Synthesis and characterization of Pt(II) and Pt(II)/Ru(II) complexes with the bidentate bridging ligand dipyrido(2,3-a:3′,2′-h)phenazine (dpop)

Three new complexes [Pt(dpop)(Cl)₂], [(Cl)₂Pt(dpop)Pt(Cl)₂] and [(bpy)₂Ru(dpop)Pt(Cl)₂](PF₆)₂ (dpop = dipyrido(2,3-a:3′,2′-h)phenazine) were prepared and studied. The electronic absorption spectra of the complexes display Pt dπ → dpop π* and Ru dπ → dpop π* MLCT transitions at longer wavelengths than for previously reported similar complexes. Results of cyclic voltammograms show reversible dpop centered reductions while for the mixed metal [(bpy)₂Ru(dpop)Pt(Cl)₂]²⁺ an irreversible Pt(II) oxidative wave precedes the Ru(II) oxidation/reduction couple. Spectroelectrochemical results show that all oxidative and reductive processes are completely reversible. The [(Cl)₂Pt(dpop)Pt(Cl)₂] complex cleaves in solution with pseudo-first order kinetics resulting in loss of the Pt dπ → dpop π* MLCT transition at 545 nm.     

DNA interaction studies of tridentate bridged Ru(II)-Pt(II) mixed-metal supramolecules

Reported herein are studies of the concentration and temperature dependent interactions with DNA of the stereochemically defined mixed-metal supramolecular complexes, [(tpy)Ru(tppz)PtCl](PF₆)₃ and [ClPt(tppz)Ru(tppz)PtCl](PF₆)₄ (tpy = 2,2′:6′,2′′-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine). These metal complexes couple a ruthenium based light absorber (LA) to the bioactive platinum sites (BAS) using a tridentate bridging ligand (BL). The complexes exhibit intense Ru → tppz(π∗) metal to ligand charge transfer (MLCT) transitions in the visible region and adopt a square planar geometry around the Pt(II) center. The effect of incubating these metal complexes with DNA on the subsequent migration of DNA through an agarose gel was found to be more dramatic than that observed for the well known anticancer drug, cis-[Pt(NH₃)₂Cl₂] (cisplatin). This effect was enhanced with increased incubation temperature. Unwinding of supercoiled plasmid DNA was found to be more pronounced for the trimetallic complex, [ClPt(tppz)Ru(tppz)PtCl](PF₆)₄, than for the bimetallic complex, [(tpy)Ru(tppz)PtCl](PF₆)₃.     

Synthesis and properties of electrochemiluminescent dinuclear Ru(II) complexes assembled with ester-bridged bis(bipyridine) ligands

New bridging ligands, such as bpy-(COOCH₂)-bpy (BL1), mbpy-(CH₂)₃COOCH₂-bpy (BL2), bpy-COO(CH₂)₆OOC-bpy (BL3), and bpy-COOCH₂PhPhCH₂OOC-bpy (BL4), have been synthesized and coordinated to [RuL₂(acetone)₂](PF₆)₂ for various [Ru(L)₂(BL)Ru(L)₂](PF₆)₄-type dinuclear ruthenium complexes (where BL = BL1, BL2, BL3, BL4, and L = bpy, o-phen, DTDP). Their electrochemical redox potentials, spectroscopic properties and relative electrochemiluminescence were investigated in detail. All dinuclear Ru complexes exhibit MLCT (metal-to-ligand charge transfer) absorption and luminescence bands in the visible region. ECL intensities of dinuclear ruthenium(II) complexes were affected not only by the kind of the ligand, but also by the nature of the bridging ligand. Among the synthesized dinuclear Ru complexes, [(DTDP)₂Ru(mbpy)-(CH₂)₃COOCH₂-(bpy)Ru(DTDP)₂](PF₆)₄ exhibited enhanced ECL intensities as high as 2.9 times greater than that of the reference, [Ru(o-phen)₃](PF₆)₂.     

