II)-ruthenium Research Articles

Chemistry of ruthenium phenolates. Synthesis, characterization and redox properties of a group of salicylaldiminato complexes of ruthenium

A group of five mixed ligand ruthenium(II) complexes of general formula [Ru(bpy)(sal-R) 2] (bby= 2, 2′-bipyridine, sal-R = salicylaldiminate anoin) has been synthesizd and characterized. the complexes are diamagnetic (low spin d 6, S = 0) and show intense MLCT transitions in the visible region in solution. In acetonitrile solution they all show a reversible ruthenium(II)-ruthenium(III) oxidation in the range −0.3 to 0.04 V versus SCE, followed by another reversible ruthenium(III)-ruthenium(IV) oxidation in the range 1.1 to 1.3 V versus SCE. The potential of these two oxidations is sensitive to the nature of the substituent R in the sal-R ligand. A reversible bpy reduction is also observed near -t-1.9 V versus SCE. The five [Ru III(bpy)(sal-R) 2] + complexes have been synthesized by chemical oxidation of their respective ruthenium(II) precursors by iodine, and isolated as perchlorate salts. These oxidized complexes are paramagnetic (low spin d 5, S = 1/2) and show rhombic ESR spectra at 77 K. They show intense LMCT transitions in the visible region in acetonitrile solution, together with weak ligand-field transitions at lower energies. Chemical reduction of these ruthenium(III) complexes by hydrazine gives back the parent ruthenium(II) complexes.

Synthesis, characterization, redox properties and reactivities of a group of phenolato complexes of ruthenium(III)

Seven complexes of the type [Ru III(PPh 3) 2(L)Cl 2] (where L = 8-quinolinolate, 4-methyl-2-(phenylazo) phenolate and salicylal-diminate anion) have been synthesized by the reaction of [Ru(PPh 3) 3Cl 2] with HL. These complexes are one-electron paramagnetic and show rhombic ESR spectra in 1:1 dichloromethanetoluene at 77 K. In CH 2Cl 2 solution, these complexes show intense LMCT transitions in the visible region together with weak ligand-field transitions at lower energies. Each of these complexes shows a ruthenium(III)-ruthenium(II) reduction (−0.12 to −0.40 V vs SCE) and a ruthenium(III)-ruthenium(IV) oxidation (0.78−0.88 V vs SCE) in acetonitrile solution. The potentials of the ruthenium(III)-ruthenium(II) reduction vary linearly with the nature of substituent in L. The [Ru III(PPh 3) 2(L)Cl 2] complexes react with bidentate chelating ligands (L′ = 8-quinolinolate anion, 2,2′-bipyridine, 1,10-phenanthroline) to afford complexes of type [Ru(PPh 3) 2(L)(L′)] n+ These complexes are diamagnetic and show intense MLCT transitions in the visible region. The potential of the ruthenium(II)-ruthenium(III) couple in these complexes depend on the nature of both L and L′.

Chemistry of 2-(arylazo)phenolate complexes of ruthenium. Synthesis, characterization and redox properties

A family of five 2-(arylazo)phenolate (ap-R) complexes of ruthenium of type [Ru II(bpy)(ap-R) 2] (bpy = 2,2′-bipyridine) has been synthesized and characterized. The complexes are diamagnetic (low-spin d 6, S = 0) and in acetonitrile solution show intense MLCT transitions in the visible region. Cyclic voltammetry of the complexes in acetonitrile solution shows a reversible ruthenium (II)-ruthenium (III) oxidation in the range 0.04–0.26 V vs SCE followed by an irreversible ruthenium(III)-ruthenium(IV) oxidation in the range 1.18–1.32 V vs SCE. The potential of these two oxidations is sensitive to the nature of substituent R in the apR ligand. A one-electron reduction of the coordinated bpy is also observed near −1.6 V vs SCE. The five [Ru III(bpy)(ap-R) 2] + complexes have been synthesized by chemical oxidation of their respective ruthenium(II) precursors by iodine and isolated as the iodide salts. These oxidized complexes are one-electron paramagnetic low-spin, d 5, S = 1 2 ) and show rhombic ESR spectra at 77 K. In acetonitrile solution they show intense LMCT transitions in the visible region together with weak ligand-field transitions at lower energies. Chemical reduction of these ruthenium(III) complexes by hydrazine gives back the parent ruthenium(II) complexes.

