postmetallocene

Postmetallocene refers to a broad class of organometallic catalysts developed to extend beyond traditional metallocenes for olefin polymerization and related transformations. Unlike conventional metallocene systems, which rely on symmetric sandwich ligands such as Cp2MR2, postmetallocene catalysts employ alternative ligand frameworks that create defined, single-site metal centers. This structural diversity enables fine-tuning of activity, stereocontrol, comonomer incorporation, and tolerance to functional or polar co-monomers.

Ligand architectures in postmetallocene catalysts are varied. They include fluorenyl- or indenyl-based ligands linked to bridging or chelating groups, as well as constrained geometries, and donor sets based on amides, phosphines, or pincer-type ligands. Many systems are activated by scavengers such as methylaluminoxane (MAO) or borate co-catalysts, which generate cationic catalytic centers. The design goal is to maintain high activity while expanding the scope of substrates beyond what traditional metallocenes could efficiently polymerize.

A prominent subset of postmetallocene catalysts is the constrained-geometry catalyst (CGC) family, developed in the 1990s, which use ligands that fix the metal coordination environment to enhance activity and comonomer tolerance. Other examples include various non-metallocene catalysts (NMCs) and broad “single-site catalysts” families that employ diverse ligand backbones but share a common feature: a well-defined, coordinatively unsaturated metal center.

Applications center on olefin polymerization to produce polyethylene and polypropylene with tailored molecular weight, comonomer incorporation, and tacticity. Postmetallocene chemistry continues to evolve, offering expanded ligand diversity and potential process advantages, while complementing traditional metallocene approaches.