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.     

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.     

Synthesis, structures and in vitro cytotoxicity of some cationic cis-platinum(II) complexes containing chelating thiocarbamates

The thiocarbamates 4-RC₆H₄NHC(S)NR₂′ (R = H, Cl; R′ = Me, Et), 4-ClC₆H₄NHC(S)NR (NR = 2-pyridylpiperazine) react with cis-[PtCl₂(PTA)₂] (PTA = 1,3,5-triaza-7-phosphaadamantane) in the presence of base to afford the monocationic platinum(II) complexes cis-[Pt{SC(NR₂′) = NC₆H₄R}(PTA)₂]⁺ (R = H, Cl; R′ = Me, Et), cis-[Pt{SC(NR) = NC₆H₄Cl}(PTA)₂]⁺ (NR = 2-pyridylpiperazine), which were isolated as their PF₆ salts in high yields. The complexes were fully characterised spectroscopically and also by X-ray crystallography. Cytotoxicity of these complexes was studied in vitro in three human cancer cell lines (CH1, A549 and SW480) using the MTT assay.     

Crystal structure, magnetic and electrochemical properties of five-coordinate copper (II) complexes with 1,10-phenanthroline-5,6-dione

Three new five-coordinate Cu^II complexes, [Cu(tpy)(phen-dione)](PF₆)₂, [Cu(phen)(phen-dione)Cl]PF₆ and [Cu(bpy)(phen-dione)Cl]PF₆ (tpy = 2,2′;6′,2″-terpyridine, phen = 1,10-phenanthroline and phen-dione = 1,10-phenanthroline-5,6-dione) have been prepared and characterized by elemental analysis, IR and UV-Vis spectroscopies and cyclic voltammetry.The complex of [Cu(tpy)(phen-dione)](PF₆)₂ crystallized with one molecule of acetonitrile. The ortep drawing of [Cu(tpy)(phen-dione)](PF₆)₂ · CH₃CN shows that the coordination geometry around Cu^II is a distorted trigonal- bipyramid. Due to the steric hindrance of in the unit cell, the tpy ligands in each complex cation cannot interact in a π-π fashion. The effective magnetic moment (μ_eff) of the complexes was measured by the Evans method. The cyclic voltammograms at Pt disk electrode for these complexes display only one reversible Cu(II)/Cu(I) redox couple.     

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.     

The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)₂(iso)NO](PF₆)₃ (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)₂(iso)Cl]PF₆ (2)_. The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO⁰)−2PF₆·CH₃OH]²⁺) and ([2−PF₆]⁺). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO^+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru^2+/3+ and bpy ^0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E_0-0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV.     

Synthesis and characterization of Os(II)(dpop′) (dpop′ = dipyrido(2,3-a;3′,2′-j)phenazine) complexes with 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)

New Os(II) complexes including [Os(dpop′)₂](PF₆)₂ (dpop′= dipyrido(2,3-a;3′,2′-j)phenazine) and a series of mixed ligand [Os(dpop′)(N-N)Cl]PF₆ (N-N = 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)) were synthesized. The Os dπ → dpop′ π^∗ MLCT transitions for [Os(dpop′)₂]²⁺ are observed at lower energy than for Os dπ → tpy π^∗ (tpy = 2,2′:6′,2″-terpyridine) and Os dπ → tppz π^∗ (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) (The ligand abbreviations tpd, tpp and tpypz have also appeared in the literature for 2,3,5,6- tetrakis(2-pyridyl)pyrazine in addition to tppz.) MLCT transitions in the comparative [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The Os dπ → dpop′ π^∗ MLCT transitions are observed at lower energy in mixed bidentate ligand N-N systems compared with [Os(dpop′)₂]²⁺. Cyclic voltammetry shows more positive osmium oxidation, and less negative ligand reduction potentials for [Os(dpop′)₂]²⁺ as compared to [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The osmium oxidation potentials in mixed ligand [Os(dpop′)(N-N)Cl]⁺ complexes are at less positive potential than for the [Os(dpop′)₂]²⁺ ion. NMR results show different chemical shifts for ring protons either trans or cis to dpop′ in mixed ligand systems, and also show two geometrical isomers for the [Os(dpop′)(dpp)Cl]⁺ complex. The [Os(dpop′)(dpp)Cl]⁺ geometric isomer with the pyrazine ring of dpp trans to dpop′ is found more predominate by 1.0/0.7 over the isomer with the pyrazine ring of dpp cis to dpop′ and that inter-conversion of geometric isomers does not occur in room temperature solution on the NMR timescale.     