Ruthenium-mediated selective activation of a C–H bond. Direct aromatic thiolation in the complexes [RuII{o-SC6H3(R)NNC 5H4N}2] (R = H, Me or Cl)

The reaction of the complexes ctc-[Ru II L 2 Cl 2 ] (L = arylazopyridine, RC 6 H 4 NNC 5 H 4 N, where R = H, m-Me, p-Me or p-Cl; ctc = cis-trans-cis with respect to chlorides, pyridine and azo nitrogens respectively) with KS 2 COR′ (R′ = Me, Et, Pr n , Bu n or CH 2 Ph) in boiling dimethylformamide afforded [Ru II {o-SC 6 H 3 (R)NNC 5 H 4 N} 2 ] where the o-carbon atom of the pendant phenyl ring of both ligands L has been selectively and directly thiolated. The newly formed tridentate thiolated ligands are bound in a meridional fashion. When one methyl group is present at the meta position of the pendant phenyl ring of L the reaction resulted in two isomeric complexes due to free rotation of the singly bonded meta-substituted phenyl ring with respect to the azo group. The molecular geometry of the complexes in solution has been determined by 1 H NMR spectroscopy. This revealed the presence of an intimate mixture of the two isomers in solution in a 2∶1 ratio. In the visible region the complexes exhibit two metal-to-ligand charge-transfer transitions at ≈700 and ≈560 nm respectively and in the UV region intraligand (π–π*, n–π*) transitions. In acetonitrile solution the complexes exhibit one reversible ruthenium(II) ruthenium(III) oxidation couple near 0.4 V and an irreversible oxidative response near 1 V due to oxidation of the co-ordinated thiol group. Reduction of the co-ordinated azo groups occurs at ca. -0.8 and -1.4 V respectively. Coulometric oxidation of the complexes [Ru II {o-SC 6 H 3 (R)NNC 5 H 4 N} 2 ] at 0.6 V versus the saturated calomel electrode in dichloromethane produced unstable ruthenium(III) congeners. When R = p-Me, the presence of trivalent ruthenium in the oxidised solution was evidenced by a rhombic EPR spectrum having g 1 = 2.359, g 2 = 2.300 and g 3 = 1.952.

Synthesis, spectroscopic characterisation, electron-transfer properties and crystal structure of [RuII(bipy)2(2-SC5H4N)]ClO 4 (bipy = 2,2′-bipyridine)

Two new ruthenium(II) mixed-ligand tris-chelated complexes of the type [Ru(bipy) 2 L]ClO 4 , (bipy = 2,2′-bipyridine; L = pyridine-2-thiolate 1 or pyridin-2-olate 2) have been synthesized. The complexes are essentially diamagnetic and behave as 1∶1 electrolytes in acetonitrile solution. They display two metal-to-ligand charge-transfer (m.l.c.t.) transitions near 500 and 340 nm respectively along with intraligand transitions in the UV region. Both exhibit room-temperature emission from the highest-energy (m.l.c.t.) band. At room temperature the lifetime of the excited states for the thiolato (1) and phenolato (2) complexes are 100 and 90 ns respectively. The geometry of the complexes in solution has been assessed by high-resolution 1 H NMR spectroscopy. The molecular structure of complex 1 in the solid state has been determined by single-crystal X-ray diffraction. It shows the expected pseudo-octahedral geometry with considerable strain due to the presence of the sterically hindered ligand L 1 . In acetonitrile solution the complexes show quasi-reversible ruthenium(II)–ruthenium(III) oxidation couples at 0.54 and 0.64 V versus saturated calomel electrode and quasi-reversible ruthenium(III)–ruthenium(IV) oxidations at 1.41 and 1.03 V respectively. Two reversible reductions are observed near -1.6 and -1.9 V for each complex due to electron transfer to the co-ordinated bipy units. The trivalent analogues of 1 and 2 are unstable at room temperature but can be generated in solution by coulometric oxidation at 263 K as evidenced by EPR spectroscopy.

