Kinetics and mechanism of epoxidation of olefins by a novel ruthenium(IV)-oxo complex

[Ru^IV(tpy)(pic)(O)]⁺ (1) was synthesized by chemical oxidation of the corresponding aqua-complex [Ru^II(tpy)(pic)(H₂O)]⁺ (2) and characterized by analytical, spectroscopic (UV-vis and IR) and magnetic moment studies. Complex 1 effected epoxidation of styrene and substituted styrenes, cis- and trans-stilbenes and cyclohexene, in CH₃CN at room temperature. Epoxides were found to be the major product for styrenes and stilbenes, whereas, the oxidation of cyclohexene yielded allylic oxidation product. Detailed kinetic studies were performed under pseudo-first order conditions of excess alkene concentrations. A working mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to the data reported for the alkene oxidation by relevant Ru^IVO system in CH₃CN.     

Reactivity of a cobalt(III)-peroxo complex in oxidative nucleophilic reactions

A mononuclear cobalt(III)-peroxo complex bearing a macrocyclic tetradentate N₄ ligand, [Co^III(TMC)(O₂)]⁺ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was generated in the reaction of [Co^II(TMC)]²⁺ and H₂O₂ in the presence of triethylamine in CH₃CN. The reactivity of the cobalt(III)-peroxo complex was investigated in aldehyde deformylation with various aldehydes and compared with that of iron(III)- and manganese(III)-peroxo complexes, such as [Fe^III(TMC)(O₂)]⁺ and [Mn^III(TMC)(O₂)]⁺. In this reactivity comparison, the reactivities of metal-peroxo species were found to be in the order of [Mn^III(TMC)(O₂)]⁺ > [Co^III(TMC)(O₂)]⁺ > [Fe^III(TMC)(O₂)]⁺. A positive Hammett ρ value of 1.8, obtained in the reactions of [Co^III(TMC)(O₂)]⁺ and para-substituted benzaldehydes, demonstrates that the aldehyde deformylation by the cobalt(III)-peroxo species occurs via a nucleophilic reaction.     

Generation of trans-dioxoruthenium(VI) porphyrins: A photochemical approach

trans-Dioxoruthenium(VI) porphyrin complexes have been developed as one of the best-characterized model systems for heme-containing enzymes. Traditionally, this type of compounds can be prepared by oxidation of ruthenium(II) precursors with peroxyacids and other terminal oxidants under different conditions, depending on the porphyrin ligands. In this work, a new photochemical generation of trans-dioxoruthenium(VI) porphyrins has been developed by extension of the known photo-induced ligand cleavage reactions. Refluxing ruthenium(II) carbonyl porphyrins [Ru^II(Por)(CO)] in carbon tetrachloride afforded dichlororuthenium(IV) complexes [Ru^IV(Por)Cl₂]. Facile exchange of the counterions in [Ru^IV(Por)Cl₂] with Ag(ClO₃) or Ag(BrO₃) gave the corresponding dichlorate [Ru^IV(Por)(ClO₃)₂] or dibromate [Ru^IV(Por)(BrO₃)₂] salts. Visible-light photolysis of the photo-labile porphyrin-ruthenium(IV) dichlorates or dibromates resulted in homolytic cleavage of the two O-Cl or O-Br bonds in the axial ligands to produce trans-dioxoruthenium(IV) species [Ru^VI(Por)O₂] bearing different porphyrin ligands.     

Oxo-transfer catalysis from t-BuOOH with C-H bond insertion using tridentate Schiff-base-chelate complexes of ruthenium(III)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived by condensation of aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) with 2-aminobenzoic acid, and bidentate ligands (2,2^′-bipyridine or picolinic acid). [Ru^III(cpsd)(bipy)(H₂O)]⁺ (1), [Ru^III(cpsd)(pic)(H₂O)] (2), [Ru^III(cppc)(bipy)(H₂O)]²⁺ (3) and [Ru^III(cppc)(pic)(H₂O)]⁺ (4) complexes (where, cpsd²⁻=(N-(2-carboxyphenyl)salicylaldiminato); cppc⁻=N-2-carboxyphenylpyridine-2-carboxaldiminato; bipy=2,2^′-bipyridine and pic⁻=picolinate) were characterized by analytical, spectral (IR and UV-Vis), conductance, magnetic moment and electrochemical studies. Catalysis of hydrocarbon oxidations for cyclohexene, cyclohexane, cyclohexanol, toluene, benzyl alcohol, and tetrahydrofuran have been studied using various O-atom transfer agents (t-BuOOH, H₂O₂, NaOCl, KHSO₅ and pyridinium-N-oxide). The influence of product yield as a function of solvent was evaluated for CH₂Cl₂, CH₃CN, and 1,4-dioxane. Coordinating solvents suppress the reactivity by inhibiting coordination of t-BuOOH, and compete for the Ru^VO group through their own intrinsic C-H reactivity. The main pathway transfers the oxo group from the [RuO(TDL)(XY)] intermediate, TDL=cpsd²⁻ and cppc²⁻; XY=bipy or pic⁻, with insertion of the oxo group into a C-H bond of all substrates tested (rather than olefin epoxidation for cyclohexene). A mechanism involving intermediacy of a high valent Ru(V)-oxo species is proposed for the catalytic oxidation processes.     