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.     

Vibrational and structural mapping of [Os(bpy)3] and [Os(phen)3]

Structural changes between [Os^IIL₃]²⁺ and [Os^IIIL₃]³⁺ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the Os^III complexes [Os^III(bpy)₃]³⁺ and [Os^III(phen)₃]³⁺ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for [Os^II(bpy)₃](PF₆)₂, [Os^III(bpy)₃](PF₆)₃, [Os^II(phen)₃](PF₆)₂, and [Os^III(phen)₃](PF₆)₃ are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ are dominated by very intense absorptions (ε = 40 000-50 000 M⁻¹ cm⁻¹) due to bpy and phen intra-ligand π → π^∗ transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm⁻¹ appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, ¹π → ³π^∗ electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t_2g(Os^III) or π(phen) → t_2g(Os^III) transitions. In the near infrared, two broad absorption features appear for oxidized forms [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ arising from dπ-dπ interconfigurational bands characteristic of dπ⁵Os^III. They are observed at 4580 and 5090 cm⁻¹ for [Os^III(bpy)₃](PF₆)₃ and at 4400 and 4990 cm⁻¹ for [Os^III(phen)₃](PF₆)₃. The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [Os^III(bpy)₃](PF₆)₃, the Os^III atom resides at a distorted octahedral site, as judged by ∠N-Os-N, which varies from 78.78(22)° to 96.61(22)°. Os-N bond lengths are also in general longer for [Os^III(bpy)₃](PF₆)₃ compared to [Os^II(bpy)₃](PF₆)₂ (0.010 Å), and for [Os^III(phen)₃](PF₆)₃ compared to [Os^II(phen)₃](PF₆)₂ (0.014 Å). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(Os^II) → π^∗ (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.     

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.     

Structure and spectroscopic studies of cis-bis(bipyridine) ruthenium(II) complexes of phenylcyanamide ligands

New ruthenium(II) complexes with cyanamide ligands, cis-[Ru(bpy)₂(Ipcyd)₂] (1) and [Ru(bpy)₂(OHpcyd)₂] (2) (bpy = 2,2′-bipyridine, Ipcyd = 4-iodophenylcyanamide anion, OHpcyd = 4-(3-hydroxy-3-methylbut-1-ynil)phenylcyanamide), have been prepared and characterized by UV-Vis, IR and ¹H NMR spectroscopies as well as electrochemical technique (CV). The complex cis-[Ru(bpy)₂(Ipcyd)₂] (1) crystallized with empirical formula of C₃₄H₂₄I₂N₈Ru in a monoclinic crystal system and space group of P2₁/c with a = 11.769(7) Å, b = 24.188(12) Å, c = 11.623(2) Å, β = 91.63(3)°, V = 3308(3) ų and Z = 4.     

Controlled nitric oxide photo-release from nitro ruthenium complexes: The vasodilator response produced by UV light irradiation

Preliminary pharmacological studies of various nitric oxide (NO) photo-releasing agents are reported based on the flash-photolysis studies of the nitro ruthenium complexes cis-[Ru^II(NO₂)L(bpy)₂]⁺ (bpy = 2,2′-bipyridine and L = pyridine, 4-picoline and pyrazine) and [Ru^II(NO₂)(bpy)(terpy)]⁺ (terpy = terpyridine) in physiological medium. The net photoreactions under these conditions are two primary photoproducts, in (I) there is Ru^II-NO₂ photoaquation, where the photoproducts are Ru^II-H₂O plus and (II) homolytic dissociation of NO from a coordinated nitrito to derive the Ru^II-OH₂ specie and NO. Based on photochemical processes, the nitro ruthenium complexes were incorporated in water in oil (W/O) microemulsion and used in the vasorelaxation induced experiment. Denuded rat aortas were contracted with KCl and nitro ruthenium complexes in microemulsion were added. Perfusion pressures were recorded while arteries were irradiated at 355 nm The time to reach maximum relaxation was longer for [Ru^II(NO₂)(bpy)(terpy)]⁺ complex (ca. 50 min, n = 6) than for cis-[Ru(NO₂)L(bpy)₂]⁺ with L = py and 4-pic complex (ca. 28 min, n = 6) and cis-[Ru(NO₂)(bpy)₂ (pz)]²⁺ complex (ca. 24 min, n = 5).     

