Showing papers on "Aquation published in 2006"

Phenylazo-pyridine and Phenylazo-pyrazole chlorido Ruthenium(II) Arene Complexes: Arene Loss, Aquation, and Cancer Cell Cytotoxicity

Abstract: Ru(II) eta6-arene complexes containing p-cymene (p-cym), tetrahydronaphthalene (thn), benzene (bz), or biphenyl (bip), as the arene, phenylazopyridine derivatives (C5H4NN:NC6H5R; R = H (azpy), OH (azpy-OH), NMe2 (azpy-NMe2)) or a phenylazopyrazole derivative (NHC3H2NN:NC6H5NMe2 (azpyz-NMe2)) as N,N-chelating ligands and chloride as a ligand have been synthesized (1-16). The complexes are all intensely colored due to metal-to-ligand charge-transfer Ru 4d6-pi* and intraligand pi -->pi* transitions (eta = 5000-63 700 M-1 cm-1) occurring in the visible region. In the crystal structures of [(eta6-p-cym)Ru(azpy)Cl]PF6 (1), [(eta6-p-cym)Ru(azpy-NMe2)Cl]PF6 (5), and [(eta6-bip)Ru(azpy)Cl]PF6 (4), the relatively long Ru-N(azo) and Ru-(arene-centroid) distances suggest that phenylazopyridine and arene ligands can act as competitive pi-acceptors toward Ru(II) 4d6 electrons. The pKa* values of the pyridine nitrogens of the ligands are low (azpy 2.47, azpy-OH 3.06 and azpy-NMe2 4.60), suggesting that they are weak sigma-donors. This, together with their pi-acceptor behavior, serves to increase the positive charge on ruthenium, and together with the pi-acidic eta6-arene, partially accounts for the slow decomposition of the complexes via hydrolysis and/or arene loss (t(1/2) = 9-21 h for azopyridine complexes, 310 K). The pKa* of the coordinated water in [(eta6-p-cym)Ru(azpyz-NMe2)OH2]2+ (13A) is 4.60, consistent with the increased acidity of the ruthenium center upon coordination to the azo ligand. None of the azpy complexes were cytotoxic toward A2780 human ovarian or A549 human lung cancer cells, but several of the azpy-NMe2, azpy-OH, and azpyz-NMe2 complexes were active (IC50 values 18-88 microM).

195Pt NMR study of the speciation and preferential extraction of Pt(IV)-mixed halide complexes by diethylenetriamine-modified silica-based anion exchangers.

Abstract: A detailed 195Pt NMR study of the distribution of Pt(IV) complex species resulting from the aquation of H2PtCl6, H2PtBr6, and mixtures of H2PtCl6/H2PtBr6 in water/dilute HClO4 has been carried out to obtain an understanding of the speciation in these solutions as relevant to the recovery of Pt(IV) complexes from process solutions. A species distribution plot of the [PtCl6]2-, [PtCl5(H2O)]-, and [PtCl4(H2O)2] shows that in equilibrated, relatively concentrated H2PtCl6 solutions ([Pt]t > 0.12 M), the [PtCl4(H2O)2] species is below the 195Pt NMR detection limit; for [Pt]t concentrations < 0.1 M, the relative concentrations of the [PtCl5(H2O)]- and [PtCl4(H2O)2] species increase significantly, as a result of relatively rapid aquation of the [PtCl6]2- and [PtCl5(H2O)]- complexes under these conditions. From this (195)Pt NMR data the aquation constants of [PtCl6]2- and [PtBr6]2- of log K6 approximately 1.75 +/- 0.05 and log K6 approximately 2.71 +/- 0.15, respectively, have been determined at 30 degrees C. In mixtures of H2PtCl6/H2PtBr6 in water, a number of previously unidentified aquated complexes of the general formula [PtCl(5-n)Br(n)(H2O)]- (n = 0-5) could be identified, including the possible geometrical isomers of these complexes. These 195Pt NMR assignments were confirmed by remarkably systematic, linear relationships between the 195Pt chemical shift increments induced by substitution of Cl- ions by n Br- ions in [PtCl(6-n)Br(n)]2- and [PtCl(5-n)Br(n)(H2O)]- complexes. Preferential extraction of the [PtX6]2- (X = Cl, Br, or a mixture of the two halides) species over their corresponding aquated [PtX5(H2O)]- counterparts by silica-based diethylenetriamine anion exchangers could be demonstrated by means of 195Pt NMR spectroscopy.

