Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O 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)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(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 CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

Oxidation of ammonia in osmium polypyridyl complexes

The oxidations of cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6), cis-[OsII(bpy)2(Cl)(NH3)](PF6), and [OsII(typ)(bpy)(NH3)](PF6)2 have been studied by cyclic voltammetry and by controlled-potential electrolysis. In acetonitrile or in acidic, aqueous solution, oxidation is metal-based and reversible, but as the pH is increased, oxidation and proton loss from coordinated ammonia occurs. cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6) are oxidized by four electrons to give the corresponding OsVI nitrido complexes, [OSVI(typ)(Cl)2(N)]+. Oxidation of [Os(typ)(bpy)(NH3)](PF6)2 occurs by six electrons to give [Os(tpy)(bpy)(NO)](PF6)3. Oxidation of cis-[OsII(bpy)2(Cl)(NH3)](PF6) at pH 9.0 gives cis-[OsII(bpy)2(Cl)(NO)](PF6)2 and the mixed-valence form of the mu-N2 dimer [cis-[Os(bpy)2(Cl)2[mu-N2)](PF6)3. With NH4+ added to the electrolyte, cis-[OsII(bpy)2(Cl)(N2)](PF6) is a coproduct. The results of pH-dependent cyclic voltammetry measurements suggest OsIV as a common intermediate in the oxidation of coordinated ammonia. For cis- and trans-[OsIII(tpy)(Cl)2(NH3)]+, OsIV is a discernible intermediate. It undergoes further pH-dependent oxidation to [OsVI(tpy)(Cl)2(N)]+. For [OsII(tpy)(bpy)(NH3)]2+, oxidation to OsIV is followed by hydration at the nitrogen atom and further oxidation to nitrosyl. For cis-[OsII(bpy)2(Cl)-(NH3)]+, oxidation to OsIV is followed by N-N coupling and further oxidation to [cis-[Os(bpy)2(Cl)2(mu-N2)]3+. At pH 9, N-N coupling is competitive with capture of OsIV by OH- and further oxidation, yielding cis-[OsII(bpy)2(Cl)(NO)]2+.     

cis-Bis(bipyridine)ruthenium Imidazole Derivatives: A Spectroscopic, Kinetic, and Structural Study

The ruthenium bis(bipyridine) complexes cis-[Ru(bpy)(2)Im(OH(2))](2+), cis-[Ru(bpy)(2)(Im)(2)](2+), cis-[Ru(bpy)(2)(N-Im)(2)](2+), cis-[Ru(dmbpy)(2)Im(OH(2))](2+), cis-[Ru(dmbpy)(2)(N-Im)(OH(2))](2+)(bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, Im = imidazole, N-Im = N-methylimidazole), have been synthesized under ambient conditions in aqueous solution (pH 7). Their electrochemical and spectroscopic properties, absorption, emission, and lifetimes were determined and compared. The substitution kinetics of the cis-[Ru(bpy)(2)Im(OH(2))](2+) complexes show slower rates and have lower affinities for imidazole ligands than the corresponding cis-[Ru(NH(3))(4)Im(OH(2))](2+) complexes. The crystal structures of the monoclinic cis-[Ru(bpy)(2)(Im)(2)](BF(4))(2), space group = P2(1)/a, Z = 4, a = 11.344(1) ?, b = 17.499(3) ?, c = 15.114(3) ?, and beta = 100.17(1) degrees, and triclinic cis-[Ru(bpy)(2)(N-Im)(H(2)O)](CF(3)COO)(2).H(2)O, space group = P&onemacr;, Z = 2, a = 10.432(4) ?, b = 11.995(3) ?, c = 13.912(5) ?, alpha = 87.03(3) degrees, beta = 70.28(3) degrees, and gamma = 71.57(2) degrees, complexes show that these molecules crystallize as complexes of octahedral Ru(II) to two bidentate bipyridine ligands with two imidazole ligands or a water and an N-methylimidazole ligand cis to each other. The importance of these molecules is associated with their frequent use in the modification of proteins at histidine residues and in comparisons of the modified protein derivatives with these small molecule analogs.     

