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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 Ru2(5+) 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 Ru2(5+/4+) and Ru2(5+/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.

The synthesis and characterization of the first paramagnetic diruthenium(III) complex containing two unpaired electrons is described. The investigated compound, represented as Ru2(hpp)4Cl2, where hpp is 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate ion, was obtained from the reaction of Ru2(CH3COO)4Cl with excess molten Hhpp under Ar (150 °C, 10 h). It was characterized by X-ray single-crystal diffraction, electrochemistry, ESR, and UV−visible spectroscopy and the data compared to that for other Ru26+ derivatives containing either four unpaired electrons (in the case of a bis-H2O complex) or zero unpaired electrons (in the case of a bis-C⋮CC6H5 derivative).

The effect of axial ligands on the structure, oxidation state, and electronic configuration of two diruthenium(II,III) and two diruthenium(III,III) complexes is reported. The investigated compounds are represented by Ru2(dpf)4Cl (1), Ru2(dpf)4(C⋮CC6H5) (2), Ru2(dpf)4(C⋮CC6H5)2 (3), and Ru2(dpf)4(CN)2 (4), where dpf is the N,N‘-diphenylformamidinate ion. The chloro and mono(phenylacetylide) complexes, which contain a Ru25+ core, are paramagnetic and contain three unpaired electrons, while the bis(phenylacetylide) and bis(cyano) species, which contain a Ru26+ core, are diamagnetic. Compound 1, Ru2(dpf)4Cl, was prepared by heating Ru2(CH3COO)4Cl and excess molten N,N‘-diphenylformamidine (Hdpf) for 10 h at 130 °C under an argon atmosphere. Compound 2, Ru2(dpf)4(C⋮CC6H5), was prepared by reaction of purified Ru2(dpf)4Cl with LiC⋮CC6H5 (in a 1:5 ratio) in THF at room temperature (2 h). Compound 3, Ru2(dpf)4(C⋮CC6H5)2, was also obtained from Ru2(dpf)4Cl by using excess LiC⋮CC6H5. A related diruthenium(III,III) ...

The synthesis, physicochemical properties, and electrochemistry of a new series of metal metal σ-bonded metalloporphyrins are reported. The investigated compounds are represented as (P)MRe(CO)5 where P is the dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP) and M = Al, Ga, In, or Tl. These compounds provide the first examples of Al and Ga metalloporphyrins with covalent metalmetal bonds as well as give the first series of compounds in which the same metalate anion is covalently bonded to four different group 13 metalloporphyrins. Each synthesized complex was characterized by 1H NMR, IR, and UV-visible spectroscopy as well as by electrochemistry. Graham Δσ and Δπ parameters, and calculated residual charges on the rhenium atom of (P)MRe(CO)5 demonstrate that the covalency of the metalmetal bond decreases in the order: Tl > In > Ga > Al. The thallium derivative is stable upon electrooxidation by either one or two electrons. However, the In, Ga, and Al complexes undergo rapid cleavage of the metalrhenium bond after formation of a [(P)MRe(CO)5]+· cation radical. The chemical reactivity and physical properties, as well as the electrochemistry, of each (P)MRe(CO)5 species were analyzed as a function of the central metal ion or porphyrin ring basicity. The spectroscopic properties and electrochemistry of these metalmetal σ-bonded species are compared with data for other metal metal bonded metalloporphyrins of the type (P)MM′(L) as well as with data for related metalcarbon bonded porphyrins of the type (P)M(R).