Enhanced DNA photocleavage properties of Ru(II) terpyridine complexes upon incorporation of methylphenyl substituted terpyridine and/or the polyazine bridging ligand dpp (2,3-bis(2-pyridyl)pyrazine)

The heteroleptic complexes, [(MePhtpy)RuCl(dpp)](PF₆) and [(tpy)RuCl(dpp)](PF₆), have been synthesized, characterized, and investigated with respect to their photophysical, redox, and DNA photocleavage properties (where MePhtpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine, tpy = 2,2′:6′,2′′-terpyridine). The X-ray crystal structure confirms the identity of the new [(MePhtpy)RuCl(dpp)](PF₆) complex. These heteroleptic complexes were found to photocleave DNA in the presence of oxygen, unlike the previously studied complex, [Ru(tpy)₂](PF₆)₂. The photophysical, redox, and DNA photocleavage properties of the heteroleptic complexes were compared with those of the homoleptic complexes, [Ru(MePhtpy)₂](PF₆)₂ and [Ru(tpy)₂](PF₆)₂. The heteroleptic complexes showed intense metal to ligand charge transfer (MLCT) transition at lower energy ([(MePhtpy)RuCl(dpp)](PF₆), 522 nm; [(tpy)RuCl(dpp)](PF₆), 516 nm) and longer excited state lifetimes as compared to the homoleptic complexes. The [Ru(MePhtpy)₂]²⁺ complex was found to photocleave DNA in contrast to [Ru(tpy)₂]²⁺. The introduction of a methylphenyl group on the tepyridine ligand not only enhances the ³MLCT excited state lifetime but also increases the lipophilicity and thereby the DNA binding ability of the molecule. An increase in lipophilicity upon addition of a methylphenyl group on the 2,2′:6′,2′′-terpyridine ligand was confirmed by determination of the partition coefficient ([(MePhtpy)RuCl(dpp)](PF₆), log P = +1.16; [(tpy)RuCl(dpp)](PF₆), log P = −1.27). The heteroleptic complexes photocleave DNA more efficiently than the homoleptic complexes, with the greatest activity being observed for the newly prepared [(MePhtpy)RuCl(dpp)](PF₆) complex.     

Communication of metal ions in the dinuclear ruthenium complexes containing 4,4′-bipyridine, 1,4-diisocyanobenzene, and pyrazine bridging ligands: Synthesis, characterization and structure determination

Reaction of [Ru(2,2′-bipyridine)(2,2′:6′,2″-terpyridine)Cl]PF₆ (abbreviated to [Ru(bipy)(terpy)Cl]PF₆) with 0.5 equiv of the bidentate ligand L produces the dinuclear complexes [{Ru(bipy)(terpy)}₂(μ-L)](PF₆)₄ (L = 4,4′-bipyridine 1, 1,4-diisocyanobenzene 2 and pyrazine 3) in moderate yields. Treating [Ru(bipy)(terpy)Cl]PF₆ with equal molar of 1,4-diisocyanobenzene affords [Ru(bipy)(terpy)(CNC₆H₄NC)](PF₆)₂ (2a). These new complexes have been characterized by mass, NMR, and UV-Vis spectroscopy, and the structures of 1-3 determined by an X-ray diffraction study. Cyclic voltammetric studies suggest that metal communication between the two ruthenium ions increases from 1 to 2 to 3.     

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium-carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR₃)(CO)Cl]⁺ (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh₃)(CO)Cl]PF₆, [Ru(tpy)(P(p-tolyl)₃)(CO)Cl]PF₆ and [Ru(tpy)(PPh₃)(CH₃CN)Cl]PF₆ were determined by X-ray crystallography.     

