Koji Yamamoto

Multinuclear metal-binding ability of a carotene

Carotenes are naturally abundant unsaturated hydrocarbon pigments, and their fascinating physical and chemical properties have been studied intensively not only for better understanding of the roles in biological processes but also for the use in artificial chemical systems. However, their metal-binding ability has been virtually unexplored. Here we report that β-carotene has the ability to assemble and align ten metal atoms to afford decanuclear homo- and heterometal chain complexes. The metallo–carotenoid framework shows reversible metalation–demetalation reactivity with multiple metals, which allows us to control the size of metal chains as well as the heterobimetallic composition and arrangement of the carotene-supported metal chains.

Modulation of benzene or naphthalene binding to palladium cluster sites by the backside-ligand effect.

The backside-ligand modulation strategy to enhance the substrate binding property of Pd clusters is reported. The benzene or naphthalene binding ability of Pd3 or Pd4 clusters is enhanced significantly by the backside cyclooctatetraene ligand, leading to the formation of the first solution-stable benzene- or naphthalene Pd clusters. The present results imply that the ligand design of the metal clusters, especially for the backside ligand of the metal cluster site, is crucial to acquire a desired reactivity of metal clusters.

σ-π Continuum in Indole-Palladium(II) Complexes.

The intrinsic features of (hetero-arene)-metal interactions have been elusive mainly because the systematic structure analysis of non-anchored hetero-arene-metal complexes has been hampered by their labile nature. We report successful isolation and systematic structure analysis of a series of non-anchored indole-palladium(II) complexes. It was revealed that there is a σ-π continuum for the indole-metal interaction, while it has been thought that the dominant coordination mode of indole to a metal center is the Wheland-intermediate-type σ-mode in light of the seemingly strong electron-donating ability of indole. Several factors which affect the σ- or π-character of indole-metal interactions are discussed.

Substrate Binding by a Parallel Metal Sheet Sandwich Complex: A Unique Role of an Additional Metal Atom

A unique metal addition to the edge of a triangular palladium sandwich cluster is reported. While the edge coordination sites of a parallel sandwich complex are narrow because of two sterically encumbering π-ligands, association of an additional metal atom to a metal sheet gives a wider coordination site. It was proved that the additional metal atom plays a crucial role in binding of cyclopentadienyl by a Pd3 sheet sandwich complex.