Nagao Hirotaka

In this work, three different types of acetylacetonato-based pincer-type nickel(ii) complexes (2) were prepared. Complex 2a possessed the tridentate ONN ligand, which was constructed by the condensation reaction of acetylacetone with N,N-diethylethylenediamine. Complex 2b contained the PPh2 donor group in contrast to the NEt2 group in 2a, i.e., an ONP ligand framework. Complex 2c was composed of the NNN ligand, which was prepared by the reaction of 4-((2,4,6-trimethylphenyl)amino)pent-3-en-2-one with N,N-diethylethylenediamine. In addition to X-ray diffraction analysis, these complexes were characterized spectroscopically. Their catalytic activity for a cross-coupling reaction of aryl halides with aryl Grignard reagents was also evaluated. Among these complexes, 2b acted as an effective catalyst for the cross-coupling reaction using aryl chlorides as electrophiles. The electronic properties of these Ni(ii) complexes were investigated by cyclic voltammetry and density functional theory calculations.

The reactions of azide ions coordinated to ruthenium(II) centers bearing two 2,2-bipyridine (bpy) ligands, that is, [Ru-II(N-3)(2)(bpy)(2)] (1), [Ru-II(N-3)(NH=CHR1)(bpy)(2)](+) (2; R-1 = CH3, C2H5), and [Ru-II(N-3)(NCCH3)(bpy)(2)](+) (3), with haloalkanes (CRRRX)-R-1-R-2-X-3 (R-1 = H, CH3, C2H5, R-2 = H, CH3, R-3 = H, CH3, X = I, Br) afforded imine (NH=(CRR2)-R-1) and ammine (NH3) ligands with dinitrogen evolution. The formation of these nitrogen-containing moieties depended on both the reaction solvent and the alkyl group of the haloalkane. Four types of imine complexes, [(RuL)-L-II(NH=(CRR2)-R-1)(bpy)(2)](n+) [L = N-3(-) (2), I- (4), NH=CHR1 (5), and CH3CN (6)], were synthesized and characterized. The oxidation reactions of the imine complexes 5 and 6 followed by electron- and proton-transfer reactions to give nitrile complexes were studied by electrochemical measurements. These results revealed new strategies for the synthesis of N-C bonds and nitrogen-containing compounds through the reactions of azido and related ligands.

A doubly nitrosyl-bridged dinuclear ruthenium complex, {Ru2(μ-NO)2}, bearing tridentate ethylbis(2-pyridylethyl)-amine (ebpea) and acetonitrile as supporting and co-existing ligands, respectively, [{Ru(μ-NO)(ebpea)(NCMe)}2]2+ ([1]2+) has been synthesized by a reaction of tris(acetonitrile)ruthenium(II) complex with sodium nitrate in ethanol. The ebpea ligand coordinated with two pyridyl- and one amine-nitrogen atoms in a meridional mode. The dinuclear ruthenium complex containing two nitrosyl ligands bridging between two ruthenium centers as a bending mode, showed two stepwise oneelectron oxidation waves at 0.03 and 0.57 V vs. Ag|0.01 M AgNO3 in MeCN and a strong characteristic NO stretching vibrational mode υ(NO) at 1336 cm-1, indicating the electronic structure of the {RuNO}-moieties was an octahedral{RuNO}8-type. The dinuclear ruthenium complex reacted with acid to give mononuclear ruthenium complexes with evolution of dinitrogen oxide.

Dinuclear ruthenium complexes in a mixed valence state of Ru-III-Ru-IV, having a doubly oxido-bridged and acetato(-) or nitrato-capped framework, [{Ru-III,Ru-IV ebpma)}(2)(mu-O)(2),(mu-L)](PF6)(2) [ebpma = ethylbis (2-pyridylmethyl) amine; L = CH3COO- (1), NO3- (2)1 were synthesized. In aqueous solutions, the diruthenium complex 1 showed multiple redox processes accompanied by proton transfers depending on the pH. The protonated complex of 1, which is described as was obtained.