Ruthenium phenolates: Synthesis, characterization and reactivities of a group of salicylaldiminato and 2-(arylazo)phenolato complexes of ruthenium

Some ruthenium(II) complexes of type [Ru 11 (trpy) (L)Cl] [trey = 2,2′: 6′,2″-terpyridine ; L = salicylaldiminate and 2-(arylazo)phenolate anion] have been synthesized and characterized. The complexes are diamagnetic (low-spin d 6, S = 0) and show intense metal-to-ligand charge transfer transitions in the visible region. Cyclic voltammetry of these complexes show a reversible ruthenium (II)-ruthenium(III) oxidation in the range 0.16–0.46 V vs saturated calomel electrode (SCE) and an irreversible ruthenium(III)-ruthenium(IV) oxidation near 1.5–1.6 V vs SCE. The ruthenium (II)-ruthenium (III) oxidation potential is sensitive to the nature of substituents on L. A reduction of coordinated trpy is also observed near −1.45 V vs SCE. Two representative [Ru III(trpy)(L)Cl] + complexes have been synthesized by chemical and electrochemical oxidation of their ruthenium(II) precursors and isolated as perchlorate salts. These oxidized complexes are paramagnetic (low-spin d 5, S = 1 2 ) and show rhombic ESR spectra at 77 K. They show intense ligand-to-metal charge transfer transitions in the visible region and weak ligand-field transitions at lower energies. Aquo complexes of type [Ru II(trpy)(L)(H 2O)] + have been prepared by displacing Cl − from [Ru II(trpy)(L)CI] by Ag + in aqueous medium.

Ruthenium phenolates. Synthesis, characterization and electron-transfer properties of some salicylaldiminato and 2-(arylazo)phenolato complexes of ruthenium

Eleven mixed-ligand ruthenium(II) complexes of the general formula [Ru(bpy) 2 (L)]CIO, [bpy = 2,2′-bipyridine, L = salicylaldiminate or 2-(arylazo) phenolate anion] have been synthesized and characterized. The complexes are diamagnetic (low-spin d 6, S = 0) and in solution show intense MLCT transitions in the visible region. In acetonitrile solution they all show a reversible ruthenium (II)-ruthenium (III) oxidation in the range 0.5–0.9 V versus SCE and an irreversible ruthenium (III)-ruthenium(IV) oxidation near 1.6 V versus SCE. The potential of the ruthenium (II)-ruthenium (III) couple is sensitive to the nature of substituents on the ligand L. Two successive one-electron reductions of the coordinated bpy are also observed near −1.5 and −1.8 V versus SCE. Two representative [Ru III(bpy) 2(L)] 2+ complexes have been synthesized by chemical oxidation of their ruthenium(II) precursors by aqueous ceric solution and isolated as perchlorate salts. These oxidized complexes are paramagnetic (low-spin d 5, S = 1 2) ) and show rhombic ESR spectra at 77 K. They show intense LMCT transitions in the visible region in acetonitrile solution together with weak ligand-field transitions at lower energies. Chemical reduction of these ruthenium(III) complexes by hydrazine gives back the parent ruthenium(II) complexes. In acetonitrile solution the [Ru III(bpy) 2(L)] 2+ complexes oxidize N,N-dimethyl aniline, 1,2-napthoquinone-l-oxime, [Ru II(bpy) 2Cl 2] and [Fe II(C 5H 5) 2] to produce N,N,N′,N′-tetramethylbenzidine, 1,2-napthoquinone-l-iminoxy radical, [Ru III(bpy) 2Cl 2] + and [Fe III(C 5H 5( 2] +, respectively, which have been characterized by spectroscopic and electrochemical techniques.

