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- Trends in properties of para-substituted 3-(phenylhydrazo)pentane-2,4-dionesPublication . Kopylovich, Maximilian; Mahmudov, Kamran; Guedes Da Silva, M. Fátima C.; Martins, Luisa; Kuznetsov, Maxim L.; Silva, Telma F. S.; Fraústo Da Silva, João; Pombeiro, ArmandoTrends between the Hammett's sigma(p) and related normal sigma(n)(p), inductive sigma(I), resonance sigma(R), negative sigma(-)(p) and positive sigma(+)(p) polar conjugation and Taft's sigma(o)(p) substituent constants and the N-H center dot center dot center dot O distance, delta(N-H) NMR chemical shift, oxidation potential (E-p/2(ox), measured in this study by cyclic voltammetry (CV)) and thermodynamic parameters (pK, Delta G(0), Delta H-0 and Delta S-0) of the dissociation process of unsubstituted 3-(phenylhydrazo)pentane-2,4-dione (HL1) and its para-substituted chloro (HL2), carboxy (HL3), fluoro (HL4) and nitro (HL5) derivatives were recognized. The best fits were found for sigma(p) and/or sigma(-)(p) in the cases of d(N center dot center dot center dot O), delta(N-H) and E-p/2(ox), showing the importance of resonance and conjugation effects in such properties, whereas for the above thermodynamic properties the inductive effects (sigma(I)) are dominant. HL2 exists in the hydrazo form in DMSO solution and in the solid state and contains an intramolecular H-bond with the N center dot center dot center dot O distance of 2.588(3)angstrom. It was also established that the dissociation process of HL1-5 is non-spontaneous, endothermic and entropically unfavourable, and that the increase in the inductive effect (sigma(I)) of para-substitutents (-H < -Cl < -COOH < -F < -NO2) leads to the corresponding growth of the N center dot center dot center dot O distance and decrease of the pK and of the changes of Gibbs free energy, of enthalpy and of entropy for the HL1-5 acid dissociation process. The electrochemical behaviour of HL1-5 was interpreted using theoretical calculations at the DFT/HF hybrid level, namely in terms of HOMO and LUMO compositions, and of reactivities induced by anodic and cathodic electron-transfers. Copyright (C) 2010 John Wiley & Sons, Ltd.
- Efficient solvent-free friedel-crafts benzoylation and acylation of m-xylene catalyzed by N-acetylpyrazine-2-carbohydrazide-Fe(III)-chloro complexesPublication . Roy Barman, Tannistha; Sutradhar, Manas; Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Pombeiro, ArmandoReaction of N-acetylpyrazine-2-carbohydrazide (H2L) with anhydrous Fe(II) or Fe(III) chloride in CH3CN or in MeOH leads to the mononuclear [Fe(kNN’O-HL)Cl2] (1) or binuclear [Fe(kNN’O-HL) Cl(μ-OMe)]2 (2) Fe(III) complex, respectively. These complexes are characterized by elemental analysis, ESI-MS, IR spectroscopy, single-crystal X-ray crystallography, electrochemical techniques and DFT calculations. The theoretical calculations indicate that the three single-electron sequential reductions of 1 are centred at the metal, at the pyrazine group and at both, respectively. The catalytic activity of 1 and 2 was screened towards Friedel-Crafts benzoylation and acylation of m-xylene. The effects of reaction parameters, such as catalyst amount, reaction time and temperature, were studied and, under optimal conditions, 96% yield of 2,4-dimethylbenzophenone and 20% yield of 2,4-dimethylacetophenone were obtained, respectively. Complex 1 exhibited the highest activity in both reactions. The structural and electrochemical properties were supported by theoretical calculations and the importance of the Lewis acid character of the catalyst in the promotion of this catalytic reaction is discussed.
