Dynamic Structure and Novel Functions of Dicobalt Complexes

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We constructed redox switchable molecular containers with dicobalt complexes. Molecuar switches are the attractive components of molecular electronic devices capable of inducing chemical and physical changes in response to external stimuli such as electrical current, light, and heat. In this study, switching systems were established by using the structural change of dicobalt complexes. Cobalt complexes prefer a six-coordinated structure at the Co(III) state while the Co(II) species prefer a four-coordinated structure. Reversible redox change of dicobalt complexes between Co(III) and Co(II) provides a stable molecular switching system. When diamine was used as axial ligand, each amino groups of diamine were coordinated to cobalt (III) center of planar dicobalt complex with bridged structure. Dissociation of diamines were accompanied by the reduction of dicobalt (III, III) centers to Co(II, II) form by electrochemical stimulus. The bridged structure was recovered with oxidation of cobalt … More centers. We constructed a switching system using this strategy as a molecular container containing a crown ether moiety in diamino-molecules.One-pot syntheses of new water-soluble dicobalt complexes having two cobalt-carbon bonds were investigated. The complexes were characterized by 'H NMR and UV-vis spectroscopies as well as ESI-MS. These complexes were photo-sensitive and the photo-cleavage of the cobaltcarbon bonds upon irradiation with visible light produced methyl radicals which were detected by ESR spin-trapping techniques. The dicobalt complexes exhibited a high ability for DNA cleavage in comparison to that for the corresponding monocobalt complex.A novel dicobalt complex, where a dinucleating ligand has two N2O2 metal-binding sites which are linked to each other with a phenyl spacer, was synthesized and its redox behavior was investigated in THF using cyclic voltammetry in comparison with that for the corresponding mononuclear complex. The controlled-potential electrolysis of alkyl halides at-1.60 V vs. Ag/AgCl in the presence of the rigid and planar dicobalt complex led to reductive coupling. The use of rigid, planar dicobalt complex to effect the reductive dimerization of alkyl halides has been demonstrated for the first time. Less