Masato Kurihara

Azo- and quinone-conjugated redox complexes photo- and proton-coupled intramolecular reactions based on d-π interaction

Abstract Novel photo- and proton-coupled behavior of azo- and quinone-conjugated metal complexes based on the d–π electronic interaction is described. The quantum yield for photoisomerization of azobenzene-bridged bis(terpyridine) complexes significantly depends on the nature of the metal, counterions, and solvents. The trans -to- cis isomerization of azoferrocene proceeds not only by the photoexcitation of the π–π* transition band but also by the photoexcitation of the MLCT (d–π* transition) band. The oxidation of the ferrocene moieties occurs at 0.3 V less positive potential, and the electronic interaction between the ferrocene moieties is significantly weaker in cis -azoferrocene than in trans -azoferrocene. In a vinylene-bridged ferrocene–hydroquinone complex, the oxidation of the ferrocenyl site promotes the elimination of the hydroxyl and the vinylene protons followed by intramolecular electron transfer to form an allene and a quinonoid structure. The protonation to carbonyl groups of the anthraquinone moiety in 1-ferrocenylethynylanthraquinone causes intramolecular electron transfer leading to a novel structural change into a η 6 -fulvene–cumulene Fe(II) complex.

Synthesis, redox behavior and electrodeposition of biferrocene-modified gold clusters ☆

Biferrocene-modified Au clusters, comprising a 2.2 ± 0.3 nm-diameter Au core covered with 20 biferrocene-terminated thiolates and 75 octyl thiolates on average, were synthesized by a substitution reaction of octanethiol-modified clusters with biferrocene-terminated alkanethiol, (η 5 -C 5 H 5 )Fe(C 10 H 8 )Fe(η 5 -C 5 H 4 CO(CH 2 ) 7 SH) (1). The biferrocene-modified cluster undergoes two-step oxidation reactions in NBu 4 ClO 4 + CH 2 Cl 2 and the second oxidation process leads to the formation of a uniform redox-active Au cluster film on electrode. The surface plasmon absorption of the cluster film depends on the oxidation state of the redox active species on the cluster surface.

Synthesis, Structure, and Redox Properties of [{(5-C5H5)Co(S2C6H4)}2Mo(CO)2], a Novel Metalladithiolene Cluster

Metal-metal bond formation by a cobaltadithiolene complex was observed for the first time in the reaction of [Co(η(5) -C5 H5 )(S2 C6 H4 )] with [Mo(CO)3 (py)3 ] and BF3 to give the Co-Mo-Co cluster 1. Cyclic voltammetry reveals that 1 undergoes two one-electron reduction steps at the Co centers, which is indicative of transmission of the Co-Co electronic interaction through the Mo center.

Synthesis of a new bis(ferrocenyl)ruthenacyclopentatriene compound with a significant inter-metal electronic communication

Abstract A new 2,5-bis(ferrocenyl)ruthenacyclopentatriene complex was synthesized by the metallacycle formation reaction of RuBrCp(cod) (Cp=η 5 -C 5 H 5 ) and ethynylferrocene. Cyclic voltammetry of the complex showed a reversible one-electron reduction due to the ruthenacycle and a two-step one-electron oxidation of the ferrocenyl moieties. Separation of the redox potentials of the ferrocenyl moieties was 0.24 V, and the electronic spectrum of one-electron oxidized species exhibited an intervalence-transfer band at 1180 nm. These results indicate the existence of significant electronic interactions between two ferrocenyl moieties through the ruthenacyclopentatriene ring.

Synthesis and physical properties of a π-conjugated ruthenium(II) dinuclear complex involving an azobenzene-bridged bis(terpyridine) ligand

Abstract A novel π-conjugated Ru(II) dinuclear complex containing a new azobenzene-bridged bis(terpyridine) ligand was synthesized and its photochemical and electrochemical properties were investigated. The ligand underwent reversible trans-cis photoisomerization, whereas the Ru complex did not show such photoisomerization behavior. Cyclic voltammetry of the complex displayed a reversible one-step 2e−oxidation wave due to Ru(III)Ru(III)/Ru(II)Ru(II) and four le− reduction waves indicating the formation of mixed-valence states when the electrons are accumulated at the ligand-based orbitals.