Nitric oxide production by visible light irradiation of aqueous solution of nitrosyl ruthenium complexes

[Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](PF(6))(5) (L is NH(3), py, or 4-acpy) was prepared with good yields in a straightforward way by mixing an equimolar ratio of cis-[Ru(NO(2))(bpy)(2)(NO)](PF(6))(2), sodium azide (NaN(3)), and trans-[RuL(NH(3))(4)(pz)] (PF(6))(2) in acetone. These binuclear compounds display nu(NO) at ca. 1945 cm(-)(1), indicating that the nitrosyl group exhibits a sufficiently high degree of nitrosonium ion (NO(+)). The electronic spectrum of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex in aqueous solution displays the bands in the ultraviolet and visible regions typical of intraligand and metal-to-ligand charge transfers, respectively. Cyclic voltammograms of the binuclear complexes in acetonitrile give evidence of three one-electron redox processes consisting of one oxidation due to the Ru(2+/3+) redox couple and two reductions concerning the nitrosyl ligand. Flash photolysis of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex is capable of releasing nitric oxide (NO) upon irradiation at 355 and 532 nm. NO production was detected and quantified by an amperometric technique with a selective electrode (NOmeter). The irradiation at 532 nm leads to NO release as a consequence of a photoinduced electron transfer. All species exhibit similar photochemical behavior, a feature that makes their study extremely important for their future application in the upgrade of photodynamic therapy in living organisms.     

The synthesis and structure of heteroleptic tris(diimine)ruthenium(II) complexes

The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.     

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO(2))L(bpy)(2)](+) complex

The synthesis of [Ru(NO(2))L(bpy)(2)](+) (bpy = 2,2'-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)(2)](PF(6))(3) to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO(2))L(bpy)(2)](+) in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS(+) and spectroelectrochemical experiment where cis-[Ru(bpy)(2)L(H(2)O)](2+) was obtained as a product of the reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 mumol L(-1) phenylephrine responded with relaxation in the presence of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The potential of rat aorta cells to metabolize cis-[Ru(II)(NO(2))L(bpy)(2)](+) was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+) inside the cell. The maximum vasorelaxation was achieved with 1 x 10(-5) mol L(-1) of cis-[Ru(II)(NO(2))L(bpy)(2)](+) complex.     

Coordination of 9-ethylguanine to the mixed-ligand compound alpha-[Ru(azpy)(bpy)Cl2] (azpy = 2-phenylazopyridine and bpy = 2,2'-bipyridine). An unprecedented ligand positional shift, correlated to the cytotoxicity of this type of [RuL2Cl2] (with L = azpy or bpy) complex

The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance.     

Surprising photochemical reactivity and visible light-driven energy transfer in heterodimetallic complexes

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been used for the synthesis of a series of novel heterodimetallic complexes starting from [Ru(bpy)(2)(dppcb)]X(2) (1; X = PF(6), SbF(6)), so-called dyads, showing surprising photochemical reactivity. They consist of [Ru(bpy)(2)](2+)"antenna" sites absorbing light combined with reactive square-planar metal centres. Thus, irradiating [Ru(bpy)(2)(dppcb)MCl(2)]X(2) (M = Pt, 2; Pd, 3; X = PF(6), SbF(6)) dissolved in CH(3)CN with visible light, produces the unique heterodimetallic compounds [Ru(bpy)(CH(3)CN)(2)(dppcb)MCl(2)]X(2) (M = Pt, 7; Pd, 8; X = PF(6), SbF(6)). In an analogous reaction the separable diastereoisomers (ΔΛ/ΛΔ)- and (ΔΔ/ΛΛ)-[Ru(bpy)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (5/6) lead to [Ru(bpy)(CH(3)CN)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (9), where only the RuP(2)N(4) moiety of 5/6 is photochemically reactive. By contrast, in the case of [Ru(bpy)(2)(dppcb)NiCl(2)]X(2) (4; X = PF(6), SbF(6)) no clean photoreaction is observed. Interestingly, this difference in photochemical behaviour is completely in line with the related photophysical parameters, where 2, 3, and 5/6, but not 4, show long-lived excited states at ambient temperature necessary for this type of photoreaction. Furthermore, the photochemical as well as the photophysical properties of 2-4 are also in accordance with their single crystal X-ray structures presented in this work. It seems likely that differences in "steric pressure" play a major role for these properties. The unique complexes 7-9 are also fully characterized by single-crystal X-ray structure analyses, clearly showing that the stretching vibration modes of the ligand CH(3)CN, present only in 7-9, cannot be directly influenced by "steric pressure". This has dramatic consequences for their photophysical parameters. The trans-[Ru(bpy)(CH(3)CN)(2)](2+) chromophore of 9 acts as efficient "antenna" for visible light-driven energy transfer to the Os-centred "trap" site, resulting in k(en) ≥ 2 × 10(9) s(-1) for the energy transfer. Since electron transfer is made possible by the use of this intervening energy transfer, in dyads like 2-4 highly reactive M(0) species (M = Pt, Pd, Ni) could be generated. These species are not stable in water and M(II) hydride intermediates are usually formed, further reacting with H(+) to give H(2). Thus, derivatives of 3, namely [M(bpy)(2)(dppcb)Pd(bpy)](PF(6))(4) (M = Os, Ru) dissolved in 1:1 (v/v) H(2)O-CH(3)CN produce H(2) during photolysis with visible light.     

