Showing papers on "Aquation published in 1999"

Novel ruthenium(III) dimers Na2[{trans-RuCl4(Me2SO-S)}2(µ-L)] and [{mer,cis-RuCl3(Me2SO-S)(Me2SO-O)}2(µ-L)] (L = bridging heterocyclic N-donor ligand) closely related to the antimetastatic complex Na[trans-RuCl4(Me2SO-S)(Him)]†

Abstract: The symmetrical dianionic and neutral ruthenium(III) dimers Na2[{trans-RuCl4(Me2SO-S)}2(µ-L)] 1 and [{mer,cis-RuCl3(Me2SO-S)(Me2SO-O)}2(µ-L)] 3 (L = pyrazine 1a, 3a; pyrimidine 1b; 4,4′-bipyridine 1c; 1,2-bis(4-pyridyl)ethane 1d; or 1,3-bis(4-pyridyl)propane 1e), which represent unprecedented examples in the general Creutz–Taube family of ruthenium dimers, were developed with the specific aim of assessing their antineoplastic properties. Each ruthenium center in 1 and 3 has a co-ordination environment similar to that of known anionic and neutral monomeric ruthenium(III) complexes endowed with a specific antimetastatic activity against animal model tumors. Beside the synthesis and spectroscopic characterization of the new dimers, and the structural characterization of 1a, 1b, 1c, and 3a, a thorough investigation of their chemical behavior in aqueous solution was made. At 25 °C and pH 7.4 the dianionic species 1a–1e maintain their dimeric structure and undergo rather slow stepwise chloride hydrolysis to yield the relatively inert diaqua species [{mer,cis-RuCl3(Me2SO-S)(H2O)}2(µ-L)]. At physiological pH dimers 1a–1e are also easily and quantitatively reduced by equivalent amounts of ascorbic acid to the corresponding RuII/II dimers which, in turn, undergo stepwise aquation with rates roughly comparable to those of the RuIII/III species of equal net charge. Since the reduction processes might occur also in vivo, the chemical behavior of the RuII/II dimers is relevant to understanding the biological mechanism of action of these compounds and was thus investigated in detail. The neutral dimer 3, which is scarcely soluble in aqueous solution, gives soluble dimeric species upon reduction with ascorbic acid. We found that reduction is accompanied by O to S linkage isomerization and by partial dissociation of the equatorial dmso. Overall, the dimeric structures of the new compounds are quite robust, both in the RuIII/III and in the RuII/II form, and they undergo aquation reactions similar to those of the monomeric analogs. However, while the monomeric species after aquation are either mono- or bi-functional binders, the new dimers might behave as bi- or even tetra-functional binders. Thus, it is likely that their interaction with biological targets might lead to adducts which are not accessible to the mononuclear species.

