Ruthenium(II) Complexes of a Xanthene-Spanned Dicarbene Ligand.

Octahedral ruthenium(II) complexes of a xanthene-di(N-heterocyclic carbene) ancillary ligand (XdC) have been prepared and structurally characterized. Examples catalyze the transfer hydrogenation of ketones {[Ru(CO)I2(C,O,C'-XdC)] (1) and [Ru(CO)(MeCN)2(C,O,C'-XdC)]2+ (22+)} and the selective electrochemical reduction of CO2 to CO {[Ru(N,N'-bpy)(CO)(C,O,C'-XdC)]2+ (32+) at 0.40 V overpotential in MeCN-H2O (1 M)}. The reaction of 1 with KBEt3H afforded isomers of [(C,C'-XdC)Ru(µ-H)(H)]2 dimers, which are stable to reductive elimination of the XdC ligand, thereby suggesting similar (XdC)Rh(coligand)(H)x species may be viable intermediates in catalyses. The electrochemical reduction of CO2 involves a double reduction of 32+ to 3••, which has been characterized by IR-SEC and DFT calculations. The DFT calculations suggest the Ru-Oxanth bond breaks in 3••, opening a metal site for CO2 binding with selectivity over protons enabled by the diffuse nature of the HOMO delocalized over the metal and the bipyridine and carbonyl coligands. The results point to the promise of metal complexes of flexible and hemilabile xanthene-(NHC)2 ancillary ligands in catalysis.

Synthesis and structural, redox and photophysical properties of tris-(2,5-di(2-pyridyl)pyrrolide) lanthanide complexes.

A first series of lanthanide complexes of tris(dipyridyl)pyrrolide ligands has been prepared. The [Ln(dppR1,R2)3] complexes (Ln = La(iii), Sm(iii), Eu(iii), Gd(iii) and Yb(iii); and dppR1,R2 = 2,5-di(2-pyridyl-3-(R1)-4-(R2)) pyrrolide) have been isolated and their structures and photophysical and redox properties characterised, both in the solid-state and in solution. In the complexes, the three dpp- ligands form a distorted tricapped trigonal prismatic coordination geometry about the lanthanide ions, with the antiparallel isomer observed in the solid state for non-symmetric (dppCO2Me,Me)-. However, 1H NMR spectroscopy of the diamagnetic and paramagnetic [Ln(dppR1,R2)3] complexes in d6-benzene solution reveal evidence for a statistical distribution of all possible isomers. Time-resolved luminescence studies suggest that the dpp- ligand (with triplet excited state T1 energy at 18 622 cm-1) sensitises red emission from [Eu(dppCO2Me,Me)3] and near-infrared emission from [Yb(dppCO2Me,Me)3] through the antenna effect. Cyclic voltammetry reveals three consecutive, reversible, one-electron oxidation processes for each [Ln(dppR1,R2)3] complex, corresponding to oxidations of each dpp- ligand between 0.3-0.8 V vs. E1/2 (Fc+/0), and for [Eu(dppCO2Me,Me)3] the EuIII/II couple was -2.099 V vs. E1/2 (Fc+/0).

A new tri-nuclear Cu-carbonate cluster utilizing CO2 as a C1-building block - reactive intermediates, a probable mechanism, and EPR and magnetic studies.

This work demonstrates that simple copper-bipyridine compounds and atmospheric CO2 react to produce useful/complex materials under appropriate conditions. Starting from a distorted square planar copper(ii) complex, [(tbubpy)CuCl2](tbubpy = 4-tert-butyl-2-(4-tert-butylpyridin-2-yl)pyridine), an air-sensitive, copper(i) complex, [(tbubpy)2CuI][BF4], which exhibits a distorted tetrahedral geometry, was synthesized and characterized. Reactions of [(tbubpy)2CuI][BF4] with CO2 inside a sealed tube and with air were carried out over a week and three weeks, respectively. A new tricopper(ii)-carbonato cluster, [{(tbubpy)2Cu}3(µ-CO3)][PF6]4, was isolated with three distorted octahedral copper(ii) centres bound by a carbonate-bridge formed from atmospheric CO2. NMR and UV-Vis spectroscopic analyses coupled with previous reports point to a multi-step process in the formation of a trinuclear CuII-carbonato cluster that includes the probable involvement of µ-hydroxo-bridged dicopper(ii) type intermediates.

