Recent advances on α-diimine Ni and Pd complexes for catalyzed ethylene (Co)polymerization: A comprehensive review

α-Diimine Ni and Pd complexes are one of the most examined late-transition organometallics in the application of catalyzed ethylene (co)polymerization. These organometallic catalysts provide unique advantages and particular opportunities to tailor the architectures, composition, and topology of synthesized polymers through catalyzed polymerization. Two decades after their initial discovery, they are still drawing extensive attention in both academia and industry. More recently, researchers have studied the effect of structural modifications on the α-diimine Ni and Pd complexes and their catalytic behaviors in ethylene (co)polymerization. This review highlights the recent progress in the developments of α-diimine Ni and Pd complexes achieved in the last decade. The chain-walking mechanism as a unique catalytic behavior of α-diimine Ni and Pd complexes is also addressed. The versatile synthesis of ligands and complexes enables researchers to tailor the catalytic performance and the microstructures of polyethylene. Correlations between their structural tunes and catalytic behaviors, polymer properties, and the ethylene copolymerization with polar monomers are comparatively presented and discussed. The heterogenization study of α-diimine Ni and Pd complexes on a solid support for heterogeneous catalysis is also comprehensively summarized. The review is broadly classified into four sections which includes i) the coordination-insertion chemistry in ethylene (co)polymerization, ii) the modification of ligand structure, iii) their application in the field of heterogeneous polymerization, iv) and the properties of the synthesized polymers, followed by the short summary and outlook for their potential studies and applications.