Trihalogenoruthenium(III) complexes bearing an ethylbis(2-pyridylmethyl) amine (ebpma) ligand, fac-[(RuX3)-X-III(ebpma)] (X = Cl, Br), were reduced by zinc in acetone that contained halogeno acid to afford a reddish-orange solution. Two kinds of dinuclear complexes were synthesized from the solution. After removing the remaining zinc and adding counterions such as PF6- and BF4- with water, the solution was allowed to stand under air until the color of the solution changed. New oxido-bridged dinuclear complexes of mixed-valence Ru-III-Ru-IV [{(RuX2)-X-III,IV(ebpma)} 2(mu-O)] Y (X = Cl, Y = PF6, [1] PF6; Y = BF4, [1] BF4; X = Br, Y = PF6, [2]PF6; Y = BF4, [2]BF4), which showed a similar framework to the reported water oxidation catalysts, were obtained as deep-colored solids. In the reaction without addition of extra water, a different mixed-valence dinuclear complex of Ru-II-Ru-III [{Ru-II,Ru-III(ebpma)}(2)(mu-Cl)(3)](2+), for which the metal centers were triply bridged by three chlorides, was formed. The synthetic procedures are useful for the development of multinuclear frameworks that function as molecular catalysts for redox reactions such as water oxidation.

Oxidation of the facial-type trichloridoruthenium(III) complex bearing ethylbis(2-pyridyl-methyl)amine (ebpma), fac-[(RuCl3)-Cl-III(ebpma)], with an equimolecular amount of (NH4)(2)[Ce-IV(NO3)(6)] in acetonitrile afforded a ligand-based oxidation product of an acetonitriledichloridoruthenium(III) complex having bis-(2-pyridylcarbonyl)aminato (bpca), [(RuCl2)-Cl-III(NCCH3)(bpca)]. The complex changed into a trichloridoruthenium(III) complex by a reaction with hydrochloric acid and the triacetonitrileruthenium(II) complex by reduction with Zn in ethanol-acetonitrile. The bpca moiety showed interactions with cations such as protons.

On treatment of bis(imidazolium) salts bound by o-xylylene, propylene, and ethylene linkers with two moles of LiBEt3H, the corresponding BEt3-adducts of bis-NHCs, (Et3B center dot ImR)(2)E (Im = imidazole; R = Me, Pr-i; E = o-xylylene, propylene, ethylene) (2), were obtained. Reaction of [Mo(CO)(6)] with compound 2 afforded the carbene complex, [Mo(CO)(4)(bis-NHC)] (3-Mo), in a good yield. Tungsten and chromium analogs of 3-Mo were obtained from [M(CO)(4)(eta(4)-norbornadiene)] (M = W, Cr). The X-ray analyses and NMR measurements of these complexes revealed that the bis-NHC ligand adopts a twisted conformation in an octahedral geometry and thus complexes 3 showed a C-2-symmmetric structure. In a reaction of 3-Mo with trimethylphosphite, a CO/P(OMe)(3) substitution reaction took place to give fac-[Mo(CO)(3)(bis-NHC) {P(OMe)(3)}] (4-Mo). The formation of the fac-form was found to be caused by a strong electron donor ability of the NHC ligand. The electronic features of the bis-NHC ligand were investigated by X-ray analysis, CO stretching frequency, and cyclic voltammetry of the complex 3-Mo. Furthermore, we estimated the donor ability of the bis-NHC ligand by comparing with those of 2,2'-bipyridine and 1,2-bis(diphenylphosphino) ethane. Density functional calculations (B3LYP/DGDZVP) showed that the C-2-symmetric structure of o-xylylene-bridged 3-Mo having N-methyl azole rings was more stable than a C-s-symmetric structure by Delta G = 6.69 kcal mol(-1). (C) 2012 Elsevier B.V. All rights reserved.

The E isomer of a [5]cumulene derivative, 2,2, 9,9-tetramethyl-3,8-diphenyldeca-3,4,5,6,7-pentaene (1), which was previously believed to be unisolable owing to very fast E/Z isomerization, was isolated and structurally characterized. The Z isomer was trapped as the transition-metal complex 5, and the molecular structure was determined. DFT calculations and an electrochemical study on 1 are also described.

The (iminium ion)ruthenium(II) complex mer(Cl, Cl,Cl)-[RuCl(3){eta(2)-NCHCH(2)py(C(2)H(4)py)C(2)H(5)}] was synthesized via a C-H activation of the bridging ethyl group of an ethylbis(2-pyridylethyl)amine ligand and characterized by X-ray structural analysis. Oxidations of alcohols by the (iminium ion)ruthenium(11) complex occurred with generation of mer-[Ru(III)Cl(3)(ebpea)].