Synthesis, reactivities, and magnetostructural properties of FeIII, FeIII-O-FeIII, and ZnIIFeIII-O-FeIIIZnII complexes of a tetraiminodiphenolate macrocycle.

Abstract: The mononuclear iron(III) complexes [Fe(LH2)(H2O)Cl](ClO4)2·2H2O (1) and [Fe(LH2)(H2O)2](ClO4)3·H2O (2) have been prepared by reacting [Pb(LH2)](ClO4)2 with FeCl3·6H2O and Fe(ClO4)3·6H2O, respectively. Complex 2 upon treatment with 1 equiv of alkali produces the oxo-bridged dimer [{Fe(LH2)(H2O)}2(μ-O)](ClO4)4·2H2O (3). In these compounds, LH2 refers to the tetraiminodiphenol macrocycle in the zwitterionic form whose two uncoordinated imine nitrogens are protonated and hydrogen-bonded to the metal-bound phenolate oxygens. The aqua ligands of complexes 1−3 get exchanged in acetonitrile. Reaction equilibria involving binding and exchange of the terminal ligands (Cl-/H2O/CH3CN) in these complexes have been studied spectrophotometrically. The equilibrium constant for the aquation reaction (Kaq) [1]2+ + H2O [2]3+ + Cl- in acetonitrile is 8.65(5) M, and the binding constant (KCl−) for the reaction [1]2+ + Cl- [1Cl]+ + CH3CN is 4.75(5) M. The pKD value for the dimerization reaction 2[2]3+ + 2OH- [3]4+ + 3H2O in 1...

Oxidation of nitrite by a trans-dioxoruthenium(VI) complex: direct evidence for reversible oxygen atom transfer.

Abstract: Reaction of trans-[RuVI(L)(O)2]2+ (1, L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, a tetradentate macrocyclic ligand with N2O2 donor atoms) with nitrite in aqueous solution or in H2O/CH3CN produces the corresponding (nitrato)oxoruthenium(IV) species, trans-[RuIV(L)(O)(ONO2)]+ (2), which then undergoes relatively slow aquation to give trans-[RuIV(L)(O)(OH2)]2+. These processes have been monitored by both ESI/MS and UV/vis spectrophotometry. The structure of trans-[RuIV(L)(O)(ONO2)]+ (2) has been determined by X-ray crystallography. The ruthenium center adopts a distorted octahedral geometry with the oxo and the nitrato ligands trans to each other. The RuO distance is 1.735(3) A, the Ru−ONO2 distance is 2.163(4) A, and the Ru−O−NO2 angle is 138.46(35)°. Reaction of trans-[RuVI(L)(18O)2]2+ (1-18O2) with N16O2- in H2O/CH3CN produces the 18O-enriched (nitrato)oxoruthenium(IV) species 2-18O2. Analysis of the ESI/MS spectrum of 2-18O2 suggests that scrambling of the 18O atoms has occu...

