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• Electrochemistry of Ru2 paddlewheel complexes spanning seven oxidation states. • Effects of bridging and axial ligands on redox potentials from 6+ decades of research. • Redox potentials for 350+ Ru2 complexes from over 120 references are tabulated. This review summarizes the known electrochemistry of metal-metal bonded diruthenium complexes containing an air-stable Ru 2 4+, Ru 2 5+ or Ru 2 6+ core or an in-situ generated Ru 2 2+, Ru 2 3+, Ru 2 7+ or Ru 2 8+ core with O,O' -, N,O - or N,N'- donor bridging ligands. The majority of published studies have been carried out in nonaqueous media and involved compounds with a Ru 2 5+ oxidation state and four anionic "ap" or "DPhF"-type bridging ligands where ap and DPhF are the 2-anilinopyridinate and N,N'-diphenylformamidinate anions, respectively. The potentials and mechanisms of electron transfer depend in part upon the properties of the electrochemical solvent and in part upon properties of the compound, the most important of which are the initial oxidation state of the air-stable dimetal unit, the number and type of axial ligands and the type of anionic bridging ligands. The vast majority of redox processes described to date for these compounds involve electron addition or abstraction at the diruthenium core, but redox reactions involving the bridging ligands or other electroactive groups on the molecule have also been observed. In most cases, the redox reactions were reversible on the cyclic voltammetry and spectroelectrochemical timescale, thus enabling the in-situ generation of new compounds in both very low and high oxidation states with dimetal units ranging from Ru 2 2+ to Ru 2 8+. [ABSTRACT FROM AUTHOR]

Reports on the first example where a triply oxidized nickel porphyrin or porphycene undergoes three reversible one-electron oxidations in nonaqueous media. Investigated compounds; Stepwise formation of a pi cation radical and dication; Nickel reaction occurring at half-wave potentials; Redox data.

Examines the electrochemistry of 29 nickel(II) porphyrins in dichloromethane in order to determine the electronic and structural factors which govern electron-transfer processes in porphyrins. Reversible half-wave potentials for the reduction and oxidation of the porphyrins; Effect of substituents on the redox behavior of the porphyrin ring; Electronic and structural effects on half-wave potentials.

Three related diruthenium complexes containing four symmetrical anionic bridging ligands were synthesized and characterized as to their electrochemical and spectroscopic properties. The examined compounds are represented as Ru2(dpb)4Cl, Ru2(dpb)4(CO), and Ru2(dpb)4(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru2(dpb)4Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru25+ form of the compound undergoes multiple redox processes involving the dimetal unit. The reversibility as well as potentials of these diruthenium-centered electrode reactions depends upon the solvent and the bound axial ligand. The Ru25+/4+ and Ru25+/6+ processes of Ru2(dpb)4Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru2(dpb)4Cl to [Ru2(dpb)4(CO)]+ was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru2(dpb)4Cl at room temperature. The chemically generated [Ru2(dpb)4(CO)]+ complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO4 under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru2(dpf)4(CO) in CH2Cl2, 0.1 M TBAClO4 under a N2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru2(dpb)4(NO) undergoes two successive one-electron reductions and a single one-electron oxidation, all of which involve the diruthenium unit. The CO and NO adducts of Ru2(dpb)4 were further characterized by FTIR spectroelectrochemistry, and the IR spectral data of these compounds are discussed in light of results for previously characterized Ru2(dpf)4(CO) and Ru2(dpf)4(NO) derivatives under similar solution conditions. [ABSTRACT FROM AUTHOR]

Abstract: Two sigma-bonded Rh2 5+ complexes, Rh2(ap)4(C6H5) and Rh2(ap)4(CH3), where ap=2-anilinopyridinate anion were synthesized and examined as to their electrochemical and spectroscopic properties in nonaqueous media. Rh2(ap)4(C6H5) was also structurally characterized. The presence of the phenyl axial ligand on Rh2(ap)4(C6H5) does not bring about a significant structural effect on the ap framework as compared to Rh2(ap)4Cl or Rh2(ap)4(Che Rh–Rh and Rh–Caxial bond lengths are both elongated due to the strong electron-donating effect of the phenyl group. The two sigma-bonded dirhodium compounds each undergo a single reversible one-electron reduction to in situ generate a stable complex and two reversible one-electron oxidations to give stable compounds in and oxidation states. These redox reactions occur at E 1/2 =−0.79, 0.28 and 0.93V for R=CH3 and −0.71, 0.35 and 0.95V for R=C6H5. The ESR spectrum of Rh2(ap)4(CH3) has g ⊥ and g || values of 2.17 and 1.89 while Rh2(ap)4(C6H5) has an ESR spectrum with signals at 2.17 (g ⊥) and 2.00 (g||), consistent with the odd electron in each dimetal unit being localized on only one of the two metal centers in . [Copyright &y& Elsevier]