In this accounts, syntheses and reactions of ruthenium complexes bearing pyridyl-containing ligands have been described. The properties and reactivity of complexes are related to their geometrical configuration around the metal center, and regulated by the combination of supporting ligands such as bpy, pyca, tpy, and bpya. Ruthenium complexes containing a nitrosyl ligand, which functions as a regulator of reactivity, have been synthesized and their structures and redox properties are investigated. We conclude that the interaction of the nitrosyl ligand through the ruthenium ion strongly depends on an electronic feature of the co-existing ligand in the series of nitrosylruthenium complexes. Conversion reactions of nitrogen-containing compounds such NO₂^- (NO), N₃^-, CH₃CN, and NO₃^- are performed under mild conditions to afford nitrogen-containing ligands. The reactions of N₃^- give two different type of ligands, imine (NH=CHR) and bridging nitrido (-N^3--), depending on supporting ligands. These reactions are important as a synthetic route of nitrogen-containing complexes. A geometrical isomerization and ligand-dissociation reactions are induced by redox of ruthenium comeplxes. The stabilities and reactivities of the ruthenium complexes have been explained by considering the electronic interaction of metal-ligand and ligand-ligand through the ruthenium center.

A mixed-valence diruthenium complex, whose metal centres were triply bridged by one chloro and two methoxo ligands, was synthesized and characterized by X-ray structural analysis, electrochemistry and spectroscopy, and its mixed-valence state was classified into Class III.

Reactions of ruthenium complexes having 2-pyridinecarboxylato and 2,2'-bipyridine ligands with sodium azide in alcohol afforded nitrido-bridged diruthenium complexes, [{Ru(OR)(pyca)(bpy)}(2)(mu-N)](+) (R = CH3, C2H5). Diruthenium complexes showed diamagnetic properties, a linear Ru-N-Ru coordination configuration, and two irreversible oxidation waves and two reversible reduction waves.

Ruthenium complexes containing a tridentate N-ethyl-N,N-bis(2-pyridylmethyl)amine (N,N-bis(2-pyridylmethyl)ethylamine: bpea) ligand having two different types of nitrogen donors, one an amine and the other pyridine rings connected with flexible CH2-arms, were synthesized and characterized. A trichlororuthenium isomeric pair of fac- and mer-[RuCl3(bpea)] was synthesized from RuCl3 center dot nH(2)O in a H2O-C2H5OH solution. A reaction of fac-[RuCl3(bpea)] in an C2H5OH-H2O-CH3CN solution under refluxing conditions afforded a triacetonitrile complex, fac-[Ru(CH3CN)(3)(bpea)](PF6)(2). Four nitrosylruthenium complexes, trans(NO, py), cis(NO, Cl), fac-[RuCl2(NO)(bpea)]PF6, trans(NO, OH), cis(NO, NO2), mer-[Ru(NO2)(OH)(NO)(bpea)]PF6, trans(NO, OCH3), cis(NO, Cl), mer-[RuCl(OCH3)(NO)(bpea)]PF6 and trans(NO, OH), cis(NO, Cl), mer-[RuCl(OH)(NO)(bpea)]PF6, were synthesized and characterized by X-ray crystallography. The bpea of three nitrosylruthenium complexes bearing an electron-donating ligand such as hydroxo or methoxo as an ancillary ligand coordinated in a meridional fashion.

cis-[Ru(NO)(CH3CN)(pyca)(2)] and trans-[Ru(NO)(OH)(pyca)(2)] (pyca = 2-pyridinecarboxylato) were synthesized and characterized by X-ray crystallography. Electrochemical behaviors of cis-[Ru(NO)(CH3CN)(pyca)(2)] and cis-[Ru(NO)(CH3O)(pyca)(2)] in acetonitrile were studied. These complexes showed two reduction processes in CH3CN. The controlled potential electrolyses of cis-[Ru(NO)(CH3O)(pyca)(2)] in a methanol-acetonitrile mixed solution were performed at the potential of the first reduction process. trans-[Ru(NO)(CH3O)(pyca)(2)] was isolated from the electrolyzed solution and characterized by IR and CV. The cis-trans geometrical change reaction occurred in the electrochemical one-electron reduction of cis-[Ru(NO)(CH3O)(pyca)(2)]. (c) 2007 Elsevier Ltd. All rights reserved.