Condensation mechanisms of tetravalent technetium in chloride media

Abstract: The condensation mechanisms of tetravalent technetium in chloride media were studied in the pH range 0-1.5. A new dimer complex of Tc(IV) has thus been discovered, Tc 2 OCl 10 4- . Spectroscopic and kinetics studies showed that the formation of this compound resulted from the condensation of TcCl 5 (H 2 O) - . An EXAFS study indicates that the dimer displays a [Tc-O-Tc] 6+ structure. As the pH increases, UV-visible measurements showed a cyclization of [Tc-O-Tc] 6+ into [Tc(μ-O) 2 Tc] 4+ leading, in fine, to the precipitation of TcO 2 ·xH 2 O. The aquation constant (K aq ) of TcCl 6 2- into TcCl 5 (H 2 O) - and the dimerisation constant (log K dim ) of TcCl 5 (H 2 O) - into Tc 2 OCl 10 4- were determined to be 2.20±0.26 and 4.68±0.09, respectively.

Water induces a structural conversion and accelerates the oxygenation of carboxylate-bridged non-heme diiron enzyme synthetic analogues.

Abstract: Recently, we reported the synthesis of a carboxylate-rich non-heme diiron enzyme model compound [Fe2(mu-O2CAr(Tol))4(4-CNPy)2] (1), where (-)O(2)CAr(Tol) is 2,6-di-p-tolylbenzoate and 4-CNPy is 4-cyanopyridine (Yoon, S.; Lippard, S. J. J. Am. Chem. Soc. 2005, 127, 8386-8397). A metal-to-ligand charge-transfer band in the visible region of the optical absorption spectrum involving the nitrogen-donor ligand endowed this complex with a distinctive red color that facilitated analysis of its chemistry. Following this strategy, we prepared and characterized two related isomeric complexes, windmill (3) and paddlewheel (4) species having the formula [Fe2(O2CAr(Tol))4(4-AcPy)2], where 4-AcPy is 4-acetylpyridine. In anhydrous solvents, 1 and 4 adopt paddlewheel structures, but upon the addition of water, they convert to aquated forms, windmill structures having the composition [Fe2(mu-O2CAr(Tol))2(O2CAr(Tol))2(4-RPy)2(H2O)2]. This conversion is favored at low temperature and was studied by NMR spectroscopy. A kinetic analysis of the aquation reaction was undertaken by stopped-flow measurements between 198 and 223 K for both 1 and 4, which revealed a first-order dependence on both the diiron compound and water. The oxygenation rates for the water-containing complexes are much faster than those for the corresponding anhydrous complexes, being 20-fold faster for 4 and 10-fold more rapid for 1. The presence or absence of water had little effect on the activation enthalpies, suggesting that the loss of water may not be necessary prior to dioxygen binding in the transition state.

Preparation, Characterization, and Aquation Kinetics of Pyridine N‐Oxide Complexes of Chromium(III)

Abstract: A series of (H 2 O) 5 Cr(X-pyO) 3+ ions (pyO = pyridine N-oxide, X = H, 3-CH 3 , 4-CH 3 , 4-OCH 3 , 4-NO 2 ) were prepared by the reduction of the corresponding pyridine N-oxide adducts of diperoxochromium(VI) species with acidic ferrous perchlorate. The (H 2 O) 5 Cr(X-pyO) 3+ complexes undergo aquation to yield Cr(H 2 O) 6 3+ and X-pyO according to the rate law k obs = k o +k -1 [H + ] -1 . The values of the rate constants extrapolated to 298 K at 1.0 M ionic strength are: k o = 2.80 × 10 -6 s -1 , k -1 = = 1.86 × 10 -8 Ms -1 (X = 4-NO 2 ); 7.80 × 10 -8 , 6.27 × 10 -10 (H); 4.80 × 10 -8 , 3.20 × 10 -10 (3-CH 3 ); 3.05 × 10 -8 , 1.60 × 10 -10 (4-CH 3 ); and 2.37 × 10 -9 , 4.76 × 10 -11 (4-OCH 3 ). The reaction of the 4-OCH 3 complex exhibits two additional terms in the rate law, k 1 [H + ]+k 2 [H + ] -2 . The binding of 4-OCH 3 -pyO to chromium is suggested to take place through the methoxy group.

