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- Catalytic performance of Fe(II)-scorpionate complexes towards cyclohexane oxidation in organic, ionic liquid and/or supercritical CO2 media: a comparative studyPublication . Da Costa Ribeiro, Ana Paula; Martins, Luisa; Alegria, Elisabete; Matias, Inês A. S.; Duarte, Tiago A. G.; Pombeiro, ArmandoThe catalytic activity of the iron(II) C-scorpionate complexes [FeCl2{HC(pz)3}] 1 (pz = pyrazol-1-yl) and [FeCl2{HOCH2C(pz)3}] 2, and of their precursor FeCl2·2H2O 3, towards cyclohexane oxidation with tert-butyl hydroperoxide was evaluated and compared in different media: acetonitrile, ionic liquids (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [bmim][FAP]), supercritical carbon dioxide (scCO2), and scCO2/[bmim][X] (X = PF6 or FAP) mixtures. The use of such alternative solvents led to efficient and selective protocols for the oxidation of cyclohexane. Moreover, tuning the alcohol/ketone selectivity was possible by choosing the suitable solvent.
- New trendy magnetic C-scorpionate iron catalyst and its performance towards cyclohexane oxidationPublication . Da Costa Ribeiro, Ana Paula; Matias, Inês; Alegria, Elisabete; Ferraria, Ana Maria; Rego, Ana; Pombeiro, Armando; Martins, LuisaFor the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl2{_3-HC(pz)3}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes.
- Simple solvent-free preparation of dispersed composites and their application as catalysts in oxidation and hydrocarboxylation of cyclohexanePublication . Alegria, Elisabete; Fontolan, Emmanuele; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Domingos, Catarina; Ferraria, Ana Maria; Bertani, Roberta; Botelho do Rego, Ana M.; Pombeiro, ArmandoA simple and clean mechanochemical synthesis at room temperature was employed to prepare CuO-Fe2O3-CoCl2 (100 nm scale), MoO3-V2O5, CuO-CoCl2, Fe2O3-CoCl2, CuO-V2O5, Cu(CH3COO)(2)-V2O5, Cu(CH3COO)(2)-MoO3 (1-100 mm scale) 3d metal based dispersed composites with different ratios of components using simple metal salts/oxides and multiwalled carbon nanotubes (CNT) or graphene oxide (GO) additives (CoCl2-CNT, CoCl2-GO). The thus prepared composite materials were characterized by Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). XPS analysis revealed no metal redox change upon ball milling treatment, which however promotes metal hydroxylation. The catalytic activity of the prepared composites in the heterogeneous low power microwave-assisted oxidation of cyclohexane with aq. H2O2 at 30 degrees C was notorious with yields up to 31% and selectivity up to 94% towards cyclohexanol (upon treatment with PPh3) for the CuO-CoCl2-based material. The hydro-carboxylation of cyclohexane with CO, water and K2S2O8 to produce cyclohexanecarboxylic acid bearing one more carbon atom at 60 degrees C is achieved with yields up to 17% for the reaction performed in the presence of the CuO-CoCl2 catalyst. The clean CuO-CoCl2 (1:2) catalyst preparation and the catalytic reaction (oxidation of cyclohexane) can be achieved in one-pot at low temperature, without any added organic solvent, and by using exclusively the mechanochemical energy input, with a marked 23% yield at 30 degrees C.
- Comparison of microwave and mechanochemical energy inputs in the catalytic oxidation of cyclohexanePublication . Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Kopylovich, Maximilian; Ferraria, Ana Maria; Rego, Ana; Pombeiro, ArmandoThe effect of microwave and mechanochemical ball milling energy inputs was studied for the peroxidative oxidation (with aqueous H2O2) of cyclohexane to cyclohexanol and cyclohexanone, over CoCl2 and/or V2O5 dispersed (μm scale) catalysts. A maximum total yield of cyclohexanol and cyclohexanone of 43% after 1 h of reaction at 30 °C, in acetonitrile and under microwave irradiation (5 W), was achieved over the CoCl2–V2O5 (3 : 1) catalyst prepared by ball milling. Cyclohexanol is the main final product with a selectivity of up to 93% over cyclohexanone. Conducting the oxidation reaction under microwave irradiation under the same conditions but without any mechanochemical treatment of the catalyst prior to use resulted in a lower total yield of 30% with a lower selectivity (69%) towards cyclohexanol over cyclohexanone. The sole application of mechanochemical treatment for the catalyst preparation and the catalytic oxidation of cyclohexane allowed to reach yields of 29% after 1 h of reaction, at room temperature, without microwave irradiation and any additive and in the absence of any organic solvent. Ball milling is shown to provide a convenient, solvent-free method to disperse these solid catalysts and to promote the above cyclohexane oxidation, although, in the latter case, not so effectively as microwave irradiation.
- C-scorpionate iron(II) complexes as highly selective catalysts for the hydrocarboxylation of cyclohexanePublication . Matias, Inês; Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Pombeiro, Armando; Martins, LuisaThe C-scorpionate iron(II) complexes [FeCl2{kappa(3)-HC(pz)(3)}](1) (pz = pyrazol-1-yl), Li[FeCl2{kappa(3)-SO3C(pz)(3)}] (2) and the new [FeCl2{kappa(3)-HOCH2C(pz)(3)}] (3) act as catalysts for the hydrocarboxylation of cyclohexane (with CO and H2O) to cyclohexanecarboxylic acid in a remarkable yield (up to 60%) and under mild conditions. The catalysts selectivity for the acid can be tuned by CO pressure, catalyst amount and reaction temperature. Complex [FeCl2{kappa(3)-HC(pz)(3)}] (1) provides the most effective catalyst requiring low CO pressure. This work constitutes an unprecedented use of iron complexes as catalysts for the hydrocarboxylation of alkanes.