Elisabete Clara Bastos do Amaral Alegria

Syntheses, Molecular Structures, Electrochemical Behavior, Theoretical Study, and Antitumor Activities of Organotin(IV) Complexes Containing 1-(4-Chlorophenyl)-1-cyclopentanecarboxylato Ligands

The organotin(IV) compounds [Me(2)Sn(L)(2)] (1), [Et(2)Sn(L)(2)] (2), [(n)Bu(2)Sn(L)(2)] (3), [(n)Oct(2)Sn(L)(2)] (4), [Ph(2)Sn(L)(2)] (5), and [PhOSnL](6) (6) have been synthesized from the reactions of 1-(4-chlorophenyl)-1-cyclopentanecarboxylic acid (HL) with the corresponding diorganotin(IV) oxide or dichloride. They were characterized by IR and multinuclear NMR spectroscopies, elemental analysis, cyclic voltammetry, and, for 2, 3, 4 and 6, single crystal X-ray diffraction analysis. While 1-5 are mononuclear diorganotin(IV) compounds, the X-ray diffraction of 6 discloses a hexameric drumlike structure with a prismatic Sn(6)O(6) core. All these complexes undergo irreversible reductions and were screened for their in vitro antitumor activities toward HL-60, BGC-823, Bel-7402, and KB human cancer cell lines. Within the mononuclear compounds, the most active ones (3, 5) are easiest to reduce (least cathodic reduction potentials), while the least active ones (1, 4) are the most difficult to reduce. Structural rearrangements (i.e., Sn-O bond cleavages and trans-to-cis isomerization) induced by reduction, which eventually can favor the bioactivity, are disclosed by theoretical/electrochemical studies.

Dinuclear Mn(II,II) complexes: magnetic properties and microwave assisted oxidation of alcohols

A series of six new mixed-ligand dinuclear Mn(II,II) complexes of three different hydrazone Schiff bases (H3L(1), H3L(2) and H3L(3)), derived from condensation of the aromatic acid hydrazides benzohydrazide, 2-aminobenzohydrazide or 2-hydroxybenzohydrazide, with 2,3-dihydroxy benzaldehyde, respectively, is reported. Reactions of Mn(NO3)2·4H2O with the H3L(1-3) compounds, in the presence of pyridine (1 : 1 : 1 mole ratio), in methanol at room temperature, yield [Mn(H2L(1))(py)(H2O)]2(NO3)2·2H2O (1·2H2O), [Mn(H2L(2))(py)(CH3OH)]2(NO3)2·4H2O (2·4H2O) and [Mn(H2L(3))(py)(H2O)]2(NO3)2 (3) respectively, whereas the use of excess pyridine yields complexes with two axially coordinated pyridine molecules at each Mn(II) centre, viz. [Mn(H2L(1))(py)2]2(NO3)2·H2O (4·H2O), [Mn(H2L(2))(py)2]2(NO3)2·2H2O (5·2H2O) and [Mn(H2L(3))(py)2]2(NO3)2·2CH3OH (6·2CH3OH), respectively. In all the complexes, the (H2L(1-3))(-) ligand coordinates in the keto form. Complexes 1·2H2O, 2·4H2O, 4·H2O, 5·2H2O and 6·2CH3OH are characterized by single crystal X-ray diffraction analysis. The complexes 1, 2 and 6, having different coordination environments, have been selected for variable temperature magnetic susceptibility measurements to examine the nature of magnetic interaction between magnetically coupled Mn(II) centres and also for exploration of the catalytic activity towards microwave assisted oxidation of alcohols. A yield of 81% (acetophenone) is obtained using a maximum of 0.4% molar ratio of catalyst relative to the substrate in the presence of TEMPO and in aqueous basic solution, under mild conditions.