9-Oxidophenalenone: a noninnocent β-diketonate ligand?

The redox systems [Ru(L)(bpy)(2)](k), [Ru(L)(2)(bpy)](m), and [Ru(L)(3)](n) containing the potentially redox-active ligand 9-oxidophenalenone = L(-) were investigated by spectroelectrochemistry (UV-vis-near-IR and electron paramagnetic resonance) in conjunction with density functional theory (DFT) calculations. Compounds [Ru(L(-))(bpy)(2)]ClO(4) ([1]ClO(4)) and [Ru(L(-))(2)(bpy)]ClO(4) ([2]ClO(4)) were structurally characterized. In addition to establishing electron-transfer processes involving the Ru(II)/Ru(III)/Ru(IV) and bpy(0)/bpy(?-) couples, evidence for the noninnocent behavior of L(-) was obtained from [Ru(IV)(L(?))(L(-))(bpy)](3+), which exhibits strong near-IR absorption due to ligand-to-ligand charge transfer. In contrast, the lability of the electrogenerated anion [Ru(L)(2)(bpy)](-) is attributed to a resonance situation [Ru(II)(L(?2-))(L(-))(bpy)](-)/[Ru(II)(L(-))(2) (bpy(?-))](-), as suggested by DFT calculations.     

Investigation of the electronic, photosubstitution, redox, and surface properties of new ruthenium(II)-containing amphiphiles

A series of pyridine- and phenol-based ruthenium(II)-containing amphiphiles with bidentate ligands of the following types are reported: [(L(PyI))Ru(II)(bpy)(2)](PF(6))(2) (1), [(L(PyA))Ru(II)(bpy)(2)](PF(6))(2) (2), [(L(PhBuI))Ru(II)(bpy)(2)](PF(6)) (3), and [(L(PhClI))Ru(II)(bpy)(2)](PF(6)) (4). Species 1 and 2 are obtained by treatment of [Ru(bpy)(2)Cl(2)] with the ligands L(PyI) (N-(pyridine-2-ylmethylene)octadecan-1-amine) and L(PyA) (N-(pyridine-2-ylmethyl)octadecan-1-amine). The imine species 3 and 4 are synthesized by reaction of [Ru(bpy)(2)(CF(3)SO(3))(2)] with the amine ligands HL(PhBuA) (2,4-di-tert-butyl-6-((octadecylamino)methyl)phenol), and HL(PhClA) (2,4-dichloro-6-((octadecylamino)methyl)phenol). Compounds 1-4 are characterized by means of electrospray ionization (ESI(+)) mass spectrometry, elemental analyses, as well as electrochemical methods, infrared and UV-visible absorption and emission spectroscopies. The cyclic voltammograms (CVs) of 1-2 are marked by two successive processes around -1.78 and -2.27 V versus Fc(+)/Fc attributed to bipyridine reduction. A further ligand-centered reductive process is seen for 1. The Ru(II)/Ru(III) couple appears at 0.93 V versus Fc(+)/Fc. The phenolato-containing 3 and 4 species present relatively lower reduction potentials and more reversible redox behavior, along with Ru(II/III) and phenolate/phenoxyl oxidations. The interpretation of observed redox behavior is supported by density functional theory (DFT) calculations. Complexes 1-4 are surface-active as characterized by compression isotherms and Brewster angle microscopy. Species 1 and 2 show collapse pressures of about 29-32 mN·m(-1), and are strong candidates for the formation of redox-responsive monolayer films.     

