Self-assembled monolayers of Ru/Os dinuclear complexes: probing monolayer structure and interaction energies by electrochemical means

Monolayers of [Ru(bpy)2(micro-1)M2][PF6]4 salts (M = Os, Ru; bpy = 2,2'-bipyridine, 1 = 4'-(2,2'-bipyridin-4-yl)-2,2':6',2' '-terpyridine, tpy = 2,2':6',2' '-terpyridine, and 2 = 4'-(4-pyridyl)-2,2':6',2' '-terpyridine) were self-assembled on platinum and investigated by fast-scan electrochemistry. The electrochemistry of the complexes in solution and confined to the surface in self-assembled monolayers (SAMs) exhibited an almost ideal behavior. Scan-rate-dependent measurements of the peak current density (jp) were used to determine interaction energies within the monolayer. It is shown that the tpy coordination sites of the dinuclear complexes interact more strongly within the SAM than the bipyridine-coordinated fragments. This result was supported by peak potential shifts, which are due to interaction forces in SAMs. The alignment of the rodlike complexes relative to the surface is discussed, and the results of molecular mechanics calculations indicate that the species adopt a tilted orientation.     

Terpyridine- and bipyridine-based ruthenium complexes as catalysts for the Belousov-Zhabotinsky reaction

We report the successful use of Ru(II)(terpy)(2) (1, terpy = 2,2':6',2'-terpyridine) as a catalyst in the Belousov-Zhabotinsky (BZ) oscillating chemical reaction. We also examine several additional Ru(II) complexes, Ru(II)(bipy)(2)(L')(2) (2, L' = 4-pyridinecarboxylic acid; bipy = 2,2'-bipyridine) and Ru(II)(bipy)(2)(L') (3, L' = 4,4'-dicarboxy-2,2'-bipy; 4, L' = N-allyl-4'-methyl-[2,2'-bipy]-4-carboxamide; 5, L' = bipy), for catalyzing the BZ reaction. While 2 is unable to trigger BZ oscillations, probably because of the rapid loss of L' in a BZ solution, the other bipyridine-based Ru(II)-complexes can catalyze the BZ reaction, although their catalytic activity is adversely affected by slow ligand substitution in a BZ solution. Nevertheless, the successfully tested Ru(II)(terpy)(2) and Ru(II)(bipy)(2)(L') catalysts may provide useful building blocks for complex functional macromolecules.     

Pseudo-base formation in the attempted synthesis of a conjugatively coupled bis(nitrosylruthenium) complex and spectroelectrochemistry of bipyrimidine-bridged dinuclear Ru(terpy)X precursor compounds (X = Cl, NO2)

Reaction of {(mu-bpym)[RuCl(terpy)]2}(PF6)2, bpym = 2,2'-bipyrimidine and terpy = 2,2':6',2'-terpyridine, with NaNO2 yields {(mu-bpym)[Ru(NO2)(terpy)]2}(PF6)2. In CH3CN/0.1 M Bu4NPF6 both dinuclear complexes can undergo two reversible bpym-centered one-electron reduction processes and two metal-centered one-electron oxidation steps, the latter involving mixed-valent intermediates with weak intermetallic coupling. Acidification of {(mu-bpym)[Ru(NO2)(terpy)]2}(PF6)2 does not lead to the expected {(mu-bpym)[Ru(NO)(terpy)]2}6+ but, probably because of the high charge, to the insoluble but structurally and IR-spectroscopically characterised pseudo-base product syn-{(mu-bpym-(4-OH))[Ru(NO)(terpy)]2}(PF6)5. The addition of one hydroxide to one of the 4-positions of bis-chelating bpym interrupts the aromatic pi conjugation and is accompanied by corresponding intra-pyrimidine bond length variations, however, the effect on the electronic interaction of the two different syn positioned {RuNO}6 moieties remains small, possibly due to their situation within the central molecular pi plane.     

Voltammetry and in situ scanning tunnelling spectroscopy of osmium, iron, and ruthenium complexes of 2,2':6',2'-terpyridine covalently linked to Au(111)-electrodes

We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(II)/(III), Fe(II)/(III), and Ru(II)/(III) and a 2,2',6',2'-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4'-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6-50 s(-1). Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2'-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism.     