Predictable Substituent Control of CoIII/II Redox Potential and Spin Crossover in Bis(dipyridylpyrrolide)cobalt Complexes.

A family of five easily prepared tridentate monoanionic 2,5-dipyridyl-3-(R1)-4-(R2)-pyrrolide anions (dppR1,R2)-, varying in the nature of the R1 and R2 substituents [R1, R2 = CN, Ph; CO2Et, CO2Et; CO2Me, 4-Py; CO2Me, Me; Me, Me], has been used to generate the analogous family of neutral [CoII(dppR1,R2)2] complexes, two of which are structurally characterized at both 100 and 298 K. Both the oxidation and spin states of these complexes can be switched in response to appropriate external stimuli. All complexes, except [CoII(dppMe,Me)2], exhibit gradual spin crossover (SCO) in the solid state, and SCO activity is observed for three complexes in CDCl3 solution. The cobalt(II) centers in the low spin (LS) complexes are Jahn-Teller tetragonally compressed along the pyrrolide-Co-pyrrolide axis. The complexes in their high spin (HS) states are more distorted than in the LS states, as is also usually the case for SCO active iron(II) complexes. The reversible CoIII/II redox potentials are predictably tuned by choice of substituents R1 and R2, from -0.95 (Me,Me) to -0.45 (CN,Ph) V vs Fc+/Fc, with a linear correlation observed between E1/2(CoIII/II) and the Swain-Lupton parameters of the pyrrolide substituents.

A Strain-Deformation Nexus within Pincer Ligands: Application to the Spin States of Iron(II) Complexes.

The substitution of a pyrrolide ring for one (or more) pyridyl rings within the ubiquitous terpyridine (tpy, A) scaffold results in more open geometries of the pyridine-pyrrolide chelate ligands. DFT calculations (B3LYP-GD3BJ/6-31G**) demonstrate that the more open geometries of the unbound ligands are mismatched with the "pinched in" geometries required to chelate transition metal ions (e.g., Zn2+). The strain which builds within these ligands (Δ EL(strain)) as they bind transition metal ions can be related to changes in a single geometric parameter: the separation between the two terminal N atoms (ρ). This relationship applies more generally to other three-ringed tridentate pincer ligands, including those with different donor groups. The approach was applied to homoleptic iron(II) complexes to investigate the contribution of the steric effects operating within the ligands to the different magnetic properties, including spin crossover (SCO) activities, of these systems.

Strategic design of a ruthenium catalyst for both CO2 reduction and H2O oxidation: the electronic influence of the co-ligands.

A new ruthenium(ii) complex capable of catalysing both CO2 reduction and water oxidation was designed and synthesised. The electro-catalytic efficiency and robustness of the complex together with the electronic effect of its co-ligands were investigated to develop next generation dual activity electrocatalysts.

Bridgehead isomer effects in bis(phosphido)-bridged diiron hexacarbonyl proton reduction electrocatalysts.

The influence of the substitution, orientation and structure of the phosphido bridges in [Fe2(CO)6(µ-PR2)2] electrocatalysts of proton reduction has been studied. The isomers e,a-[Fe2(CO)6{µ-P(Ar)H}2] (1a(Ar): Ar = Ph, 2'-methoxy-1,1'-binaphthyl (bn')), e,e-[Fe2(CO)6{µ-P(Ar)H}2] (1b(Ar): Ar = Ph, bn') were isolated from reactions of iron pentacarbonyl and the corresponding primary phosphine, syntheses that also afforded the phosphinidene-capped tri-iron clusters, [Fe3(CO)9(µ-CO)(µ3-Pbn')] (2) and [Fe3(CO)9(µ3-PAr)2] (3(Ar), Ar = Ph, bn'). A ferrocenyl (Fc)-substituted dimer [Fe2(CO)6{µ:µ'-1,2-(P(CH2Fc)CH2)2C6H4}] (4), in which the two phosphido bridges are linked by an o-xylyl group, was also prepared. The molecular structures of complexes 1a(Ph), 1b(Ph), 1b(bn'), 2 and 4 were established by X-ray crystallography. All complexes have been examined as electrocatalysts for proton reduction using p-toluene sulfonic acid in tetrahydrofuran. Cyclic voltammograms of the dimers with acid exhibit two catalysis waves for proton reduction. The first wave, which appears at the potential of the primary reduction, reaches maximum current (turnover) at moderate acid concentrations and is rapidly overtaken by the second wave, which appears at more negative potential. Both of these reductive waves show an initial first order dependence on acid. The electrochemistry and electrocatalyses of the [Fe2(CO)6(µ-PR2)2] dimers show subtle variations with the nature of the bridging phosphido group(s), including the orientation of bridgehead hydrogen atoms.

