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- C-scorpionate Au(III) complexes as pre-catalysts for industrially significant toluene oxidation and benzaldehyde esterification reactionsPublication . Lapa, Hugo; Guedes Da Silva, M. Fátima C.; Pombeiro, Armando; Alegria, Elisabete; Martins, LuisaThe new Au(III) complex [AuCl2(Tpms)] (1) and the previously reported [AuCl2(Tpm)]Cl (2), bearing the potentially tridentate ligands tris(1-pyrazolyl)methanesulfonate (SO3C(C3H3N2)(3)(-), Tpms) or hydrotris(1-pyrazolyl) methane (HC(C3H3N2)(3), Tpm), respectively, were synthesized in water at room temperature and characterized using NMR and IR spectroscopy. The molecular structure of 1 was authenticated by single crystal X-ray diffraction analysis. The catalytic performance of the Au(III) complexes was tested, for the first time, in toluene and benzyl alcohol oxidation reactions. The oxidative esterification of benzaldehyde, by-product of toluene oxidation, was further explored. In order to optimize the catalytic systems, the influence of parameters such as temperature, reaction time, amount of pre-catalyst and the presence of additives was evaluated. In the peroxidative (by H2O2 or t-BuOOH) oxidation reactions, a maximum total yield (benzylic alcohol and benzaldehyde) of 8% for toluene oxidation with pre-catalyst 1 (6 h, 80 degrees C, H2O2 30% aq. sol.) and a maximum total yield (benzaldehyde and benzoic acid) of 43% for benzyl alcohol oxidation with pre-catalyst 2 (24 h, 80 degrees C, t-BuOOH 70% aq. sol.) with a selectivity of 72% for benzaldehyde, were obtained. The esterification of benzaldehyde yielded, in the presence of 1, a maximum of 27% and 48% of methyl benzoate, at room temperature and 80 degrees C, respectively, and with a selectivity of 78% for methyl benzoate.
- 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%).