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- 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.
- 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.
- Iron(III) and cobalt(III) complexes with both tautomeric (keto and enol) forms of aroylhydrazone ligands: catalysts for the microwave assisted oxidation of alcoholsPublication . Sutradhar, Manas; Alegria, Elisabete; Mahmudov, Kamran; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoTwo Schiff bases derived from the condensation of 2-hydroxybenzohydrazide with 3,5-di-tert-butyl-2-hydroxybenzaldehyde (H2L1) or with 2,3-dihydroxy benzaldehyde (H2L2) were used to synthesize the Fe(III) and Co(III) complexes [Fe(L-1)(HL1)] (1) and [Co(L-2)(HL2)] (2), respectively. The compounds were characterized by elemental analysis, IR, ESI-MS and single crystal X-ray analysis. Structural studies indicated the presence of both keto and enol tautomeric forms of the ligand in 1 and 2. The complexes (mainly 1) act as catalysts in the microwave-assisted solvent-free peroxidative oxidation (by tert-butylhydroperoxide, TBHP) of primary and secondary alcohols. A facile, efficient and selective synthesis of ketones was achieved with a yield up to 96% and a TON up to 500, after 30 min under low power (15 W) microwave irradiation (complex 1 as catalyst). 2-Pyrazinecarboxylic acid (Hpca) shows a promoting effect.
- 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.