ルテニウム錯体による有機化合物の活性化と触媒反応

Recent progress in chemistry on ruthenium complexes is reviewed from a viewpoint of homogeneous ruthenium complex-catalyzed organic synthesis. Some real active intermediary species of the ruthenium complex-catalysis are isolated from the catalytic reaction mixtures or their model complexes are synthesized by stoichiometric methods. This article deals with the following subjects : (i) Progress on the ruthenium (II) -BINAP complexes which exhibits higher activity and stereoselectivity in catalytic asymmetric hydrogenation, (ii) Ruthenium (II) complex-promoted activation of some organic compounds such as alkenes, alkynes and nitriles, forming various types of complexes with the activated ligands, (iii) Relationship between the active ruthenium (0) complexes and the ruthenium-catalyzed C-H activation.

Electron Transfer through Norbornadiene and Quadricyclane Moieties as a Model for Molecular Switching

The bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized. Its photochemical conversion into a dicyanoquadricyclane complex by irradiation in methanol has been followed by UV−visible spectroscopy, IR spectroscopy, 1H NMR spectroscopy, and cyclic voltammetry. The dicyanonorbornadiene complex exhibits an intervalence transition in the 1000−1600 nm range when oxidized to the ruthenium(II)−ruthenium(III) state. This allows the determination of the effective coupling Vab through the dicyanonorbornadiene ligand, which is found as 0.023 eV. No such band is observed in the case of the dicyanoquadricyclane complex. These results show the possibility to modulate an intramolecular electron transfer process by using a photoisomerizable bridging ligand.

Complexes of some platinum group metals with hydrazone ligands and their catalytic oxidative properties

New complexes of ruthenium(II), ruthenium(III), osmium(III) and palladium(II) have been prepared with a neutral bidendate hydrazone ligand derived from antipyrine-4-carboxaldehyde and benzoylhydrazine. Ruthenium(III) complexes have also been synthesized from monobasic bidendate ligands prepared from benzaldehyde and benzoyl orp-substituted (Me, Cl) benzoyl hydrazine. The complexes were characterized by spectroscopic techniques and investigated by cyclic voltammetry. The efficient catalytic oxidation of alcohols and 3,5-di-tbutyl catechol in the presence of N-methylmorpholine-N-oxide orm-chloroperbenzoic acid as co-oxidants is reported.

Chemistry of ruthenium in N2P2X2 (X = Cl, Br) coordination sphere: Synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh3)3X2] (X = Cl, Br) in dichloromethane solution affords [Ru(PPh3)2(pap)X2]. These diamagnetic complexes exhibit a weakdd transition and two intense MLCT transitions in the visible region. In dichloromethane solution they display a one-electron reduction of pap near − 0.90 V vs SCE and a reversible ruthenium(II)-ruthenium(III) oxidation near 0.70 V vs SCE. The [RuIII(PPh3)2(pap)Cl2]+ complex cation, generated by coulometric oxidation of [Ru(PPh3)2(pap)Cl2], shows two intense LMCT transitions in the visible region. It oxidizes N,N-dimethylaniline and [RuII(bpy)2Cl2] (bpy = 2,2′-bipyridine) to produce N,N,N′,N′-tetramethylbenzidine and [RuIII(bpy)2Cl2]+ respectively. Reaction of [Ru(PPh3)2(pap)X2] with Ag+ in ethanol produces [Ru(PPh3)2(pap)(EtOH)2]2+ which upon further reaction with L (L = pap, bpy, acetylacetonate ion(acac−) and oxalate ion (ox2−)) gives complexes of type [Ru(PPh3)2(pap)(L)]n+ (n = 0, 1, 2). All these diamagnetic complexes show a weakdd transition and several intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation potential decreases in the order (of L): pap > bpy > acac− > ox2−. Reductions of the coordinated pap and bpy are also observed.

