Carboxylato Complexes Research Articles

Factors Governing the Catalytic Insertion of CO2 into Arenes - A DFT Case Study for Pd and Pt Phosphane Sulfonamido Complexes.

The potential of Pd/Pt complexes for catalytic carboxylation of arenes with CO2 is investigated by means of computational chemistry. Recently we reported that the bis[(2‐methoxyphenyl)phosphino]‐benzenesulfonamido palladium complex 1 inserts CO2 reversibly in its Pd−C(aryl) bond generating carboxylato complex 2. In the present work we study how geometric and electronic factors of various ligands and substrates influence the overall activation barrier (energy span, ES) of a potential catalytic cycle for arene carboxylation comprising this elementary step. The tendency of the key intermediates to dimerize and thus deactivating the potential catalysts is examined as well as the role of the base, which inevitably is needed to stabilize the reaction product. We show that Pd and Pt complexes I(Pd)‐L16‐S1 and I(Pt)‐L16‐S1 do not dimerize, enable the computation of complete catalytic cycles, and show interestingly low ES values of 26.8 and 24.5 kcal/mol, respectively.

Luminescent fac-[Re(CO)3(phen)] carboxylato complexes with non-steroidal anti-inflammatory drugs: synthesis and mechanistic insights into the in vitro anticancer activity of fac-[Re(CO)3(phen)(aspirin)

Luminescent fac-[Re(CO)3(phen)(aspirin)]: insights into in vitro anticancer activity and confocal microscopy imaging in HeLa cells.

Comparative stability, toxicity and anti-leishmanial activity of triphenyl antimony(v) and bismuth(v) α-hydroxy carboxylato complexes.

A series of triphenyl Sb(v) and Bi(v) α-hydroxy carboxylato complexes of the general formula [MPh3(O2CROH)2] and [MPh3(O2CRO)] have been successfully synthesised and characterised, and subsequently assayed for their comparative activity towards Leishmania parasites and human fibroblast cells. Four complexes are novel; [SbPh3Gly], [BiPh3(GlyH)2], [SbPh3(R-ManH)2] and [SbPh3(S-ManH)2], and have been structurally characterised through X-ray diffraction. These were combined in the study with the known complexes; ([SbPh3(R-Man)], [SbPh3(S-Man)], [BiPh3(R-ManH)2], [BiPh3(R-ManH)2], [SbPh3(BenzH)2], [BiPh3(BenzH)2], for which the crystal structures of [BiPh3(S-ManH)2] and [BiPh3(R-Man)2] have now been authenticated (GlyH2 = glycolic acid, R/S-ManH2 = mandelic acid, BenzH2 = benzilic acid). The complexes adopt a typical bipyramidal 7-coordinate geometry with the phenyl rings occupying the equatorial plane, and the ligands on the axial. In contrast to previous studies the Bi(v) compounds show a relatively high degree of stability in DMEM culture media. Promastigote and human fibroblast cell assays showed the Bi(v) analogues to be non-selectively toxic with a respective IC50 range of 3.58-6.33 μM and 5.83-7.01 μM. In contrast, the Sb(v) analogues provided much greater selectivity (promastigotes 12.5-20.7; fibroblasts 72.8-≥100 μM). Assessment of the Sb(v) complexes against amastigotes at 10 μM showed them to be effective with % infection values ranging from 9.5 ± 0.5-30 ± 1.3.

Unprecedented anticancer activities of organorhenium sulfonato and carboxylato complexes against hormone-dependent MCF-7 and hormone-independent triple-negative MDA-MB-231 breast cancer cells.

