and, in particular, focuses on dinuclear complexes, which are typically applied without any cocatalyst. We have developed mechanistic hypotheses in tandem with our catalysts, and throughout the Account, we describe the kinetic, computational, and structure–activity studies that underpin the performance of these catalysts. Our initial research on homodinuclear M(II)M(II) complexes for cyclohexene oxide (CHO)/CO2 ROCOP provided data to support a chain shuttling catalytic mechanism, which implied different roles for the two metals in the catalysis. This mechanistic hypothesis inspired the development of mixed-metal, heterodinuclear catalysts. The first of this class of catalysts was a heterodinuclear Zn(II)Mg(II) complex, which showed higher rates than either of the homodinuclear [Zn(II)Zn(II) and Mg(II)Mg(II)] analogues for CHO/CO2 ROCOP. Expanding on this finding, we subsequently developed a Co(II)Mg(II) complex that showed field leading rates for CHO/CO2 ROCOP and allowed for unique insight into the role of the two metals in this complex, where it was established that the Mg(II) center reduced transition state entropy and the Co(II) center reduced transition state enthalpy. Following these discoveries, we subsequently developed a range of heterodinuclear M(III)M(I) catalysts that were capable of catalyzing a broad range of copolymerizations, including the ring-opening copolymerization of CHO/CO2, propylene oxide (PO)/CO2, and CHO/phthalic anhydride (PA). Catalysts featuring Co(III)K(I) and Al(III)K(I) were found to be exceptionally effective for PO/CO2 and CHO/PA ROCOP, respectively. Such M(III)M(I) complexes operate through a dinuclear metalate mechanism, where the M(III) binds and activates monomers while the M(I) species binds the polymer change in close proximity to allow for insertion into the activated monomer. Our research illustrates how careful catalyst design can yield highly efficient systems and how the development of mechanistic understanding aids this process. Avenues of future research are also discussed, including the applicability of these heterodinuclear catalysts in the synthesis of sustainable materials.
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