Synthesis and physical properties of azo-ferrocene oligomers and polymers

Abstract Reaction of 1.1′-dilithioferrocene with N 2 O gave azo-bridged ferrocene oligomers andpolymers. Two trimers, Fc-Fc′-N 2 -Fc ( 1 ) and Fc-N 2 -Fc′-N 2 -Fc ( 2 ) were isolated, where Fc and Fc′ refer to ( η 5 -C 5 H 5 )Fe( η 5 -C 5 H 4 − ) and Fe( η 5 -C 5 H 4 − ) 2 , respectively. Oxidation processes of the trimers via mixed-valence states are entirely different from the process of terferrocene due to the strong electron-withdrawing effect of the azo group. Polymers with high content of azo-ferrocenyl units were prepared under high pressure conditions of N 2 O. The CT complex of the polymer with TCNQ was prepared and its conductivity was slightly enhanced upon irradiation of NIR and visible lights.

Reversible trans–cis photoisomerization of azobenzene-attached bipyridine ligands coordinated to cobalt using a single UV light source and the Co(III)/Co(II) redox change

The trans/cis ratio of the azobenzene-attached bipyridine ligands in a cobalt complex is reversibly altered by a combination of photoirradiation with a single UV light source and the reversible redox change between Co(II) and Co(III).

Formation of a novel porphyrin–gold nanoparticle network film induced by IR light irradiation

IR light irradiation of a mixed toluene solution of ammonium salt-stabilized gold nanoparticles with 3.8 +/- 0.8 nm core diameter and a porphyrin thioacetate derivative affords a thin photoactive film of the cluster-porphyrin network.

Synthesis and Redox Properties of a π-Conjugated Cyclobutadienecobalt Polymer Containing Ferrocenyl Groups

The reaction of CpCo(PPh3)2, in which Cp=η5-cyclopentadienyl, with a π-conjugated diacetylene, FcC≡C–o-C6H4–C≡CFc, in which Fc=ferrocenyl, was found to give a cyclobutadienecobalt mononuclear complex, {η4-C4Fc2(o-FcC6H4)2}CoCp (1), the crystal structure of which was determined by X-ray crystallography. In contrast, the reaction of CpCo(PPh3)2 with FcC≡C–p-C6H4–C≡CFc affords a cyclobutadienecobalt polymer, [p-C6H4(η4-C4Fc2)CoCp]n (2). The monocobalt complex 1 shows reversible 1e− and 3e− redox waves at E0′=0.116 and 0.350 V vs Ag/Ag+, and the polymer complex 2 shows two chemically reversible redox waves at E0′=0.143 and 0.219 V for the oxidation of the ferrocenyl moieties in the cyclic voltammogram. Crystal data are as follows: (1, C65H49CoFe4), triclinic, space group P={1} (No. 2), a=13.547(4), b=16.197(4), c=11.763(4) Å, α=106.79(2), β=97.93(3), γ=97.12(3), V=2410(1) Å3, Z=2.

Photo‐ and protonation‐induced changes in structures and physical properties of azo‐conjugated metal complex systems

Novel photo- and proton-coupled behavior of azo-conjugated metal complexes is described. The trans-to-cis isomerization of azoferrocene proceeds not only by the photoexcitation of the π-π* transition band but also by photoexcitation of the MLCT (d-π* transition) band, by a protonation-deprotonation cycle (proton-coupled isomerization), and by an oxidation-reduction cycle (redox isomerization). A platinum tolylazophenylenedithiolato complex shows reversible trans-to-cis photoisomerization, protochromism, and novel proton-coupled cis-to-trans isomerization.