Cisplatin and other metal-based drugs often display side effects and tumor resistance after prolonged use. Because rhenium-based anticancer complexes are often less toxic, a novel series of organorhenium complexes were synthesized of the types: XRe(CO)3Z (X=α-diimines and Z=p-toluenesulfonate, 1-naphthalenesulfonate, 2-naphthalenesulfonate, picolinate, nicotinate, aspirinate, naproxenate, flufenamate, ibuprofenate, mefenamate, tolfenamate, N-acetyl-tryptophanate), and their biological properties were examined. Specifically, in hormone-dependent MCF-7 and hormone-independent triple-negative MDA-MB-231 breast cancer cells, the p-toluenesulfonato, 1-naphthalenesulfonato, 2-naphthalenesulfonato, picolinato, nicotinato, acetylsalicylato, flufenamato, ibuprofenato, mefenamato, and N-acetyl-tryptophanato complexes were found to be far more potent than conventional drug cisplatin. DNA-binding studies were performed in each case via UV-Vis titrations, cyclic voltammetry, gel electrophoresis, and viscosity, which suggest DNA partial intercalation interaction, and the structure-activity relationship studies suggest that the anticancer activities increase with the increasing lipophilicities of the compounds, roughly consistent with their DNA-binding activities.

Synthesis and characterization of mononuclear ruthenium complexes with carboxylato, chlorido and phosphine ligands. Crystal structures of [RuCl2{κ2-O,O-O2CC[dbnd]CH2(CH3)}(PPh3)2], [RuCl2(κ2-O,O-O2CC6H4-2-Cl)(PPh3)2], and [Et3NH][RuCl(SO2)(κ2-C,O-C6H4-2-CO2)(PPh3)2

Reaction of [Ru(PPh3)3Cl2] with the 2-methyl-acrylic acid 3-trimethoxysilane propyl ester in the presence of triethylamine (Et3N) afforded the neutral 17e ruthenium(III)-carboxylato complex [RuCl2{κ2-O,O-O2CCCH2(CH3)}(PPh3)2] (1) as a result of the break of ester functional group. Interaction of [Ru(PPh3)3Cl2] with 2-chlorobenzoic acid under similar reaction conditions gave the 17e carboxylato ruthenium(III) complex [RuCl2(κ2-O,O-O2CC6H4-2-Cl)(PPh3)2] (2). Treatment of 2 with two equivalent n-BuLi, followed by addition of SO2 and Et3N resulted the cyclometalated 18e ruthenium(II) complex [Et3NH][RuCl(SO2)(κ2-C,O-C6H4-2-CO2)(PPh3)2] (3). When [Et4N]Cl was used instead of SO2 and Et3N, the reaction yielded the cyclometalated 18e ruthenium(II) complex [Et4N]2[RuCl2(κ2-C,O-C6H4-2-CO2)(PPh3)2] (4). Formation mechanisms of complexes 3 and 4 are supposed. The four complexes were spectroscopically characterized and the crystal structures of complexes 1–3 have been established by X-ray crystallography. Molecular orbital calculations of complexes 1–3 are presented by the B3LYP functional methods.

Platinum(II) carboxylato complexes containing 7-azaindoles as N-donor carrier ligands showed cytotoxicity against cancer cell lines

The platinum(II) malonato (Mal) and decanoato (Dec) complexes of the general formulas [Pt(Mal)(naza)2] (1–3) and cis-[Pt(Dec)2(naza)2] (4–7) were prepared, characterized and tested for their in vitro cytotoxicity against cisplatin-sensitive (A2780) and cisplatin-resistant (A2780R) human ovarian carcinoma cell lines and non-cancerous human lung fibroblasts (MRC-5); naza=halogeno-derivatives of 7-azaindole. Complexes 1–7 effectively overcome the acquired resistance of ovarian carcinoma cells to cisplatin. Complexes 2 (IC50=26.6±8.9μM against A2780 and 28.9±6.7μM against A2780R), 4 (IC50=14.5±0.6μM against A2780 and 14.5±3.8μM against A2780R) and 5 (IC50=13.0±1.1μM against A2780 and 13.6±4.9μM against A2780R) indicated decreased toxicity against healthy MRC-5 cells (IC50>50.0μM for 2 and >25.0μM for 4 and 5). The representative complexes 2 and 4 showed mutually different effect on the A2780 cell cycle at IC50 concentrations after 24h exposure. Concretely, the complex 2 caused cell cycle arrest at G0/G1 phase, while 4 induced cell death by apoptosis with high population of cells in sub-G1 cell cycle phase. The hydrolysis and interactions of the selected complexes with biomolecules (glutathione (GSH) and guanosine monophosphate (GMP)) were also studied by means of 1H NMR and ESI+ mass spectra.