Synthesis, characterization and cyclic voltammetric studies of monopicolinate complexes of ruthenium(II)

Two stable monopicolinate complexes of ruthenium(II), [Ru(bipy)2(pic)]ClO4 and [Ru(pap)2(pic)]ClO4 [bipy = 2,2′-bipyridine, pic = picolinate anion, pap = 2-(phenylazo)-pyridine], were prepared and characterized. The complexes are diamagnetic and behave as 1:1 electrolytes in MeCN solution. In the i.r. spectra, they show characteristic vibrations of bipy or pap, pic and ClO inf4 p− . In MeCN solution, both complexes display three intense absorption bands in the visible region, which have been assigned to metal-to-ligand charge-transfer transitions. Each complex shows a reversible ruthenium(II)-ruthenium(III) oxidation in MeCN, the formal potential (E inf298 p0 ) being 0.75 V versus a saturated calomel reference electrode (SCE) for [Ru-(bipy)2(pic)]+ and 1.44 V versus SCE for [Ru(pap)2(pic)]+. Multiple reductions of the coordinated bipy and pap ligands have also been observed.

Ruthenium picolinates. Synthesis, characterization and reactivities of some picolinate complexes of ruthenium(II)

Reaction of Ru(PPh 3) 3X 2 (X = Cl, Br) with equimolar picolinic acid (Hpic) in dichloromethane solution at ambient temperature gave diamagnetic [Ru(PPh 3) 2(pic)(H 2O)X], which in solution showed intense absorption bands in the visible region assigned to MLCT transitions. Each complex displayed a reversible ruthenium(II)-ruthenium(III) oxidation near 0.60 V vs SCE. Reaction of [Ru(PPh 3) 2(pic)(H 2O)X] with base eliminated a molecule of HX and then dimerized to produce the hydroxo-bridged [{Ru(PPh 3) 2(pic)(OH)} 2] complex. In solution it showed intense MLCT transitions in the visible region. Two successive quasi-reversible ruthenium(II)-ruthenium(III) oxidations were observed in this dimer at 0.75 V and 1.01 V vs SCE. Reaction of Ru(PPh 3) 3X 2 with two equivalents of Hpic in refluxing ethanol afforded [Ru(PPh 3) 2(pic) 2]. This diamagnetic complex exhibited several intense MLCT transitions in solution. The ruthenium(II)-ruthenium(III) oxidation took place reversibly at 0.54 V vs SCE in this complex.

Synthesis, characterization, electron-transfer properties and reactivities of a group of ruthenium(II) complexes with RuN 2P 2X 2 (X = Cl, Br) coordination spheres

Four dihaloruthenium(II) complexes of general formula Ru(PPh 3) 2(L)X 2 [L = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen); X = Cl, Br] have been synthesized by the reaction of L with Ru(PPh 3) 3X 2 in dichloromethane. The complexes are diamagnetic and show intense absorptions in the visible region which are assigned to the MLCT transitions. In dichloromethane solution they show a reversible ruthenium(II)-ruthenium-(III) oxidation near 0.4 vs SCE. Two [Ru III(PPh 3) 2(L)(Cl 2)] + ions have been generated in solution by electrochemical oxidation of Ru II(PPh 3) 2(L)Cl 2. Solutions of the oxidized complexes show LMCT transitions in the visible region and at 77 K show rhombic EPR spectra. The distortions from octahedral symmetry have been quantified, in these species, with the help of EPR data analysis. The axial distortion is much larger than the rhombic one. The two X − ligands are easily displaced from Ru(PPh 3) 2(L)X 2 by its reaction with Ag + in ethanol producing [Ru(PPh 3) 2(L)(EtOH) 2] 2+, which upon reacting with L′ [L′ = bpy, phen, acetylacetonate ion (acac−), oxalate ion (ox 2−)] affords complexes of type [Ru)PPh 3) 2(L)(L′) n+ ( n = 0, 1, 2). Five such complexes have been synthesized and characterized. They all are diamagnetic and show intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation is very sensitive to the nature of L′. The potential decreases in the order (of L′); bpy (or phen) > acac − > ox 2−. Reductions of the coordinated bpy and phen are also observed.