Oxorhenium Complexes Bearing the Water-Soluble Tris(pyrazol-1-yl)methanesulfonate, 1,3,5-Triaza-7-phosphaadamantane, or Related Ligands, as Catalysts for Baeyer–Villiger Oxidation of Ketones

New rhenium(VII or III) complexes [ReO3(PTA)2][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4]I (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)2][ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(η(2)-Tpm)(PTA)][ReO4] (4) [Tpm = hydrotris(pyrazol-1-yl)methane, HC(pz)3, pz = pyrazolyl], [ReO3(Hpz)(HMT)][ReO4] (5) (Hpz = pyrazole), [ReO(Tpms)(HMT)] (6) [Tpms = tris(pyrazol-1-yl)methanesulfonate, O3SC(pz)3(-)] and [ReCl2{N2C(O)Ph}(PTA)3] (7) have been prepared from the Re(VII) oxide Re2O7 (1-6) or, in the case of 7, by ligand exchange from the benzoyldiazenido complex [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2], and characterized by IR and NMR spectroscopies, elemental analysis and electrochemical properties. Theoretical calculations at the density functional theory (DFT) level of theory indicated that the coordination of PTA to both Re(III) and Re(VII) centers by the P atom is preferable compared to the coordination by the N atom. This is interpreted in terms of the Re-PTA bond energy and hard-soft acid-base theory. The oxo-rhenium complexes 1-6 act as selective catalysts for the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g., 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone or pinacolone) to the corresponding lactones or esters, in the presence of aqueous H2O2. The effects of a variety of factors are studied toward the optimization of the process.

Hexanuclear and undecanuclear iron(III) carboxylates as catalyst precursors for cyclohexane oxidation

Two multinuclear complexes [Fe6(μ3-O)2(μ4-O2)L10(OAc)2(H2O)2]·2.625Et2O·2.375H2O (1) and [Fe(III)11Cl(μ4-O)3(μ3-O)5L16(dmf)(2.5)(H2O)(0.5)]·Et2O·1.25dmf·3.8H2O (2), where HL = 3,4,5-trimethoxybenzoic acid and dmf = dimethylformamide, have been prepared from trinuclear iron(III) carboxylates via their structural rearrangement in dimethylformamide or diethyl ether-dimethylformamide 9:1, respectively, and slow vapor diffusion of diethyl ether into the reaction mixture. Both compounds have been characterized by X-ray diffraction, optical, Mössbauer spectroscopy, and magnetic measurements. Complex 1 possesses a hexanuclear ferric peroxido-dioxido {Fe6(O2)(O)2}(12+) core unit, which adopts a recliner conformation, while complex 2 contains an unprecedented {Fe11O8Cl}(16+) core, in which 9 ferric ions are six-coordinate and the remaining two are five-coordinate. Another structural feature of note of the undecanuclear core is the presence of a deformed cubane entity {Fe4(μ3-O)(μ4-O)3}(4+). Both complexes act as catalyst precursors for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with aqueous H2O2, in the presence of pyrazinecarboxylic acid. Remarkable TONs and TOFs (the latter mainly for 1) with concomitant quite good yields have been achieved under mild conditions. Moreover, 1 exhibits remarkably high activity in an exceptionally short reaction time (45 min), being unprecedented for any metal catalyzed alkane oxidation by H2O2. The catalytic reactions proceed via Fenton type chemistry.

Effect of 1,10-phenanthroline on DNA binding, DNA cleavage, cytotoxic and lactate dehydrogenase inhibition properties of Robson type macrocyclic dicopper(II) complex

DNA targeting macrocyclic dicopper(II) complex, [Cu2L(H2O)2](phen)2(ClO4)2 (L = μ-11,23-dimethyl-3,7,15,19-tetraazatricyclo-[19.3.1.19,13,21] he p t a c o s a-1(24), 2, 7, 9, 11, 13(26), 14, 19, 21(25), 22-decaene-25,26-diol) (2), has been synthesized and characterized. This has been synthesized by reacting a Robson type macrocyclic precursor dicopper(II) complex [Cu2L(H2O)2](ClO4)2 (1) and 1,10-phenanthroline in ethanol. Solution ESR, electronic, and ESI-MS spectral studies suggest that 1,10-phenanthroline replaces coordinated water in 1, giving 2. The influence of the phenanthroline on DNA binding, cleavage, and anticancer properties of 2 have been investigated. Complex 2 displays better DNA binding and cleavage than 1. The dicopper(II) complexes 1 and 2 show cytotoxicity in human cervical HeLa cancer cells, giving IC50 values of 79.41 and 15.82 μM, respectively. Antiproliferative properties of 1 and 2 were confirmed by Trypan Blue exclusive assay and lactate dehydrogenase enzyme level in HeLa cancer cell lysate and content media.

