The research in our group focuses on the development of new methodology of organic synthesis with metal-based catalysts. We have mainly used indium or gallium halides that have moderate Lewis acidity for efficient catalysts in the reaction with carbonyls, alcohols, esters, or amides. High chemo-, stereo-, and regioselectivities are accomplished owing to their moderate Lewis acidity. Alkynes or alkenes are also activated by indium or gallium accompanied by nucleophilic attack, and the reactions afford carbometallation compounds.
On the contrary to indium or gallium, boron or aluminum generally show high Lewis acidity and thus they are unlikely to be used as a catalyst. However, design of cage-shaped boron complex that has chelated carbon-framework overcomes this problem to exhibit high catalytic activities. The novel cage-shaped metal complexes give variety of catalysts with finely tuned Lewis acidity. Some complexes show new type of selectivity for aromatic compounds over aliphatic ones.
While many organometallic reagents contribute to selective organic synthesis by their appropriate reactivity and coordination ability toward substrates, it is generally difficult to identify the real active species. However, the identification should be important to propose the reaction mechanisms involving the species. We have been investigating details of reaction mechanism by isolation of reactive species, their X-ray analyses, or theoretical calculations. The obtained insight will give an idea of new type of reaction.