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The electroreductive dechlorination of γ-hexachlorocyclohexane (lindane) was investigated in non-aqueous media using as a catalyst the dirhodium complex Rh2(dpf)4, where dpf = the anion of N, N′-diphenylformamidinate. Rh2(dpf)4 undergoes two reversible one-electron redox processes in pyridine and/or N,N′-dimethylformamide (DMF), corresponding respectively to Rh24+/Rh25+ and Rh24+/Rh23+. Electrochemical and spectroelectrochemical measurements indicate that lindane reacts with the Rh23+ center in singly reduced [Rh2(dpf)4]−, giving a transient carbon-bonded dirhodium complex along with Cl−. Further catalytic dechlorination of lindane subsequently occurs with the activity of Rh2(dpf)4 as a catalyst depending upon the solvent conditions. Rh2(dpf)4 shows a higher catalytic reduction current in pyridine than in DMF for the degradation of lindane. This catalytic current can be further enhanced if 6% water (v/v) is added to the pyridine solution. Bulk controlled-potential electrolysis combined with GC–MS verified that although the addition of water to the neat pyridine increased the catalytic activity of Rh2(dpf)4, neat pyridine is still a better solvent for the formation of more extensively dechlorinated products of lindane. In neat pyridine, lindane can be converted stepwise to tetrachlorocyclohexene, dichlorobenzene isomers, chlorobenzene and the fully dechlorinated product benzene, the last of which becomes predominant at the end of the electrolysis. In pyridine having 6% added water, other than those dechlorinated products seen above, trichlorobenzene isomers are formed upon lindane degradation. Meanwhile, the relative concentrations of dichlorobenzene isomers and chlorobenzene become higher, while the yield of benzene becomes lower than the corresponding results obtained in neat pyridine. Based on the measured distribution of the products under the different solvent conditions, an overall pathway for the degradation of lindane is proposed.

Iron(II) 2,3- and 3,4-tetrapyridinoporphyrazine complexes (2,3-PyD and 3,4-PyD) were synthesized and characterized as to their electrochemistry, UV-visible spectroelectrochemistry and catalytic properties towards the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (p,p′-DDT) in pyridine, dimethyl sulfoxide (DMSO), N,N′-dimethylacetamide (DMA) and N,N′-dimethylformamide (DMF). These properties were compared with those of the unsubstituted iron(II) phthalocyanine ((Pc) Fe ). Electrochemistry indicates that there are up to three reductions and one oxidation in the three investigated derivatives. The easiest reduction takes place for 3,4-PyD while the most difficult one occurs for (Pc) Fe in all of the solvents investigated. The first reduction is metal-centered corresponding to the formation of [P(-2)Fe(I)]- while the second and third reductions are ring-centered leading stepwise to the generation of [P(-3)Fe(I)]2- · and [P(-4)Fe(I)]3- , where P = phthalocyanine or tetrapyridinoporphyrazine rings. Aggregation exists in the solutions of all three iron complexes and its extent depends upon the nature and concentration of the iron compounds and the binding property of each solvent. The order of the extent of aggregation for the three iron derivatives is 3,4-PyD > 2,3-PyD > (Pc) Fe . Stronger binding solvents such as pyridine and DMSO do not favor the aggregation. The singly and doubly reduced species of investigated complexes, [P(-2)Fe(I)]- and [P(-3)Fe(I)]2- · , are active in DDT reductive dechlorination, the latter of which has better catalytic performance. As a result, three products, 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (p,p′-DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (p,p′-DDE), and 1,1-bis(4-chlorophenyl)-2-chloroethylene (p,p′-DDMU), were obtained after the dechlorination of DDT catalyzed by each iron complex. The increasing order of catalytic performance is 3,4-PyD < 2,3-PyD < (Pc) Fe in pyridine, which is superior to DMSO and DMA for the DDT dechlorination reaction. An overall electrocatalytic mechanism is proposed for DDT reductive degradation based on the electrochemical and UV-visible spectroelectrochemical results.

Neutral cobalt(II) phthalocyanine and 2,3- and 3,4-tetrapyridoporphyrazine complexes were examined in pyridine, dimethyl sulfoxide and N,N-dimethylformamide to evaluate their catalytic properties in the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (p,p'-DDT). Cyclic voltammetry, controlled potential bulk electrolysis and thin-layer UV-visible spectroelectrochemistry of each compound in the presence of DDT indicated that both the singly and doubly reduced species, [Co(I)]- and [Co(I)]2- , can catalyze the dechlorination of DDT through the formation of, and a photoinduced or electrochemically induced cleavage of, the Co-C bond in the organometallic intermediates. GC-MS analysis revealed that DDT was converted to 1,1-bis(4-chlorophenyl)-2, 2-dichloroethane (p,p'-DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (p,p'-DDE) and 1,1-bis(4-chlorophenyl)-2-chloroethylene (p,p'-DDMU), upon dechlorination. The catalytic performance of the three cobalt complexes depends upon the reactive nature of each compound, the solvent, the reaction time and the equivalence of DDT. In addition, either DDD or DDE can be catalytically dechlorinated to generate DDMU, possibly through a similar mechanism.

