后过渡金属有机配合物催化乙烯和极性单体共聚机理与催化剂理论分子设计

The synthesis of functional polyolefins via copolymerization of ethylene and polar monomer catalyzed by organometallic complexes has attracted considerable attention. To date, it is generally considered that the relatively low catalytic copolymerization activity of late transition metal complexes is mainly due to the coordination of functional group of the polar monomer to the metal center and thus deactivating the catalysts. However, recent studies indicated that the stereoselective copolymerization of ethylene and some polar monomers catalyzed by rare-earth metal complexes was improved by the coordination of the functional group of these polar monomers, but the scope of polar monomer was limited and the copolymerization of vinyl polar monomer and ethylene was not reported for such rare-earth metal catalyst systems. The related mechanisms of regulating such copolymerization activity and incorporation of polar monomer have remained unclear, which is hard to be elucidated only through the current experimental approaches. In this project, the method of computational chemistry will be utilized to study the copolymerization mechanism of ethylene and polar monomer catalyzed by late transition metal complexes at the molecular level. The main purpose of this research is to elucidate, at the molecular level, the steric and electronic factors governing the copolymerization activity and selectivity as well as the β-H elimination and chain propagation. The elucidation of the effects of functional group coordination to the metal center on the insertion of polar monomer is also focused on. On the basis of the combination of theory and experiment, it is expected to provide valuable information on the rational design and development of new catalysts for copolymerization of ethylene and polar monomers.

金属有机配合物催化乙烯与极性单体共聚因其可调控等优势在合成功能化聚烯烃领域一直受到高度关注。目前普遍认为后过渡金属配合物催化乙烯与极性单体的共聚活性与极性单体插入率均偏低的一个重要原因是由于极性单体中杂原子的配位毒化作用。然而，最新研究表明稀土金属配合物催化的乙烯与部分极性单体共聚反应中却因杂原子的配位促进了极性单体的选择性聚合，但尚未实现大宗乙烯基极性单体的共聚。这种配体和金属调控共聚活性和极性单体插入率的相关分子机制不明，仅通过现有实验手段又难以阐明。针对这一问题，本项目提出通过计算化学方法系统研究后过渡金属有机配合物催化乙烯与极性单体共聚的分子机制，旨在从分子层面探明配体和金属中心调控乙烯和极性单体共聚活性与选择性、以及β-H消除与链增长相对难易的立体和电子因素，阐明杂原子配位影响极性单体插入的微观机制，通过理论与实验相结合，为设计新型高效的乙烯与极性单体共聚催化体系提供理论认识。

过渡金属催化乙烯和极性单体共聚是制备极性聚合物直接且原子经济性的有效路径。本项目通过研究不同类型金属有机配合物催化乙烯和不同类型极性单体共聚反应机理，明确了配体和金属调控共聚活性与选择性、β-H消除与链增长相对难易的立体和电子因素；明确了极性单体中杂原子的配位作用对抑制或促进极性单体插入反应的影响机制。在此基础上，提出了关于提高乙烯与极性单体共聚活性与选择性、调控聚合物分子量和支化度的理论认识，为设计新型乙烯和极性单体共聚的金属有机配合物催化剂新体系提供了有用信息.首先基于实验数据，系统筛选了适用于计算二亚胺钯催化乙烯与极性单体共聚体系的计算方法。在此基础上的机理研究表明，二亚胺配体的芳环上取代基对极性单体插入存在位阻作用；链行走机理研究表明，极性单体插入后的“链行走”过程相比乙烯插入更有利，反应过程的决速步是乙烯插入极性链端形成六元螯合物中间体的过程。由于极性单体和催化剂之间较强的相互作用使得生成的六元螯合物中间体过于稳定，进而导致乙烯插入能垒升高，从而降低了共聚活性。其它类型催化剂（膦-磺酸配体、双膦氧配体、双膦胺单氧配体）较难发生“链行走”。双膦氧钯配合物存在大位阻取代基时，极性单体插入后的乙烯插入过程中trans/cis异构化能垒较高，降低了共聚活性；配体上若有卤素原子，则可能与中心金属存在非共价作用，一定程度上稳定过渡态，从而有利于提高共聚活性。 .综上，分子内的非共价作用、极性单体插入后形成的五/六元螯合中间体、杂原子配位能力对金属配合物催化乙烯与极性单体共聚的活性起着重要作用。以上理论研究，为设计新型极性单体共聚催化体系提供了理论认识。.本项目研究成果共发表SCI论文18篇，包括J. Am. Chem. Soc. 、Nat. Commun. Nat. Chem.等高水平论文。通过项目研究，培养了三名博士生和两名硕士生。