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- Fe(III) complexes in cyclohexane oxidation: comparison of catalytic activities under different energy stimuliPublication . Roy Barman, Tannistha; Sutradhar, Manas; Alegria, Elisabete; Silva, M. Fátima C. Guedes Da; Pombeiro, ArmandoIn this study, the mononuclear Fe(III) complex [Fe(HL)(NO3)(H2O)2]NO3 (1) derived from N0 -acetylpyrazine-2-carbohydrazide (H2L) was synthesized and characterized by several physicochemical methods, e.g., elemental analysis, infrared (IR) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single crystal X-ray diffraction analysis. The catalytic performances of 1 and the previously reported complexes [Fe(HL)Cl2] (2) and [Fe(HL)Cl(µ-OMe)]2 (3) towards the peroxidative oxidation of cyclohexane under three different energy stimuli (microwave irradiation, ultrasound, and conventional heating) were compared. 1-3 displayed homogeneous catalytic activity, leading to the formation of cyclohexanol and cyclohexanone as final products, with a high selectivity for the alcohol (up to 95%). Complex 1 exhibited the highest catalytic activity, with a total product yield of 38% (cyclohexanol + cyclohexanone) under optimized microwave-assisted conditions.
- Microwave-assisted peroxidative oxidation of toluene and 1-phenylethanol with monomeric keto and polymeric enol aroylhydrazone Cu(II) complexesPublication . Sutradhar, Manas; Alegria, Elisabete; Roy Barman, Tannistha; Scorcelletti, Francesco; Guedes Da Silva, M. Fátima C.; Fatima, C.; Pombeiro, ArmandoCu(II) complexes in two different tautomeric forms (keto and enol) derived from the aroylhydrazone Schiff base 2-hydroxy(2-hydroxybenzylidene)benzohydrazide (H2L) have been synthesized and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray crystallography. While the compound with the enol form of the ligand exists as the 1D polymer [Cu(kappa KNOO',2 kappa O',3 kappa O"-L)](n) (1), that with the keto form of the ligand occurs as the monomer [Cu(KNOO'-HL)CI(CH3OH)] (2). Both complexes act as good catalysts for the microwave-assisted peroxidative oxidation of toluene and 1-phenylethanol with tert-butyl hydroperoxide. Complex 2 exhibits the highest activity in both reactions, leading selectively to,a maximum product yield of 39 and 92%, respectively.
- 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.
- New copper(II) tetramer with arylhydrazone of barbituric acid and its catalytic activity in the oxidation of cyclic C5–C8 alkanesPublication . Sutradhar, Manas; Alegria, Elisabete; Roy Barman, Tannistha; Guedes Da Silva, M. Fátima C.; Mahmudov, Kamran T.; Guseynov, Firuddin I.; Pombeiro, Armando2-(2-(2,4,6-Trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazinyl)terephthalic acid (H5L) was synthesized by azocoupling of diazonium salts of 2-aminoterephthalic acid with barbituric acid and characterized by IR, 1H and 13C NMR spectroscopies and ESI-MS analysis. In solution and solid state, H5L exists in the hydrazone form. The reaction of H5L with copper(II) nitrate hydrate in methanol affords the tetramer species [Cu2(μ2-1κNOO′:2κO′O″-H3L)2]2 (1) where carboxylate groups bridge two Cu(II) centers in a bridging chelate μ2-(O,O′,O′) fashion, giving rise to a cyclic Cu4O4 core. A rare and intense intermolecular non-covalent interaction of the type Ocarboxylic(lone pair)⋯π(pyrimidine), with O⋯centroid distance of 2.705 Å, was found in 1. In addition, medium intense N H⋯O and O H⋯O contacts expand the structure to a 3D network. Compound 1 behaves as efficient catalyst in the mild oxidation, by aqueous H2O2 in acidic MeCN/H2O media, of different cyclic C5–C8 alkanes to produce the corresponding alcohols and ketones. Overall product yields up to ca. 25% (based on alkane) were achieved.
- Cd(II) coordination compounds as heterogeneous catalysts for microwave-assisted peroxidative oxidation of toluene and 1-phenylethanolPublication . Sutradhar, Manas; Roy Barman, Tannistha; Alegria, Elisabete; Lapa, Hugo M.; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoThe aroylhydrazone Schiff bases 2-hydroxy(2-hydroxybenzylidene)benzohydrazide (H2L1) and 2-amino(2hydroxybenzylidene)benzohydrazide (H2L2) have been used to synthesize the new Cd(II) coordination polymer [Cd(m-1kONO0:2kO:3kO00-L1)(DMF)]n (1) and the dinuclear complex [Cd(1kONO0:2kO-HL2)(kOO0Ac)]2 2DMF (2). Both 1 and 2 have been characterized by elemental analysis, FT-IR and single crystal X-ray diffraction analysis. The catalytic performances of 1 and 2 were evaluated towards the microwave (MW) assisted peroxidative oxidation (with tert-butylhydroperoxide, TBHP) of toluene and 1-phenylethanol under heterogeneous conditions. The MW-assisted peroxidative oxidation of toluene by a Cd(II) catalytic system is reported for the first time. At 50 1C, the 2/TBHP/MW catalytic system shows good activity for toluene oxidation with a total (benzaldehyde + benzyl alcohol) product yield of 49% in 1 h, in the absence of any additives. In the case of neat solvent-free peroxidative oxidation of 1-phenylethanol the 1/TBHP/MW catalytic system resulted in 24% total yield of acetophenone under optimized conditions. After the catalytic reactions, both 1 and 2 were successfully recovered and reused.