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.     

Synthesis, properties and solution speciation of lanthanide chloride complexes of triphenylphosphine oxide

The reaction of Ph₃PO with LnCl₃ · nH₂O (Ln=La-Lu ≠ Pm) in a 3.5:1 ratio in acetone produces [LnCl₃(Ph₃PO)₃], whilst from a 6:1 ratio in ethanol the products are [LnCl₂(Ph₃PO)₄]Cl · n(solvate). In the presence of [NH₄][PF₆] in ethanol solution, [LnCl₂(Ph₃PO)₄]PF₆ can be isolated. The last complexes are stable in solution but the [LnCl₃(Ph₃PO)₃] and [LnCl₂(Ph₃PO)₄]Cl partially interconvert in non-coordinating solvents, the neutral species being preferred by the lighter lanthanides, the cationic tetrakis complexes becoming more favoured towards the end of the series. The complexes have been characterised in the solid state by analysis and IR spectroscopy and in solution by ³¹P{¹H} NMR spectroscopy and conductance measurements. The crystal structures of trans-[LnCl₂(Ph₃PO)₄]Cl · nEtOH (Ln=Tb or Yb) and mer-[LnCl₃(Ph₃PO)₃] · 0.5Me₂CO (Ln=La or Ce) are reported and discussed.     

Mixed-valent and radical states of complexes [(bpy)2M(μ-abpy)M′(bpy)2], M,M′ = Ru or Os, abpy = 2,2′-azobispyridine: Electron transfer vs. hole transfer mechanism in azo ligand-bridged complexes

The title complexes were obtained as M^IIM′^II species [(bpy)₂M(μ-abpy)M′(bpy)₂](PF₆)₄, M,M′ = Ru or Os, using the new mononuclear precursor [(bpy)₂Os(abpy)](PF₆)₂ for the osmium-containing dinuclear complexes. One-electron reduction produces radical complexes [(bpy)₂M(μ-abpy)M′(bpy)₂]³⁺ and [(bpy)₂M(abpy)]⁺ with significant contributions from the metals, as evident from the EPR effects on successive replacement of ruthenium by osmium with its much higher spin-orbit coupling constant. The diruthenium and diosmium radical complexes were also studied by EPR at high-frequency (285 GHz), the latter shows an unusually large g anisotropy g₁ − g₃ = 0.25 in frozen solution. Further reduction was monitored by UV/Vis spectroelectrochemistry. Oxidation produced Os^III EPR signals for [(bpy)₂Os(abpy)]³⁺ and [(bpy)₂Os(μ-abpy)Ru(bpy)₂]⁵⁺, indicating a Ru^IIOs^III species for the latter. The diosmium(III,II) and diruthenium(III,II) mixed-valent species remained EPR silent at 4 K, however, they exhibit weak inter-valence charge transfer (IVCT) bands at about 1460 nm. Whereas the cyclic voltammetric response towards reduction is only marginally different for the three dinuclear complexes, successive replacement of ruthenium by osmium causes the first oxidation potential to decrease. The much higher comproportionation constant K_c for the mixed valent diosmium(III,II) state (K_c > 10¹⁵) in comparison to the diruthenium(III,II) analogue with K_c = 10¹⁰ confirms the electron transfer alternative for the valence exchange mechanism, in contrast to the hole transfer established for analogous dinuclear complexes with the formally related diacylhydrazido(2−) bridging ligands.     