New chromium(III)–picolinamide complexes. Kinetics and mechanism of picolinamide liberation in HClO4 solutions

Abstract: Two new chromium(III) complexes with picolinamide (pica) and oxalates, [Cr(C2O4)2(N,N′-pica)]2− and [Cr(C2O4)2(N,O-pica)]−, were obtained and the kinetics of their aquation in HClO4 solutions were studied. The aquation leads to pica liberation and proceeds in two stages: (i) the chelate-ring opening at the Cr–amide bond and (ii) the Cr–N-pyridine bond breaking, which gives free pica and cis-[Cr(C2O4)2(H2O2)2]−. In the case of N,N′-bonded pica the kinetics of both stages was determined and in the case of the N,O-bonded pica only the second stage was investigated. The following rate laws were established: (kobs)1 = k0 + k1Q1[H+] and (kobs)2 = k2Q2[H+], where k0 and k1 are the rate constants of the chelate-ring opening in the unprotonated and protonated starting complex, and k2 is the rate constant of the pica liberation from the protonated intermediate. Kinetic parameters are calculated and the aquation mechanism is discussed.

Kinetics and Mechanism of Ligand Substitution in Some Chromium(III) Tetraaza Macrocyclic Complexes in Acidic Media: Differences in Reactivity Between cis and trans Isomers

Abstract: Thiocyanate anation of the macrocyclic complexes cis-[Cr(cycb)(OH2)2]3+ and trans-[Cr(cyca)(OH2)2]3+ (cycb and cyca are rac- and meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, respectively), and mercury(II)-induced aquation of the product thiocyanato-N complexes, has been studied in acidic solution. The rate retardation with an increase of the acid concentration for both types of reactions follows the rate expression kobs = (k1 + k2Ka/[H+(aq)])/(1 + Ka/[H+(aq)]), corresponding to parallel reaction paths through aqua and hydroxo complexes. Some general trends in the differences in reactivity between the two geometrical isomers have been observed and are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Photochemical behaviour of Tc2OCl104– and TcnOy4n–2y+ in chloride media

Abstract: The stabilities of the technetium polymers: Tc 2 OCl 10 4- and Tc n O y 4n-2y+ have been studied under light irradiation in 3 M chloride media with a pH range from 0 to 1.3. It has been shown that under irradiation, Tc 2 OCl 10 4- is not stable and undergoes dissociation to TcCl 5 (H 2 O) - at pH = 0 and pH = 0.3. At pH = 1, irradiation of Tc 2 OCl 10 4- leads to a stationary state involving TcCl 5 (H 2 O) - and Tc 2 OCl 10 4- . At pH = 1.3, Tc n O y 4n-2y+ remains stable under irradiation. Under light irradiation, the predominance diagram of Tc(IV) species obtained from Tc 3 OCl 10 4- aquation in a pH range from 0 to 1 is drawn. The chemical behaviour of Tc 2 OCl 10 4- and the influence of the light on the condensation of Tc(IV) and solubility of TcO 2 ·xH 2 O are discussed.

Kinetics of Hydrolysis of Diperiodatoargentate(III) Ion and its Reduction by Paracetamol

Abstract: The kinetics of hydrolysis and reduction of the diperiodatoargentate(III) ion (DPA) has been studied in aqueous acidic medium spectrophotometrically. Upon dilution the silver (III) complex was found to be unstable in the presence of H2O. Addition of [H+], largely increased the hydrolysis rate, whereas [OH−] does not have any effect. Under pseudo-first-order conditions ([paracetamol] > [DPA]), the reduction rate was very fast. Second-order conditions were used to determine the reaction rate. The reaction was acid-catalyzed and the rate decreased by the addition of periodate. The Arrhenius equation was valid for the reaction. The changes observed in the direction of the rate constant-[H+] profile correspond to aquation of the diperiodatoargentatate(III) complex. The proposed mechanism and the derived rate law are consistent with the observed kinetics.