Amidation of unfunctionalized hydrocarbons catalyzed by ruthenium cyclic amine or bipyridine complexes

Selective amidation of simple hydrocarbons with pre-isolated and in-situ formed iminoiodanes catalyzed by ruthenium complexes [Ru(III)(Me(3)tacn)(CF(3)CO(2))(3).H(2)O] (2b, Me(3)tacn = N,N', N"-trimethyl-1,4,7-triazacyclononane) and cis-[Ru(II)(6, 6'-Cl(2)bpy)(2)Cl(2)] (3, 6,6'-Cl(2)bpy = 6,6'-dichloro-2, 2'-bipyridine) was investigated. With PhI=NTs as nitrogen source, both catalysts efficiently promote the amidation of adamantane, cyclohexene, ethylbenzene, cumene, indan, tetralin, and diphenylmethane to afford N-substituted sulfonamides in 80-93% yields with high selectivity. Competitive amidations of para-substituted ethylbenzenes and kinetic isotope effect for the amidation of cyclohexene/cyclohexene-d(10) suggest that the amidation processes probably proceed via the hydrogen abstraction by a reactive Ru=NTs species to form a carboradical intermediate. The amidation with PhI(OAc)(2)/TsNH(2) gave results comparable to those obtained with PhI=NTs. Extension of the "PhI(OAc)(2)/TsNH(2) + catalyst 2b or 3" protocol to MeSO(2)NH(2) and PhCONH(2) with ethylbenzene as substrate produced the corresponding N-substituted amides in up to 89% yield.     

Dinitrogen formation by oxidative intramolecular N---N coupling in cis,cis-[(bpy)2(NH3)RuORu(NH3)(bpy)2]4+

The (15)N-labeled diammine(mu-oxo)ruthenium complex cis,cis-[(bpy)(2)(H(3)(15)N)Ru(III)ORu(III)((15)NH(3))(bpy)(2)](4+) ((2-(15)N)(4+)) was synthesized from cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(H(2)O)(bpy)(2)](4+) by using ((15)NH(4))(2)SO(4) and isolated as its perchlorate salt in 17% yield. A 1:1 mixture of (2-(15)N)(4+) and nonlabeled cis,cis-[(bpy)(2)(H(3)(14)N)Ru(III)ORu(III)((14)NH(3))(bpy)(2)](4+) were electrochemically oxidized in aqueous solution. The gaseous products (14)N(2) and (15)N(2) were formed in equimolar amounts with only a small amount of (14)N(15)N detected. This demonstrates that dinitrogen formation by oxidation of the diammine complex proceeds by intramolecular N---N coupling.     

Synthesis of mononuclear and dinuclear ruthenium(II) tris(heteroleptic) complexes via photosubstitution in bis(carbonyl) precursors

A novel, and quite general, approach for the preparation of tris(heteroleptic) ruthenium(II) complexes is reported. Using this method, which is based on photosubstitution of carbonyl ligands in precursors such as [Ru(bpy)(CO)(2)Cl(2)] and [Ru(bpy)(Me(2)bpy)(CO)(2)](PF(6))(2), mononuclear and dinuclear Ru(II) tris(heteroleptic) polypyridyl complexes containing the bridging ligands 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) and 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (Hbpzt) have been prepared. The complexes obtained were purified by column chromatography and characterized by HPLC, mass spectrometry, 1H NMR, absorption and emission spectroscopy and by electrochemical methods. The X-ray structures of the compounds [Ru(bpy)(Me(2)bpy)(bpt)](PF(6))x0.5C(4)H(10)O [1x0.5C(4)H(10)O], [Ru(bpy)(Me(2)bpy)(bpzt)](PF(6))xH(2)O (2xH(2)O) and [Ru(bpy)(Me(2)bpy)(CH(3)CN)(2)](PF(6))(2)xC(4)H(10)O (6xC(4)H(10)O) are reported. The synthesis and characterisation of the dinuclear analogues of 1 and 2, [{Ru(bpy)(Me(2)bpy)}(2)bpt](PF(6))(3)x2H(2)O (3) and [{Ru(bpy)(Me(2)bpy)}(2)bpzt](PF(6))(3) (4), are also described.     