Nitrosylruthenium complexes containing 2,2':6',2 ''-terpyridine (terpy) have been synthesized and characterized. The three alkoxo complexes trans-(NO, OCH3), cis-(Cl, OCH3)-[RuCl(OCH3)(NO)(terpy)]PF6 ([2]PF6), trans-(NO, OC2H5), cis-(Cl, OC2H5)-[RuCl(OC2H5)(NO)(terpy)]PF6 ([3]PF6), and [RuCl(OC3H7)(NO)(terpy)]PF6 ([4]PF6) were synthesized by reactions of trans-(Cl, Cl), cis-(NO, Cl)-[RuCl2(NO)(terpy)]PF6 ([1]PF6) with NaOCH3 in CH3OH, C2H5OH, and C3H7OH, respectively. Reactions of [3]PF6 with an acid such as hydrochloric acid and trifluoromethansulforic acid afford nitrosyl complexes in which the alkoxo ligand is substituted. The geometrical isomer of [1]PF6, trans-(NO, Cl), cis-(Cl, Cl)-[RuCl2(NO)(terpy)]PF6 ([5]PF6), was obtained by the reaction of [3]PF6 in a hydrochloric acid solution. Reaction of [3]PF6 with trifluoromethansulforic acid in CH3CN gave trans-(NO, Cl), cis-(CH3CN, Cl)-[RuCl(CH3CN)(NO)(terpy)](2+) ([6](2+)) under refluxing conditions. The structures of [3]PF6, [4]PF6 center dot CH3CN, [5]CF3SO3, and [6](PF6)(2) were determined by X-ray crystallograpy.

Three phenols with pendant, hydrogen-bonded bases (HOAr-B) have been oxidized in MeCN with various one-electron oxidants. The bases are a primary amine (-CPh2NH2), an imidazole, and a pyridine. The product of chemical and quasi-reversible electrochemical oxidations in each case is the phenoxyl radical in which the phenolic proton has transferred to the base, (OAr)-O-center dot-BH+, a proton-coupled electron transfer (PCET) process. The redox potentials for these oxidations are lower than for other phenols, predominately from the driving force for proton movement. One-electron oxidation of the phenols occurs by a concerted proton-electron transfer ( CPET) mechanism, based on thermochemical arguments, isotope effects, and Delta Delta G(double dagger)/Delta Delta G degrees. The data rule out stepwise paths involving initial electron transfer to form the phenol radical cations [center dot+HOAr-B] or initial proton transfer to give the zwitterions [-OAr-BH+]. The rate constant for heterogeneous electron transfer from HOAr-NH2 to a platinum electrode has been derived from electrochemical measurements. For oxidations of HOAr-NH2, the dependence of the solution rate constants on driving force, on temperature, and on the nature of the oxidant, and the correspondence between the homogeneous and heterogeneous rate constants, are all consistent with the application of adiabatic Marcus theory. The CPET reorganization energies, lambda = 23-56 kcal mol(-1), are large in comparison with those for electron transfer reactions of aromatic compounds. The reactions are not highly non-adiabatic, based on minimum values of H-rp derived from the temperature dependence of the rate constants. These are among the first detailed analyses of CPET reactions where the proton and electron move to different sites.

Dinuclear tris(acetylacetonato)ruthenium(III) complexes bridged by one sulfur atom (1) or two sulfur atoms (2) at the gamma-position of the acetylacetonate have been synthesized by the reactions of tris(acetylacetonato)ruthenium(III) With SCl2 or S2O2. The molecular structure of 2 has been determined by single crystal X-ray diffraction study. The cyclic voltammograms of both the dinuclear complexes exhibit two one-electron reduction waves in acetonitrile (AN), dichloromethane (DM), benzonitrile (BN), and N,N-dimethylformamide (DMF). While the complex 1 exhibited two one-electron oxidation waves in AN, DM, and BN, complex 2 showed only irreversible waves in all the solvents. The comproportionation constants (K-c) for mixed-valence states of both Ru-II/Ru-III. and Ru-III/Ru-IV were calculated from the redox potentials of dinuclear complexes, The values of log,, K, (Ru-II/Ru-III.) (for complexes I and 2) and log(10)K(c) (Ru-III/Ru-IV) (for complex 1) were between 1.35 and 3.55. These values are not so large and hence, the complexes may be classified as class 11 in the Robin and Day classification. Although no relationship could be found between K, and the dielectric constant of the solvent, there exists a correlation between donor number (DN) of the solvent and log, 0 K, values. (C) 2004 Elsevier B.V. All rights reserved.

