Browsing by Author "Kuznetsov, Maxim L."
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- 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.
- Cobalt complexes with pyrazole ligands as catalyst precursors for the peroxidative oxidation of cyclohexane: Z-ray absorption spectroscopy studies and biological applicationsPublication . Silva, Telma F. S.; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Fernandes, Alexandra R.; Silva, Ana; Pan, Chun-Jern; Lee, Jyh-Fu; Hwang, Bing Joe; Pombeiro, Armando[CoCl(-Cl)(Hpz(Ph))(3)](2) (1) and [CoCl2(Hpz(Ph))(4)] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))(3) and Hpz(Ph), respectively (Hpz(Ph)=3-phenylpyrazole). The compounds were isolated as air-stable solids and fully characterized by IR and far-IR spectroscopy, MS(ESI+/-), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single-crystal X-ray diffraction. Electrochemical studies showed that 1 and 2 undergo single-electron irreversible (CoCoIII)-Co-II oxidations and (CoCoI)-Co-II reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). Insitu X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co-III site. Complex 2 showed low invitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.
- 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.
- Core-shell catalysts for conventional oxidation of alcohols: a brief reviewPublication . Correia, Luís M. M.; Kuznetsov, Maxim L.; Alegria, ElisabeteThis review highlights recent research on the application of core–shell structured materials as catalysts in the oxidation of alcohols to value-added products, such as benzaldehyde, acetophenone, benzophenone, cinnamaldehyde, and vanillin, among others. While the application of various unconventional energy inputs (such as microwave and ultrasound irradiation) was reported, this paper focuses on conventional heating. The oxidation of homocyclic aromatic, heterocyclic aromatic, aliphatic, and alicyclic alcohols catalyzed by core–shell composite catalysts is addressed. This work also highlights some unique advantages of core–shell nanomaterial catalysis, namely the flexibility of combining individual functions for specific purposes as well as the effect of various parameters on the catalytic performance of these materials.
- 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.
- 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(kappa NN'O-HL)Cl-2] (1) or binuclear [Fe(kNN'O-HL) Cl(mu-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.
- 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.
- 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 ketonesPublication . Martins, Luisa; Alegria, Elisabete; Smolenski, Piotr; Kuznetsov, Maxim L.; Pombeiro, ArmandoNew rhenium(VII or III) complexes [ReO3(PTA)(2)][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4] (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)(2)] [ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(eta(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 Re2O2 (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.
- 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.