Rate constants for intramolecular electron-transfer reactions of ruthenium-modified histidine mutants of cytochrome b2

The cytochrome b2 core derived from flavocytochrome b2 has been expressed in Escherichia coli and four mutants Lys-56→His, Lys-51→His, Asn-42→His and Pro-41→His have been generated by site-directed mutagenesis. Ruthenium modification of the first three mutants with [Ru(NH3)5(H2O)]2+ led to the formation of singly modified His-56[Ru(NH3)5], His-51 [Ru(NH3)5] and His-42[Ru(NH3)5] derivatives in 30–45% yield. However no modification was observed with Pro41His. Moreover no evidence was obtained for the formation of His-19[Ru(NH3)5], where His-19 is the unco-ordinated histidine present in wild-type and mutant cytochrome b2 forms. Characterisation of the singly modified products by inductively coupled plasma analyses indicates an Fe : Ru ratio of 1 : 1 for all three derivatives. The NMR spectra of the Ru-modified proteins reveal specific broadening by the paramagnetic RuIII of the characteristically sharp CIµH and CδH resonances assigned to His-56, His-51 and His-42, while the CIµH resonance due to His-19 is unaffected. Whereas the titration of unmodified His-56, His-51, His-42 and His-41 residues by 1H NMR spectroscopy gave pKa 6.4, 6.2, 6.5 and 6.4 respectively, His-19 did not similarly titrate in the pH 4.8–10.0 range, which is attributed to hydrogen bonding to a nearby residue. Using pulse radiolysis to generate the methyl viologen radical, MV˙+, the metastable iron(II)ruthenium(III) form of the protein was obtained. Rate constants for intramolecular electron transfer from FeII to RuIII were determined; 3.5 (His-56), 2.8 (His-51) and 78 s–1(His-42) at I= 0.100 M. Edge-to-edge distances, from the nearest point on one or other of the axial haem ligands to the nearest point on the imidazole ring, are 10.8 (His-56), 9.8 (His-51) and 8.5 A(His-42), and the driving force is close to 145 mV. Using the Beratan–Onuchic approach the most favourable pathways for electron transfer have been identified. For His-42 a direct through-bond pathway via axial His-43 to the haem Fe is indicated. In the case of the His-56 and His-51 derivatives, pathways that include through-space interactions appear to be dominant.

Synthesis, characterization and reactivity of a ruthenium-quinone complex

A mixed ligand ruthenium-quinone complex, Ru(trpy)(DBQ)Cl [trpy = 2,2′: 6′,2″-terpyridine, DBQ = 3,5-di-tert-butylquinone] has been synthesized. The complex is paramagnetic (1 upe) and shows a sharp EPR signal at g ≈ 2. A Ru II-DBSQ [DBSQ = semiquinonate form of DBQ] charge distribution is therefore assigned to this complex. It shows intense absorption bands in the visible and near-infrared regions which are assigned to allowed charge-transfer transitions. In dichloromethane solution it shows three reversible cyclic voltammetric responses, one ruthenium(II)-ruthenium(III) oxidation and the reductions of DBSQ and trpy ligands. The chloride ligand in Ru(trpy)(DBSQ)Cl can be replaced in aqueous medium by reacting it with Ag + to afford the [Ru(trpy)(DBSQ)(H 2O] + ioin, which has been isolated and characterized as the perchlorate salt. This aquo complex is easily converted back to the parent chloro complex by reaction with the chloride ion.