Synthesis and technique in inorganic chemistry : a laboratory manual

Abstract: Introduction Safety Laboratory Procedures Research Notebook Standard References Part I. Solid State Chemistry Experiment 1--High-Temperature Synthesis of the Superconductor YBa2Cu3O7 Tube Furnace Preparation Superconductivity Iodometric Titrations Experiment 2--The Layered Solids VOPO4(H2O)2 and VO(HPO4)(H2O)0.5 Powder X-Ray Diffraction Oxidation of Alcohols to Ketones Experiment 3--The Molecular Sieve Zeolite-X Sol-gel Synthesis High Pressure Synthesis Ion Exchange in Microporous Solids Part II. Main Group Chemistry Experiment 4--The Borane-Amine Adduct BH3NH2C(CH3)3 Lewis Acids and Bases Experiment 5--Buckminsterfullerene, C60, and Its Electrochemistry Soxhlet Extraction Cyclic Voltammetry Experiment 6--Vacuum-Line Synthesis of GeH4 Vacuum Line and Trap-to-Trap Purification Vapor Pressure and Molecular Weight Determination of a Volatile Compound Gas Phase IR Spectroscopy Experiment 7--Tin Chemistry: Coordination Complexes and Organometallic Derivatives NMR Spectroscopy Linkage Isomerism Experiment 8--Synthesis of (C6H5)2PCH2CH2P(C6H5)2 in Liquid Ammonia Synthesis in Liquid Ammonia Experiment 9--Electrolytic Synthesis of K2S2O8 Electrolytic Preparation Part III. Coordination Chemistry Experiment 10--Ion Exchange Separation of Chromium Complexes Ion Exchange Chromatography Experiment 11--Metal-Metal Quadruple Bonds Molecular Orbital Theory Experiment 12--The Magnetic Susceptibility of Mn(acac)3 Magnetism of Transition Metal Complexes The Gouy Method The Evans Methods Experiment 13--Cobalt Ammines and their Ligand Substitution Kinetics Conductivity of Ionic Complexes Kinetics of Aquation of [Co(NH3)5Cl]2+ Experiment 14--Optical Resolution of Co(en)33+ Separation of Diastereomers by Crystallization Optical Rotations Suction Filtration Experiment 15--Metal Dithiolenes and the Use of Quaternary Ammonium Salts Quaternary Ammonium Salts Part IV. Organometallic Chemistry Experiment 16--The Metal-Arene Complex [1,3,5-C6H3(CH3)3]Mo(CO)3 IR Spectra of Metal Carbonyls Experiment 17--Organo-iron Chemistry: (C5H5)2Fe2(CO)4 and (C5H5)Fe(CO)2(CH3) Schlenk Line Synthesis Infrared Spectra of Solutions Experiment 18--The Metal Carbonyl Cluster Fe3(CO)12 Mass Spectrometry Experiment 19--Microscale Synthesis of Vaska's Complex Microscale Synthesis Solid State IR Spectra Experiment 20--The Air-Sensitive Sandwich Complex Nickelocene Glove Bag Manipulations Sublimation Part V. Bioinorganic Chemistry Experiment 21--Cobaloximes: Models of Vitamin-B12 Coenzymes Enzyme Models Experiment 22--Amino Acid Complexes: Stability Constants of Ni(glycinate)n(2 - n)+ Amino Acid Chemistry pH Titrations pKa and Successive Stability Constant Determination Experiment 23--Bioinorganic Coordination Chemistry: Copper (II) Tetraphenylporphyrinate Porphyrin Chemistry Thin-Layer Chromatography Column Chromatography Notes to the Instructor Appendices NMR and Mass Spectra Index

Kinetic and mechanistic analysis of the reactions in the aqueous system pentacyanoferrate(ii)-ammonia-nitrite

Abstract: The pentacyanoferrate(II)–ammonia–nitrite system was subjected to a kinetic and mechanistic study as a function of NH3 and NO2– concentration, pH, temperature and pressure. A detailed study was performed on the formation of [FeII(CN)5(NO)]2– in the system consisting of NO2– and [FeII(CN)5L]3– (L = H2O or NH3). Two equilibria were taken into consideration, viz. the pH dependent aquation of the ammine complex, and the transformation of the nitro into the nitrosyl complex. Based on the reported activation parameters, the substitution of water or ammonia in [FeII(CN)5L]3– (L = H2O or NH3) by nitrite follows a limiting dissociative mechanism. The reaction of [FeII(CN)5(NO)]2– with ammonia leading to the formation of dinitrogen was investigated in a more qualitative way, and found to depend strongly on pH with a maximum nitrogen yield at a pH of ca. 10.5. The trend was accounted for on the basis that the process involves nucleophilic attack of NH3 on the N (NO) atom in [FeII(CN)5(NO)]2–. This reaction was found to be the rate-limiting step in the catalytic cycle occurring in this system and leading to the overall reduction of NOx to dinitrogen.

Aquation of the Chloro Pentaammine Complexes of Cobalt(III) and Chromium(III): Do the Almost Equal Activation Parameters Arise from a Common Mechanism?

Abstract: The activation parameters for the aquation of Co(NH3)5Cl2+ and Cr(NH3)5Cl2+ are almost equal, and the strongly negative volumes of activation, ΔV⧧ (−9.9 and −10.6 cm3 mol-1 for Co and Cr, respectively), might at the first glance suggest a common associative mechanism for both complexes. Computations of the corresponding reaction coordinates indicate that, in agreement with Swaddle and co-workers' studies and as expected, a dissociative interchange mechanism (Id) operates for cobalt(III), but an associative interchange one (Ia) for chromium(III). For these two asymmetric reactions, the bond lengths changes δCo and δCr that are involved in the formation of the transition state and defined with respect to the fully concerted I pathway allow the attribution of the reaction mechanism. The signs of δCo and δCr, being positive and negative, suggest a d and a activation for the above aquations.