- Mono-alkylation of cyanoimide at a molybdenum(IV) diphosphinic center by alkyl halides: synthesis, cathodically induced isomerization and theoretical studiesPublication . Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Martins, Luisa; Pombeiro, ArmandoTreatment of trans-[Mo(NCN)(2)(dppe)(2)] with alkyl halides (RX) affords the alkylated cyanoimidocomplexes trans-[Mo(NCN)(NCNR)(dppe)(2)]X [R = Me, X = I (1); R = Et, X = I (2); R = Pr, X = I (3); R = Pr-i, X = I (4); R = CH2Ph, X = Br (5); R = CH2C6H4NO2-4, X = Br (6)], while its reaction with the trimethyloxonium salt [Me3O][BF4] affords trans-[Mo(NCN)(NCNMe)(dppe)(2)][BF4] (7). The reactions are accelerated by microwave irradiation. Complexes 1-7 were fully characterized by elemental analyses, IR and NMR spectroscopies, FAB-MS spectrometry, cyclic voltammetry and controlled potential electrolysis. The electrophilic addition to the exo-N atom of one of the cyanoimide ligands was confirmed by single crystal X-ray crystal analysis of 1. In aprotic medium and at a Pt electrode, compounds 1-7 undergo, apart from two consecutive single-electron reversible oxidations, also two successive single-electron reductions at different potentials, involving a cathodically induced trans-to-cis isomerization, following a double square ECEC-type mechanism which was studied in detail by digital simulation of the cyclic voltammograms. Quantum-chemical calculations indicate that the oxidations and reductions are mainly metal centered (although the latter with some involvement of the cyanoimide moieties), and that the reduction leads to a decrease of the relative stability of the trans isomer vs. the cis one.
- Acylated cyanoimido-complexes trans-[Mo(NCN){NCN(O)R}(DPPE)(2)]Cl and their reactons with electrophiles: Chemical, electrochemical and theoretical studyPublication . Alegria, Elisabete; Silva, Maria de Fátima Costa Guedes da; Kuznetsov, Maxim L.; Cunha, S. M. P. R. M.; Martins, Luisa; Pombeiro, ArmandoTreatment of a dichloromethane solution of trans-[Mo(NCN){NCNC(O)R}(dppe)(2)]Cl [R = Me (1a), Et (1b)] (dppe = Ph2PCH2CH2PPh2) with HBF4, [Et3O][BF4] or EtC(O)Cl gives trans-[Mo(NCN)Cl-(dppe)(2)]X [X = BF4 (2a) or Cl (2b)] and the corresponding acylcyanamides NCN(R')C(O)Et (R' = H, Et or C(O)Et). X-ray diffraction analysis of 2a (X = BF4) reveals a multiple-bond coordination of the cyanoimide ligand. Compounds 1 convert to the bis(cyanoimide) trans-[Mo(NCN)(2)(dppe)(2)] complex upon reaction with an excess of NaOMe (with formation of the respective ester). In an aprotic medium and at a Pt electrode, compounds 1 (R = Me, Et or Ph) undergo a cathodically induced isomerization. Full quantitative kinetic analysis of the voltammetric behaviour is presented and allows the determination of the first-order rate constants and the equilibrium constant of the trans to cis isomerization reaction. The mechanisms of electrophilic addition (protonation) to complexes 1 and the precursor trans[Mo(NCN)(2)(dppe)(2)], as well as the electronic structures, nature of the coordination bonds and electrochemical behaviour of these species are investigated in detail by theoretical methods which indicate that the most probable sites of the proton attack are the oxygen atom of the acyl group and the terminal nitrogen atom, respectively.
- Syntheses, molecular structures, electrochemical behavior, theoretical study, and antitumor activities of organotin(IV) complexes containing 1-(4-chlorophenyl)-1-cyclopentanecarboxylato ligandsPublication . Shang, Xianmei; Meng, Xianggao; Alegria, Elisabete; Li, Qingshan; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Pombeiro, ArmandoThe organotin(IV) compounds [Me2Sn(L)2] (1), [Et2Sn(L)2]( 2), [nBu2Sn(L)2]( 3), [nOct2Sn(L)2]( 4), [Ph2Sn(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 Sn6O6 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 cel llines. 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.