8-Quinolinolate complexes of ruthenium(ii). Synthesis, characterization and electron transfer properties

Two stable 8-quinolinolate complexes of ruthenium(II), [Ru(bpy)(Q)]ClO 4 and [Ru(tap) 2(Q)]ClO 4 [bpy = 2,2′-bipyridine, Q=8-quinolinolate anion, tap = 2-( m-tolylazo) pyridine] have been synthesized. The complexes are diamagnetic and show strong absorption near 1100 cm −1 in the IR spectra due to the presence of ClO − 4. In acetonitrile solution they behave as 1:1 electrolytes. The complexes display intense absorption bands in the visible region (400–700 nm) which are assigned to MLCT transitions. The formal potential ( E 0 298), determined cyclic voltammetrically for the ruthenium(II)-ruthenium(III) oxidation, is 0.48 V vs SCE for [Ru(bpy) 2(Q)] +. The same oxidation takes place irreversibly at 1.00 V vs SCE ( E pa value) in the case of [Ru(tap) 2(Q)] +. Reductions of the bound bpy and tap ligands are also observed.

Reactivity of ruthenium complexes with uninegative (X,S)-donor ligands (X  S,P)—II. Phosphine substitution in [Ru(S,S) 2(PR 3) 2] derivatives. Crystal structure of trans-bis(O-ethyldithiocarbonate)bis(dimethylphenylphosphine)-ruthenium(II)

The complexes [Ru(S,S) 2(PPh 3) 2] [S,S  EtCOCS 2 −, (CH 2) 4NCS 2 −] react with a variety of tertiary phosphines with the substitution of triphenylphosphine and the formation of [Ru(S,S) 2(PR 3) 2]. The reaction occurs with the formation ofthe cis isomer, except for the complex with PMe 2Ph that gives rise to the trans isomer as the crystal structure shows. The effect of the different phosphines on the ruthenium complex is analysed in terms of the spectroscopic and electrochemical properties of the isolated compounds. The cyclic voltammetric studies of the cis complexes show that isomerization to the trans isomer occurs on oxidation. This isomerization is not observed in the trans-[Ru(S,S) 2(PMe 2Ph) 2] complexes that give rise to stable trans-ruthenium(II)/ruthenium(III) couples. In a similar way the diphosphine complexes afford a quasi-reversible cis-ruthenium(II)/ruthenium(III) process.

Voltammetry of the complexes of the platinum metals with organic sulphides in acetonitrile

The electrochemical behaviour of palladium(II), ruthenium(III), rhodium(III), osmium(IV), iridium(IV) and platinum(IV) complexes with a number of sulphides was investigated at a glassy carbon electrode in acetonitrile. Complexes of Ru(III), Os(IV) and Ir(IV) have been found to undergo a reversible one-electron transfer yielding Ru(II), Os(III) and Ir(III) complexes. Electroreduction of the Ru(II) and Ir(III) compounds is of the EC type and is accompanied by the rearrangement of the complex coordination sphere. Compounds of Pd(II), Rh(III) and Pt(IV) are reduced with the transfer of 2 electrons in the first stage. The electrode process differs from a reversible one and is complicated by the dissociation reaction of the ligands. The influence of the nature of the donor atoms on the oxidation potentials of the complexes is considered.

Bimetallic ruthenium(II)ruthenium(III) complexes. A molecular orbital view

The strustures of bimetallic ruthenium(II)ruthenium(III) ions with a variety of bridging ligands are considered using molecular orbital methods. These ions may by symmetrical with equivalent metal centers or may be distorted with nonequivalent sites, which in the extreme can be identified as Ru(II) and Ru(III). Certain ions with ligands such as 4,4′-bipyridine or nonconjugated dicyano species would have degenerate ground state if they were symmetrical and are thus distorted. In other ions the odd electron will be located in a coupled orbital and there will be less of a tendency toward distortion. The original Creutz and Taube pyrazine bridged complex is of this type.