Organometallic Chemistry Laboratory

Outline

The main objective of our research is to develop new generations of molecular catalysts. Novel catalysts can facilitate novel reactions that have been previously considered impossible, lead to more efficient, selective chemical transformations, and help us to make innovative functional materials that were not previously possible. The primary focus of our research is the development of original catalysts. We have paid special attention to rare earth elements (group 3 and lanthanide metals), as we believe that the exploration of the potential of untapped elements is an important strategy for the development of new catalysts that are complementary or superior to existing ones. Our research interests span broad areas of organometallic chemistry, ranging from the preparation, structural characterization, and reactivity of metal complexes with novel structures to the design, synthesis, and application of organometallic catalysts for precision polymerization, fine-chemical synthesis, small molecule activation and utilization, and materials innovation.

Recent Research Topic

Innovation of chemical synthesis by rare-earth catalysts

Fig. 1 Rare-earth-catalyzed novel regio- and stereospecific olefin polymerization and copolymerization

Rare earth elements, including scandium, yttrium and the lanthanides, possess unique chemical and physical properties. The reactivity of rare earth metal complexes can be tuned by changing the central metal ions in a series of complexes with similar structures, thanks to the lanthanide contraction. Moreover, rare earth elements usually adopt the 3+ oxidation state as the most stable state, which is not easily changed to other oxidation states under usual conditions. These features could make rare earth complexes unique candidates for single-site polymerization catalysts.

By use of appropriate metal/ligand combinations, we have succeeded in the isolation and structural characterization of a new series of rare earth dialkyl complexes, which were previously thought difficult to isolate. Treatment of the dialkyl complexes with a borate compound such as [Ph3C][B(C6F5)4] has generated the corresponding cationic monoalkyl species. The cationic rare earth monoalkyl species can serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins such as ethylene, styrene, 1,3-conjugated dienes, and cyclic olefins, to yield a new family of polymer materials that show novel properties but were previously difficult to prepare.

Cationic half-sandwich scandium alkyls have also proven to be excellent catalysts for the methylalumination of internal alkynes and alkenes, showing unprecedented regio- and stereoselectivity. On the other hand, studies on the rare-earth-catalyzed regio- and stereoselective dimerization of terminal alkynes have led to the discovery of π-conjugated aromatic enynes as a novel single-emitting component for white electroluminescence.

By hydrogenation of the half-sandwich dialkyl rare earth complexes with H2, we have prepared a novel class of polynuclear rare earth polyhydride complexes. These hydride clusters showed unique reactivities towards various unsaturated molecules. For example, the reaction of the yttrium hydride cluster with carbon monoxide resulted in unprecedented selective formation of ethylene under mild conditions. The reactions with transition metal carbonyl complexes, such as Cp*Rh(CO)2, afforded novel heteromultimetallic methyl/oxo and carbene/oxo complexes through hydrogenative cleavage of the C≡O triple bonds.

Fig. 2 Rare-earth-catalyzed selective synthesis of π-conjugated enyne compounds and their application to a novel single-emitting component white electroluminescence device

Fig. 3 Synthesis and some novel reactions of polynuclear rare earth metal polyhydrides