Benchtop-Stable Carbyl Iminopyridyl Ni^II Complexes for Olefin Polymerization

Design of catalysts for Ni-catalyzed olefin polymerization predominantly focuses on ligand design rather than the activation process when attempting to achieve a broader scope of polyolefin micro- and macrostructures. Air-stable alkyl-or aryl-functionalized NiII precatalysts were designed which eliminate the need of in situ alkylating processes and are activated solely by halide abstraction to generate the cationic complex for olefin polymerization. These complexes represent an emerging class of olefin polymerization catalysts, enabling the study of various cocatalysts forming either inner- or outer-sphere ion pairs. It is demonstrated that an organoboron cocatalyst activation produces a well-defined ion pair, which in contrast to ill-defined organoaluminum cocatalysts, can directly activate the complex by halide abstraction to yield comparatively higher molecular weight homo/copolymers. Under high ethylene pressure, broader branching densities and the gradual incorporation of short-chain branches were achieved, circumventing the need for elaborate ligand design and copolymerization with α-olefins. The underlying chain-walking mechanism and ion pair interactions were further elucidated by DFT calculations. A phenyl group on the bridging carbon functioned as a rotational barrier, producing higher molecular weight polymers compared to methyl-substituted analogs. Here, we provide a perspective to manipulate the iminopyridyl NiII system, leveraging ion pair interactions and ligand design to govern polyolefin molecular weights and microstructures.在拓展聚烯烃微观与宏观结构维度的研究中，镍催化烯烃聚合催化剂的设计大多聚焦于配体修饰，而非活化过程。本研究设计了空气稳定的烷基或芳基官能化二价镍（NiII）预催化剂，无需进行原位烷基化步骤，仅需通过卤离子夺取即可活化生成用于烯烃聚合的阳离子配合物。此类配合物代表了一类新兴的烯烃聚合催化剂，可用于研究可形成内球或外球离子对的各类助催化剂。研究表明，有机硼助催化剂活化可得到结构明确的离子对；与结构模糊的有机铝助催化剂不同，有机硼助催化剂可直接通过卤离子夺取活化该配合物，从而得到分子量更高的均聚物与共聚物。在高乙烯压力条件下，可实现更宽范围的支化密度分布，并逐步引入短支链，无需进行复杂的配体修饰或与α-烯烃共聚。本研究通过密度泛函理论（DFT）计算进一步阐明了其内在的链行走机制与离子对相互作用。桥连碳原子上的苯基可充当旋转势垒，相较于甲基取代的同类配合物，其制备的聚合物分子量更高。本研究为调控亚胺吡啶基二价镍体系提供了一种思路，即通过离子对相互作用与配体设计来调控聚烯烃的分子量与微观结构。