Design aspects for the development of mixed-metal supramolecular complexes capable of visible light induced photocleavage of DNA

Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a central rhodium(III) core have been designed which photocleave DNA upon irradiation with visible light. The complexes [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5), [[(bpy)(2)Os(dpp)](2)RhCl(2)](PF(6))(5), and [[(tpy)RuCl(dpp)](2)RhCl(2)](PF(6))(3), where bpy = 2,2'-bipyridine, tpy = 2,2':6',2' '-terpyridine, and dpp = 2,3-bis(2-pyridyl)pyrazine, all exhibit intense metal to ligand charge transfer (MLCT) based transitions in the visible but possess lower lying metal to metal charge transfer (MMCT) excited states. These supramolecular complexes with low lying MMCT states photocleave DNA when excited into their intense MLCT transitions. Structurally similar complexes without this low lying MMCT state do not exhibit DNA photocleavage, establishing the role of this MMCT state in the DNA photocleavage event. Design considerations necessary to produce functional DNA photocleavage agents are presented herein.     

Electrochemical and luminescent properties of new mononuclear ruthenium(II) and binuclear iridium(III)-ruthenium(II) terpyridine complexes.

Hexafluorophosphate salts of mononuclear complexes [Ru(II)Cl(L)(terpy)]+ (L = dmbpy (1); dpbpy (2), sambpy (3), and dpp (7), and binuclear complexes [Ru(II)2Cl2(dpp)(terpy)2]2+ (8) and [Ir(III)Ru(II)Cl2(dpp)(terpy)2]3+ (9) were prepared and characterized. Abbreviations of the ligands are bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, dpbpy = 4,4'-diphenyl-2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, sambpy = 4,4'-bis((S)-(+)-alpha-1-phenylethylamido)-2,2'-bipyridine, and terpy = 2,2':6',2'-terpyridine. The absorption spectra of 8 and 9 are dominated by ligand-centered bands in the UV region and by metal-to-ligand charge-transfer bands in the visible region. The details of their spectroscopic and electrochemical properties were investigated. In both binuclear complexes, it has been found that the HOMO is based on the Ru metal, and LUMO is dpp-based. [Ir(III)Ru(II)Cl2(dpp)(terpy)2]3+, indicating intense emission at room temperature, and a lifetime of 154 ns. The long lifetime of this bimetallic chromophore makes it a useful component in the design of supramolecular complexes.     

From model compounds to protein binding: syntheses, characterizations and fluorescence studies of [RuII(bipy)(terpy)L]2+ complexes (bipy = 2,2'-bipyridine; terpy = 2,2':6',2''-terpyridine; L = imidazole, pyrazole and derivatives, cytochrome c)

Compounds [RuII(bipy)(terpy)L](PF6)2 with bipy = 2,2'-bipyridine, terpy = 2,2':6',2"-terpyridine, L = H2O, imidazole (imi), 4-methylimidazole, 2-methylimidazole, benzimidazole, 4,5-diphenylimidazole, indazole, pyrazole, 3-methylpyrazole have been synthesized and characterized by 1H NMR, ESI-MS and UV/Vis (in CH3CN and H2O). For L = H2O, imidazole, 4,5-diphenylimidazole and indazole the X-ray structures of the complexes have been determined with the crystal packing featuring only few intermolecular C-H...pi or pi-pi interactions due to the separating action of the PF6-anions. Complexes with L = imidazole and 4-methylimidazole exhibit a fluorescence emission with a maximum at 662 and 667 nm, respectively (lambdaexc= 475 nm, solvent CH3CN or H2O). The substitution of the aqua ligand in [Ru(bipy)(terpy)(H2O)]2+ in aqueous solution by imidazole to give [Ru(bipy)(terpy)(imi)]2+ is fastest at a pH of 8.5 (as followed by the increase in emission intensity). Coupling of the [Ru(bipy)(terpy)]2+ fragment to cytochrome c(Yeast iso-1) starting from the Ru-aqua complex was successful at 35 degrees C and pH 7.0 after 5 d under argon in the dark. The [Ru(bipy)(terpy)(cyt c)]-product was characterized by UV/Vis, emission and mass spectrometry. The location where the [Ru(bipy)(terpy)] complex was coupled to the protein was identified as His44 (corresponding to His39 in other numbering schemes) using digestion of the Ru-coupled protein by trypsin and analysis of the tryptic peptides by HPLC-high resolution MS.     