Bio-inspired transition metal-organic hydride conjugates for catalysis of transfer hydrogenation: experiment and theory.

Taking inspiration from yeast alcohol dehydrogenase (yADH), a benzimidazolium (BI(+) ) organic hydride-acceptor domain has been coupled with a 1,10-phenanthroline (phen) metal-binding domain to afford a novel multifunctional ligand (L(BI+) ) with hydride-carrier capacity (L(BI+) +H(-) ⇌L(BI) H). Complexes of the type [Cp*M(L(BI) )Cl][PF6 ]2 (M=Rh, Ir) have been made and fully characterised by cyclic voltammetry, UV/Vis spectroelectrochemistry, and, for the Ir(III) congener, X-ray crystallography. [Cp*Rh(L(BI) )Cl][PF6 ]2 catalyses the transfer hydrogenation of imines by formate ion in very goods yield under conditions where the corresponding [Cp*Ir(L(BI) )Cl][PF6 ] and [Cp*M(phen)Cl][PF6 ] (M=Rh, Ir) complexes are almost inert as catalysts. Possible alternatives for the catalysis pathway are canvassed, and the free energies of intermediates and transition states determined by DFT calculations. The DFT study supports a mechanism involving formate-driven RhH formation (90 kJ mol(-1) free-energy barrier), transfer of hydride between the Rh and BI(+) centres to generate a tethered benzimidazoline (BIH) hydride donor, binding of imine substrate at Rh, back-transfer of hydride from the BIH organic hydride donor to the Rh-activated imine substrate (89 kJ mol(-1) barrier), and exergonic protonation of the metal-bound amide by formic acid with release of amine product to close the catalytic cycle. Parallels with the mechanism of biological hydride transfer in yADH are discussed.

An easy one-pot synthesis of diverse 2,5-di(2-pyridyl)pyrroles: a versatile entry point to metal complexes of functionalised, meridial and tridentate 2,5-di(2-pyridyl)pyrrolato ligands.

A wide variety of 2,5-di(2-pyridyl)pyrroles (dppHs) substituted at the C3 and C4 positions of the pyrrole core were obtained by direct condensation of a 2-pyridylcarboxaldehyde (2 equiv), an α-methylene ketone with at least one electron-withdrawing substituent and ammonium acetate. A novel 2,5-di(1,10-phenanthrolin-2-yl)pyrrole was also characterised. The dppHs provide a direct, quick entry to dipyridylpyrrolato (dpp(-) )-metal complexes. The meridial tridentate dpp(-) ligand is a useful anionic analogue of the terpyridyl ligand. The first (dpp)Ru complexes are described; the 3,4-substitution of the central pyrrole significantly perturbs the potentials of the redox processes of these complexes. A [(dpp)Ru(bpy)(MeCN)](+) (bpy=2,2'-bipyridine) complex is an electrocatalyst for the reductive disproportionation of carbon dioxide to carbon monoxide and the carbonate ion.

Macrocyclic bis(phenanthroline-pyrrole): a convenient one-pot synthesis, structure(s), spectroscopic, and redox properties, and the binding of amine guests, protons, and lanthanide ions.

This paper reports a convenient, one-pot, easily scalable and readily modifiable synthesis of a novel large-ring bis(1,10-phenanthrolinyl-2,5-pyrrole) macrocycle, H2LMC, and describes its spectroscopic and electrochemical properties, protonation, cooperative amine binding, electrocatalysis of the oxidation of primary amines, photosensitization of the decomposition of dichloromethane, and the first lanthanide complexes of the hexaaza-dianion LMC(2-) including the novel dimer, [(NO3)(LMC)Eu(µ-OH)Eu(LMC )(H2 O)2]·2py.

The coordination chemistry of organo-hydride donors: new prospects for efficient multi-electron reduction.