Two cobalt porphyrazines, 2,3-tetrapyridoporphyrazine and 3,4-tetrapyridoporphyrazine, were examined in N,N-dimethylformamide, dimethyl sulfoxide and pyridine solutions as to their electrochemical, spectroelectrochemical and ESR spectroscopic properties. These results were compared with those of the unsubstituted cobalt phthalocyanine. At high concentrations, aggregation was observed for each investigated compound in the three solvents. The intensity of ESR signals of each derivative depends upon the extent of aggregation in its solution. The g values shift towards high field with an increase in the strength of the axial ligand and the number of axial ligands on the cobalt center. Both tetrapyridoporphyrazine complexes undergo one oxidation and three reductions in N,N-dimethylformamide, dimethyl sulfoxide or pyridine solution. Thin-layer UV-visible spectroelectrochemical results confirmed that the first oxidation and first reduction of both compounds are metal-centered while the second and third reductions are ring-centered. An overall electron transfer mechanism for both porphyrazine derivatives is proposed.

Two sigma-bonded Rh 2 5+ complexes, Rh 2 (ap) 4 (C 6 H 5 ) and Rh 2 (ap) 4 (CH 3 ), where ap = 2-anilinopyridinate anion were synthesized and examined as to their electrochemical and spectroscopic properties in nonaqueous media. Rh 2 (ap) 4 (C 6 H 5 ) was also structurally characterized. The presence of the phenyl axial ligand on Rh 2 (ap) 4 (C 6 H 5 ) does not bring about a significant structural effect on the ap framework as compared to Rh 2 (ap) 4 Cl or Rh 2 (ap) 4 (C CH) but the Rh–Rh and Rh–C axial 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 Rh 2 4 + complex and two reversible one-electron oxidations to give stable compounds in Rh 2 6 + and Rh 2 7 + oxidation states. These redox reactions occur at E 1/2 = −0.79, 0.28 and 0.93 V for R = CH 3 and −0.71, 0.35 and 0.95 V for R = C 6 H 5 . The ESR spectrum of Rh 2 (ap) 4 (CH 3 ) has g ⊥ and g || values of 2.17 and 1.89 while Rh 2 (ap) 4 (C 6 H 5 ) 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 Rh 2 5 + .

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 syntheses and characterization of the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4Cl and Ru2(F5ap)4(C⋮CC6H5)2 are reported where F5ap is the 2-(2,3,4,5,6-pentafluoroanilino)pyridinate an...

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 relationship between half-wave potential, the site of electron transfer, and the catalytic activity of a given [(P)Ni] - complex toward CH 3 I reduction was investigated for seven nickel(II) porphyrins.

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.

Two neutral diruthenium complexes and one anionic diruthenium complex, Ru2(dpf)4(NO), Ru2(dpf)4(NO)2, and [Ru2(dpf)4(NO)]-, where dpf is diphenylformamidinate anion, were synthesized and characterized as to their electrochemical and spectroscopic properties. Two of the compounds, Ru2(dpf)4(NO) and Ru2(dpf)4(NO)2, were also structurally characterized. Ru2(dpf)4(NO) undergoes reversible one-electron reductions under N2 at E1/2=0.06 and -1.24 V in CH2Cl2, 0.1 M TBABr. These processes are shifted to E1/2=0.18 and -0.78 V under CO due to the trans-coordination of a CO molecule which stabilizes the singly and doubly reduced forms of the metal-metal bonded complexes, thus leading to easier reductions. CO does not coordinate to Ru2(dpf)4(NO), but it does bind to the singly reduced species to generate [Ru2(dpf)4(NO)(CO)]- under a CO atmosphere in solution; characteristic NO and CO bands are seen for this compound at nuNO=1674 cm(-1) and nuCO=1954 cm(-1). Ru2(dpf)4(NO)2 displays a reversible one-electron reduction at E1/2=-1.24 V versus SCE and an irreversible reduction at Epc=-1.96 V in CH2Cl2, 0.1 M TBAP under N2. There are also two reversible one-electron oxidations at E1/2=0.24 and 1.15 V. Spectroelectrochemical monitoring of the Ru2(dpf)4(NO)2 oxidation processes in a thin-layer cell shows only a single NO vibration for each electrogenerated product and nuNO is located at 1726 (neutral), 1788 (singly oxidized), or 1834 (doubly oxidized) cm(-1). Finally, a labile CO complex, [Ru2(dpf)4(NO)(CO)]-, could be generated by passing CO into a solution of [Ru2(dpf)4(NO)]-. Formation of the mixed CO/NO adduct was confirmed by electrochemistry and infrared spectroscopy. Analysis of the NO and CO stretching vibration frequencies for [Ru2(dpf)4(NO)(CO)]- by in-situ FTIR spectroelectrochemistry and comparisons with data for Ru2(dpf)4(NO) and Ru2(dpf)4(CO) reveal the presence of a strong interaction between NO and CO across the Ru-Ru bond.

A monocarbonyl diruthenium(II,II) complex of the type (dpf)4Ru2(CO), where dpf is N,N‘-diphenylformamidinate, was characterized as to its electrochemical and spectroscopic properties (UV−vis, FTIR, and ESR) under a N2 or CO atmosphere. The synthesis and X-ray structural characterization of (dpf)4Ru2(CO) are also presented.