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.     

Synthesis and redox behavior of biferrocenyl-functionalized ruthenium(II) terpyridine gold clusters

Spectroscopic and electrochemical characterizations of ferrocene- and biferrocene-functionalized terpyridine octanethiolate monolayer-protected clusters were investigated and reported. The electrochemical measurements of Ru2+ coordinated with 4'-ferrocenyl-2,2':6',2' '-terpyridine and 4'-biferrocenyl-2,2':6',2' '-terpyridine complexes were dominated by the Ru2+/Ru3+ redox couple (E(1/2) at approximately 1.3 V), Fe(2+)/Fe(3+) redox couples (E(1/2) from approximately 0.6 to approximately 0.9 V), and terpy/terpy-/terpy2- redox couples (E(1/)(2) at ca. -1.2 and ca. -1.4 V). The substantial appreciable variations detected in the Ru2+/Ru3+ and Fe2+/Fe3+ oxidation potentials indicate that there is an interaction between the Ru2+ and Fe2+ metal centers. The coordination of the Ru2+ metal center with 4'-ferrocenyl-2,2':6',2' '-terpyridine and 4'-biferrocenyl-2,2':6',2' '-terpyridine leads to an intense 1[(d(pi)Fe)6] --> 1[d(pi)Fe)5(pi*terpyRu)1] transition in the visible region. The 1[(d(pi)Fe)6] -->1[d(pi)Fe)5(pi*terpyRu)1] transition observed at approximately 510 nm revealed that there was a qualitative electronic coupling between metal centers. The coordination of the Ru2+ transition metal center lowers the energy of the pi*terpy orbitals, causing this transition.     

A donor--acceptor--donor bridging ligand in a class III mixed-valence complex

The novel mononuclear and dinuclear complexes [Ru(trpy)(bpy)(apc)][PF(6)] and [(Ru(trpy)(bpy))(2)(mu-adpc)][PF(6)](2) (bpy = 2,2'-bipyridine, trpy = 2,2':6',2' '-terpyridine, apc(-) = 4-azo(phenylcyanamido)benzene, and adpc(2)(-) = 4,4'-azodi(phenylcyanamido)) were synthesized and characterized by (1)H NMR, UV-vis, and cyclic voltammetry. Crystallography showed that the dinuclear Ru(II) complex crystallizes from diethyl ether/acetonitrile solution as [(Ru(trpy)(bpy))(2)(mu-adpc)][PF(6)](2).2(acetonitrile).2(diethyl ether). Crystal structure data are as follows: crystal system triclinic, space group P1, with a, b, and c = 12.480(2), 13.090(3) and 14.147(3) A, respectively, alpha, beta, and gamma = 79.792(3), 68.027(3), and 64.447(3) degrees, respectively, V = 1933.3(6) A(3), and Z = 1. The structure was refined to a final R factor of 0.0421. The mixed-valence complex with metal ions, separated by a through-space distance of 19.5 A, is a class III system, having the comproportionation constant K(c) = 1.3 x 10(13) and an intervalence band at 1920 nm (epsilon(max) = 10 000 M(-1) cm(-1)), in dimethylformamide solution. The results of this study strongly suggest that the bridging ligand adpc(2-) can mediate metal-metal coupling through both hole-transfer and electron-transfer superexchange mechanisms.     

Rapid energy transfer in bichromophoric tris-bipyridyl/cyclometallated ruthenium(II) complexes

The synthesis, characterization, and photophysical properties of the N6-N5C bichromophoric [(bpy)2Ru(I)Ru(ttpy)][PF6]3 (bpy is 2,2'-bipyridine and ttpy is 4'-p-tolyl-2,2':6',2'-terpyridine) and [(bpy)2Ru(II)Ru(ttpy)][PF6]3 (I and II are bpy-dipyridylbenzene ditopic ligands bridged by an ethynyl and phenyl unit, respectively) complexes are reported together with the model mononuclear complexes [(bpy)2Ru(I)][PF6]2, [(bpy)2Ru(II)][PF6]2, [Ru(VI)(ttpy)][PF6] (VI is 3,5-di(2-pyridyl)-biphenyl) and [Ru(dpb)(ttpy)][PF(6)] (Hdpb is 1,3-di(2-pyridyl)-benzene). The electrochemical data show that there is little ground state electronic communication between the metal centers in the bimetallic complexes. Selective excitation of the N(5)C unit in the bichromophoric systems leads to luminescence typical for a bis-tridentate cyclometallated ruthenium complex and is similar to the [Ru(VI)(ttpy)][PF6] model complex. In contrast, the luminescence from the tris-bidentate N6 unit is efficiently quenched by energy transfer to the N5C unit. The energy transfer rate has been determined by femtosecond pump-probe measurements to 0.7 ps in the ethynyl-linked [(bpy)2Ru(I)Ru(ttpy)][PF6]3 and to 1.5 ps in the phenyl-linked [(bpy)2Ru(II)Ru(ttpy)][PF6]3 (in acetonitrile solution at 298 K), and is inferred to occur via a Dexter mechanism.     

