1. Rare Earth Catalysts for Regio- and Stereospecific Polymerization

 Unlike the majority of transition metals which display multiple oxidation states, rare-earth metals typically exist in the 3+ oxidation state under normal conditions. This “redox-inactive” feature makes rare-earth metals unique candidates for the formation of true “single-site” polymerization catalysts. With an aim to create novel high-performance polymeric materials, our research program in part focuses on the development of highly active and selective polymerization catalysts based on cationic rare-earth metal monoalkyl complexes. Utilizing the singular character of these catalytic systems, we have achieved various novel polymerization and copolymerization reactions. These have led to the formation of a new family of polymeric materials showing unique chemical, physical and mechanical properties.

2. Rare-Earth Catalysts for Efficient Organic Synthesis

 We have found that the aforementioned cationic rare-earth alkyl species can also serve as unique catalysts for a number of important chemical transformations in organic synthesis. These include the regio- and stereoselective methylalumination of alkynes and alkenes, the hydroarylation of alkenes, styrenes and allenes, and the enantioselective C-H alkylation of pyridines with simple alkenes.

3. Utilization of CO2 as a C1-Building Block for Fine Chemical Synthesis

 Carbon dioxide (CO2) is a naturally abundant, readily available, non-toxic, and inherently renewable carbon resource. Accordingly, the use of CO2 as a chemical feedstock for preparing value-added chemicals currently attracts much interest from synthetic organic chemists as well as chemical industry. We have recently found that N-heterocyclic carbene copper (NHC-Cu) complexes can serve as excellent catalysts for the carboxylation of various organic substrates with CO2. This catalyst system features broad substrate scope, high regio- and stereoselectivity, excellent functional group tolerance, and occurs via a well-defined reaction mechanism.

4. Activation of Inactive Molecules by Molecular Metal Hydride Clusters

 The cooperation of multiple metal centers can facilitate the activation of unreactive molecules which is difficult to achieve by just a single metal site. Metal hydrides are among the most reactive organometallic compounds and are fundamental components in a wide range of stoichiometric and catalytic reactions. The investigation of the reactivity of multi-metallic hydride complexes with inactive molecules is therefore of much interest and importance. We have recently found that multi-metallic rare-earth and group 4 metal hydride complexes can show unique synergistic effects on the activation of small molecules such as CO, CO2, H2 and N2 as well as on the activation of the carbon skeleton of aromatic compounds such as benzene and toluene.

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