Platinum (II) and palladium (II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes as intramolecular hydroamination catalysts in aqueous and organic media

Complexes of the general formula cis-[MX₂(PTA)₂] (M = Pd, Pt; X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were used to study the catalytic intramolecular hydroamination/cyclization of 4-pentyn-1-amine into 2-methyl-pyrroline in water, methanol, and dimethyl sulfoxide (DMSO). Kinetic data were measured via ¹H NMR under homogeneous conditions at 50 °C and showed the following trends in rate: (i) Fastest rates were observed in D₂O. (ii) The Pd complexes of this study produced faster rates than the Pt complexes. (iii) The identity of the halide had no effect on the catalytic rate. Cyclization by the catalytic precursor cis-[PdCl₂(PTA)₂] (4) in D₂O was zero-order in substrate and first-order in metal complex with ΔH^‡ = 20.0 ± 2.1 kcal/mol, ΔS^‡ = −7.4 ± 6.3 cal/mol K, and E_a = 20.6 ± 2.1 kcal/mol. The acetylide complex, trans-[Pt(CC(CH₂)₃NH₂)₂(PTA)₂] (6) precipitated from a catalytic mixture involving cis-[PtBr₂(PTA)₂] (2). Spectroscopic and kinetic studies indicated that 6 and its cis analog, 7, were the predominant species in solution and that they were both active catalysts for the cyclization reaction. These data, in conjunction with the rate trends, indicated that the mechanism of the Pd(II) and Pt(II) catalyzed hydroamination of terminal alkynylamines in aqueous solution followed a unique mechanism with cyclization of an acetylenic-amine ligand being rate determining.     

Cyclometalated ruthenium(II) complexes of benzo[h]quinoline (bzqH)[Ru(bzq)(NCMe)4], [Ru(bzq)(LL)(NCMe)2], and [Ru(bzq)(LL)2] (LL = bpy, phen)

Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η⁶-C₆H₆)]₂ in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)₄]PF₆ (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)₄]PF₆ (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)₄]PF₆ complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)₂]PF₆, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)₂]PF₆ {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)₂]PF₆ {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF₆ as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)₂]PF₆, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4-7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography.     

Synthesis and characterization of binuclear mercury(II) complexes of phosphorus ylides, X-ray analysis and multinuclear NMR measurements

The reactions of phosphorus ylide (p-tolyl)₃PCHC(O)CH₃ (Y₁) with HgX₂ (X = Cl and Br) and (p-tolyl)₃PCHC(O)C₆H₄NO₂ (Y₂) with HgX₂ (X = Cl, Br and I) in equimolar ratios using methanol as a solvent are reported. These reactions led to binuclear complexes. C-Coordination of ylides and trans-like structure of complexes [(Y₁) · HgBr₂]₂ and [(Y₂) · HgBr₂]₂ · 2DMSO are demonstrated by single crystal X-ray analyses. The IR, ¹H, ¹³C and ³¹P NMR data for the other synthesized compounds are similar to the latter complexes, indicating similar structures. Elemental analyses indicate a 1:1 stoichiometry between the ylide and Hg(II) halide in all the products. The ab initio studies indicated that for all dimeric compounds, the observed trans-like structures are 7-10 kcal/mol more stable than the alternative possible cis-like isomers. Although the calculated bond lengths are slightly longer than the measured ones, the similarity of calculated and measured bond angles reflects the similar geometrical structures for these compounds in both the solid state and the gas phase.     

Synthesis, characterization, photophysics and intramolecular energy transfer process in bimetallic rhenium(I)-ruthenium(II) complexes

Two new heterobimetallic complexes of rhenium(I) and ruthenium(II) [(CO)₃(NN)Re(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂ and already known monometallic complexes [Cl(NN)₂Ru(4,4′-bpy)](PF₆) and [(CO)₃(NN)Re(4,4′-bpy)](PF₆) and bimetallic complexes [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂, [(CO)₃(NN)Re(4,4′-bpy)Re(NN)(CO)₃](PF₆)₂ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized by spectral techniques. The photophysical properties of all the complexes are studied. It is found that attachment of rhenium(I) altered the photophysical characteristics of ruthenium(II). Excited state energy transfer from the rhenium(I) chromophore to the ruthenium(II) is observed upon excitation at 355 nm.