Reactivity of [Ru(pac)(H2O)] (pac = polyaminocarboxylate) complexes with 5′-nucleotides and their antitumor activity

The reaction of [Ru^III(edta)(H₂O)]⁻ (edta⁴⁻ = ethylenediaminetetraacetate) and [Ru^III(hedtra)(H₂O)] (hedtra³⁻ = N-hydroxyethylethylenediaminetriacetate) with various purine based 5′-nucleotides (Nu) viz. adenosin-5′-monophosphate (AMP), guanosin-5′-monophosphate (GMP), inosin-5′-monophosphate (IMP) was studied kinetically as a function of [Nu] at various temperatures (15-35 °C) at a fixed pH (4.5). Kinetic results suggest that the binding of 5′-nucleotides takes place in a rapid [Nu] dependent rate-determining step. Kinetic data and activation parameters are accounted for the operation of an associative mechanism. The antitumor activities of both [Ru^III(edta)(H₂O)]⁻ (1) and [Ru^III(hedtra)(H₂O] (2) have been evaluated using MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.     

Stepwise syntheses, structure and spectroscopic studies of ruthenium complexes of 2,6-bis(benzimidazol-2-yl)pyridine with o-iminoquinone ancillary ligand

The ruthenium complexes [Ru^II(bbp)(L)(Cl)] (1), [Ru^II(bbp)(L)(H₂O)] (2) and [Ru^II(bbp)(L)(DMSO)] (3) {bbp = 2,6-bis(benzimidazol-2-yl)pyridine, L = o-iminoquinone} have been synthesized in a stepwise manner starting from [Ru^III(bbp)Cl₃]. The single crystal X-ray structures, except for the complex 2, have been determined. All the complexes were characterized by UV-Vis, FT-IR, ¹H NMR, Mass spectroscopic techniques and cyclic voltammetry. The Ru^III/Ru^II couple for complexes 1, 2, and 3 appears at 0.63, 0.49, 0.55 V, respectively versus SCE. It is observed that complex 2, on refluxing in acetonitrile, results into [Ru^II(bbp)(L)(CH₃CN)], 4 which has been prepared earlier in a different method. The structural, spectral and electrochemical properties of complexes 1, 2 and 3 were compared to those of earlier reported complex 4, [Ru^II(bbp)(L)(CH₃CN)].     

Oxidation of hydroquinones by a nonheme iron(IV)-oxo species

The reactivity of an isolated, well-characterized nonheme iron(IV)-oxo complex, [(TMC)Fe^IVO]²⁺ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been examined in the oxidation of hydroquinones. This complex has been shown to oxidize a series of hydroquinones, resulting in the production of the corresponding quinone products. Kinetic studies performed with substituted hydroquinones revealed a good correlation between reaction rates of the iron(IV)-oxo complex and the electron-donating ability of the substituents and the bond dissociation energy (BDE) of substrate O-H bonds. These results with a kinetic isotope effect (KIE) of 2.7 led us to propose a hydrogen-atom abstraction mechanism for the oxidation of hydroquinones by the nonheme iron(IV)-oxo species.     