On the elusive, non-emissive yet reactive, upper excited states of [(4,4′-bpy)Re(CO)3(dppz)]PF6 (dppz = dipyridil[3,2-a:2′3′-c]phenazine)

Gradual solvation of [(4,4′-bpy)Re^I(CO)₃(dppz)]⁺ (dppz = dipyridil[3,2-a:2′3′-c]phenazine) by water molecules causes a quenching of the emission in accordance with Perrin’s model of spheres. The calculated radius of the sphere, r = 2.6 ± 0.2 ?, is therefore very close to the distance from the Re center to the oxygen atom of the CO ligands, i.e., l = 2.73 ?. In addition, excited state reactions with TEA produce [(4,4′-bpy⁻)Re^I(CO)₃(dppz)] and [(4,4′-bpy)Re^I(CO)₃(dppz⁻)]. This experimental observation is inconsistent with the formation of the products in the lowest lying and emissive dppz-centered ³ππ* excited state. Jablonski schemes based on the participation of excited states other than the lowest ³ππ* excited state are proposed.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

Electrogenerated chemiluminescence of (bis-bipyridyl)ruthenium(II) acetylacetonate complexes

The synthesis, electrochemistry, spectroscopy and electrogenerated chemiluminescence (ECL) of five bis-bipyridine ruthenium(II) complexes containing acetylacetonate complexes are reported. More specifically, (bpy)₂Ru(BA)₂(PF₆) (bpy = 2,2′-bipyridine; BA = benzoylacetonate), (bpy)₂Ru(TTFA)(PF₆) (TTFA =  thenoyltrifluoroacetonate), (bpy)₂Ru(TFPB)(PF₆) (TFPB = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate), (bpy)₂Ru(TFPD)(PF₆) (TFPD =  1,1,1-trifluoro-2-4-pentanedionate), and (bpy)₂Ru(DBM)(PF₆) (DBM = dibenzoylmethide) display UV-Vis, photoluminescence, electrochemical and ECL properties characteristic of ruthenium bipyridyl complexes. All complexes display absorptions in the UV and visible regions of the spectra, with visible absorptions ranging from 350 to 700 nm, typical of metal-to-ligand charge transfer (MLCT) transitions. Photoluminescence emission maxima are also characteristic of MLCT transitions with wavelength maxima from 575 to 600 nm depending on the nature of the acetylacetonate ligand. ECL efficiencies for the complexes (?_ecl ∼ 0.013-0.051) are much lower than a standard (?_ecl = 1) with electron-withdrawing substituents resulting in lower efficiencies.     

Bipyrimidine-bridged rhenium(I)/rhenium(I) and ruthenium(II)/rhenium(I) complexes. Synthesis,electronic absorption and emission spectra

The binuclear complexes [Cl(OC)₃Re^I(bipym)Re^I(CO)₃Cl] (bipym=2,2′-bipyrimidine), [(bipy)₂Ru^II(bipym)Re^I(CO)₃Cl](PF₆)₂ (bipy=2,2′-bipyridine) and their mononuclear component [Re(bipym)(CO)₃Cl] were prepared. The electronic absorption spectra of these complexes display low-energy Re(I) →π*(bipym) and Ru(II)→π*(bipym) charge transfer (CT) bands. While [Re(bipym)(CO)₃Cl] shows a strong emission from its lowest CT state, the dimer [Cl(OC)₃Re(bipym)Re(CO)₃Cl] is not luminescent. The cation [(bipy)₂Ru(bipym)Re(CO)₃Cl]²⁺ emits from the lowest-energy Ru→bipym CT state. The emission behavior of the binuclear complexes is described in terms of intramolecular excited state electron or energy transfer.     