In biological reduction processes the dihydronicotinamides NAD(P)H often transfer hydride to an unsaturated substrate bound within an enzyme active site. In many cases, metal ions in the active site bind, polarize and thereby activate the substrate to direct attack by hydride from NAD(P)H cofactor. This review looks more widely at the metal coordination chemistry of organic donors of hydride ion--organo-hydrides--such as dihydronicotinamides, other dihydropyridines including Hantzsch's ester and dihydroacridine derivatives, those derived from five-membered heterocycles including the benzimidazolines and benzoxazolines, and all-aliphatic hydride donors such as hexadiene and hexadienyl anion derivatives. The hydride donor properties--hydricities--of organo-hydrides and how these are affected by metal ions are discussed. The coordination chemistry of organo-hydrides is critically surveyed and the use of metal-organo-hydride systems in electrochemically-, photochemically- and chemically-driven reductions of unsaturated organic and inorganic (e.g. carbon dioxide) substrates is highlighted. The sustainable electrocatalytic, photochemical or chemical regeneration of organo-hydrides such as NAD(P)H, including for driving enzyme-catalysed reactions, is summarised and opportunities for development are indicated. Finally, new prospects are identified for metal-organo-hydride systems as catalysts for organic transformations involving 'hydride-borrowing' and for sustainable multi-electron reductions of unsaturated organic and inorganic substrates directly driven by electricity or light or by renewable reductants such as formate/formic acid.

A dimer of bis-(N-heterocyclic carbene)rhodium(I) centres spanned by a dibenzo-18-crown-6 bridge from synchrotron radiation.

The compound (µ-3,3',3'',3'''-{[2,5,8,15,18,21-hexa-oxatricyclo-[20.4.0.0(9,14)]hexa-cosa-1(22),9,11,13,23,25-hexa-ene-11,12,24,25-tetra-yl]tetra-kis-(methyl-ene)}tetra-kis-(1-methyl-1H-imidazol-2-yl))bis-[(η(4)-cyclo-octa-1,4-diene)rhodium(I)] bis-(hexa-fluoridophosphate) acetonitrile sesquisolvate dihydrate, [Rh2(C8H12)2(C40H42N8O6)](PF6)2·1.5CH3CN·2H2O, crystallized from acetonitrile under an atmosphere of diethyl ether. In the crystal structure, the complex cation exhibits two square-planar Rh(I) centres, each bound by a cyclo-octa-diene (COD) ligand and by two adjacent imidazolyl-idene N-heterocyclic carbene (NHC) donors from the same phen-oxy ring of the {[dibenzo-18-crown-6-11,12,24,25-tetra-yl]tetra-kis-(methyl-ene)}tetra-kis-(1-methyl-1H-imidazol-2-yl) (L) ligand. The dibenzo-crown ether bridge of L spans the Rh centres and forms hydrogen bonds with water mol-ecules. One water mol-ecule with half occupancy bridges adjacent macrocycles in the lattice. Another water with full occupancy forms weak hydrogen bonds to the crown ether O atoms and is, in turn, part hydrogen bonded by a lattice water with half occupancy. The latter water is within hydrogen-bonding distance of a fourth water also with partial occupancy. The result of these inter-actions is the formation of a layer in the ab plane. Two PF6(-) ions, one of which is twofold disordered, and one ordered and one twofold disordered (with 0.5 occupancy) lattice acetonitrile mol-ecules complete the crystal structure.

Low oxidation state iron(0), iron(I), and ruthenium(0) dinitrogen complexes with a very bulky neutral phosphine ligand.

The synthesis of a series of iron and ruthenium complexes with the ligand P(2)P3(Cy), P(CH2CH2PCy2)3 is described. The iron(0) and ruthenium(0) complexes Fe(N2)(P(2)P3(Cy)) (1) and Ru(N2)(P(2)P3(Cy)) (2) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with an excess of potassium graphite under a nitrogen atmosphere. The Fe(I) and Ru(I) species [Fe(N2)(P(2)P3(Cy))](+) (3) and RuCl(P(2)P3(Cy)) (4) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with 1 equiv of potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N2)H(P(2)P3(Cy))](+) (6) and [Ru(N2)H(P(2)P3(Cy))](+) (7) were formed by treatment of 1 and 3, respectively, with 1 equiv of a weak organic acid. The iron(II) complex Fe(H)2(P(2)P3(Cy)) (5) was also synthesized and characterized. Complexes [RuCl(P(2)P3(Cy))][BPh4], 1, 2, 3[BPh4], 4, 5, 6[BF4], and 7[BF4] were characterized by X-ray crystallography. The Fe(I) and Ru(I) complexes 3 and 4 were characterized by electron paramagnetic resonance (EPR) spectroscopy, and the Fe(I) complex has an EPR spectrum typical of a metal-centered radical.

trans-Chloridobis(4-methyl-pyridine-κN)(4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine-κN,N',N'')ruthenium(II) hexa-fluoridophosphate acetone monosolvate.