cis-[Ru(NO)Cl(pyca)(2)] (pyca = 2-pyridinecarboxylato), in which the two pyridyl nitrogen atoms of the two pyca ligands coordinate at the trans position to each other and the two carboxylic oxygen atoms at the trans position to the nitrosyl ligand and the chloro ligand, respectively (type I shown as in Chart 1), reacted with NaOCH3 to generate cis-[Ru(NO)(OCH3)(pyca)(2)] (type I). The geometry of this complex was confirmed to be the same as the starting complex by X-ray crystallography: C13.5H13N3O6.5Ru; monoclinic, P2(1)/n; a = 8.120(1), b = 16.650(1), c = 11.510(1) Angstrom; beta = 99.07(1)degrees; V = 1536.7(2) Angstrom(3); Z = 4. The cis-trans geometrical change reaction occurred in the reactions of cis-[Ru(NO)(OCH3)(pyca)(2)] (type I) in water and alcohol (ROH, R = CH3, C2H5) to form [{trans-Ru-(NO)(pyca)(2)}(2)(H3O2)](+) (type V) and trans-[Ru(NO)(OR)(pyca)(2)] (type V). The reactions of the trans-form complexes, trans-[Ru(NO)(H2O)(pyca)(2)](+) (type V) and trans-[Ru(NO)(OCH3)(pyca)(2)] (type V), with Cl- in hydrochloric acid solution afforded the cis-form complex, cis-[Ru(NO)Cl(pyca)(2)] (type I). The favorable geometry of [Ru(NO)X(pyca)(2)](n+) depended on the nature of the coexisting ligand X. This conclusion was confirmed by theoretical, synthetic, and structural studies. The mono-pyca-containing nitrosylruthenium complex (C2H5)(4)N[Ru(NO)Cl(3)pyca)] was synthesized by the reaction of [Ru(NO)Cl-5](2-) with Hpyca and characterized by X-ray structural analysis: C14H24N3O3Cl3Ru; triclinic, P (1) over bar, a = 7.631 (1), b = 9.669(1), c = 13.627(1) Angstrom; alpha = 83.05(2), beta = 82.23(1), gamma = 81.94(1)degrees; V = 981.1(1) Angstrom(3); Z = 2. The type II complex of cis-[Ru(NO)Cl(pyca)(2)] was synthesized by the reaction of [Ru(NO)Cl-3(pyca)(2)](-) or [Ru(NO)CI5]2- with Hpyca and isolated by column chromatography. The structure was determined by X-ray structural analysis: C12H8N3O5ClRu; monoclinic, P2(1)/n; a = 10.010(1), b = 13.280(1), c = 11.335(1) Angstrom; beta = 113.45(1)degrees; V = 1382.4(2) Angstrom(3); Z = 4.

The reaction of cis-[Ru(NO)(CH3CN)(bPY)(2)](3+) (bpy = 2,2'-bipyridine) in H2O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH3)(bPY)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH3)(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH3CN-H2O solution of cis-[Ru(NO)(NH=C(O)CH3)(bPY)(2)](PF6)(3) has been performed: C22H20.5N6O2P2.5F15Ru, orthorhombic, Pccn, a = 15.966(1) Angstrom, b = 31.839(1) Angstrom, c = 11.707(1) Angstrom, V = 5950.8(4) Angstrom(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH3)(bpy)(2)(2+) and cis-[Ru(NO)(NH=C(OH)CH3)(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH0.5)CH3)-(bpy)(2)](PF6)(2.5). The reaction of cis-[Ru(NO)(CH3CN)(bPY)2]3+ in dry CH3OH-CH3CN at room temperature afforded a nitrosyl ruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH3)CH3)-(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C25H29N8O18Cl3Ru, monoclinic, P2(1)/c, a = 13.129(1) Angstrom, b = 17.053(1) Angstrom, c = 15.711 (1) Angstrom, beta = 90.876(5)degrees, V = 3517.3(4) Angstrom(3), and Z = 4.