Synthesis and reactivity of cationic bipyridine tungsten(0) and molybdenum(0) nitrosyl complexes

A variety of Group 6 mono bipyridine (bpy) complexes were prepared, and substitution reactions of [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes (MeIm = 1-methylimidazole, M = W or Mo) were investigated. Nitrosylation of complexes having the general formula (bpy)(L)M(CO)₃ (L = a variable ligand) gave cationic complexes of the form [(bpy)(L)M(CO)₂(NO)]PF₆. The structure of [(bpy)(MeIm)W(CO)₂(NO)]PF₆ was confirmed by single-crystal X-ray diffractometry. [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes undergo facile substitutions with mono-, tri- and tetra-dentate ligands, yielding di- or mono-carbonyl mononitrosyl complexes. The structures of [(bpy)(PMe₃)₂W(CO)(NO)]PF₆ and [(dien)(PMe₃)W(CO)(NO)]PF₆ (dien = diethylenetriamine) were determined by X-ray diffraction.     

Novel [Ru(polypyridine)(CO)2Cl2] and [Ru(polypyridine)2(CO)Cl]-type complexes: Characterizing the effects of introducing azopyridyl ligands by electrochemical, spectroscopic and crystallographic measurements

The reaction of ruthenium carbonyl polymer ([Ru(CO)₂Cl₂]_n) with azopyridyl compounds (2,2′-azobispyridine; apy or 2-phenylazopyridine; pap) generated new complexes, [Ru(azo)(CO)₂Cl₂] (azo = apy, pap). [Ru(apy)(CO)₂Cl₂] underwent photodecarbonylation to give a chloro-bridged dimer complex, whereas the corresponding pap complex ([Ru(pap)(CO)₂Cl₂]) was not converted to a dimer. The reactions of the chloro-bridged dimer containing the bpy ligand (bpy = 2,2′-bipyridine) with either apy or pap resulted in the formation of mixed polypyridyl complexes, [Ru(azo)(bpy)(CO)Cl]⁺. The novel complexes containing azo ligands were characterized by various spectroscopic measurements including the determination of X-ray crystallographic structures. Both [Ru(azo)(CO)₂Cl₂] complexes have two CO groups in a cis position to each other and two chlorides in a trans position. The azo groups are situated cis to the CO ligand in [Ru(azo)(bpy)(CO)Cl]⁺. All complexes have azo N-N bond lengths of 1.26-1.29 Å. The complexes exhibited azo-based two-electron reduction processes in electrochemical measurements. The effects of introducing azopyridyl ligands to the ruthenium carbonyl complexes were examined by ligand-based redox potentials, stretching frequencies and force constants of CO groups and bond parameters around Ru-CO moieties.     

Photoinduced energy transfer between Re(I) and Ru(II) termini connected through a new exo-ditopic bis-phenanthroline ligand fused to a central macrocycle spacer: Synthesis, structure, and electrochemical and photophysical properties of a heterodinuclear complex

A new ligand L¹ has been prepared in which two 1,10-phenanthroline fragments are separated by an 18-crown-6 macrocyclic spacer. This was used to prepare the heterodinuclear complex [(bipy)₂Ru(μ-L¹)Re(CO)₃Cl][PF₆]₂ [Ru(L¹)Re] in which the {Ru(bipy)₂(phen)}²⁺ and {Re(CO)Cl(phen)} chromophores are separated by a saturated and fairly flexible crown-ether fragment. On the basis of photophysical studies on Ru(L¹)Re and associated mononuclear Ru(II) and Re(I) complexes, Re → Ru photoinduced energy-transfer occurs with a rate constant of 1.9 × 10⁸ s⁻¹ in solution room temperature leading to near-complete quenching of the Re(I)-based luminescence. At 77 K the Re(I)-based luminescence component is completely quenched. Calculations on the efficiency of both Förster and Dexter energy-transfer as a function of Re?Ru distance in this system suggest that a folded conformation of the complex, in which the Re?Ru separation is much shorter than that implied by the extended conformation detected crystallographically, is responsible for the energy-transfer, since neither Förster nor Dexter Re → Ru energy-transfer should be possible with the complex in an extended conformation. Addition of K⁺ or Ba²⁺ salts to solutions of Ru(L¹)Re had no effect on the photophysical properties, probably because the association constants are too low to give significant metal-ion binding in the macrocycle at the low concentrations employed.     