Synthesis, structure and spectral and redox properties of new mixed ligand monomeric and dimeric Ru(II) complexes: predominant formation of the "cis-alpha" diastereoisomer and unusual 3MC emission by dimeric complexes

The tetradentate ligands 1,8-bis(pyrid-2-yl)-3,6-dithiaoctane (pdto) and 1,8-bis(benzimidazol-2-yl)-3,6-dithiaoctane (bbdo) form the complexes [Ru(pdto)(mu-Cl)](2)(ClO(4))(2) 1 and [Ru(bbdo)(mu-Cl)](2)(ClO(4))(2) 2 respectively. The new di-mu-chloro dimers 1 and 2 undergo facile symmetrical bridge cleavage reactions with the diimine ligands 2,2'-bipyridine (bpy) and dipyridylamine (dpa) to form the six-coordinate complexes [Ru(pdto)(bpy)](ClO(4))(2) 3, [Ru(bbdo)(bpy)](ClO(4))(2) 4, [Ru(pdto)(dpa)](ClO(4))(2) 5 and [Ru(bbdo)(dpa)](ClO(4))(2) 6 and with the triimine ligand 2,2':6,2'-terpyridine (terpy) to form the unusual seven-coordinate complexes [Ru(pdto)(terpy)](ClO(4))(2) 7 and [Ru(bbdo)(terpy)](ClO(4))(2) 8. In 1 the dimeric cation [Ru(pdto)(mu-Cl)](2)(2+) is made up of two approximately octahedrally coordinated Ru(II) centers bridged by two chloride ions, which constitute a common edge between the two Ru(II) octahedra. Each ruthenium is coordinated also to two pyridine nitrogen and two thioether sulfur atoms of the tetradentate ligand. The ligand pdto is folded around Ru(II) as a result of the cis-dichloro coordination, which corresponds to a "cis-alpha" configuration [DeltaDelta/LambdaLambda(rac) diastereoisomer] supporting the possibility of some attractive pi-stacking interactions between the parallel py rings at each ruthenium atom. The ruthenium atom in the complex cations 3a and 4 exhibit a distorted octahedral coordination geometry composed of two nitrogen atoms of the bpy and the two thioether sulfur and two py/bzim nitrogen atoms of the pdto/bbdo ligand, which is actually folded around Ru(II) to give a "cis-alpha" isomer. The molecule of complex 5 contains a six-coordinated ruthenium atom chelated by pdto and dpa ligands in the expected distorted octahedral fashion. The (1)H and (13)C NMR spectral data of the complexes throw light on the nature of metal-ligand bonding and the conformations of the chelate rings, which indicates that the dithioether ligands maintain their tendency to fold themselves even in solution. The bis-mu-chloro dimers 1 and 2 show a spin-allowed but Laporte-forbidden t(2g)(6)((1)A(1g))--> t(2g)(5) e(g)(1)((1)T(1g), (1)T(2g)) d-d transition. They also display an intense Ru(II) dpi--> py/bzim (pi*) metal-to-ligand charge transfer (MLCT) transition. The mononuclear complexes 3-8 exhibit dpi-->pi* MLCT transitions in the range 340-450 nm. The binuclear complexes 1 and 2 exhibit a ligand field ((3)MC) luminescence even at room temperature, whereas the mononuclear complexes 3 and 4 show a ligand based radical anion ((3)MLCT) luminescence. The binuclear complexes 1 and 2 undergo two successive oxidation processes corresponding to successive Ru(II)/Ru(III) couples, affording a stable mixed-valence Ru(II)Ru(III) state (K(c): 1, 3.97 x 10(6); 2, 1.10 x 10(6)). The mononuclear complexes 3-7 exhibit only one while 8 shows two quasi-reversible metal-based oxidative processes. The coordinated 'soft' thioether raises the redox potentials significantly by stabilising the 'soft' Ru(II) oxidation state. One or two ligand-based reduction processes were also observed for the mononuclear complexes.     