Assessment of intercomponent interaction in phenylene bridged dinuclear ruthenium(II) and osmium(II) polypyridyl complexes

The synthesis and characterisation of [Ru(bipy)(2)(L1)](2+) and the homodinuclear complexes [M(bipy)(2)(L1)M(bipy)(2)](4+)(where M = Ru or Os), employing the ditopic ligand, 1,4-phenylene-bis(1-pyridin-2-ylimidazo[1,5-a]pyridine)(L1), are reported. The complexes are identified by elemental analysis, UV/Vis, emission, resonance Raman, transient resonance Raman and (1)H NMR spectroscopy, mass spectrometry and electrochemistry. The X-ray structure of the complex [Ru(bipy)(2)(L1)(bipy)(2)Ru](PF(6))(4) is also reported. DFT calculations, carried out to model the electronic properties of the compounds, are in good agreement with experiment. Minimal communication between the metal centres is observed. The low level of ground state electronic interaction is rationalized in terms of the poor ability of the phenyl spacer in facilitating superexchange interactions. Using the electronic and electrochemical data a detailed picture of the electronic properties of the RuRu compound is presented.     

Metal-directed synthesis and photophysical studies of trinuclear v-shaped and pentanuclear x-shaped ruthenium and osmium metallorods and metallostars based upon 4'-(3,5-dihydroxyphenyl)-2,2':6',2''-terpyridine divergent units

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2'-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant.     

Synthesis, luminescence, and electrochemical studies of tris(homoleptic) ruthenium(II) and osmium(II) complexes of 6'-tolyl-2,2':4',2'-terpyridine

The synthesis and photophysical and electrochemical properties of tris(homoleptic) complexes [Ru(tpbpy)3](PF6)2 (1) and [Os(tpbpy)3](PF6)2 (2) (tpbpy = 6'-tolyl-2,2':4',2' '-terpyridine) are reported. The ligand tpbpy is formed as the side product during the synthesis of 4'-tolyl-2,2':6',2' '-terpyridine (ttpy) and characterized by single-crystal X-ray diffraction: monoclinic, P21/c. The tridentate tpbpy coordinates as a bidentate ligand. The complexes 1 and 2 exhibit two intense absorption bands in the UV region (200-350 nm) assignable to the ligand-centered (1LC) pi-pi* transitions. The ruthenium(II) complex exhibits a broad absorption band at 470 nm while the osmium(II) complex exhibits an intense absorption band at 485 nm and a weak band at 659 nm assignable to the MLCT (dpi-pi*) transitions. A red shifting of the dpi-pi* MLCT transition is observed on going from the Ru(II) to the Os(II) complex as expected from the high-lying dpi Os orbitals. These complexes exhibit ligand-sensitized emission at 732 and 736 nm, respectively, upon light excitation onto their MLCT band through excitation of higher energy LC bands at room temperature. The MLCT transitions and the emission maxima of 1 and 2 are substantially red-shifted compared to that of [Ru(bpy)3](PF6)2 and [Os(bpy)3](PF6)2. The emission of both the complexes in the presence of acid is completely quenched indicating that the emission is not due to the protonation of the coordinated ligands. Our results indicate the occurrence of intramolecular energy transfer from the ligand to the metal center. Both the complexes undergo quasi-reversible metal-centered oxidation, and the E1/2 values for the M(II)/M(III) redox couples (0.94 and 0.50 V versus Ag/Ag+ for 1 and 2, respectively) are cathodically shifted with respect to that of [Ru(bpy)3](PF6)2 and [Os(bpy)3](PF6)2 (E1/2 = 1.28 and 1.09 V versus Ag/Ag+, respectively). The tris(homoleptic) Ru(II) and Os(II) complexes 1 and 2 could be used to construct polynuclear complexes by using the modular synthetic approach in coordination compounds by exploiting the coordinating ability of the pyridine substituent. Furthermore, these complexes offer the possibility of studying the influence of electron-withdrawing and electron-donating substituents on the photophysical properties of Ru(II) and Os(II) polypyridine complexes.     