Photoactivation of Diiodido-Pt(IV) Complexes Coupled to Upconverting Nanoparticles.

The preparation, characterization, and surface modification of upconverting lanthanide-doped hexagonal NaGdF4 nanocrystals attached to light sensitive diiodido-Pt(IV) complexes is presented. The evaluation for photoactivation and cytotoxicity of the novel carboxylated diiodido-Pt(IV) cytotoxic prodrugs by near-infrared (NIR) light (λ = 980 nm) is also reported. We attempted two different strategies for attachment of light-sensitive diiodido-Pt(IV) complexes to Yb,Er- and Yb,Tm-doped β-NaGdF4 upconverting nanoparticles (UCNPs) in order to provide nanohybrids, which offer unique opportunities for selective drug activation within the tumor cells and subsequent spatiotemporal controlled drug release by NIR-to-visible light-upconversion: (A) covalent attachment of the Pt(IV) complex via amide bond formation and (B) carboxylate exchange of oleate on the surface of the UCNPs with diiodido-Pt(IV) carboxylato complexes. Initial feasibility studies showed that NIR applied by a 980 nm laser had only a slight effect on the stability of the various diiodido-Pt(IV) complexes, but when UCNPs were present more rapid loss of the ligand-metal-charge transfer (LMCT) bands of the diiodido-Pt(IV) complexes was observed. Furthermore, Pt released from the Pt(IV) complexes platinated calf-thymus DNA (ct-DNA) more rapidly when NIR was applied compared to dark controls. Of the two attachment strategies, method A with the covalently attached diiodido-Pt(IV) carboxylates via amide bond formation proved to be the most effective method for generating UCNPs that release Pt when irradiated with NIR; the released Pt was also able to bind irreversibly to calf thymus DNA. Nonetheless, only ca. 20% of the Pt on the surface of the UCNPs was in the Pt(IV) oxidation state, the rest was Pt(II), indicating chemical reduction of the diiodido-Pt(IV) prodrug by the UCNPs. Cytotoxicity studies with the various UCNP-Pt conjugates and constructs, tested on human leukemia HL60 cells in culture, indicated a substantial increase in cytotoxicity when modified UCNPs were combined with five rounds of 30 min irradiation with NIR compared to dark controls, but NIR alone also had a significant cytotoxic effect at this duration.

The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization.