Self assembled composites of luminescent Ru(II) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4-

The interaction of two luminescent metallopolymers; [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP)co-poly(7)](+), where bpy is 2,2'-bipyridyl, PVP is polyvinylpyridine, and (CAIP)co-poly(7) is poly(styrene(6)-co-p-(aminomethyl)styrene) amide linked to 2-(4-carboxyphenyl)imidazo[4,5-f] [1,10]phenanthroline, with the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-) is described. Both metallopolymers undergo electrostatic association with the polyoxometalate. From both electronic and luminescence spectroscopy the thermodynamic products were determined to be {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) and {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+), i.e. in both instances, the number of ruthenium centres in the cluster exceeds the number required for charge neutralization of the molybdate centre. Association quenches the luminescence of the metallopolymer although, consistent with the excess of Ru(ii) present in the associated composites, emission is not completely extinguished even when a large excess of [Mo(18)O(54)(SO(4))(2)](4-) is present. The observed emission lifetime was not affected by [Mo(18)O(54)(SO(4))(2)](4-) therefore quenching was deemed static. The luminescent intensity data was found to fit best to a (sphere of action) Perrin model from which the radii of the quenching were calculated as 4.6 ? and 5.8 ? for [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP co-poly)(7)](+) respectively. Both UV/Vis and resonance Raman data indicate the presence of a new optical transition centered around 490 nm for the composite, {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). This indicates strong electronic interaction between the metal centres in the former composite, which despite good thermodynamic analogy, is not observed for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). These results are consistent with photoelectrochemical studies of layer by layer assemblies of these films which indicate that the ruthenium centre sensitizes polyoxometalate photo-oxidation of benzyl alcohol in {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not in {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+).     

Three-component self-assembly of a series of triply interlocked Pd12 coordination prisms and their non-interlocked Pd6 analogues

Template-assisted formation of multicomponent Pd(6) coordination prisms and formation of their self-templated triply interlocked Pd(12) analogues in the absence of an external template have been established in a single step through Pd-N/Pd-O coordination. Treatment of cis-[Pd(en)(NO(3))(2)] with K(3) tma and linear pillar 4,4'-bpy (en=ethylenediamine, H(3) tma=benzene-1,3,5-tricarboxylic acid, 4,4'-bpy=4,4'-bipyridine) gave intercalated coordination cage [{Pd(en)}(6)(bpy)(3)(tma)(2)](2)[NO(3)](12) (1) exclusively, whereas the same reaction in the presence of H(3) tma as an aromatic guest gave a H(3) tma-encapsulating non-interlocked discrete Pd(6) molecular prism [{Pd(en)}(6)(bpy)(3)(tma)(2)(H(3)tma)(2)][NO(3)](6) (2). Though the same reaction using cis-[Pd(NO(3))(2)(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO(3))(2)] gave triply interlocked coordination cage [{Pd(pn)}(6)(bpy)(3)(tma)(2)](2)[NO(3)](12) (3) along with non-interlocked Pd(6) analogue [{Pd(pn)}(6)(bpy)(3) (tma)(2)](NO(3))(6) (3'), and the presence of H(3) tma as a guest gave H(3) tma-encapsulating molecular prism [{Pd(pn)}(6)(bpy)(3)(tma)(2)(H(3) tma)(2)][NO(3)](6) (4) exclusively. In solution, the amount of 3' decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4'-bpy gave triply interlocked coordination cage [{Pd(pn)}(6) (pz)(3)(tma)(2)](2)[NO(3)](12) (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO(3))(2)(tmen)] (tmen=N,N,N',N'-tetramethylethylene diamine) instead of cis-[Pd(NO(3))(2)(pn)] gave non-interlocked [{Pd(tmen)}(6)(pz)(3)(tma)(2)][NO(3)](6) (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR ((1)H and (13)C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H(3) tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations.     