- Redox-active cytotoxic diorganotin(IV) cycloalkylhydroxamate complexes with different ring sizes: Reduction behaviour and theoretical interpretationPublication . Shang, Xianmei M.; Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Li, Qingshan S.; Pombeiro, ArmandoTwo series of new diorganotin(IV) cycloalkylhydroxamate complexes with different ring sizes (cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl), formulated as the mononuclear [R2Sn(HL)(2)] (1:2) (a, R=Bu-n and Ph) and the polymeric [R2SnL](n) (1:1) (b, R=Bu-n) compounds, were prepared and fully characterized. Single crystal X-ray diffraction for [(Bu2Sn)-Bu-n{C5H9C(O)NHO}(2)] (3a) discloses the cis geometry and strong intermolecular NH center dot center dot center dot 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 [(Bu2Sn)-Bu-n(HL)(2)] [HL=C3H5C(O)NHO (1a), C6H11C(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 [R2Sn(C5H9C(O)NHO)(2)] [R=Bu-n (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 Sn-O and Sn-C ruptures, whereas for the alkyl (R=Bu-n) complex the first reduction step is centred on one of the hydroxamate ligands and is followed by a second reduction with Sn-O 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.
- Tuning cyclohexane oxidation: combination of microwave irradiation and ionic liquid with the c-scorpionate [FeCl2(Tpm)] catalystPublication . Da Costa Ribeiro, Ana Paula; Martins, Luisa; Kuznetsov, Maxim L.; Pombeiro, ArmandoFor the first time, microwave (MW) irradiation was successfully applied to peroxidative cyclohexane oxidation catalyzed by a C-scorpionate complex, [FeCl2(Tpm)] (1; Tpm = hydrotris(pyrazol-1-yl)methane), providing a highly selective and fast eco-friendly procedure to produce a KA (cyclohexanol + cyclohexanone) oil mixture (up to ca. 100% selectivity) with 28% yield in 1 h at 50 degrees C in MeCN. Water, organics, and ionic liquids (ILs, [bmim][N(CN)(2)] and [brnim][BF4]) were used as solvents, and their interactions with 1 were determined by DFT calculations. The possibility to recycle and reuse 1 (up to nine consecutive cycles) without loss of activity is also observed for the IL [bmim] [BF4]. Moreover, higher catalytic activities under additive-free conditions are obtained with the ILs in comparison to those with the other solvents. Tuning the alcohol/ketone selectivity is also possible by choosing the appropriate IL solvent.
- Complexes of copper(II) with 3-(ortho-substituted phenylhydrazo)pentane-2,4-diones: syntheses,properties and catalytic activity for cyclohexane oxidationPublication . Kopylovich, Maximilian N.; Nunes, Andreia C. C.; Mahmudov, Kamran; Haukka, Matti; Mac Leod, Tatiana C. O.; Martins, Luisa; Kuznetsov, Maxim L.; Pombeiro, ArmandoReactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C6H4-NHN = C{C(= O)CH3}(2) bearing a substituent in the ortho-position [X = OH (H2L1) 1, AsO3H2 (H3L2) 2, Cl (HL3) 3, SO3H (H2L4) 4, COOCH3 (HL5) 5, COOH (H2L6) 6, NO2 (HL7) 7 or H (HL8) 8] lead to a variety of complexes including the monomeric [CuL4(H2O)(2)]center dot H2O 10, [CuL4(H2O)(2)] 11 and [Cu(HL4)(2)(H2O)(4)] 12, the dimeric [Cu-2(H2O)(2)(mu-HL2)(2)] 9 and the polymeric [Cu(mu-L-6)](n)] 13 ones, often bearing two fused six-membered metallacycles. Complexes 10-12 can interconvert, depending on pH and temperature, whereas the Cu(II) reactions with 4 in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H2O)(4){NCNC(NH2)(2)}(2)](HL4)(2)center dot 6H(2)O 14 and the heteroligand polymer [Cu(mu-L-4)(im)](n) 15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, H-1 and C-13 NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1-8 on the HOMO-LUMO gap and the relative stability of the model compounds [Cu(OH)(L-8)(H2O)]center dot H2O, [Cu(L-1)(H2O)(2)]center dot H2O and [Cu(L-4)(H2O)(2)]center dot H2O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12 and 13 act as catalyst precursors for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H2O (total yields of ca. 20% with TONs up to 566), under mild conditions.