Novel mononuclear η-pentamethylcyclopentadienyl complexes of platinum group metals bearing pyrazolylpyridazine ligands: Syntheses and spectral studies

Condensation of 3,6-dichloropyridazine with 3,5-dimethylpyrazole in 1:1 ratio yielded one side substituted pyrazolylpyridazine ligand 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine (L) while condensation of 3,6-dichloropyridazine with substituted pyrazoles in 1:2 ratio yielded both side substituted pyrazolylpyridazine ligands such as 3,6-bis(pyrazolyl)pyridazine (L1), 3,6-bis(3-methylpyrazolyl)pyridazine (L2) and 3,6-bis(3,5-dimethylpyrazolyl)pyridazine (L3). A new series of cationic mononuclear complexes of the type [(η⁵-Cp)M_a(L)(PPh₃)]PF₆, [(η⁵-Cp*)M_b(L)Cl]PF₆, [(η⁵-Cp*)Ru(L′)(PPh₃)]PF₆ and [(η⁵-Cp*)M_b(L′)Cl]⁺ (where M_a = Ru, Os; M_b = Rh, Ir and L′ = L1, L2, L3) bearing pyrazolylpyridazine and η⁵-cyclopentadienyl ligands are reported. The complexes have been completely characterized by spectral studies. The molecular structures of representative complexes have been determined by single crystal X-ray crystallography.     

Synthesis, spectral and structural studies of water soluble arene ruthenium (II) complexes containing 2,2′-dipyridyl-N-alkylimine ligand

A series of water soluble complexes of general formula [(η⁶-arene)Ru{(C₅H₄N)₂CNRi}Cl]PF₆ have been prepared by the reaction of [{(η⁶-arene)RuCl₂}₂] with appropriate 2,2′-dipyridyl-N-alkylimine ligands (dpNRi) in the presence of NH₄PF₆ (where; R = Me or Et; arene = p-cymene, C₆Me₆, C₆H₆). The 2,2′-dipyridyl-N-alkylimine ligands are prepared by reaction of 2,2′-dipyridyl ketone with the corresponding alkylamine. The complexes are readily obtained as air stable yellow to dark brown solids by simple stirring at room temperature. The complexes are isolated as their hexafluorophosphate salts and characterized on the basis of spectroscopic data. The molecular structure of representative complex [(η⁶-C₆Me₆)Ru{(C₅H₄N)₂CN-Me}Cl]PF₆ has been determined by single crystal X-ray diffraction studies.     

Synthesis and characterization of β-diketonato ruthenium(II) complexes with two 4-bromo or protected 4-ethynyl-2,2′-bipyridine ligands

Two new mononuclear mixed-ligand ruthenium(II) complexes with acetylacetonate ion (2,4-pentanedionate, acac) and functionalized bipyridine (bpy) in position 4, [Ru(bpyBr)₂(acac)](PF₆) (2; bpyBr = 4-Bromo-2,2′-bipyridine, acac = 2,4-pentanedionate ion) and [Ru(bpyOH)₂(acac)](PF₆) (3; bpyOH = 4-[2-methyl-3-butyn-2-ol]-2,2′-bipyridine) were prepared as candidates for building blocks. The ¹H NMR, ¹³C NMR, UV-Vis, electrochemistry and FAB mass spectral data of these complexes are presented.     

