I have researched mainly about coordination chemistry. A new class of complexes have been designed, synthesized, and analyzed by a variety of spectroscopies, spectrometries, kinetics, and theoretical calculations to clarify their structures and properties, aiming for functionalization of them focusing on their assemblies and dynamic behaviors.
1. Cyclometallated corannulenes
Corannulene with a bowl-like curved aromatic compound known as a substructure of fullerene C60 with a ball-like shape. Its surfaces are unequal sterically and electronically due to its curved structure. The unique dynamic behavior, which is the inversion of the surfaces, is also interesting as a supramolecular motif.
Introduction of a pyridil-pendant to a corannulene gave a ligand available for cylometallation. Cyclopalladated corannulene assembles to form columnar structures (Dalton Trans., 2013, 42, 3300). By the reacion with iridium, a C-C bond cleavage occurs with the aid of coordination to iridium and the relief of strain in the curved corannulene (Angew. Chem. Int. Ed., 2015, 54, 5351).
2. Photoinduced electron transfer between aromatic curvatures
Photoinduced electron transfer reactions and long-lived charge separated states, which play important roles in the photosynthesis, have been researched aiming for the artificial photosynthesis. Although fullerene C60 is known as an efficient electron acceptor, the electron transfer reaction between aromatic curvatures using it, which is expected to be sterically preferred, had not been researched. With a combination of fullerene and corannulene skeletons, electron transfer between curved aromatic compounds can be researched.
The reaction of a lithium encapsulated fullerene (Li+@C60) with an efficient electron acceptability and a corannulene having a curvature available for the recognition of C60 skeleton forms charge transfer complex at the ground state. When Li+@C60 or the formed charge transfer complex is photoirradiated, a short-lived singlet charge-separated state （t = 1.4 ns） or a long-lived triplet charge-separated state (t = 240 ms) is formed respectively. The detailed electron transfer pathways were clarified by laser flash photolysis. The strong complexationa at the excited state （KT = 1.3 × 103 M–1） was also found (J. Am. Chem. Soc., 2014, 136, 13240).
3. One-step benzene hydroxylation by hydrogen peroxide with a copper complex catalyst incorporated in a mesoporous material
Cumene process is known as a industrial synthetic method of phenol from benezene but still have difficulties in reaction conditions and byproducts, which have promoted development of environmentally friendly processes. One-step benezene hydroxylation by hydrogen peroxide with copper catalysts is one of the examples but reaction efficiency or selectivity had not been enough. Encouraged by this situation, we researched selective benzene hydroxylation by hydrogen peroxide with tris(2-pyridylmethyl)amine copper complex (1).
The reaction of benezene with hydrogen peroxide in the presence of a catalytic amount of complex 1 in acetone solution at room temperature produced phenol. The radical reaction mechanism was proposed according to the kinetics, spin trap, and theoretical calculations. The reaction selectivity and efficiency was enhanced by incorporation of the complex 1 into a mesoporous silica-alumina (turnover nmber 4320) （Chem. Sci. 2016, 7, 2856）.
4. Catalase-like catalytic reaction by a metallosupramolecular ionic crystals
Control of heterogeneous catalyts, which have attracted attentions due to their durability and easy handling, have been reported using metals or metal oxides. Prof. Konno et al. reported metallosupramolecular ionic crystals [Au4Co2(dppe)2(D-pen)4]Xn ([2]Xn; Xn = (Cl–)2, (ClO4–)2, (NO3–)2, SO42–) consisting of an AuI4CoIII2 hexanuclear complex-cations, which are obtained as octahedral or cubic crystals depending on the anion species. Using these, we researched size- and shape-dependent catalytic activity of metallosupuramolecular ionic crystals.
Heterogeneous Catalase-like catalytic activity was shown in the reaction of [2]Xn with H2O2 evolving O2 in aqueous solution. The dependencies of the catalytic activity onassembled structures, anion species, and crstal shapes and high catalytic activity (TOF 1.4 x 105 h–1) could be rationalized by the presence of CoII centers on the surface and their efficiency of the exposure based on morphological and theoretical studies （Chem. Sci., 2017, 8, 2671）.
I appreciate coauthors, collaborators, and all supprted the research.