The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization was investigated. A novel intercluster compound, [{(AuLCl)2(μ-OH)}2]3[α-PMo12O40]2·3EtOH (1-PMo12), was obtained as orange-yellow plate crystals in 12.0% yield from a 6 : 1 molar ratio reaction of the monomeric phosphanegold(i) carboxylato complex [Au(RS-pyrrld)(LCl)] (RS-Hpyrrld = RS-2-pyrrolidone-5-carboxylic acid; LCl = tris(4-chlorophenyl)phosphane) in CH2Cl2 with the free acid-form of Keggin polyoxometalate (POM), H3[α-PMo12O40]·14H2O. An EtOH/H2O (5 : 1, v/v) solvent mixture was used. The dimeric cation [{(AuLCl)2(μ-OH)}2](2+) in 1-PMo12 was in a parallel-edge arrangement that was formed by self-assembly through the inter-cationic aurophilic interactions of the μ-OH-bridged dinuclear phosphanegold(i) cation. The POM anion in 1-PMo12 was successfully exchanged with a smaller PF6(-) anion by the use of an anion-exchange resin. POM-free, colorless block crystals of [{(AuLCl)3(μ3-O)}2](PF6)2·4CH2Cl2 (2-PF6) were obtained by vapor diffusion in 14.1% yield. During the synthesis of 2-PF6, a compound with mixed counteranions (one POM and one PF6(-) anion), i.e. [{(AuLCl)4(μ4-O)}]2[α-PMo12O40]PF6 (3-PMo12PF6), was obtained in 66.4% yield. Both products were characterized by elemental analysis, TG/DTA, FT-IR, (31)P{(1)H} NMR, (1)H NMR, and X-ray crystallography. X-ray crystallography revealed that the countercation in 2-PF6 was the dimeric cation of the μ3-O-bridged tris{phosphanegold(i)} species, whereas that in 3-PMo12PF6 consisted of an unusual μ4-O-bridged tetragonal-pyramidal tetrakis{phosphanegold(i)} cation. Therefore, we concluded that the POM anion significantly contributed to the stabilization of these countercations (parallel-edged arrangement in 1-PMo12 and μ4-O-bridged tetragonal-pyramid in 3-PMo12PF6). Moreover, the previously reported yellow crystals of [{(AuLF)2(μ-OH)}2]3[PMo12O40]2·3EtOH (4-PMo12: LF = tris(4-fluoro phenyl)phosphane) were successfully converted to the POM-free crystalline OTf(-) salt [{(AuLF)2(μ-OH)}2](OTf)2·0.5Et2O (4-OTf) by the use of an anion-exchange resin. X-ray crystallography also revealed that the parallel-edge arrangement of the dimeric cation in 4-PMo12 was converted to the crossed-edge arrangement of that in 4-OTf. These results illustrate that the AuOPOM and hydrogen-bonding (C-HOPOM and O-HOPOM) interactions between the phosphanegold(i) cluster cation and the Keggin POM anion in the solid state significantly contribute to the structure, composition, and stability of the phosphane gold(i) cluster cations in 4-PMo12.

Oxido-molybdenum complexes obtained by Cl/O interchange between MoCl5 and carboxylic acids: a crystallographic, spectroscopic and computational study.

The direct interaction of MoCl5 with a series of carboxylic acids has been elucidated for the first time. The reactions proceed with release of hydrogen chloride and Cl/O interchange between the metal centre and one equivalent of organic substrate: this feature is unique in the context of the chemistry generally shown by transition metal halides with carboxylic acids. The dinuclear complexes [MoOCl2(κ(1)-CX3CO2H)(μ-Cl)]2 (X = H, 1a; X = Cl, 1b) and Mo2O2Cl6(μ-CH3CO2H), 2a, were isolated as the prevalent metal products of the 1:2 molar reactions of MoCl5 with CH3COOH and CCl3COOH. Evidence for the formation of Mo2O2Cl6(μ-CCl3CO2H), 2b, was achieved by allowing MoCl5 to react with CCl3COOH in 2:3 ratio. Instead the reactions of MoCl5 with a three-fold molar excess of RCOOH afforded the mononuclear complexes MoOCl3(κ(1)-RCO2H)2 (R = CH3, 3a; CCl3, 3b; CHCl2, 3c; CMe3, 3d) in 50–60% yields. The new compounds were characterized by analytical and spectroscopic techniques, moreover the X-ray molecular structures were ascertained for 1a, 1b and 2a; 1a and 1b display single Mo–Mo bond. DFT calculations were carried out in order to shed light into structural aspects.