Kinetics and Mechanism of Chromium(III)-oxalates-2-hydroxynicotinate and Chromium(III)-oxalates-3-hydroxypicolinate Aquation in HClO4 Solutions

Abstract: New chromium(III) complexes, [Cr(C2O4)2(2-hnic)]2− and [Cr(C2O4)2(3-hpic)]2− (where 2-hnic = O,O′-bonded 2-hydroxynicotinic acid and 3-hpic = N,O-bonded 3-hydroxypicolinic acid), were obtained and characterized in solution. The acid-catalyzed aquation of the both complexes leads to liberation of the appropriate pyridinecarboxylic acid and formation of cis-[Cr(C2O4)2(H2O)2]−. Kinetics of these reactions were studied spectrophotometrically in the 0.1–1.0 M HClO4 range, at I = 1.0 M. In the case of [Cr(C2O4)2(2-hnic)]2−, a slow chelate-ring opening at the Cr–O (phenolate) bond is followed by a fast Cr–O (carboxylate) bond breaking. The rate law: kobs = kHQH[H+] was established, where kH is the acid-catalyzed rate constant and QH is the protonation constant of the coordinated phenolate oxygen atom. In the case of [Cr(C2O4)2(3-hpic)]2−, the reversible chelate-ring opening at Cr–N bond is followed by the rate determining step – the one-end bonded ligand liberation. The rate law for the first step was determined: kobs = k1+k−1/Q1[H+], where k1 and k−1 are the rate constants of the chelate-ring opening and closure and Q1 is the protonation constant of the pyridine nitrogen atom. The aquation mechanisms are proposed and the effect of ligand coordination mode on complex reactivity is discussed.

Synthesis, spectra and electrochemistry of dinitro-bis-2-(phenylazo)pyrimidine ruthenium(II). Nitro*#x2014;nitroso derivatives and reactivity of the electrophilic nitrosyl centreruthenium(II). Nitro*#x2014;nitroso derivatives and reactivity of the electrophilic nitrosyl centre

Abstract: Silver-assisted aquation of bluecis-trans-cis-RuCl2(Raapm)2 (1a-1e) leads to the synthesis of solvento species, blue-violetcis-trans-cis-[Ru(OH2)2(Raapm)2](ClO4)2 [Raapm =p-R-C6H4-N=N-C4H3-NN, (2a-2e), abbreviated as N,N′-chelator, where N(pyrimidine) and N(azo) represent N and N′ respectively; R = H (a),p-Me (b),p-Cl (c),m-Me (d),m-Cl (e) that react with NO2 in warm EtOH to give violet dinitro complexes of the type, Ru(NO2)2(Raapm)2 (3a-3e). The nitrite complexes are useful synthons of electrophilic nitrosyls, and on triturating the dinitro compounds with conc. HClO4, nitro-nitrosyl derivatives are isolated. The solution structure and stereoretentive transformation in each step have been established from1H NMR results. The compounds are redox active and display one metal-centred oxidation and successive ligand-based reductions. The v (NO) > 1900 cm-1 strongly suggests the presence of linear Ru-N-O bonding. The electrophilic behaviour of metal-bound nitrosyl has been proved in one case by reacting with a bicyclic ketone, camphor, containing an active methylene group and an arylhydrazone with an active methine group. Diazotization of primary aromatic amines with strongly electrophilic mononitrosyl complexes in acetonotrile and dichloromethane solutions has been thoroughly studied.