- Catalytic oxidation of a model volatile organic compound (toluene) with tetranuclear Cu(II) complexesPublication . Sutradhar, Manas; Alegria, Elisabete; Roy Barman, Tannistha; Lapa, Hugo; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoA tetranuclear Cu(II) cubane [Cu-2(mu-1 kappa ONO':2 kappa OO':3 kappa O-HL)(mu-1 kappa ONO':2 kappa OO'-HL)](2).4dmf (1) derived form (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) was synthesized at room temperature and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. The known tetranuclear Cu(II) open-cubane [Cu(HL)](4).4EtOH (2) was synthesized from the same pro-ligand following a similar method or the reported one. The different tautomeric forms (keto and enol) of the organic ligands in 1 and 2 explain their different structural features. Both complexes were screened as catalysts for the peroxidative oxidation of toluene with tert-butyl hydroperoxide, achieving benzaldehyde and o-cresol as the main products. Complex 1 exhibits the highest activity (maximum product yield of 11%).
- Cu(II) complexes of N-rich aroylhydrazone: magnetism and catalytic activity towards microwave-assisted oxidation of xylenesPublication . Sutradhar, Manas; Roy Barman, Tannistha; Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Liu, Cai-Ming; Kou, Hui-Zhong; Pombeiro, ArmandoThe new aroylhydrazone N'-(di(pyridin-2-yl) methylene) pyrazine-2-carbohydrazide (HL) species, rich in N-donor sites, has been used to synthesize Cu(II) compounds with different nuclearities, viz. the binuclear [Cu2(mu-1.N3,2.N2O-L)(Cl) 3(MeOH)] (1), the octanuclear [Cu4(mu-1.N3,2.N2O-L) 2(mu-Cl) 3(Cl) 3] 2 (2) and the 1D coordination polymer [Cu3(mu 3-1.N3,2.N2O, 3.N-L)(mu-NO3)(NO3) 3(H2O) 3] n center dot nNO3 (3). They have been characterized by elemental analysis, FT-IR and single crystal X-ray diffraction. The magnetic properties of 2 and 3 have been explored using variable temperature magnetic measurements. The catalytic performances of the compounds were evaluated towards the peroxidative oxidation of o-, p-and m-xylenes under microwave irradiation, leading to the formation of the corresponding methyl benzyl alcohol, tolualdehyde and toluic acid as the major products. Complex 3 exhibits the best catalytic activity towards the oxidation of p-xylene with a total yield of 37% (4-methylbenzyl alcohol + p-tolualdehyde + p-toluic acid).
- 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.
- 1D Copper(II)-aroylhydrazone coordination polymers: magnetic properties and microwave assisted oxidation of a secondary alcoholPublication . Sutradhar, Manas; Alegria, Elisabete; Roy Barman, Tannistha; Guedes Da Silva, M. Fátima C.; Liu, Cai-Ming; Pombeiro, ArmandoThe 1D Cu(II) coordination polymers [Cu-3(L-1)(NO3)(4)(H2O)(2)](n) (1) and [Cu-2(H2L2)(NO3)(H2O)(2)](n)(NO3)(n) (2) have been synthesized using the aroylhyrazone Schiff bases N'(1),N'(2)-bis(pyridin-2-ylmethylene)oxalohydrazide (H2L1) and N'(1),N'(3)-bis(2-hydroxybenzylidene)malonohydrazide (H4L2), respectively. They have been characterized by elemental analysis, infrared (IR) spectroscopy, UV-Vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), single crystal X-ray diffraction and variable temperature magnetic susceptibility measurements (for 2). The ligand (L-1)(2-) coordinates in the iminol form in 1, whereas the amide coordination is observed for (H2L2)(2-) in 2. Either the ligand bridge or the nitrate bridge in 2 mediates weak antiferromagnetic coupling. The catalytic performance of 1 and 2 has been investigated toward the solvent-free microwave-assisted oxidation of a secondary alcohol (1-phenylethanol used as model substrate). At 120 degrees C and in the presence of the nitroxyl radical 2,2,6,6-tetramethylpiperydil-1-oxyl (TEMPO), the complete conversion of 1-phenylethanol into acetophenone occurs with TOFs up to 1,200 h(-1).