cis-[Ru(NO)Cl(pyca)(2)] (pyca = 2-pyridinecarboxylate) ([1]), reacts with nucleophiles such as OH- and N-3(-) in H2O to generate the dimeric nitrosylruthenium complex, [{Ru(NO)(pyca)(2)}(2)(mu-H3O2)]PF6.2H(2)O([2]PF6.2H(2)O). The bridging unit of [2]PF6 is a hydroxide hydrate anion (H3O2-) composed of a hydroxo and an aqua moiety. Coordinated to each of the ruthenium centers are two pyca ligands in the trans-form with the pyridyl nitrogen atoms and the carboxylic oxygen atoms being at the trans position to each other (trans-form; trans(N,N), trans(O,O)-configuration). [2]PF6 has also been isolated by the reaction of [1] with N-3(-) in H2O. The reaction of [1] with CH3O- in CH3OH gives the transform nitrosylruthenium complex, trans-[Ru(NO)(OCH3)(pyca)(2)].CH3OH (trans(N,N), trans(O,O)-configuration) ([3].CH3OH). The rare cis- trans isomerizations have thus occurred during the reaction between [1] (cis-form; trans(N,N), cis(O,O)-configuration)and OH-, N-3(-) or CH3O-.

The ligands bis[3-(X-2-hydroxybenzylideneamino)phenyl] sulfones (X = none: BHBAPS, X = 3-tert-butyl: BH(t-Bu)BAPS and X = 3,5-dichloro: BHCl(2)BAPS) were prepared. These, together with Cu(OAc)(2) were used in the syntheses of the dinuclear copper complexes Cu-2(BBAPS)(mu -OMe)(2) (1), Cu-2[B(t-Bu)BAPS] (mu -OH)(2) (2), and Cu-2[BCl(2)BAPS] (mu -OMe)(2) (3). Complex 1 was crystallographically characterized. The structures of 2 and 3 are similar to 1 by comparison of IR, UV-Vis, FAB-MS and elemental analyses results. Complexes 1-3 (1 mol%) were used in the oxidation of 2,4- and 2,6-di-t-butylphenol (dtbp) at -50 degreesC with H2O2. The results show that (1) the coupling products are preferred when CH2Cl2 is used; and (2) the quinone yield increases when THF is utilized. In CH2Cl2 with 2,4-dtbp, the yield of the coupling product based on the complex amount, is in the order 2, 1, and 3 with yields of 6300, 4700 and 200%, respectively, Low temperature UV-Vis results of the reaction of 1 with H2O2 showed the growth of peaks at 390 and 580 nm indicative of a mu-eta (2):eta (2)-peroxo or mu-eta (1):eta (1)-hydroperoxo intermediate. At -50 degreesC, this spectrum does not change. But when warmed to 0 degreesC, a spectrum similar to the original spectrum was obtained. This probably indicates hydrogen radical abstractions of the peroxo intermediate from solvents, and if excess H2O2 is present, the peroxo intermediate may again be formed. This reusability of the complex explains the high yield using 1 and 2. (C) 2001 Elsevier Science B.V. All rights reserved.

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)(2)](n+) (bpy = 2,2'-bipyridine, py = pyridine; X = O, Y = NO2 for n = 0, and Y = py for n = 1; X = S, Y = NO2 for n = 0, Y = NO for n = 2, and Y = py for n = 1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO2)(bpy)(py)(2)] and [Ru(NCO)(bpy)(py)(3)](+), react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH3)(bpy)(py)(2)](3+). The molecular structures of [Ru(NCO)(bpy)(py)(3)]ClO4, [Ru(NCS)(NO)(bpy)(py)(2)](PF6)(2) and [Ru(NO)(NH3)(bpy)(py)(2)](PF6)(3) were determined by X-ray crystallography. (C) 2001 Elsevier Science B.V. All rights reserved.

