A review of immobilized molecular transition metal catalysts for ethylene oligomerization and polymerization reactions.

Transformations of olefins into valuable feedstocks and their end products are among the most versatile chemical processes in modern science and technology. Among these reactions, olefin oligomerization and polymerization are instrumental in producing a wide range of products, including fuels, plasticizers, lubricants, surfactants, detergents, co-monomers, and plastics. Over the past century, homogeneous late-transition-metal catalysts have successfully facilitated olefin oligomerization reactions, but not without major drawbacks, such as a lack of catalyst recyclability and reusability. On the other hand, while heterogeneous catalysts are recyclable, they suffer from poor selectivity, thus limiting their application in the production of fine and specialty chemicals. This has necessitated the evolution of a third generation of catalysts in the form of supported single-site ("hybrid") catalysts that bridge both the advantages of homogeneous and heterogeneous catalysts of high selectivity and recovery, respectively. Therefore, in this review, we present the use of inorganic, organic, and polymer supports to immobilize molecular catalysts reported to date in the literature. The review covers the immobilization strategies, types of inorganic and polymer supports, and the application of these supported catalysts in ethylene oligomerization and polymerization reactions. It further presents a comparative analysis of the different classes of supports, a critical evaluation of the immobilization strategies, and their influence on the performance of the resultant immobilized catalysts. The major findings and critical analyses of the literature data, together with future perspectives, are also summarized.