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- Vanadium complexes: recent progress in oxidation catalysisPublication . Sutradhar, Manas; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoOxidovanadium complexes and, to a less extent, some non-oxido ones, are widely used as catalysts or catalyst precursors for various oxidative catalytic reactions by H2O2, (BuOOH)-Bu-t or O-2 under mild conditions. Oxidation reactions (oxidation of alkanes and alcohols, epoxidation of alkenes and allylic alcohols, oxidative bromination, sulfoxidation and oxidative Strecker reactions) of organic compounds are the most relevant ones and are reviewed considering the recent advances in the last five years (2010-2014). The main types of both homogeneous and supported vanadium catalysts and the most efficient catalytic systems in the different reactions are presented and compared. The proposed mechanisms of various catalytic oxidation processes are also outlined. (C) 2015 Elsevier B.V. All rights reserved.
- Trinuclear Cu-II structural isomers coordination, magnetism, electrochemistry and catalytic activity towards the oxidation of alkanesPublication . Sutradhar, Manas; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Mahmudov, Kamran; Liu, Cai-Ming; Pombeiro, ArmandoThe reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu-3(L)(2)(MeOH)(4)] (1), [Cu-3(L)(2)(MeOH)(2)]2MeOH (2) and [Cu-3(L)(2)(MeOH)(4)] (3), respectively, in which the ligand L exhibits dianionic (HL2-, in 1) or trianionic (L3-, in 2 and 3) pentadentate 1O,O,N:2N,O chelation modes. Complexes 1-3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1-3 the Cu-II ions can be reduced, in distinct steps, to Cu-I and Cu-0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31% (TON = 1.55x10(3)) after 6 h in the presence of pyrazinecarboxylic acid.
- Aroylhydrazone Cu(II) complexes in keto form: structural characterization and catalytic activity towards cyclohexane oxidationPublication . Sutradhar, Manas; Alegria, Elisabete; Guedes Da Silva, M. Fátima C.; Martins, Luisa; Pombeiro, ArmandoThe 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]center dot 2MeOH (2) and the binuclear complex [{Cu(H2L)}(2)(mu-SO4)]center dot 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.
- Dinuclear Mn (II,II) complexes: magnetic properties and microwave assisted oxidation of alcoholsPublication . Sutradhar, Manas; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Alegria, Elisabete; Liu, Cai-Ming; Pombeiro, ArmandoA series of six new mixed-ligand dinuclear Mn(II, II) complexes of three different hydrazone Schiff bases (H3L1, H3L2 and H3L3), 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) center dot 4H(2)O with the H3L1-3 compounds, in the presence of pyridine (1 : 1 : 1 mole ratio), in methanol at room temperature, yield [Mn(H2L1)(py)(H2O)](2)(NO3)(2) center dot 2H(2)O (1 center dot 2H(2)O), [Mn(H2L2)(py)(CH3OH)](2)(NO3)(2) center dot 4H(2)O (2 center dot 4H(2)O) and [Mn(H2L3)(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(H2L1)(py)(2)] 2(NO3)(2) center dot H2O (4 center dot H2O), [Mn(H2L2)(py) H-O (6 center dot 2CH(3)OH), respectively. In all the complexes, the (H2L1-3)-ligand coordinates in the keto form. Complexes 1 center dot 2H(2)O, 2 center dot 4H(2)O, 4 center dot H2O, 5 center dot 2H(2)O and 6 center dot 2CH(3)OH 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.
- Oxidovanadium(V) complexes anchored on carbon materials as catalysts for the oxidation of 1-phenylethanolPublication . Sutradhar, Manas; Martins, Luisa; Carabineiro, Sónia A. C.; Guedes Da Silva, M. Fátima C.; Buijnsters, Josephus; Figueiredo, José L.; Pombeiro, ArmandoSix oxidovanadium(V) aroylhydrazone complexes derived from (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H2L1) and (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-aminobenzohydrazide (H2L2), namely, [VOL1(OEt)][VOL1(OEt) (EtOH)] (1), [VOL2(OEt)] (2), [Et3NH][VO2L1] (3), [VO2(HL2)]center dot 2EtOH (4), [(VOL1)(2)(mu-O)] (5), and [(VOL2)(2)(mu-O)] (6), were synthesized and characterized by elemental analysis, IR, H-1 NMR, and V-51 NMR spectroscopies, ESI-MS and, for 1-5, single-crystal XRD. The compounds have VO3+ (1 and 2), VO2+ (3 and 4), and V2O34+ (5 and 6) cores. They are active homogeneous catalysts in the microwave-assisted, solvent-free peroxidative oxidation of 1-phenylethanol to acetophenone by tBuOOH. The immobilization of the oxidovanadium complexes (1, 2, 4, and 5) on oxidized carbon materials improved the oxidation efficiency and allowed catalyst reuse with the preservation of activity.
- A Hexanuclear Mixed-Valence Oxovanadium(IV,V) Complex as a Highly Efficient Alkane Oxidation CatalystPublication . Sutradhar, Manas; Kirillova, Marina V.; Guedes Da Silva, M. Fátima C.; Martins, Luisa; Pombeiro, ArmandoThe new hexanuclear mixed-valence vanadium complex [V3O3(OEt)(ashz)(2)(mu-OEt)](2) (1) with an N,O-donor ligand is reported. It acts as a highly efficient catalyst toward alkane oxidations by aqueous H2O2. Remarkably, high turnover numbers up to 25000 with product yields of up to 27% (based on alkane) stand for one of the most active systems for such reactions.