Structural, spectroscopic and redox studies of a new ruthenium(III) complex with an imidazole-rich tripodal ligand

The present paper describes a new tripodal ligand containing imidazole and pyridine arms and its first cis-[Ru^III(L)(Cl)₂]ClO₄ complex (1). The crystal structure of 1 shows Ru^III in a distorted octahedral geometry, in which two chloride ions, cis-positioned to each other, are coordinated besides the four nitrogen atoms from the tetradentate ligand L. The cyclic voltammogram of 1 exhibits three redox processes at −67, +73 and +200 mV versus SCE, which are attributed to the Ru^III/Ru^II couple in the cis-[Ru^III(L)(Cl)₂]⁺, cis-[Ru^II(L)(H₂O)(Cl)]⁺ and cis-[Ru^II(L)(H₂O)₂]²⁺, respectively. After chemical reduction (Zn(Hg) or Eu^II) only the cis-[Ru^II(L)(H₂O)₂]²⁺ species is observed in the cyclic voltammetry. Complex 1 absorbs at 470 nm (ε=1.4×10³ mol⁻¹ L cm⁻¹), 335 nm (ε=7.9×10³ mol⁻¹ L cm⁻¹), 301 nm (ε=6.7×10³ mol⁻¹ L cm⁻¹) and 264 nm (ε=9.9×10³ mol⁻¹ L cm⁻¹), in water solution (CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ with CF₃COONa). Spectroelectrochemical experiments show a decrease of the bands at 335 and 301 nm, which are attributed to LMCT transitions from the chloride to the Ru^III center and the appearance of a broad band at 402 nm ascribed to MLCT transition from the Ru^II center to the pyridine ligand. The lability of the water ligands in the cis-[Ru^II(L)(H₂O)₂]²⁺ species has been investigated using the auxiliary ligand pyrazine. Reactions in the presence of stoichiometric and excess of pyrazine yield the same species, cis-[Ru^II(L)(H₂O)(pz)]²⁺, which exhibits a reversible redox process at 493 mV versus SCE and absorbs at 438 nm (ε=5.1×10³ mol⁻¹ L cm⁻¹) and 394 nm (ε=4.2×10³ mol⁻¹ L cm⁻¹). Experiments performed with a large excess of pyrazine gave a specific rate constant k₁=(2.8±0.5)×10⁻² M⁻¹ s⁻¹, at 25 °C, in CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ (with CF₃COONa).     

Iron-oxidation-state-dependent O-O bond cleavage of meta-chloroperbenzoic acid to form an iron(IV)-oxo complex

The mechanism of formation of [Fe^IV(O)(N4Py)]²⁺ (2, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) from the reaction of [Fe^II(N4Py)(CH₃CN)]²⁺ (1) with m-chloroperbenzoic acid (mCPBA) in CH₂Cl₂ at −30 °C has been studied on the basis of the visible spectral changes observed and the reaction stoichiometry. It is shown that the conversion of 1 to 2 in 90% yield requires 1.5 equiv. peracid and takes place in two successive one-electron steps via an [Fe^III(N4Py)OH]²⁺(3) intermediate. The first oxidation step uses 0.5 equiv. peracid and produces 0.5 equiv. 3-chlorobenzoic acid, while the second step uses 1 equiv. peracid and affords byproducts derived from chlorophenyl radical. We conclude that the Fe^II(N4Py) center promotes O-O bond heterolysis, while the Fe^III(N4Py) center favors O-O bond homolysis, so the nature of O-O bond cleavage is dependent on the iron oxidation state.     

Trans-pyridine tetraammine complexes of RuII and RuIII with N7-coordninated purine nucleosides

 The synthesis, spectroscopic, and electrochemical properties of trans-[L(Pyr)(NH₃)₄Ru^II/III] (Pyr=py, 3-phpy, 4-phpy, 3-bnpy, or 4-bnpy; L=H₂O, Guo, dGuo, 1MeGuo, Gua, Ino, or G⁷-DNA) are reported. As expected, the Pyr ligand slows DNA binding by trans-[(H₂O)(Pyr)(NH₃)₄Ru^II]²⁺ relative to [(H₂O)(NH₃)₅Ru^II]²⁺ and favors reduction of Ru^III by about 150 mV. The pyridine ligand also promotes the disproportionation of Ru^III to afford the corresponding complexes of Ru^II and, presumably, Ru^IV. For L=Ino, disproportionation follows the rate law: d[Ru^II]/dt=k ₀[Ru^III]+k ₁[OH^–][Ru^III], k ₀=(2.7±0.7)×10^–4s^–1 and k ₁=70±1 M^–1s^–1. Received: 11 May 1998 / Accepted: 3 March 1999     

Synthesis, structure and solution chemistry of mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands

In the title family, the ONO donor ligands are the acetylhydrazones of salicylaldehyde (H₂L¹) and 2-hydroxyacetophenone (H₂L²) (general abbreviation, H₂L). The reaction of bis(acetylacetonato)oxovanadium(IV) with a mixture of tridentate H₂L and a bidentate NN donor [e.g., 2,2′-bipyridine(bpy) or 1,10-phenanthroline(phen), hereafter B] ligands in equimolar ratio afforded the tetravalent complexes of the type [V^IVO(L)(B)]; complexes (1)-(4) whereas, if B is replaced by 8-hydroxyquinoline(Hhq) (which is a bidentate ON donor ligand), the above reaction mixture yielded the pentavalent complexes of the type [V^VO(L)(hq)]; complexes (5) and (6). Aerial oxygen is most likely the oxidant (for the oxidation of V^IV → V^V) in the synthesis of pentavalent complexes (5) and (6). [V^IVO(L)(B)] complexes are one electron paramagnetic and display axial EPR spectra, while the [V^VO(L)(hq)] complexes are diamagnetic. The X-ray structure of [V^VO(L²)(hq)] (6) indicates that H₂L² ligand is bonded with the vanadium meridionally in a tridentate dinegative fashion through its phenolic-O, enolic-O and imine-N atoms. The general bond length order is: oxo < phenolato < enolato. The V-O (enolato) bond is longer than V-O (phenolato) bond by ∼0.07 Å and is identical with V-O (carboxylate) bond. ¹H NMR spectrum of (6) in CDCl₃ solution indicates that the binding nature in the solid state is also retained in solution. Complexes (1)-(4) display two ligand-field transitions in the visible region near 820 and 480 nm in DMF solution and exhibit irreversible oxidation peak near +0.60 V versus SCE in DMSO solution, while complexes (5) and (6) exhibit only LMCT band near 535 nm and display quasi-reversible one electron reduction peak near −0.10 V versus SCE in CH₂Cl₂ solution. The VO³⁺-VO²⁺E_1/2 values shift considerably to more negative values when neutral NN donor is replaced by anionic ON donor species and it also provides better VO³⁺ binding via phenolato oxygen. For a given bidentate ligand, E_1/2 increases in the order: (L²)²⁻ < (L¹)²⁻.     

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2′-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)₂(mppne)]²⁺ (bpy is 2, 2′–bipyridyl), [Ru(bpy)₂(mppae)]²⁺, [Ru(bpy)₂(mpppe)]²⁺, [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, ¹H NMR, fast-atom bombardment or electron-impact mass, UV–vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d _Ru→π*_sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d _Ru→π*_bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the ¹H NMR method. [Ru(bpy)₂(mppne)]²⁺, [Ru(bpy)₂(mppae)]²⁺ and [Ru(bpy)₂(mpppe)]²⁺ exhibit redox waves corresponding to the Ru^III/Ru^II couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH₃CN, 0.1 M tetrabutylammonium hexafluorophosphate)—corresponding voltammograms of [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)₂(mppne)]²⁺ and [Ru(bpy)₂(mppae)]²⁺ are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10⁵ to 10⁶ M⁻¹. Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)₂(mppne)]²⁺>[Ru(bpy)₂(mppae)]²⁺, although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)₂(sq)]⁺-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.Electronic Supplementary Material Supplementary material is available for this article at .     

Synthesis and molecular structure of trinuclear mixed-metal cluster cations containing arene and hydrido ligands

The mixed-metal trinuclear cluster cations [H₃Ru₂(C₆Me₆)₂Os(C₆H₆)(O)]⁺ (1), [H₃Ru₂(1,2,4,5-C₆H₂Me₄)₂Os(p-MeC₆H₄ⁱPr)(O)]⁺ (2) and [H₃Ru₂(1,2,4,5-C₆H₂Me₄)₂Os(C₆H₆)(O)]⁺ (3) have been synthesised from the corresponding dinuclear precursors [H₃Ru₂(arene)₂]⁺ and the corresponding mononuclear complexes [Os(arene)(H₂O)₃]²⁺, isolated and characterised as the tetrafluoroborate and hexafluorophosphate salts. The cations 1, 2 and 3 are heteronuclear analogues of the cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺ that possesses a homonuclear metallic core. The single-crystal X-ray structure analyses of [1][BF₄], [2][PF₆] and [3][PF₆] reveal an equiangular metal triangle despite the presence of an osmium atom in the metallic core.     