The complex [Mn-2(BPMAPS)(mu -OAc)(2)(hemi)]PF6 (1), where hemi is the hemiacetal group, methoxy(2-pyridyl)methoxo, was prepared from bis[3-(2-pyridylmethyleneamino)phenyl] sulfone (BPMAPS), 2-pyridinecarbaldehyde. and manganese(II) acetate in methanol. The complexes Mn-2(BPMAPS)(mu -OAc)(2)(mu -1,1-OAc)(eta (1)-OAc) (2) and Co-2(BPMAPS)(mu -OAc)(2)-[mu-(eta (2):eta (1))OAc](eta (1)-OAc) (3) were prepared from manganese(II) acetate and cobalt(IT) acetate, respectively, with BPMAPS in methanol. All three complexes were characterized by elemental analysis, FT-IR, MS, UV-Vis spectroscopy, and X-ray crystallography. The manganese ions of complex 1 are bridged by a hemiacetal through the oxygen atom of the alkoxo with the nitrogen atom of the pyridine group coordinating to one of the manganese atoms. The metal ions of complexes 2 and 3 are bridged by acetato groups in mu -1,1 or mu-eta (2):eta (1) modes, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.

Degradation sequences of cis-[Ru(NO.)X(bpy)(2)](n+) (X = ONO2, OCHO, OCOMe, NO2, Cl for n = 1; X = CH3CN, H2O for n = 2) ({RuNO}(7)-type), a one-electron reduction species of {RuNO}(6)-type complexes, were investigated in CH3CN by monitoring using electrochemical techniques (both cyclic and hydrodynamic voltammetries). The results show that an oxygen transfer occurs effectively at the nitrosyl site of cis-[Ru(NO.)X(bpy)(2)](n+) (X = ONO2 for n = 1, X = CH3CN, H2O for n = 2) to give identical nitro species, cis-[Ru(NO2)(CH3CN)(bpy)(2)](+). The extent that the nitrosyl-to-nitro conversion proceeded, however, differs depending on the X ligands; X = CH3CN and H2O complexes gave the nitro species in almost 40% yield, while X = ONO2 complex afforded nearly 80%. The monitoring results of the degradation sequences, along with the differences in yields, suggest that different processes are operating separately in the oxygen-transfer reaction. We propose some possible processes for both reactions, although a further investigation is needed for a detailed explanation.

The crystal structure and the electrochemical behavior of a Ru-complex, which was obtained from a reaction of [Ru-2(MeCOO)(4)Cl] with 2-pyridinecarboxylic acid and NO2-, were investigated: the complex consists of nitrosyl, 2-pyridinecarboxylato, and acetato ligands. The cyclic voltammogram showed no redox wave in the region of the potential window, unlike common Ru(NO)-complexes.

The reaction between cis-[Ru(NO)(H2O)(bpy)(2)](3+) ({RuNO}(6)) and formic acid gives [{Ru(mu-NO)}(2)(bpy)(4)](2+) (2) ({RuNO}(8)-{RuNO}(8)), along with some other products species: cis-[Ru(NO)(OCHO)(bpy)(2)](2+) (1)({RuNO}(6)), and cis-[Ru(OCHO)(H2O)(bpy)(2)](+). The mu-nitrosyl complex (2) consists of two cis-Ru(bpy)(2) fragments connected by two formally negatively charged bridging nitrosyl ligands. Electrochemical study of the complex shows that two successive one-electron oxidation waves to give [{Ru(mu-NO)}(2)(bpy)(4)](4+) ({RuNO}(7)-{RuNO}(7)) are found. The generated two-electron oxidation species is disintegrated to afford a one-electron reduction species, cis- [Ru(NO.)(CH3CN)(bpy)(2)](2+) ({RuNO}(7)), along with a small amount of an unexpected nitro species, cis-[Ru(NO2)(CH3CN)(bpy)(2)](+). The characteristics of electrochemically generated one-electron reduction species cis-[Ru(NO.)X(bpy)(2)]((n-1)+) ({RuNO}(7)) (X = H2O, OCHO) are investigated in the connection. During the degradation process of the one-electron reduction species, a nitrosyl-to-nitro conversion was found to proceed in cis-[Ru(NO.)(H2O)(bpy)(2)](2+), via the formation of cis-[Ru(NO.)(CH3CN)(bpy)(2)](2+) mentioned above; this is the first observation which explains the electrochemically-induced nitrosyl-to-nitro conversion observed in the reduction process of {RuNO}(6)-type complexes.

