Kinetic study of metal-metal bonded rhenium complexes

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The purpose of this project is to understand the correlation between the oxidation states and reactivity and that of metal-to-metal interaction and redox properties by using rhenium complexes. Rhenium is the most versatile element with respect to its variety of oxidation states, and thus its complexes are the most appropriate to study redox preperties of metal complexes. Various important complexes have been prepared at Hokkaid Universty, and their reactivities have been studied by the foreign colleagues. Also, Dr.Sayse11 of the University of Newcastle-upon-Tyne and Dr.Botha of the University of Orange-Free-State, stayd at Hokkaido University for 3 months each and contributed to significant progress of the project.By using N,N,N,O-and N,N,O-type chelating ligands, we have isolated several mononuclear rhenium (V) complexes having incompletely chelated ligands. X-Ray structural determination of these complexes revealed complex formation steps of these chelating ligands, information which … More is impossible to obtain by using substitution labile metal ions. Dinuclear rhenium doubly oxo-bridged complexes have been isolated in two neighboring oxidation states, (III,IV) and (IV,IV). Their structural and redox studies show the correlation between the Re-Re bond-order and redox reactions. Study on hexanuclear rhenium sulfide clusters also revealed characteristic properties of Re-Re bond. The hexarhenium cluster, [Re_6S_8(H_2O)_6]_<2+> clusters, shows unexpectedly slow anation reactions with Cl^- or NCS^-. The remarkable inertness is difficult to understand for mononuclear rhenium (III) complexes and the effect of metal-metal bond should be taken into account. This inert nature enabled us to prepare partially substituted species of the type, [Re_6S_8(pyridine)_<6-n>Cl_n]^<(2-n)+>(n=1-3). Further studies to prepare the hexarhenium (III) complexes with pyridine derivative ligands show some redox interaction between the ligands at hexarhenium center.We have also studied redox reactions of some dinuclear ruthenium (III) complexes with oxide and acetate bridges. Protonation at the oxide bridge remarkable change the redox potentials of the diruthenium moiety. Relevance of the proton-coupled redox reactions to some enzyme dimetal active centers have been suggested. Less