- New RuII(arene) complexes with halogen-substituted bis- and tris(pyrazol-1-YL)borate ligandsPublication . Orbisaglia, Serena; Di Nicola, Corrado; Marchetti, Fabio; Pettinari, Riccardo; Martins, Luisa; Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Rocha, Bruno G. M.; Kuznetsov, Maxim L.; Pombeiro, Armando; Skelton, Brian; Sobolev, Alexandre; White, Allan H.[RuCl(arene)(-Cl)](2) dimers were treated in a 1:2 molar ratio with sodium or thallium salts of bis- and tris(pyrazolyl)borate ligands [Na(BpBr3)], [Tl(TpBr3)], and [Tl(Tp(iPr,4Br))]. Mononuclear neutral complexes [RuCl(arene)((2)-BpBr3)] (1: arene=p-cymene (cym); 2: arene=hexamethylbenzene (hmb); 3: arene=benzene (bz)), [RuCl(arene)((2)-TpBr3)] (4: arene=cym; 6: arene=bz), and [RuCl(arene)((2)-Tp(iPr,4Br))] (7: arene=cym, 8: arene=hmb, 9: arene=bz) have been always obtained with the exception of the ionic [Ru-2(hmb)(2)(-Cl)(3)][TpBr3] (5), which formed independently of the ratio of reactants and reaction conditions employed. The ionic [Ru(CH3OH)(cym)((2)-BpBr3)][X] (10: X=PF6, 12: X=O3SCF3) and the neutral [Ru(O2CCF3)(cym)((2)-BpBr3)] (11) have been obtained by a metathesis reaction with corresponding silver salts. All complexes 1-12 have been characterized by analytical and spectroscopic data (IR, ESI-MS, H-1 and (CNMR)-C-13 spectroscopy). The structures of the thallium and calcium derivatives of ligand TpBr3, [Tl(TpBr3)] and [Ca(dmso)(6)][TpBr3](2)2DMSO, of the complexes 1, 4, 5, 6, 11, and of the decomposition product [RuCl(cym)(Hpz(iPr,4Br))(2)][Cl] (7) have been confirmed by using single-crystal X-ray diffraction. Electrochemical studies showed that 1-9 and 11 undergo a single-electron (RuRuIII)-Ru-II oxidation at a potential, measured by cyclic voltammetry, which allows comparison of the electron-donor characters of the bis- and tris(pyrazol-1-yl)borate and arene ligands, and to estimate, for the first time, the values of the Lever E-L ligand parameter for BpBr3, TpBr3, and Tp(iPr,4Br). Theoretical calculations at the DFT level indicated that both oxidation and reduction of the Ru complexes under study are mostly metal-centered with some involvement of the chloride ligand in the former case, and also demonstrated that the experimental isolation of the (3)-binuclear complex 5 (instead of the mononuclear 5) is accounted for by the low thermodynamic stability of the latter species due to steric reasons.
- Syntheses, molecular structures, electrochemical behavior, theoretical study, and antitumor activities of organotin(IV) complexes containing 1-(4-chlorophenyl)-1-cyclopentanecarboxylato ligandsPublication . Shang, Xianmei; Meng, Xianggao; Alegria, Elisabete; Li, Qingshan; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Pombeiro, ArmandoThe organotin(IV) compounds [Me2Sn(L)(2)] (1), [Et(2)sn(L)(2)] (2), [(Bu2Sn)-Bu-n(L)(2)] (3), [(n)Oct(2)Sn(L)(2)] (4), [Ph2Sn(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 Sn6O6 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.