Synthesis, reactivities, and magnetostructural properties of Fe III , Fe III -O-Fe III , and Zn II Fe III -O-Fe III Zn II complexes of a tetraiminodiphenolate macrocycle

Abstract: The mononuclear iron(III) complexes [Fe(LH 2 )(H 2 O)Cl](ClO 4 ) 2 ·2H 2 O (1) and [Fe(LH 2 )(H 2 O) 2 ](ClO 4 ) 3 ·H 2 O (2) have been prepared by reacting [Pb(LH 2 )](ClO 4 ) 2 with FeCl 3 ·6H 2 O and Fe(ClO 4 )3·6H 2 O, respectively. Complex 2 upon treatment with 1 equiv of alkali produces the oxo-bridged dimer [{Fe(LH 2 )(H 2 O)} 2 (μ-O)](ClO 4 ) 4 ·2H 2 O (3). In these compounds, LH 2 refers to the tetraiminodiphenol macrocycle in the zwitterionic form whose two uncoordinated imine nitrogens are protonated and hydrogen-bonded to the metal-bound phenolate oxygens. The aqua ligands of complexes 1-3 get exchanged in acetonitrile. Reaction equilibria involving binding and exchange of the terminal ligands (Cl - /H 2 O/CH 3 CN) in these complexes have been studied spectrophotometrically. The equilibrium constant for the aquation reaction (K aq ) [1] 2+ + H 2 O ⇔ K aq [2] 3+ + Cl - in acetonitrile is 8.65(5) M, and the binding constant (K Cl - ) for the reaction [1] 2+ + Cl - ⇔ K aq [1Cl] + + CH 3 CN is 4.75(5) M. The pK D value for the dimerization reaction 2[2] 3+ + 2OH - ⇔K aq [3] 4+ + 3H 2 O in 1:1 acetonitrile-water is 9.38(10). Complexes 1-3 upon reaction with Zn(ClO 4 ) 2 ·6H 2 O and sodium acetate (OAc), pivalate (OPiv), or bis(4-nitrophenyl)phosphate (BNPP) produce the heterobimetallic complexes [{FeLZn(μ-X)} 2 (μ-O)](ClO 4 ) 2 , where X = OAc (4), OPiv (5), and BNPP (6). The pseudo-first-order rate constant (k obs ) for the formation of 4 at 25 °C from either 1 or 3 with an excess of Zn(OAc) 2 ·2H 2 O in 1:1 acetonitrile-water at pH 6.6 is found to be the same with k obs = 1.6(2) × 10 -4 s -1 . The X-ray crystal structures of 3, 4, and 6 have been determined, although the structure determination of 3 was severely affected because of heavy disordering. In 3, the Fe-O-Fe angle is 168.6(6)°, while it is exactly 180.0° in 4 and 6. Cyclic and square-wave voltammetric (CV and SWV) measurements have been carried out for complexes 1-4 in acetonitrile. The variation of the solvent composition (acetonitrile-water) has a profound effect on the E ½ and ΔE p values. The binding of an additional chloride ion to an iron(III) center in 1-3 is accompanied by a remarkable shift of E ½ to more negative values. The observation of quasi-reversible CV for complexes containing a Fe III -O-Fe III unit (3 and 4) indicates that in the electrochemical time scale unusual Fe III -O-Fe II is produced. The 1 H NMR spectra of complexes 3-6 exhibit hyperfine-shifted signals in the range 0-90 ppm with similar features. The metal-hydrogen distances obtained from T 1 measurements are in good agreement with the crystallographic data. Variable-temperature (2-300 K) magnetic susceptibility measurements carried out for 3 and 4 indicate strong antiferromagnetic exchange interaction (H = -2JS 1 ·S 2 ) between the high-spin iron(III) centers in the Fe-O-Fe unit with J =-114 cm -1 (3) and -107 cm -1 (4).

Estudos Cinéticos da aquação do trans-[Co(en)2Cl2]Cl

Abstract: The trans-dichlorobis(ethylenediamine)cobalt(III) chloride was synthesized in an undergraduate laboratory and its aquation reaction was carried out at different temperatures. This reaction follows pseudo-first-order kinetics and the rate constants, determined at 25, 35, 45, 55 and 70 o C, are 1.44 x 10-3; 5.14 x 10-3; 1.48 x 10-2; 4.21 x 10-2 and 2.21 x 10-1 s-1, respectively. The activation energy is 93.99 ± 2.88 kJ mol-1.