Ruthenium(II)-polyazine light absorbers bridged to reactive cis-dichlororhodium(III) centers in a bimetallic molecular architecture

Bimetallic complexes of the form [(bpy)(2)Ru(BL)RhCl(2)(phen)](PF(6))(3), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and BL = 2,3-bis(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm), were synthesized, characterized, and compared to the [{(bpy)(2)Ru(BL)}(2)RhCl(2)](PF(6))(5) trimetallic analogues. The new complexes were synthesized via the building block method, exploiting the known coordination chemistry of Rh(III) polyazine complexes. In contrast to [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) and [{(bpy)(2)Ru(bpm)}(2)RhCl(2)](PF(6))(5), [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) have a single visible light absorber subunit coupled to the cis-Rh(III)Cl(2) moiety, an unexplored molecular architecture. The electrochemistry of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) showed a reversible oxidation at 1.61 V (vs Ag/AgCl) (Ru(III/II)), quasi-reversible reductions at -0.39 V, -0.74, and -0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. The electrochemistry of [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) exhibited a reversible oxidation at 1.76 V (Ru(III/II)). A reversible reduction at -0.14 V (bpm(0/-)), and quasi-reversible reductions at -0.77 and -0.91 V each corresponded to a one electron process, bpm(0/-), Rh(III/II), and Rh(II/I). The dpp bridged bimetallic and trimetallic display Ru(dpi)-->dpp(pi*) metal-to-ligand charge transfer (MLCT) transitions at 509 nm (14,700 M(-1) cm(-1)) and 518 nm (26,100 M(-1) cm(-1)), respectively. The bpm bridged bimetallic and trimetallic display Ru(dpi)-->bpm(pi*) charge transfer (CT) transitions at 581 nm (4,000 M(-1) cm(-1)) and 594 nm (9,900 M(-1) cm(-1)), respectively. The heteronuclear complexes [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) had (3)MLCT emissions that are Ru(dpi)-->dpp(pi*) CT in nature but were red-shifted and lower intensity than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4). The lifetimes of the (3)MLCT state of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) at room temperature (30 ns) was shorter than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4), consistent with favorable electron transfer to Rh(III) to generate a metal-to-metal charge-transfer ((3)MMCT) state. The reported synthetic methods provide means to a new molecular architecture coupling a single Ru light absorber to the Rh(III) center while retaining the interesting cis-Rh(III)Cl(2) moiety.     

Sensitization and stabilization of TiO(2) photoanodes with electropolymerized overlayer films of ruthenium and zinc polypyridyl complexes: a stable aqueous photoelectrochemical cell

Overlayer thin films of vinylbipyridine (vbpy)-containing Ru and Zn complexes have been formed on top of ruthenium dye complexes adsorbed to TiO(2) by reductive electropolymerization. The goal was to create an efficient, water-stable photoelectrode or electrodes. An adsorbed-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Ru(vbpy)(3)](PF(6))(2) surface composite displays excellent stability toward dissolution in water, but the added overlayer film greatly decreases incident photon-to-current conversion efficiencies (IPCE) in propylene carbonate with I(3)(-)/I(-) as the carrier couple. An ads-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Zn(vbpy)(3)](PF(6))(2) composite displays no loss in IPCE compared to ads-[Ru(vbpy)(2)(dcb)](PF(6))(2) but is susceptible to film breakdown in the presence of water by solvolysis and loss of the cross-linking Zn(2+) ions. Success was attained with an ads-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Ru(vbpy)(2)(dppe)](PF(6))(2) composite. In this case the electropolymerized layer is transparent in the visible. The composite electrode is stable in water, the IPCE in propylene carbonate with I(3)(-)/I(-) is comparable to the adsorbed complex, and a significant IPCE is observed in water with the quinone/hydroquinone carrier couple. The assembly [(bpy)(2)(CN)Ru(CN)Ru(vbpy)(2)(NC)Ru(CN)(bpy)(2)](PF(6))(2) ([Ru(CN)Ru(NC)Ru](PF(6))(2)) adsorbs spontaneously on TiO(2), and electropolymerization of thin layers of the assembly to give ads-[Ru(CN)Ru(NC)Ru](PF(6))(2)/poly-[Ru(CN)Ru(NC)Ru](PF(6))(2) enhances IPCE and has no deleterious effect on the IPCE/Ru.     