Disproportionation of pentaammineruthenium(III)–nucleoside complexes leads to two-electron oxidation of nucleosides without involving oxygen molecules

Pentaammineruthenium(III) complexes of deoxyinosine (dIno) and xanthosine (Xao) ([Ru^III(NH₃)₅(L)], L?is?dIno, Xao) in basic solution were studied by UV?Cvis spectroscopy, liquid chromatography/electrospray ionization mass spectrometry, and high-performance liquid chromatography. Both Ru^III complexes disproportionate to Ru^II and Ru^IV. Disproportionation followed the rate law d[Ru^II]/dt?=?(k _o?+?k ₁[OH^?])[Ru^III]. k _o and k ₁ of disproportionation at 25?°C were 2.1 (±0.1)?×?10^?3?s^?1 and 21.4?±?3.2?M^?1 s^?1, respectively, for [Ru^III(NH₃)₅(dIno)], and 3.5 (±0.7)?×?10^?4?s^?1 and 59.7?±?3.6?M^?1?s^?1, respectively, for [Ru^III(NH₃)₅(Xao)]. The [Ru^III(NH₃)₅(Xao)] complex disproportionates at a faster rate than [Ru^III(NH₃)₅(dIno)] owing to the stronger electron-withdrawing effect of exocyclic oxygen in Xao. The activation parameters ??H ^? and ??S ^? for k ₁ of [Ru^III(NH₃)₅(dIno)] were 80.2?±?15.2?kJ?mol^?1 and 47.6?±?9.8?J?K^?1 mol^?1, respectively, indicating that the disproportionation of Ru^III to Ru^II and Ru^IV is favored owing to the positive entropy of activation. The final products of both complexes in basic solution under Ar were compared with those under O₂. Under both conditions [Ru(NH₃)₅(8-oxo-L)] was produced, but via different mechanisms. In both aerobic and anaerobic conditions, the deprotonation of highly positively polarized C8-H of Ru-L by OH^? initiates a two-electron redox reaction. For the next step, we propose a one-step two-electron redox reaction between L and Ru^IV under anaerobic conditions, which differentiates from Clarke??s mechanism of two consecutive one-electron redox reactions between L, Ru^III, and O₂.     

Infrared and Raman studies of [UO2(salen)(L)] (L=H2O and CH3OH)

The infrared and Raman spectra of [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)] (salen=N,N′-ethylenebis(salicylideneimine) have been recorded. Assignments for the fundamental vibrations are proposed on the basis of C_2v symmetry for the former species and C_s for the latter. The calculated values of the stretching force constant of the uranyl group, F_UO, are 6.87 and 6.63 mdyn Å⁻¹ for [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)], respectively. The corresponding values of the UO bond lengths calculated as 1.738 and 1.745 Å.     

Ternary oxovanadium(IV) complexes with amino acid-Schiff base and polypyridyl derivatives: synthesis, characterization, and protein tyrosine phosphatase 1B inhibition

To investigate the structure-activity relationship of vanadium complexes in inhibiting protein tyrosine phosphatase1B (PTP1B), eight mixed-ligand oxovanadium(IV) complexes, [V^IVO(SalAla)(NN)] (H₂SalAla for salicylidene alanine, NN for N,N′-donor heterocyclic base, namely, 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 3), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 4)), [V^IVO(SalLys)(dpq)] (5), [V^IVO(SalLys)(dppz)] (6), [V^IVO(SalAsp)(dppz)], (7) and [V^IVO(SalTrp)(dppz)] (8)), of which 3-8 are new, have been prepared and characterized by elemental analysis, infrared, UV-visible, electrospray ionization mass spectrometry and conductivity. The molar conductance data confirmed the non-electrolytic nature of the complexes in DMSO solution. The coordination in [V^IVO (SalAla)(phen)] (2) was confirmed by X-ray crystal structure analysis. The oxidation state of V(IV) with d¹ configuration in 2 was confirmed by EPR. The speciation of VO-SalAla-phen in aqueous solution was investigated by potentiometric pH titrations. The results indicate that the main species are two ternary complexes at the pH range 7.0-7.4. Biochemical assays demonstrate that the mixed-ligand oxovanadium(IV) complexes are potent inhibitors of PTP1B with IC₅₀ values in the range of 62-597 nM, approximately 3-10 fold weaker in potency than those of similar mixed-ligand oxovanadium(IV) complexes of salicylidene anthranilic acid (SAA) derivative with polypyridyl ligands, except complex 8, which exhibits comparable or better inhibition activity than those of the mixed-ligand oxovanadium(IV) complexes of SAA derivative with polypyridyl ligands. The results demonstrate that the structures of vanadium complexes influence the PTP1B inhibition activity. Kinetics assays reveal that complex 2 inhibits PTP1B in a competitive manner.     

