1 Recent advances in Ni-mediated ethylene enchainment: N-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure Zheng Wang a,b,c , Qingbin Liu,* ,c Gregory A. Solan,* ,a,d Wen-Hua Sun * ,a,b,e A special issue in honor of Prof. Pierre Braunstein a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China b CAS Research/Education Center for Excellence in Molecular Sciences, University of Chinese Academy of Sciences, Beijing 100049, China c College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang 050024, China d Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK e State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China Contents 1. Introduction 2. Nickel pre-catalysts bearing N^N-chelating ligands 2.1 α-Diimine and related nickel catalysts 2.2 Pyridinylimine and related nickel catalysts 3. Nickel pre-catalysts bearing N^N^N-chelating ligands 4. Dinuclear nickel pre-catalysts 5. Conclusions and outlook Acknowledgments References ABSTRACT Homogeneous nickel catalysts have a considerable track record for mediating ethylene enchainment in the form of oligomerization and more recently polymerization. Within the polymerization arena, high molecular weight materials incorporating various degrees of