Synthesis, characterization and electrochemistry of 4'-functionalized 2,2':6',2'-terpyridine ruthenium(II) complexes and their biological activity

The synthesis and characterization of Ru(II) terpyridine complexes derived from 4'-functionalized 2,2':6',2'-terpyridine ligands by a multi step procedure have been described. The complexes are redox-active, showing both metal-centred (oxidation) and ligand-centred (reduction) processes. The antibacterial and antifungal activity of the synthesized ruthenium(II) complexes [Ru(attpy)2](PF6)2 (attpy = 4'-(4-acryloyloxymethylphenyl)-2,2':6',2'-terpyridine); [Ru(mttpy)2](PF6)2 (mttpy = 4'-(4-methacryloyloxymethylphenyl)-2,2':6',2'- terpyridine); [Ru(mttpy)(MeOPhttpy)](PF6)2 (MeOPhttpy = 4'-(4-methoxyphenyl)-2,2':6',2'-terpyridine); and [Ru(mttpy)(ttpy)](PF6)2 (ttpy = 4'-(4-methylphenyl)-2,2':6',2'-terpyridine) were tested against four human pathogens (Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli) and five plant pathogens (Curvularia lunata, Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina and Rhizoctonia solani) by the well diffusion method and MIC values of the complexes are reported. A biological study of the complexes indicated that the complexes [Ru(mttpy)2](PF6)2 and [Ru(mttpy)(MeOPhttpy)](PF6)2 exhibit very good activity against most of the test pathogens and their activity is better than those of some of the commercially available antibiotics like tetracycline and the fungicide carbendazim.     

Heteronuclear bipyrimidine-bridged Ru-Ln and Os-Ln dyads: low-energy 3MLCT states as energy-donors to Yb(III) and Nd(III)

The complexes [Ru((t)Bu(2)bipy)(bpym)X(2)] (X = Cl, NCS) and [M((t)Bu(2)bipy)(2)(bpym)][PF(6)](2) (M = Ru, Os) all have a low-energy LUMO arising from the presence of a 2,2'-bipyrimidine ligand, and consequently have lower-energy (1)MLCT and (3)MLCT states than analogous complexes of bipyridine. The vacant site of the bpym ligand provides a site at which [Ln(diketonate)(3)] units can bind to afford bipyrimidine-bridged dinuclear Ru-Ln and Os-Ln dyads; four such complexes have been structurally characterised. UV/Vis and luminescence spectroscopic studies show that binding of the Ln(III) fragment at the second site of the bpym ligand reduces the (3)MLCT energy of the Ru or Os fragment still further. The result is that in the dyads [Ru((t)Bu(2)bipy)X(2)(mu-bpym)Ln(diketonate)(3)] (X = Cl, NCS) and [Os((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT is too low to sensitise the luminescent f-f states of Nd(III) and Yb(III), but in [Ru((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT energy of 13,500 cm(-1) permits energy transfer to Yb(III) and Nd(III) resulting in sensitised near-infrared luminescence on the microsecond timescale.     

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.     