Photolysis of Fe(III) carboxylato complexes: Fe(II) quantum yields and reaction mechanisms

Fe(III) carboxylato complex photochemistry can be of interest for environmental aqueous systems, oxidative processing of wastewater or laboratory photochemical applications in general. A comprehensive dataset of Fe2+ quantum yields from the photolysis of aqueous Fe(III) complexes with malonate, succinate, glutarate, dl-tartrate, tartronate, gluconate, dl-lactate, dl-malate, pyruvate and glyoxalate has been measured. Irradiation techniques included single laser flash photolysis at 308 and 351 nm and continuous photolysis with a Hg(Xe) lamp-monochromator system at 313, 366, 405 and 436 nm. Complexes with ligands having a higher oxygen to carbon ratio tend to exhibit better photoreduction ability. Ligands containing OH, keto or diol functional groups in the α-position exhibit higher quantum yields than unsubstituted carboxylates (R-CH2-COOH). Generally, dissolved O2 lowers the Fe2+ quantum yield but at certain wavelengths, for some ligands this is the opposite. The influence of transient decay pathways and secondary red-ox reactions including interactions with dissolved O2 has been investigated for Fe(III) glyoxalato complexes using kinetic simulations. Some complexes show a dependence of Fe2+ quantum yield on the irradiation energy.

Stoichiometric CH Bond Cleavage Reaction in a Bis(carboxylato)ruthenium(II) Complex and Its Application to the Catalytic H–D Exchange Reaction of Carboxylic Acids

AbstractA cationic complex [Ru{OC(O)CMeCH2‐κ2O,O′}(PMe3)4]+CH2CMeCO2− (5 a) and its related carboxylato complexes are newly prepared by the reaction of [cis‐RuH2(PMe3)4] (4) with carboxylic acids in methanol in 76–100 % yield. Complex 5 a reversibly transforms to the neutral form [cis‐Ru{OC(O)CMeCH2‐κ1O}2(PMe3)4] (2 a) in nonpolar solvents. Complex 2 a reversibly liberates a PMe3 group to give [Ru{OC(O)CMeCH2‐κ1O}{OC(O)CMeCH2‐κ2O,O′}(PMe3)3] (12 a) from which a stereoselective CH bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMeCH‐κ2O,C}(PMe3)4] (1 a) from the release of methacrylic acid. Complexes 2 a and 5 a also give 1 a but the prior dissociation of a PMe3 is indispensable for the CH bond cleavage reaction. Complex 1 a establishes an equilibrium with 2 a (or 5 a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the CH bond cleavage reaction as a proton acceptor, but neither the added carboxylato anion nor typical proton acceptors such as proton sponge assist the reaction. In [D4]MeOH, a catalytic stereospecific deuteration of carboxylic acids has been achieved by 4, in which the equilibrium between 5 a and 1 a plays a key role.

Assembly of alternating spin-chains with magnetically anisotropic cobalt(ii) dimers

A dimeric carboxylato complex of cobalt(II), [Co(2)(II)(1,2-chedc)(2)(Im)(2)] (1) (1,2-chedc = cyclohex-1-ene-1,2-dicarboxylate and Im = imidazole), has been isolated. This complex can be further linked by chloro- or carboxylato-ligands, affording respectively one-dimensional chain structures of (1)(∞)[Co(2)(II)(μ-Cl)(2)(1,2-chedc)(Im)(2)] (2) and (1)(∞)[Co(II)(1,2-chedc)(Im)] (3). Compound 1 shows weak antiferromagnetic interactions passing through the body of the dicarboxylate as well as substantial single-ion magnetic anisotropy (zero-field splitting energy Δ = 8.5 cm(-1)). Both 2 and 3 exhibit typical alternating spin-chain behaviour in the higher-temperature region, but they display disparate behaviours at lower temperatures. For 2, alternating F-AF interactions compete (J(1) = 6.7 K and J(2) = -8.2 K), resulting in paramagnet-like behaviour with no clear evidence of three-dimensional contact. Compound 3 exhibits stronger intrachain AF-AF exchange-coupling interactions (J(1) = -9.3 K and J(2) = -4.3 K), leading to non-diamagnetic ground state due to the tiling of adjacent spins. Long-range magnetic ordering was observed below 10 K. Its narrow hysteresis loop suggests the use of 3 as a soft magnet.