The title compound, [RuCl(C(6)H(7)N)(2)(C(27)H(35)N(3))]PF(6)·C(3)H(6)O, was obtained unintentionally as the product of the reaction of 1,1'-methyl-enebis(4-methyl-pyridinium) hexa-fluoriso-phos-phate and RuCl(3)(tpy*) (tpy* is 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine) in the presence of triethyl-amine and LiCl. The mol-ecular structure of the complex displays an octa-hedral geometry around the Ru(II) ion and the unit cell contains an acetone solvent mol-ecule and one orientationally disordered PF(6) (-) anion (occupancy ratio 0.75:0.25) which is hydrogen bonded to two H atoms of the tpy* ligand of the nearest [RuCl(pic)(2)(tpy*)](+) cation (pic is 4-methyl-pyridine). One of the tert-butyl groups of the tpy* ligand is also disordered over two sets of sites in a 0.75:0.25 ratio.

Rhodium complexes of a chelating ligand with imidazol-2-ylidene and pyridin-2-ylidene donors: the effect of C-metalation of nicotinamide groups on uptake of hydride ion.

Rhodium complexes of the imidazolylidene (C-im) N-heterocyclic carbene (NHC) ligand, C-im-pyH(+), bearing a nicotinamide cation substituent (pyH(+)) have been targeted for ligand-centered uptake and delivery of hydride ion. This work reveals that rhodium(I) complexes such as [Rh(C-im-pyH(+))(COD)X][PF(6)] (1, a: X = Cl, b: X = I) undergo facile C-metalation of the nicotinamide ring to afford rhodium complexes of a novel chelate ligand, C,C'-im-py, with coordinated imidazolylidene (C(im)) and pyridylidene (C(py)) NHC-donors. Seven examples were characterized and include rhodium(III) monomers of the general formula [Rh(C,C'-im-py)L(x)I(2)](z+) (2: z = 1, L = H(2)O or solvent, x = 2; 3, 5, 7: z = 0, L = carboxylate, x = 1) and novel rhodium(II) dimers, the anti/syn-isomers of [Rh(2)(C,C'-im-py)(2)(µOAc)(2)I(2)] (4-anti/syn). The NMR data, backed by DFT calculations, is consistent with attribution of the C,C'-im-py ligand as a bis(carbene) donor. Single crystal X-ray diffraction studies are reported for 2, 3, 4-anti, 4-syn and 7. Consistently, within the each complex, the Rh-C(im) bond length is shorter than the Rh-C(py) bond length, which is the opposite trend to that expected based on simple electronic considerations. It is proposed that intramolecular steric interactions imposed by different rings in the rigid C,C'-im-py chelate ligand dictate the observed Rh-C(NHC) bond lengths. Attempts to add hydride to the C-metalated nicotinamide ring in 3 were unsuccessful. The redox behavior of 3 and 4 and, for comparison, an analogous bis(imidazolylidene)rhodium(III) monomer (8), were characterized by cyclic voltammetry, electron paramagnetic resonance (EPR), and UV-vis spectroelectrochemistry. In 3 and 4, the C-metalated nicotinamide ring is found to exhibit a one-electron reduction process at far lower potential (-2.34 V vs. Fc(+)/Fc in acetonitrile) than the two-electron nicotinamide cation-dihydronicotinamide couple found for the corresponding nonmetalated ring (-1.24 V). The C,C'-ligand is electrochemically silent over a large potential range (from -2.3 V to the anodic solvent limit), thus for both 3 and 4 the first reduction processes are metal-centered. For 4-anti, the cyclic voltammetry and UV-vis spectrochemical results are consistent with a diamagnetic [Rh(I)Rh(II)](2) tetrameric reduction product. Density functional theory (DFT) calculations were used to further probe the uptake of hydride ion by the nicotinamide ring, both before and after C-metalation. It is found that C-metalation significantly decreases the ability of the nicotinamide ring to take up hydride ion, which is attributed to the "carbene-like" character of a C-metalated pyridylidene ring.

Hydride ion-carrier ability in Rh(I) complexes of a nicotinamide-functionalised N-heterocyclic carbene ligand.