The reaction between cis-[Ru(NO)(CH3CN)(bpy)(2)](3+) and a free NO2- gives an appreciable amount of the nitro species cis-[Ru(NO2)(CH3CN)(bpy)(2)](+). Although definitive evidence for the mechanistic illustration of the nitrosyl-to-nitro conversion is still unavailable, an oxide abstraction from NO2- to the nitrosyl ligand appears to be the key reaction. In addition, cis-[Ru(NO)(CH3C(O)NH)(bpy)(2)](2+) having an acetamide ligand is formed during the reaction. The structure of the complex, used as a starting material of the present reaction, was determined by single-crystal X-ray diffraction methods; for cis-[Ru(NO)(CH3CN)(bpy)(2)](ClO4)(3). CH3CN: FW = 823.91, monoclinic, P2(1)/n, a = 12.471(3), b = 15.041(7), c = 17.598(4) Angstrom, beta = 94.65(2)degrees, V = 3289(1) Angstrom(3), Z = 4, R = 0.081, R-w = 0.050. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis of the title complex was accomplished. The structure involving a four-membered cyclic unit with negatively charged NO moieties could be established by C-13 NMR measurements. Its electrochemical behavior was compared with that of [{Ru(mu(2)-NO)}(2)(acac)(4)], which has the same cyclic unit, but with neutral charge on NO(. )moieties. ( )

The title complex, which has two cis-{Ru(acac)(2)} fragments connected doubly by mu-N(O) bridges, undergoes both a one-electron reversible and a second one-electron irreversible reduction, in addition to a one-step, two-electron irreversible oxidation. In the oxidation process, the binuclear structure is disintegrated to give two moles of cis-[Ru(NO)(CH3CN)(acac)(2)](+) from one mole of the title complex. (C) 1998 Elsevier Science S.A.

The electrochemical behavior of several complexes with the general formula [M(NO)Cl5-2n(acac)(n)](m) (M=Ru, Os; n=1, 2; acac=acetylacetonato) was investigated: mer-[Ru(NO)Cl-3(acac)](-)(1, n=1), cis-[Ru(NO)Cl(acac)(2)] (2, n=2), mer-[Os(NO)Cl-3(acac)](-) (3, n=1), cis-[Os(NO)CI(acac)(2)] (4, n=2). The study includes the known corresponding n=0 complexes, [M(NO)Cl-5](2-) (M=Ru, Os), for comparison. All these complexes undergo a one-electron oxidation, which is rather unusual redox behavior in the {MNO}(6)-type nitrosyl complexes. The behavior of some of these complexes as electrophiles was also described. Molecular structures with a meridional configuration were established for the n=1 complexes ([Ru(NO)Cl-3(acac)](-) (1) and [Os(NO)Cl-3(acac)](-) (3)) by X-ray structure determinations. Crystal data for 1 (Bu4N salt): C21H43N2O3Cl3Ru, a=31.443(9), b=21.86(1), c=19.852(6) Angstrom, beta=119.65(2)degrees, monoclinic, C2/c, Z=16. Crystal data for 3 (Cs salt): C5H7NO3Cl3OsCs, a=7.942(1), b=12.602(2), c=7.451(2) Angstrom, alpha=105.91(2), beta=98.20(2), gamma=90.31(1)degrees, triclinic, P (1) over bar, Z=2.

A facile redox-induced nitrito-to-nitro isomerization occurs in cis-[Ru(NO)(ONO)(bpy)(2)](2+) ({RuNO}(6)-type nitrosyl, bpy=2,2'-bipyridine). At room temperature, the one-electron reduction species (cis-[Ru(NO .)(ONO)(bpy)(2)](+)({RuNO}(7))) changes immediately to cis-[Ru(NO .)(NO2)(bpy)(2)](+) ({RuNO}(7)), which can be converted to cis-[Ru(NO)(NO2)(bpy)(2)](2+) ({RuNO}(6)) by one-electron oxidation. The nitro species is an isomeric twin of the original nitrito species. A mechanistic investigation has established that, during the nitrito-nitro redox-induced rearrangement, an oxygen-atom transfer reaction proceeded between the nitrosyl and the adjacent nitrite Ligands. Such a behavior could not be found in the thermally-induced nitrito-nitro rearrangement of the {RuNO}(6)-type nitrosyl complex mentioned above. The {RuNO}(7)-type nitrosyl complex appears to behave as a key intermediate species of the oxygen-atom transfer reaction.