Catalytic Polymerization of Rare Earth Metal Complexes

Rare earth metal complexes have emerged as powerful catalysts for the coordination–insertion polymerisation of unsaturated hydrocarbons, notably 1,3‐dienes and olefins. The large ionic radii and electropositive character of lanthanides, scandium and yttrium enable flexible coordination geometries and facile monomer activation. Tailored ligand environments—from cyclopentadienyl and constrained‐geometry frameworks to pincer and homoleptic scaffolds—govern catalytic activity, molecular weight control and stereoselectivity. Activation protocols employing aluminium alkyls or perfluorinated borate/borane co‐catalysts generate cationic or heterobimetallic species that insert monomers with high cis-1,4 or trans-1,4 selectivity. Spectroscopic and crystallographic studies have illuminated key intermediates and cooperative effects in multimetallic assemblies. These catalysts deliver high-performance elastomers, stereoregular polybutadienes and speciality copolymers for applications in tyre tread, medical devices and advanced coatings. Current efforts focus on expanding the monomer scope to polar and functionalised olefins, enhancing catalyst longevity and integrating sustainability through catalyst recovery and earth-abundant co-catalyst systems.

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Catalytic Polymerization of Rare Earth Metal Complexes publication trend

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Technical terms

Coordination–insertion polymerisation: A mechanism in which an unsaturated monomer binds to a metal centre and inserts into a metal–carbon bond to elongate a polymer chain.

Cocatalyst: A secondary reagent, often an aluminium alkyl or perfluorinated borate/borane, used to convert a neutral precatalyst into an active cationic species.

Metallocene: A sandwich complex comprising a metal centre bound between cyclopentadienyl ligands, commonly used in single‐site olefin polymerisation catalysts.

Pincer ligand: A tridentate ligand that binds meridionally to a metal, offering a rigid framework to control electronic and steric properties.

Cis-1,4 selectivity: A stereochemical outcome in diene polymerisation where monomer units add in a cis configuration at the 1 and 4 positions along the polymer backbone.

References

1. 1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals. Catalysts (2018).
2. C–H-Bond Activation and Isoprene Polymerization Studies Applying Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Bis(Tetramethylaluminate) and Dimethyl Complexes. Molecules (2019).
3. Cis-1,4-Polymerization of Isoprene by 1,3-Bis(oxazolinymethylidene)isoindoline-Ligated Rare-Earth Metal Dialkyl Complexes. Polymers (2017).