(Spectro-)electrochemical results demonstrate ligand-centred hydride ion-carrier capacity for a Rh(I) complex of a novel 'non-innocent' N-heterocyclic carbene ligand created by nicotinamide functionalisation.

Production and isolation of ligated metal(IV)-oxo ions by tandem mass spectrometry.

High valent metal(IV)-oxo species, [M(==O)(MeIm)(n)(OAc)](+) (M = Mn-Ni, MeIm = 1-methylimidazole, n = 1-2), which are relevant to biology and oxidative catalysis, were produced and isolated in gas-phase reactions of the metal(II) precursor ions [M(MeIm)(n)(OAc)](+) (M = Mn-Zn, n = 1-3) with ozone. The precursor ions [M(MeIm)(OAc)](+) and [M(MeIm)(2)(OAc)](+) were generated via collision-induced dissociation of the corresponding [M(MeIm)(3)(OAc)](+) ion. The dependence of ozone reactivity on metal and coordination number is discussed.

Fluxionality in a paramagnetic seven-coordinate iron(II) complex: a variable-temperature, two-dimensional NMR and DFT study.

The preparation and detailed characterizations of the high-spin seven-coordinate complexes [M(kappa(7)N-L)](ClO(4))(2) (M = Mn(II), Fe(II); L = N,N,N',N'-tetrakis(2-pyridylmethyl)-2,6-bis(aminomethyl)pyridine) are described. The X-ray crystal structures reveal seven-coordinate metal complex ions. Consideration of continuous shape measures reveals that the coordination environments about the metal ions are better described as having (C(s)) face-capped trigonal prismatic symmetry than (C(2)) pentagonal bipyramidal symmetry. The (S = (5)/(2)) Mn(II) species shows complicated X-band electron paramagnetic resonance (EPR) spectra and broad, unrevealing (1)H NMR spectra. In contrast, the (S = 2) Fe(II) complex is EPR-silent and shows completely interpretable (1)H NMR spectra containing the requisite number of paramagnetically shifted peaks in the range delta +150 to -60. The (13)C NMR spectra are likewise informative. Variable-temperature (1)H NMR spectra show coalescences and decoalescences indicative of an intramolecular process that pairwise-exchanges the nonequivalent pyridylmethyl "arms" of the two bis(pyridylmethyl)amine (bpa) domains. A suite of NMR techniques, including T(1) relaxation measurements and variable-temperature (1)H-(1)H correlation spectroscopy, (1)H-(1)H total correlation spectroscopy, (1)H-(1)H nuclear Overhauser effect spectroscopy/exchange spectroscopy, and (1)H-(13)C heteronuclear multiple-quantum coherence experiments, has been used to assign the NMR spectra and characterize the exchange process. Analysis of the data from these experiments yields the following thermodynamic parameters for the exchange: DeltaH++ = 53.6 +/- 2.8 kJ mol(-1), DeltaS++ = -10.0 +/- 9.8 J K(-1) mol(-1), and DeltaG++ (298 K) = 50.6 kJ mol(-1). Density functional theory (B3LYP) calculations have been used to explore the energetics of possible mechanistic pathways for the underlying fluxional process. The most plausible mechanism found involves dissociation of a pyridylmethyl arm to afford a strained six-coordinate species followed by rebinding of the arm in a different position to afford a new seven-coordinate transition state in which the pyridylmethyl arms within each bpa domain are essentially equivalent; the calculated energy barrier for this process is 53.5 kJ mol(-1), in good agreement with the observations.

Ruthenium phthalocyanine-bipyridyl dyads as sensitizers for dye-sensitized solar cells: dye coverage versus molecular efficiency.

The application of ruthenium phthalocyanine complexes as sensitizing dyes in dye-sensitized solar cells (DSCs) is explored. Four monomeric complexes are reported which vary in peripheral substitution and axial ligand anchoring groups. Sensitizing dyes containing two ruthenium centers are also presented. These dyads, which contain ruthenium phthalocyanine and bipyridyl chromophores, were prepared using a protection/deprotection strategy that allows for convenient purification. DSCs fabricated using the phthalocyanine complexes and dyads were less efficient than those incorporating a standard DSC dye. However, on the basis of the number of molecules bound to the TiO(2) electrode surfaces, several of the new complexes were more efficient at photocurrent generation. The results highlight the importance of molecular size, and thus the dye coverage of the electrode surface in the design of new sensitizing dyes.