Dipalladium Complexes with Triazolidin-Diylidene Bridges and Their Catalytic Activities

The 1,2,4-trimethyltriazolidin-3,5-diylidene (ditz) bridged dipalladium heterotetracarbene complex [PdBr2(iPr2-bimy)]2(μ-ditz) (3) (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene) was prepared by Ag–carbene transfer involving the 1,2,4-trimethyltriazolium dication (C), Ag2O, and the precursor complex (iPr2-bimyH)[PdBr3(iPr2-bimy)] (2). Bromido substitution of 3 with AgO2CCH3 and AgO2CCF3afforded the carboxylato complexes [Pd(O2CCH3)2(iPr2-bimy)]2(μ-ditz) (4) and [Pd(O2CCF3)2(iPr2-bimy)]2(μ-ditz) (5). Multinuclei NMR spectroscopies and X-ray diffraction analyses showed that the all-trans isomers of 3, 4, and 5 are the predominant products in all three cases. In addition, the decomposition product of complex 4, trans-[Pd(O2CCH3)2(iPr2-bimy)2] (trans-6) was structurally determined by X-ray crystallography. A comparative catalytic study revealed the superiority of complexes 3, 4, and 5 over the previously reported mononuclear bis(benzimidazolin-2-ylidine) complexes without ditz bridges in the Mizoroki–He...

Pyridine-2-Carbaldehyde Thiosemicarbazonecopper System: Extending Some Findings to Other Thiosemicarbazone and Coordination Compounds

The study of thiosemicarbazones and their metal complexes has become a fruitful area of the coordination chemistry due to the interesting properties exhibited by these compounds, in particular those dealing with the biological activity. Our efforts have focused on the structure-properties relationship in copper(II) derivatives of pyridine-2- carbaldehyde thiosemicarbazone. Usually, this molecule acts as a NNS terdentate ligand and gives rise to [Cu(HL)]2+ / [CuL]+ rigid planar blocks, which can form dimers by bonds through the thiosemicarbazone S atom (S-bridged systems) or the X atom belonging to different coligands (X-bridged systems). Such structural features, together with the high stability of these compounds, allow the synthesis of complexes with small structural modifications. This fact has prompted us to carry out systematic studies in which variations of physic and chemical parameters (as pH, temperature or reactants present in the reaction medium) induce changes in the ligand or modify the structural, spectroscopic and magnetic properties of the complexes. In this sense, an appropriate choice of ancillary ligands (halides, oxalate, carboxylates, polyoxometalate or biomolecules, among others) is essential to attain different behaviors. Oxalato derivatives with relatively high ferromagnetism and unusually twisted carboxylato groups, structures of thiosemicarbazone-polyoxometalate hybrid systems and nucleic acid base-thiosemicarbazone complexes, reactivity with glutathione, interaction and cleavage of DNA and biological activity against tumoral cell lines are some of the aspects discussed here. Some conclusions of our research can be extrapolated to a broad range of compounds. Keywords: Carboxylato complexes, coordination compounds, copper, magnetic properties, spectroscopic properties, structure, polyoxometalate, thiosemicarbazone, Pyridine-2-Carbaldehyde, Thiosemicarbazone copper(II) System

Self-assembly of 1D coordination polymers of two rare-earth complexes with carboxylate linkages: Synthesis, crystal structure and DFT studies

Two new lanthanide carboxylato complexes [Ln(3,5-DNBA) 3(H 2O) 2] n , (Ln = La III in 1 and Gd III in 2, DNBA = dinitrobenzoic acid) have been synthesized hydrothermally and characterized structurally by single crystal X-ray analysis. Alternate (μ-η 1:η 1) 4 and (μ-η 1:η 1) 2 type bridging modes by carboxylate ligands provide eightfold coordination around the Ln center in both complexes, which result in two different Ln ⋯ Ln distances, with polymeric chains propagating along the [1 0 0] direction. Intermolecular O–H ⋯ O hydrogen bonds and π–π stacking interactions form R 2 2 (20), R 4 4 (40) rings, thus generating three-dimensional supramolecular frameworks in 1 and 2. Density functional theory (DFT) calculations were carried out using the hybrid exchange–correlation functional, PBE. The HOMO–LUMO energy gap of 2.63 eV in 1 is found to be greater than that of 1.86 eV in 2.