[1H,15N] N.M.R. Kinetic Studies of Reactions of cis- and trans-[PtCl2(15NH3)(c-C6H1115NH2)] with Guanosine 5'-Monophosphate

Abstract: cis-[PtCl2(15NH3)(c-C6H11NH2)] is an active metabolite of the oral platinum(IV) anticancer drug cis,trans,cis-[PtCl2(CH3CO2)2(NH2)(c-C6H11NH2)]. Since it is likely that guanine bases on DNA are targets for this drug, we have analysed the kinetics of reaction of this platinum(II) metabolite with guanosine 5′-monophosphate (5′-GMP) at 310 K, pH 7, using [1H, 15N] n.m.r. methods. Reactions of the trans isomer are reported for comparison. The reactions proceed via aquated intermediates, and, for the cis isomer, the rates of aquation and substitution of H2O by 5′-GMP are 2-5 times faster trans to the amine ligand (c-C6H11NH2) compared to trans to NH3 for both the first and second steps. For the trans complex, the first aquation step is c. 3 times faster than for the cis complex, as expected from the higher trans influence of Cl¯, whereas the rate of the second aquation step (trans to N7 of 5′-GMP) is comparable to that trans to NH3. These findings have implications for the courses of reactions with DNA.

Variable temperature and pressure study of the aquation reactions of cobalt(III) and chromium(III) penta- and tetra-amines†

Abstract: Preparation of a series of specific penta- and tetra-amine derivatives of CoIII and CrIII with a neutral leaving ligand has been carried out in order to accomplish a fine tuning of the associativeness/dissociativeness of their substitution reactions. Spontaneous aquation reactions of the neutral ligands have been studied at variable temperature and pressure. Although rate constants and thermal activation parameters show an important degree of scatter, the values determined for the activation volumes of the substitution process illustrate the mechanistic fine tuning that may be achieved for these reactions. In all cases, in the absence of important steric constraints in the molecule, electronic inductive effects seem to be the most important factor accounting for the dissociative shifts observed both for pentaamine (i.e. ΔV‡ = +4.0 or +14.0 cm3 mol–1 and +5.2 or +16.5 cm3 mol–1 for the aquation of cis- or trans-[Co(MeNH2)(NH3)4(DMF)]3+ and cis- or trans-[CoL15(DMF)]3+ respectively, where L15 represents a pentaamine macrocyclic ligand), and tetraamine systems (i.e. ΔV ‡ = +4.1 or +8.4 cm3 mol–1 and –10.8 or –7.4 cm3 mol–1 for the aquation of cis-[Co(NH3)4Cl(DMAC)]2+ (DMAC = dimethylacetamide) or cis-[Co(en)2Cl(DMAC)]2+ and cis-[Cr(NH3)4Cl(DMF)]2+ or cis-[Cr(en)2Cl(DMF)]2+). From the results, clear evidence is obtained which indicates that, only when the situation is borderline Ia/Id, or the steric demands are increased dramatically, dissociative shifts are observed; in all other cases electronic inductive effects seem to be dominant for such a tuning of the substitution process.

Synthesis and characterization of sodium cis-dichlorochenodeoxycholylglycinato(O,N) platinum(II)--cytostatic activity.

Abstract: With a view to using bile acids as shuttles for delivering platinum-related cytostatic drugs to liver tumors, a chenodeoxycholylglycinato(CDCG)-derivative of platinum(II) has been synthesized. The complex - named Bamet-M2- was chemically characterized by elemental analysis, FT-IR, NMR, FAB-MS, and UV spectroscopy. The results indicate the following composition: C26H42N2O5Cl2NaPt(II), the metal Pt(II) being bound to two Cl− and one bidentate CDCG moiety, i.e., Na[Pt CDCG(N,O) Cl2]. The compound is highly soluble (up to 20 mM) in water and (up to 35 mM) in ethanol, methanol and DMSO. Hydrolysis was investigated because this is assumed to be an important step in intracellular activation and interaction with DNA of this type of compounds. The reaction kinetics of this complex in aqueous solution show unusual behaviour; the substitution process with the displacement of two Cl− was almost instantaneous, and the resulting species were found to be very stable. Kinetic studies carried out in the presence of different NaCl concentrations (up to 500 mM) revealed similar fast and nonreversible aquations of Bamet-M2. This contrasts with the slow aquation of cisplatin in extracellular-line solutions (i.e., at high NaCl concentrations) as compared with fast hydrolysis in cells. This difference may partly account for the low cytostatic activity observed here for Bamet-M2 against several tumor cell-lines.