- Mn-II and Cu-II complexes with arylhydrazones of active methylene compounds as effective heterogeneous catalysts for solvent- and additive-free microwave-assisted peroxidative oxidation of alcoholsPublication . Mahmudov, Kamran; Sutradhar, Manas; Martins, Luisa; Silva, Maria de Fátima C. Guedes da; Ribera, Alice; Nunes, Ana V. M.; Gahramanova, Shahnaz; Marchetti, Fabio; Pombeiro, ArmandoA one-pot template reaction of sodium 2-(2-(dicyanomethylene) hydrazinyl) benzenesulfonate (NaHL1) with water and manganese(II) acetate tetrahydrate led to the mononuclear complex [Mn(H2O)(6)](HL1a)(2)center dot 4H(2)O (1), where (HL1a) -= 2-(SO3-)C6H4(NH)=N=C(C N) (CONH2) is the carboxamide species derived from nucleophilic attack of water on a cyano group of (HL1) . The copper tetramer [Cu-4(H2O)(10)(-) (1 kappa N: kappa O-2: kappa O, 2 kappa N: k(O)-L-2)(2)]center dot 2H(2)O (2) was obtained from reaction of Cu(NO3)(2)center dot 2.5H(2)O with sodium 5-(2( 4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-4-hydroxybenzene-1,3-disulfonate (Na2H2L2). Both complexes were characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. They exhibit a high catalytic activity for the solvent-and additive-free microwave (MW) assisted oxidation of primary and secondary alcohols with tert-butylhydroperoxide, leading to yields of the oxidized products up to 85.5% and TOFs up to 1.90 x 103 h(-1) after 1 h under low power (5-10 W) MW irradiation. Moreover, the heterogeneous catalysts are easily recovered and reused, at least for three consecutive cycles, maintaining 89% of the initial activity and a high selectivity.
- Trinuclear CuII Structural isomers: coordination, magnetism, electrochemistry and catalytic activity towards the oxidation of alkanesPublication . Sutradhar, Manas; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Mahmudov, Kamran; Liu, Cai-Ming; Pombeiro, ArmandoThe reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu3(L)2(MeOH)4] (1), [Cu3(L)2(MeOH)2]·2MeOH (2) and [Cu3(L)2(MeOH)4] (3), respectively, in which the ligand L exhibits dianionic (HL2–, in 1) or trianionic (L3–, in 2 and 3) pentadentate 1κO,O′,N:2κN′,O″ chelation modes. Complexes 1–3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1–3 the CuII ions can be reduced, in distinct steps, to CuI and Cu0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31 % (TON = 1.55 × 103) after 6 h in the presence of pyrazinecarboxylic acid.
- Oxidovanadium complexes with tridentate aroylhydrazone as catalyst precursors for solvent-free microwave-assisted oxidation of alcoholsPublication . Sutradhar, Manas; Martins, Luisa; Silva, Maria de Fátima C. Guedes da; Pombeiro, ArmandoAroylhydrazone oxidovanadium compounds, viz, the oxidoethoxidovanadium(V) [VO(OEt)L1] (1) (H2L =salicylaldehyde-2-hydroxybenzoylhydrazone), the salt like dioxidovanadium(V) (NH3CH2CH2OH)(+) [VO2L](-) (2), the mixed-ligand oxidovanadium(V) [VO(hq)L](Hhq = 8-hydroxyquinoline) (3) and the vanadium(IV) [VO(phen)L] (phen=1,10-phenanthroline) (4) complexes (3 and 4 obtained by the first time), have been tested as catalysts for solvent-free microwave-assisted oxidation of aromatic and alicyclic secondary alcohols with tert-butylhydroperoxide. A facile, efficient and selective solvent-free synthesis of ketones was achieved with yields up to 99% (TON= 497, TOF= 993 h(-1) for 3) and 58% (TON =291, TOF= 581 h(-1) for 2) for acetophenone and cyclohexanone, respectively, after 30 min under low power (25W) microwave irradiation. (C) 2015 Elsevier B.V. All rights reserved.
- Trinuclear CuII Structural Isomers: Coordination, Magnetism, Electrochemistry and Catalytic Activity towards the Oxidation of AlkanesPublication . Sutradhar, Manas; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Mahmudov, Kamran; Liu, Cai-Ming; Pombeiro, ArmandoThe reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu3(L)2(MeOH)4] (1), [Cu3(L)2(MeOH)2]·2MeOH (2) and [Cu3(L)2(MeOH)4] (3), respectively, in which the ligand L exhibits dianionic (HL2–, in 1) or trianionic (L3–, in 2 and 3) pentadentate 1κO,O′,N:2κN′,O″ chelation modes. Complexes 1–3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1–3 the CuII ions can be reduced, in distinct steps, to CuI and Cu0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31 % (TON = 1.55 × 103) after 6 h in the presence of pyrazinecarboxylic acid.