The reaction of bis(isopropylphosphino)methane with ruthenium carbonyl

Reaction of ⁱPrHPCH₂PHⁱPr with [Ru₃(CO)₁₂] in the presence of [(Ph₃P)₂N]CN catalyst gave sequentially [Ru₃(CO)₁₀(μ-ⁱPrHPCH₂PHⁱPr)] and [Ru₃- (CO)₉(μ-H)(μ₃-ⁱPrHPCH₂PⁱPr)]. The former complex exists in two isomeric forms. The structures were determined by ¹H and ³¹P NMR spectroscopy.     

Ternary oxovanadium(IV) complexes of ONO-donor Schiff base and polypyridyl derivatives as protein tyrosine phosphatase inhibitors: synthesis, characterization, and biological activities

Abstract  A series of oxovanadium complexes with mixed ligands, a tridentate ONO-donor Schiff base ligand [viz., salicylidene anthranilic acid (SAA)], and a bidentate NN ligand [viz., 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), dipyrido[3,2-a:2′,3′-c]phenazine (dppz), or 7-methyldipyrido[3,2-a:2′,3′-c]phenazine (dppm)], have been synthesized and characterized by elemental analysis, electrospray ionization mass spectrometry, UV–vis spectroscopy, Fourier transform IR spectroscopy, EPR spectroscopy, and X-ray crystallography. Crystal structures of both complexes, [V^IVO(SAA)(bpy)]·0.25bpy and [V^IVO(SAA)(phen)]·0.33H₂O, reveal that oxovanadium(IV) is coordinated with one nitrogen and two oxygen atoms from the Schiff base and two nitrogen atoms from the bidentate planar ligands, in a distorted octahedral geometry (VO₃N₃). The oxidation state of V(IV) with d ¹ configuration was confirmed by EPR spectroscopy. The speciation of VO–SAA–bpy in aqueous solution was investigated by potentiomtreic pH titrations, and the results revealed that the main species are two ternary complexes at a pH range of 7.0–7.4, and one is the isolated crystalline complex. The complexes have been found to be potent inhibitors against human protein tyrosine phosphatase 1B (PTP1B) (IC₅₀ approximately 30–61 nM), T-cell protein tyrosine phosphatase (TCPTP), and Src homology phosphatase 1 (SHP-1) in vitro. Interestingly, the [V^IVO(SAA)(bpy)] complex selectively inhibits PTP1B over the other two phosphatases (approximate ninefold selectivity against SHP-1 and about twofold selectivity against TCPTP). Kinetics assays suggest that the complexes inhibit PTP1B in a competitive and reversible manner. These suggest that the complexes may be promising candidates as novel antidiabetic agents. Graphical Abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Electrochemical oxidation of Mo(CO)4(LL) and Mo(CO)3(LL)(CH3CN): Generation, infrared characterization, and reactivity of [Mo(CO)4(LL)] and [Mo(CO)3(LL)(CH3CN)] (LL = 2,2′-bipyridine, 1,10-phenanthroline and related ligands)

Mo(CO)₄(LL) complexes, where LL = polypyridyl ligands such as 2,2′-bipyridine and 1,10-phenanthroline, undergo quasi-reversible, one-electron oxidations in methylene chloride yielding the corresponding radical cations, [Mo(CO)₄(LL)]⁺. These electrogenerated species undergo rapid ligand substitution in the presence of acetonitrile, yielding [Mo(CO)₃(LL)(CH₃CN)]⁺; rate constants for these substitutions were measured using chronocoulometry and were found to be influenced by the steric and electronic properties of the polypyridyl ligands. [Mo(CO)₃(LL)(CH₃CN)]⁺ radical cations, which could also be generated by reversible oxidation of Mo(CO)₃(LL)(CH₃CN) in acetonitrile, can be irreversibly oxidized yielding [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ after coordination by an additional acetonitrile. Infrared spectroelectrochemical experiments indicate the radical cations undergo ligand-induced net disproportionations that follow first-order kinetics in acetonitrile, ultimately yielding the corresponding Mo(CO)₄(LL) and [Mo(CO)₂(LL)(CH₃CN)₃]²⁺ species. Rate constants for the net disproportionation of [Mo(CO)₃(LL)(CH₃CN)]⁺ and the carbonyl substitution reaction of [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ were measured. Thin-layer bulk oxidation studies also provided infrared characterization data of [Mo(CO)₄(ncp)]⁺ (ncp = neocuproine), [Mo(CO)₃(LL)(CH₃CN)]⁺, [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ and [Mo(CO)₂(LL)(CH₃CN)₃]²⁺ complexes.