1,10]-Phenanthrolin-2-yl ketones and their coordination chemistry

A synthetic protocol involving the Friedl?nder reaction of 8-amino-7-quinolinecarbaldehyde followed by potassium dichromate oxidation was applied to 2,3,4-pentanetrione-3-oxime and 1-(pyrid-2'-yl)propane-1,2-dione-1-oxime to provide the ligands di-(phenathrolin-2-yl)-methanone (1) and phenanthrolin-2-yl-pyrid-2-yl-methanone (8), respectively. Ligand 1 complexed as a planar tetradentate with Pd(II) to form [Pd(1)](BF4)2 and with Ru(II) and two 4-substituted pyridines (4-R-py) to form [Ru(1)(4-R-py)2](PF6)2 where R = CF3, CH3, and Me2N. With [Ru(bpy)2Cl2], the dinuclear complex [(bpy)2Ru(1)Ru(bpy)2](PF6)4 was formed (bpy = 2,2'-bipyridine). Ligand 8 afforded the homoleptic Ru(II) complex [Ru(8)2](PF6)2, as well as the heteroleptic complex [Ru(8)(tpy)](PF6)2 (tpy = 2,2';6,2'-terpyridine). The ligands and complexes were characterized by their NMR and IR spectra, as well as an X-ray structure determination of [Ru(1)(4-CH3-py)2](PF6)2. Electrochemical analysis indicated metal-based oxidation and ligand-based reduction that was consistent with results from electronic absorption spectra. The complexes [Ru(1)(4-R-py)2](PF6)2 were sensitive to the 4-substituent on the axial pyridine: electron donor groups facilitated the oxidation while electron-withdrawing groups impeded it.     

Hydride ion transfer from ruthenium(II) complexes in water: kinetics and mechanism

Reactions of hydride complexes of ruthenium(II) with hydride acceptors have been examined for Ru(terpy)(bpy)H(+), Ru(terpy)(dmb)H(+), and Ru(η(6)-C(6)Me(6))(bpy)(H)(+) in aqueous media at 25 °C (terpy = 2,2';6',2'-terpyridine, bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine). The acceptors include CO(2), CO, CH(2)O, and H(3)O(+). CO reacts with Ru(terpy)(dmb)H(+) with a rate constant of 1.2 (0.2) × 10(1) M(-1) s(-1), but for Ru(η(6)-C(6)Me(6))(bpy)(H)(+), the reaction was very slow, k ≤ 0.1 M(-1) s(-1). Ru(terpy)(bpy)H(+) and Ru(η(6)-C(6)Me(6))(bpy)(H)(+) react with CH(2)O with rate constants of (6 ± 4) × 10(6) and 1.1 × 10(3) M(-1) s(-1), respectively. The reaction of Ru(η(6)-C(6)Me(6))(bpy)(H)(+) with acid exhibits straightforward, second-order kinetics, with the rate proportional to [Ru(η(6)-C(6)Me(6))(bpy)(H)(+)] and [H(3)O(+)] and k = 2.2 × 10(1) M(-1) s(-1) (μ = 0.1 M, Na(2)SO(4) medium). However, for the case of Ru(terpy)(bpy)H(+), the protonation step is very rapid, and only the formation of the product Ru(terpy)(bpy)(H(2)O)(2+) (presumably via a dihydrogen or dihydride complex) is observed with a k(obs) of ca. 4 s(-1). The hydricities of HCO(2)(-), HCO(-), and H(3)CO(-) in water are estimated as +1.48, -0.76, and +1.57 eV/molecule (+34, -17.5, +36 kcal/mol), respectively. Theoretical studies of the reactions with CO(2) reveal a "product-like" transition state with short C-H and long M-H distances. (Reactant) Ru-H stretched 0.68 ?; (product) C-H stretched only 0.04 ?. The role of water solvent was explored by including one, two, or three water molecules in the calculation.     

cis-[Ru(2,2':6',2' '-terpyridine)(DMSO)Cl(2)]: useful precursor for the synthesis of heteroleptic terpyridine complexes under mild conditions

[Ru(II)(terpy)(DMSO)Cl(2)] complexes were synthesized as a 5/1 mixture of cis and trans isomers, and their reactivities with CO and with substituted 2,2':6',2' '-terpyridine (terpy) moieties have been investigated. The structure of a trans isomer and its CO adduct have been unambiguously assigned by spectroscopy and X-ray diffraction. The [Ru(terpy)(terpy-Br)](2+) complex prepared either from the cis-[Ru(II)(terpy)(DMSO)Cl(2)] or from the cis-[Ru(II)(terpy-Br)(DMSO)Cl(2)] precursor appeared to be reactive in cross-coupling reactions promoted by low-valent palladium(0) and is an attractive target for the stepwise synthesis of polynuclear complexes bearing vacant coordination sites (terpy-Br for 4'-bromo-2,2':6',2' '-terpyridine). Several bipyridine, phenanthroline, and bipyrimidine complexes were prepared this way and their optical and redox properties determined and discussed.