Reactivity studies of η6-p-cymene ruthenium(II) carboxylato complexes towards azide some neutral ligands

Reactivity studies of η6-p-cymene ruthenium(II) carboxylato complexes towards azide some neutral ligands

Visualizing Chromatographic Separation of Metal Ions on a Surface-Enhanced Raman Active Medium

Metal ion carboxylato complexes possess ion-specific carboxylate Raman bands. Using this attribute we follow the chromatographic separation of a microliter aliquot of an initially equimolar solution of Pb(2+) and Hg(2+) using the surface-enhanced Raman spectroscopy spectra of their carboxylato complexes as unique identifiers. A glass capillary whose interior is lined with a dense layer of gold nanoparticles treated with 4-mercaptobenzoic acid simultaneously acts as a separation medium and an efficient SERS reporter of the step-by-step separation process. The observed adsorption-desorption equilibrium along the capillary is shown to conform with theory. Although Hg(2+) complexes with COO(-) much more strongly than Pb(2+), it is the Pb(2+) that survives the separation process as the sole surface species. We show that this is because so much mercury is taken out of solution during early separation steps that the surface equilibrium is ultimately driven toward adsorbed Pb(2+).

Dependence of the Chemical Properties of Macrocyclic [NiII2L(μ-O2CR)]+ Complexes on the Basicity of the Carboxylato Coligands (L2− = macrocyclic N6S2 ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.

Hydrothermal synthesis of dimeric lanthanide compounds: X-ray structure, magnetic study and heterogeneous catalytic epoxidation of olefins

A series of dimeric lanthanide carboxylato complexes [La(5-Br-NIC) 3(H 2O) 2] 2·H 2O ( 1); [Gd(5-Br-NIC) 3(H 2O) 2] 2 ( 2), [5-Br-NIC = 5-bromonicotinate] and [Sm(NIC) 3(H 2O) 2] 2 ( 3) [NIC = nicotinate], have been hydrothermally synthesized and structurally characterized by single crystal X-ray analysis. Complexes 1, 2 and 3 are of similar structure and consist of a basic unit [La(carboxylato) 3(H 2O) 2] 2. In compound 1 lanthanide cation is surrounded by one chelating 5-bromo-nicotinato ligand, two bridging oxygen atoms from 5-bromo-nicotinato and two water molecules, in which each La(III) ion is nine coordinated in a tricapped prismatic geometry. However, in compounds 2 and 3 four carboxylate groups link a pair of lanthanide atoms in the O,O′-bridging mode to generate a paddle-wheel-like centrosymmetric dimer. All the compounds exhibit excellent catalytic performance in olefin epoxidation reaction. The variable temperature magnetic susceptibility measurements showed that the magnetic interaction in [Gd(5-Br-NIC) 3(H 2O) 2] 2 ( 2), is antiferromagnetic ( J = −0.048 cm −1), while compound [Sm(NIC) 3(H 2O) 2] 2 ( 3), showed a complicated low-temperature magnetic property.

ChemInform Abstract: Practical Synthesis of (S)-2-(4-Fluorophenyl)-3-methylbutanoic Acid, Key Building Block for the Calcium Antagonist Mibefradil.

Abstract A short, technically feasible route was developed for the synthesis of (S)2-(4-fluorophenyl)-3-methylbutanoic acid (S)- 2 with an overall yield of 80% starting from 4-fluorophenylacetic acid. Asymmetric hydrogenation of the easily accessible unsaturated acid 3 in the presence of ruthenium(II) carboxylato complexes containing chiral atropisomeric diphosphines afforded (S)- 2 in up to 94% ee. The ee of (S)- 2 was upgraded to 98% by crystallization of its sodium salt. The same protocol was also applied to the synthesis of (S)-2-(4-chlorophenyl)-3-methylbutanoic acid.