Electronic and photophysical properties of adducts of [Ru(bpy)3]2+ and Dawson-type sulfite polyoxomolybdates α/β-[Mo18O54(SO3)2]4-

The spectroscopic and photophysical properties of [Ru(bpy)(3)](2)[[Mo(18)O(54)(SO(3))(2)], where bpy is 2,2'-bipyridyl and [Mo(18)O(54)(SO(3))(2)](4-) is either the α or β-sulfite containing polyoxomolybdate isomer, have been measured and compared with those for the well known but structurally distinct sulfate analogue, α-[Mo(18)O(54)(SO(4))(2)](4-). Electronic difference spectroscopy revealed the presence of new spectral features around 480 nm, although they are weak in comparison with the [Ru(bpy)(3)](2)[Mo(18)O(54)(SO(4))(2)] analogue. Surprisingly, Stern-Volmer plots of [Ru(bpy)(3)](2+) luminescence quenching by the polyoxometallate revealed the presence of both static and dynamic quenching for both α and β-[Mo(18)O(54)(SO(3))(2)](4-). The association constant inferred for the ion cluster [Ru(bpy)(3)](2)α-[Mo(18)O(54)(SO(4))(2)] is K = 5.9 ± 0.56 × 10(6) and that for [Ru(bpy)(3)](2)β-[Mo(18)O(54)(SO(4))(2)] is K = 1.0 ± 0.09 × 10(7). Unlike the sulfate polyoxometalates, both sulfite polyoxometalate-ruthenium adducts are non-luminescent. Despite the strong electrostatic association in the adducts resonance Raman and photoelectrochemical studies suggests that unlike the sulfato polyoxometalate analogue there is no sensitization of the polyoxometalate photochemistry by the ruthenium centre for the sulfite anions. In addition, the adducts exhibit photochemical lability in acetonitrile, attributable to decomposition of the ruthenium complex, which has not been observed for other [Ru(bpy)(3)](2+) -polyoxometalate adducts. These observations suggest that less electronic communication exists between the [Ru(bpy)(3)](2+) and the sulfite polyoxoanions relative to their sulfate polyoxoanion counterparts, despite their structural and electronic analogy. The main distinction between sulfate and sulfite polyoxometalates lies in their reversible reduction potentials, which are more positive by approximately 100 mV for the sulfite anions. This suggests that the capacity for [Ru(bpy)(3)](2+) or analogues to sensitize photoreduction in the adducts of polyoxometalates requires very sensitive redox tuning.     

Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes

We report the synthesis of free 1,6,7,12-tetraazaperylene (tape). Tape was obtained from 1,1'-bis-2,7-naphthyridine by potassium promoted cyclization followed by oxidation with air. Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes of the general formulas [Ru(L-L)(2)(tape)](PF(6))(2), [1](PF(6))(2)-[5](PF(6))(2), and [{Ru(L-L)(2)}(2)(μ-tape)](PF(6))(4), [6](PF(6))(4)-[10](PF(6))(4), with{L-L = phen, bpy, dmbpy (4,4'-dimethyl-2,2'-bipyridine), dtbbpy (4,4'-ditertbutyl-2,2'-bipyridine) and tmbpy (4,4'5,5'-tetramethyl-2,2'-bipyridine)}, respectively, were synthesized. The X-ray structures of tape·2CHCl(3) and the mononuclear complexes [Ru(bpy)(2)(tape)](PF(6))(2)·0.5CH(3)CN·0.5toluene, [Ru(dmbpy)(2)(tape)](PF(6))(2)·2toluene and [Ru(dtbbpy)(2)(tape)](PF(6))(2)·3acetone·0.5H(2)O were solved. The UV-vis absorption spectra and the electrochemical behavior of the ruthenium(ii) tape complexes were explored and compared with the data of the analogous dibenzoeilatin (dbneil), 2,2'-bipyrimidine (bpym) and tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazin (tpphz) species.