Syntheses and properties of hydride–cyanamide and derived hydrogen-cyanamide complexes of molybdenum(IV). Crystal structure of [MoH2(NCNH2)2(Ph2PCH2CH2PPh2)2][BF4]2

The first hydride–cyanamide (or –cyanoguanidine) complexes of molybdenum, [MoH2(NCR)2(dppe)2][BF4]2 (R = NH21a, NMe21b, NEt21c or NC(NH2)21d; dppe = Ph2PCH2CH2PPh2), have been prepared by treatment of [MoH4(dppe)2] in THF with the appropriate cyanamide (or cyanoguanidine) in the presence of HBF4. Reaction of 1a with a base leads to the bis(hydrogen-cyanamide) [or bis(hydrogen-cyananoimide)] complex trans-[Mo(NCNH)2(dppe)2][BF4]22 or to the bis(cyanoimide) complex trans-[Mo(NCN)2(dppe)2] 3, via base-catalysed or base-promoted dehydrogenation, whereas cathodically-induced dehydrogenation appears to form [MoH2(NCNH)(NCNH2)(dppe)2]+4. The spectroscopic properties of the complexes are also reported along with their electrochemical behaviours and the molecular structure of 1a as established by X-ray crystallography which indicates the presence of the NCNH2 ligands involved in two hydrogen bonds connecting the ions in dimeric units.

Aroylhydrazone Cu(II) Complexes in keto Form: Structural Characterization and Catalytic Activity towards Cyclohexane Oxidation

The reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with a copper(II) salt of a base of a strong acid, i.e., nitrate, chloride or sulphate, yielded the mononuclear complexes [Cu(H2L)(NO3)(H2O)] (1), [Cu(H2L)Cl]·2MeOH (2) and the binuclear complex [{Cu(H2L)}2(µ-SO4)]·2MeOH (3), respectively, with H2L− in the keto form. Compounds 1–3 were characterized by elemental analysis, Infrared (IR) spectroscopy, Electrospray Ionisation Mass Spectrometry (ESI-MS) and single crystal X-ray crystallography. All compounds act as efficient catalysts towards the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, under mild conditions. In the presence of an acid promoter, overall yields (based on the alkane) up to 25% and a turnover number (TON) of 250 (TOF of 42 h−1) after 6 h, were achieved.

Redox-active cytotoxic diorganotin(IV) cycloalkylhydroxamate complexes with different ring sizes: Reduction behaviour and theoretical interpretation

Two series of new diorganotin(IV) cycloalkylhydroxamate complexes with different ring sizes (cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl), formulated as the mononuclear [R(2)Sn(HL)(2)] (1:2) (a, R=(n)Bu and Ph) and the polymeric [R(2)SnL](n) (1:1) (b, R=(n)Bu) compounds, were prepared and fully characterized. Single crystal X-ray diffraction for [(n)Bu(2)Sn{C(5)H(9)C(O)NHO}(2)] (3a) discloses the cis geometry and strong intermolecular NH⋯O interactions. The in vitro cytotoxic activities of the complexes were evaluated against HL-60, Bel-7402, BGC-823 and KB human tumour cell lines, the greater activity concerning [(n)Bu(2)Sn(HL)(2)] [HL=C(3)H(5)C(O)NHO (1a), C(6)H(11)C(O)NHO (4a)] towards BGC-823. The complexes undergo, by cyclic voltammetry and controlled-potential electrolysis, one irreversible overall two-electron cathodic process at a reduction potential that does not appear to correlate with the antitumour activity. The electrochemical behaviour of [R(2)Sn{C(5)H(9)C(O)NHO}(2)] [R=(n)Bu (3a), Ph (7a)] was also investigated using density functional theory (DFT) methods, showing that the ultimate complex structure and the mechanism of its formation are R dependent: for the aromatic (R=Ph) complex, the initial reduction step is centred on the phenyl ligands and at the metal, being followed by a second reduction with SnO and SnC ruptures, whereas for the alkyl (R=(n)Bu) complex the first reduction step is centred on one of the hydroxamate ligands and is followed by a second reduction with SnO bond cleavages and preservation of the alkyl ligands. In both cases, the final complexes are highly coordinative unsaturated Sn(II) species with the cis geometry, features that can be of biological significance.