A tetrapodal pentaamine for stabilizing square pyramidal co-ordination modules: synthesis, structure and reactivity of cobalt( III ) complexes of 2,2′-dimethyl-2,2′-iminodimethylenebis(1,3-propanediamine)

Abstract: A facile synthesis of the tetrapodal pentaamine ligand 2,2′-dimethyl-2,2′-iminodimethylenebis(1,3-propanediamine), ditame, has been achieved and some unusual effects of its topology and preference for square pyramidal co-ordination in cobalt(III) complexes explored. Potential influences of the ditame structure on substitution chemistry in [Co(ditame)X]n+ systems are defined by crystal structure analyses for [Co(ditame)Cl][ZnCl4] and [Co(ditame)(NH3)]Cl[ZnCl4]. Proton exchange, nitrogen inversion and chloride anation reactivity, and substitution stereochemistry studies have been carried out on the [Co(ditame)Cl]2+ and [Co(ditame)(OD2)]3+ complexes by using 13C NMR spectroscopy. The base hydrolysis rate constant for [Co(ditame)Cl]2+ (68 dm3 mol–1 s–1 at 25 °C, I 1.0 mol dm–3) is 250 fold greater than that for the analogous [Co(NH3)5Cl]2+ ion. This difference is attributed to an enhanced trans influence and a bond-coupled co-operative mechanism that facilitate the Cl– dissociation in the conjugate base of [Co(ditame)Cl]2+. The bond-coupled mechanism also aids dissociative processes for the relatively fast aquation and anation chemistry of [Co(ditame)Cl]2+ and [Co(ditame)(OH2)]3+. Two results for the reactivity of the [Co(ditame)X]n+ (X = Cl– or H2O) ions are attributed to restricted rearrangement of the square pyramidal Co(ditame) fragment in the course of Xn – 3 substitutions. One is the very small amount of [Co(ditame)(N3)]2+ (1.1 ± 0.3%) formed in competition with [Co(ditame)(OH)]2+ during base hydrolysis in aqueous 1 mol dm–3 NaN3, which indicates an unusually short lifetime for the proposed intermediate. Also, there were no species detected that arise from partial dissociation of the amine, neither in the base hydrolysis nor in the aquation and anation experiments, even at temperatures >50 °C and in the presence of strong acids. There are important consequences for substitution chemistry in other [M(pentaamine)X]n+ systems where rearrangement of the MN5(amine) fragment is restricted. The quantitatively simple substitution processes also make these reagents valuable as protective groups in synthetic applications such as peptide cleavage and synthesis.

Studies on kinetics and mechanism of imidazole substitution from cis-equatorial-[Cr(S-pdtra)(Him)]0 complex in acidic and alkaline aqueous solutions [S-pdtra = (S)-propylenediaminetriacetate]†

Abstract: Aquation of the cis-equatorial-[Cr(S-pdtra)(Him)]0 complex [S-pdtra = (S)-propylenediaminetriacetate] has been studied within the pH range 0–14. Liberation of imidazole in acidic medium leads to the cis-eq-[Cr(S-pdtra)(H2O)]0 complex. Deprotonation of coordinated imidazole in alkaline solutions stimulates a reversible one-end dechelation of S-pdtra, which precedes substitution of imidazole; a characteristic bell-shaped kobsvs. [H+] dependence is observed. The values of ΔS ‡ = –52.8 J mol–1 K–1, ΔH ‡ = 84.2 kJ mol–1 and ΔV ‡ = –10.1 cm3 mol–1 for aquation in acidic medium are consistent with an Ia mechanism, whereas substitution of the imidazolate from the hydroxo complex with a tetradentate S-pdtra proceeds via an Id mechanism on the basis of ΔS ‡ = 49.6 J mol–1 K–1 and ΔH ‡ = 117.5 kJ mol–1. One-end dechelation of the S-pdtra ligand from the complex with imidazolate (pH > 13) is characterised by k298 = 6.43 × 10–3 s–1, ΔS ‡ = –57.2 J mol–1 K–1 and ΔH ‡ = 68.5 kJ mol–1.