Ruthenium(II/III) mediated transformation of 1,2-bis(2′-pyridylmethyleneimino)benzene (L) to 2-(2′-benzimidazolyl)pyridine (L′H) and its in situ formed complexes with Ru(II): X-ray structure of trans-[Ru(PPh3)2(L′H)2](ClO4)2

A series of ruthenium (II) complexes of formulae trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ (1), [Ru(bpy)(L′H)₂](ClO₄)₂ (2), [Ru(bpy)₂(L′H)](ClO₄)₂ (3), cis-[Ru(DMSO)₂(L′H)₂]Cl₂ (4), and [Ru(L′H)₃](PF₆)₂ (5) (where L′H = 2-(2′-benzimidazolyl)pyridine) have been synthesized by reaction of the appropriate ruthenium precursor with 1,2-bis(2′-pyridylmethyleneimino)benzene (L). The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. All the complexes were found to be diamagnetic and hence metal is in +2 oxidation state. The molecular structure of trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ has been determined by the single crystal X-ray diffraction studies. The molecular structure shows that Ru(II) is at the center of inversion of an octahedron with N₄P₂ coordination sphere. The ligand acts as a bidentate N,N′donor. The electronic spectra of the complexes display intense MLCT bands in the visible region.Cyclic voltammetric studies show quasi-reversible oxidative response at 0.99-1.32 V (vs Ag/AgCl reference electrode) due to Ru(III)/Ru(II) couple.     

Preparation and photophysical studies of copper(I) and ruthenium(II) complexes of 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine

We report the synthesis of a new ligand, 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine, optimised for binding to copper(I) and with pendant functionality that can eventually be developed into metallodendritic structures. The synthesis and photophysical properties of complexes with copper(I) and ruthenium(II) are reported. The solid state structure of the complex [Cu(1)₂][PF₆] · MeCN (1 = 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine) is also described.     

Studies on synthesis, characterization, and G-quadruplex binding of Ru(II) complexes containing two dppz ligands

In this work, the interaction between the guanine-rich single-strand oligomer AG₃(T₂AG₃)₃ quadruplex and two Ru(II) complexes, [Ru(L¹)(dppz)₂](PF₆)₄ (1) and [Ru(L²)(dppz)₂](PF₆)₄ (2) (L¹ = 5,5′-di(1-(trimethylammonio)methyl)-2,2′-dipyridyl cation, L² = 5,5′-di(1-(triethylammonio)methyl)-2,2′-dipyridyl cation, dppz = dipyrido[3,2-a:2′,3′-c] phenazine), has been studied by UV-Visible, fluorescence, DNA melting, and circular dichroism in K⁺ buffer. The two complexes after binding to G-quadruplex have shown different DNA stability and fluorescence enhancement. The results show that both complexes can induce the stabilization of quadruplex DNA. ΔT_m values of complexes 1 and 2 at [Ru]/[DNA] ratio of 1:1 were 9.4 and 7.0, respectively. Binding stoichiometry along with the quadruplex was investigated through a luminescence-based Job plot. The major inflection points for complexes 1 and 2 were 0.49 and 0.46, respectively. The data were consistent with the binding mode at a [quadruplex]/[complex] ratio of 1:1. In addition, the conformation of G-quadruplex was not changed by the complexes at the high ionic strength of K⁺ buffer.     

Efficiency enhancement of the electrocatalytic reduction of CO2: fac-[Re(v-bpy)(CO)3Cl] electropolymerized onto mesoporous TiO2 electrodes

As the greenhouse effect increases, the development of systems able to convert with high efficiency CO₂ to energetically rich molecules owns a crucial weight in the technological and environmental domain. As catalyst, rhenium complexes, of the type fac-[Re(L)(CO)₃Cl] (i.e. L = 2,2′-bipyridyl or 4,4′-bipyridyl), have attracted a large interest demonstrating promising catalytic properties. fac-[Re(v-bpy)(CO)₃Cl]-based polymer deposited onto a solid support has been already investigated as heterogeneous catalyst in the reduction of CO₂. Here, we deposited by electrochemical polymerization fac-[Re(v-bpy)(CO)₃Cl] onto a nanocrystalline TiO₂ film on glass and we investigated by cyclic voltammetry the properties of such heterogeneous catalyst in the electrochemical reduction of CO₂. We demonstrated that the nanoporous nature of the substrate allows to increase the two-dimensional number of redox sites per surface area and hence to get a significant enhancement of the catalytic yield.