Metal Azolate/Carboxylate Frameworks as Catalysts in Oxidative and C-C Coupling Reactions

The five metal azolate/carboxylate (MAC) compounds [Cd(dmpzc)(DMF)(H2O)] (Cd-dmpzc), [Pd(H2dmpzc)2Cl2] (Pd-dmpzc), [Cu(Hdmpzc)2] (Cu-dmpzc), [Zn4O(dmpzc)3]·Solv (Zn-dmpzc·S), and [Co4O(dmpzc)3]·Solv (Co-dmpzc·S) were isolated by coupling 3,5-dimethyl-1H-pyrazol-4-carboxylic acid (H2dmpzc) to cadmium(II), palladium(II), copper(II), zinc(II), and cobalt(II) salts. While Cd-dmpzc and Pd-dmpzc had never been prepared in the past, for Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S we optimized alternative synthetic paths that, in the case of the copper(II) and cobalt(II) derivatives, are faster and grant higher yields than the previously reported ones. The crystal structure details were determined ab initio (Cd-dmpzc and Pd-dmpzc) or refined (Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S) by means of powder X-ray diffraction (PXRD). While Cd-dmpzc is a nonporous 3D MAC framework, Pd-dmpzc shows a 3D hybrid coordination/hydrogen-bonded network, in which Pd(H2dmpzc)2Cl2 monomers are present. The thermal behavior of the five MAC compounds was investigated by coupling thermal analysis to variable-temperature PXRD. Their catalytic activity was assessed in oxidative and C-C coupling reactions, with the copper(II) and cadmium(II) derivatives being the first nonporous MAC frameworks to be tested as catalysts. Cu-dmpzc is the most active catalyst in the partial oxidation of cyclohexane by tert-butyl hydroperoxide in acetonitrile (yields up to 12% after 9 h) and is remarkably active in the solvent-free microwave-assisted oxidation of 1-phenylethanol to acetophenone (yields up to 99% at 120 °C in only 0.5 h). On the other hand, activated Zn-dmpzc·S (Zn-dmpzc) is the most active catalyst in the Henry C-C coupling reaction of aromatic aldehydes with nitroethane, showing appreciable diastereoselectivity toward the syn-nitroalkanol isomer (syn:anti selectivity up to 79:21).

Molybdenum – and tungsten(II) monometallic 3-(2-pyridyl)pyrazole and bimetallic 3-(2-pyridyl)pyrazolate complexes

Molybdenum and tungsten complexes containing the pypzH (3-(2-pyridyl)pyrazole) ligand as a chelating bidentate are prepared: [Mo(CO)(4)(pypzH)], cis-[MoBr(η(3)-allyl)(CO)(2)(pypzH)], cis-[MoCl(η(3)-methallyl)(CO)(2)(pypzH)], [MI(2)(CO)(3)(pypzH)] (M = Mo, W) from [Mo(CO)(4)(NBD)] or the adequate bis(acetonitrile) complexes. The deprotonation of the molybdenum allyl or methallyl complexes affords the bimetallic complexes [cis-{Mo(η(3)-allyl)(CO)(2)(μ(2)-pypz)}](2) or [cis-{Mo(η(3)-methallyl)(CO)(2)(μ(2)-pypz)}](2) (μ(2)-pypz = μ(2)-3-(2-pyridyl-κ(1)N)pyrazolate-2κ(1)N). The allyl complex was subjected to an electrochemical study, which shows a marked connection between both metallic centres through the bridging pyridylpyrazolates.