THE CONVERSION OF Rh(m) CHLOROCOMPLEXES TO BROMOCOMPLEXES AND THEIR SOLVENT EXTRACTION BEHAVIOUR

Abstract: This paper details investigations on the conversion of Rh(HI) chlorocomplexes to bromocomplexes, followed by the extraction of the tatter with an alkylated 8-hydroxyquinoline and their subsequent stripping with hydrobromic acid. It was found that in contrast to Rh(III) chlorocomplexes, the analogous bromocomplexes underwent significantly less aquation, thus rendering themselves to qualitative solvent extraction. Of the extractants tested, Kelex 100 proved to give the best performance. On the other hand, stripping was problematic. It was apparent that complex transformation of the extracted Rh(HI) occurred in the organic phase upon aging, which resulted in metal lock up.

Solvent effects on the aquation of cationic, anionic and nonionic chlorocobalt(iii) complexes

Abstract: The kinetics of aquation of α- and β- cis[Co(edda)Cl2]−, α- cis[Co(edda)(H2O)Cl] and α- cis[Co(trien)Cl2]+ were investigated in aqueous mixtures of t-BuOH, MeOH, DMSO, ethylene carbonate and urea. The transfer Gibbs energy values for the reactants, evaluated from the solubility of the complexes, confirm the decisive role of the reactant solvation on the aquation rate.

Reactions of beta -cis-(diaqua) (triethylenetetramine) cobalt(iii) with sulphur(iv) in aqueous medium : a thermal and photochemical study

Abstract: 1dm) mol· 1 S-I, Mi' = 42. 1 ± 5.1 kJ mol-I, LlS' = 43 ± 17 J K-I mol -I at 25"C and I = 1.0 mol dm-' . The O-sulphito complex undergoes W-catalysed aquation with k = (1.1 ± 0.2) x 10" dm' mol -I :;-1 (25"C, 1 = 1.0 mol dm-'). These data are consistent with the rate limiting addition of SOz to Co'"-OH and breakage of S-O bond in the formation and aquation of the 0sulphito complex respectively. The O-sulphito complex undergoes intramolecular electron transfer and ligand linkage isomerisation . Co-OSO/ -7 Co-SO, + for which k",I(3()"C) = (0.28 ± 0.03) x 10-' S-I, LlW = 76 ± 12 kJ mol-I, LlS' = -81 ± 39 J K-I mol-I and ki.PO''C) = (0 .44 ± 0.12) x 10-' S·I, Mi' = 57 ± 7 kJ mol-I, LlS' = - 138 ± 24 J K-I mol-I respectively. The P-cis-[Co(trien)(OH1)(SO,-S)]+ has been isolated in the solid state and characterised . It does not show exceptional lability of the aqua li gand for substitution and is substantia ll y stable to intramolecular electron transfer between COlli and SIV under thermal condition. The conventional fla sh photolysis of th is S­ bonded sulphito complex has been shown to generate the corresponding O-sulphito complex as a tran sient while it s steady state photolysis (254 nm) resulted in photo reduction without signific ant build up of any intermediate. We have a long standing interest on the reactions of sulphur(IV) with redox active transition metal ions and their complexes due to their relevance to atmospheric and environmental chemistry!. In continuation of our earlier work 2 we present here a study of the reaction of sulphur(IV) with ~-cis-(diaqua)(t rien)cobalt(III) (trien = tri eth ylenetetramine) in aqueous medium. The purpose of undertak ing this hitherto unreported study was to ex­ amine the effect of this tetradentate amine ligand on the kineti cs of the formation of the sulphito cobalt(III) spe­ cies (both 0- and S- bonded isomers) and the correspond­ ing redox reaction between the reactants . The possibil­ ity of the rearrangement of the trien skeleton in the [(aqua)Co(trien)(S03-SW qnder the trans-activating in­ fluence of the S-bonded sulphite was an additional con­ sideration .