The effect of temperature, porphyrin macrocycle, and solvent on the electroreduction of (P) Ni{sup II} where P is the dianion of meso-tetrakis(p-(diethylamino)phenyl)porphyrin (T(p-Et{sub 2}N)PP) or meso-tetrakis(o,o,m,m-tetrafluoro-p-(dimethylamino)phenyl)porphyrin (T(p-Me{sub 2}N)F{sub 4}PP) is reported. Both compounds were reduced by controlled potential electrolysis and characterized by ESR and UV-visible spectroscopy. The site of electron transfer varied as a function of experimental conditions and the stable electrogenerated products were assigned as Ni(I) porphyrins, Ni(II) porphyrin {pi}-anion radicals, or Ni(II) porphyrin {pi}-anion radicals with some Ni(I) character. Ni(I) ESR spectra were obtained for ((T(p-Et{sub 2}N)PP)Ni){sup {minus}} and ((T(p-Me{sub 2}N)F{sub 4}PP)Ni){sup {minus}} at low temperature in THF under a CO atmosphere as well as in DMF or pyridine under N{sub 2}. In contrast, ESR spectra of Ni(II) porphyrin {pi}-anion radicals or Ni(II) porphyrin {pi}-anion radicals with some Ni(I) character were obtained in THF under N{sub 2} at room and low temperature, respectively. ((T(p-Et{sub 2}N)PP)Ni){sup {minus}} catalytically reduces CH{sub 3}I at room temperature, consistent with the presence of some Ni(I) character in the reactive species.

The one-electron catalytic reduction of dioxygen by electrogenerated meso-tetrakis(1-methylpyridinium-4-yl)-porphinatocobalt(I), ((TMpyP)Co{sup I}){sup 3+}, was investigated by cyclic voltammetry, controlled potential coulometry, rotating ring-disk voltammetry, ESR, and UV-visible spectroelectrochemistry. The first reduction of ((TMpyP)Co{sup II}){sup 4+} in DMF containing 0.1 M tetrabutylammonium perchlorate occurs at E{sub 1/2} = {minus}0.49 V and leads to the formation of ((TMpyP)Co{sup I}){sup 3+}. This cobalt(I) complex is stable under an N{sub 2} atmosphere but in the presence of dissolved O{sub 2} is converted to ((TMpyP)Co{sup II}(O{sub 2}{sup {minus}})){sup 3+}, which is also stable at all potentials up to the reduction of free O{sub 2} (i.e., about {minus}0.80 to {minus}0.90 V vs SCE). A catalytic reduction of dioxygen occurs at E{sub p} = {minus}0.50 V by cyclic voltammetry (scan rate = 0.1 V s{sup {minus}1}) in DMF solutions containing ((TMpyP)Co{sup II}){sup 4+} and benzoic anhydride under O{sub 2}. The homogeneous reactions of ((TMpyP)Co{sup II}){sup 4+} and electrogenerated ((TMpyP)Co{sup I}){sup 3+} with O{sub 2} or O{sub 2}{sup {minus}} were characterized and monitored by ESR and UV-visible spectroscopic techniques.

The synthesis and characterization of 10 different ionic and σ-bonded aluminum(III) porphyrins are reported. These compounds were studied by mass spectroscopy and IR, UV-visible, and 1 H NMR spectroscopy as well as by electrochemistry. The spectroscopically investigated compounds are represented by (P)AlCl an (P)Al(R), where P is the dianion of tetraphenylporphyrin (TPP) or octaethylporphyrin (OEP) and R is CH 3 , n-C 4 H 9 , C 6 H 5 , or C 6 F 4 H. The molecular structure of (OEP)Al(CH 3 ) was determined by X-ray diffraction

The synthesis and characterization of a new structural type of diruthenium(III) complex is reported. The investigated compound is represented by Ru2(F4Oap)(F5ap)3Cl where F5ap is the 2-(2,3,4,5,6-pentafluoroanilino)pyridinate ion and F4Oap is 2-(3,4,5,6-tetrafluoro-2-oxoanilino)pyridinate dianion, a ligand which derives from F5ap by substitution of an oxygen for a fluorine atom at the ortho position of the pentafluorophenyl ring. Ru2(F4Oap)(F5ap)3Cl was characterized by room temperature magnetic susceptibility, X-ray single-crystal diffraction, electrochemistry, and mass spectrometry and is the first example of a diruthenium(III) derivative having a tridentate dianionic ligand bound to the two metal centers.