Transition metal imido compounds as Ziegler-Natta olefin polymerisation catalysts

Transition metal imido compounds having the general formula [(L)(n)M(NR)] [where (L)(n) is a supporting ligand or ligand set, and R typically is alkyl or aryl] have been known for nearly 50 years, and during the last two decades have been the focus of considerable attention. Relatively recently their potential application in the Ziegler-Natta polymerisation of olefins has been realised. In this contribution we review the Ziegler-Natta polymerisation of olefins by transition metal imido compounds. A general introduction to homogeneous Ziegler-Natta olefin polymerisation and key aspects of transition metal imido chemistry is given, followed by a short description of a related imido-based polyrnerisation process, namely ring-opening olefin metathesis polymerisation catalysed by imido-supported molybdenum and tungsten alkylidenes. A summary of the "design principles" that have been employed in the development of certain imido-based Ziegler-Natta catalysts is presented, followed by a comprehensive survey of the literature in the title area. 1 Introduction 1.1. Homogeneous Ziegler-Natta Olefin Polymerisation 1.2 Aspects of Transition Metal Imido Chemistry 1.3 Ring-Opening Olefin Metathesis Polymerisation with Imido-Supported Molybdenum- and Tungsten-Alkylidene Catalysts 2 Imido Compounds as Ziegler-Natta Catalysts: Design Principles 3 Survey of Systems 3.1 Group 4 3.2 Group 5 3.3 Group 6 4. Summary and Outlook.