Browsing by Author "Gomes, Ana C."
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- A 5-(2-Pyridyl) tetrazolate complex of Molybdenum(VI), its structure, and transformation to a Molybdenum Oxide-Based Hybrid Heterogeneous Catalyst for the Epoxidation of OlefinsPublication . Nunes, Martinique S.; Gomes, Diana M.; Gomes, Ana C.; Neves, Patrícia; Mendes, Ricardo F.; Paz, Filipe A. Almeida; Lopes, A. D.; Valente, Anabela A.; Gonçalves, Isabel S.; Pillinger, MartynThere is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2 (pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO3 (Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 ◦C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products.
- A hydrogen-bonded assembly of cucurbit[6]uril and [MoO2Cl2(H2O)(2)] with catalytic efficacy for the one-pot conversion of olefins to alkoxy productsPublication . Nogueira, Lucie S.; Antunes, Margarida M.; Gomes, Ana C.; Cunha-Silva, Luis; Pillinger, Martyn; Lopes, Andre D.; Valente, Anabela A.; Goncalves, Isabel S.The reaction of the macrocyclic cavitand cucurbit[6]uril (CB[6]) and the diaqua complex [MoO2Cl2(H2O)(2)] in hydrochloric acid solution gave a water insoluble supramolecular compound with the general composition 2[MoO2Cl2(H2O)(2)]center dot CB[6]center dot xH(2)O center dot yHCl center dot z(CH3COCH3) (2). Single crystal X-ray diffraction (XRD) analysis revealed the presence of barrel-shape supramolecular entities, {CB[6]center dot 10(H2O)}, aligned in layers which are shifted relative to adjacent layers to form a brick-like pattern. The CB[6]/water hydrogen-bonded entities further engage in intermolecular interactions with water, HCl and [MoO2Cl2(H2O)(2)] molecules to form a three-dimensional (3D) framework. Compound 2 was characterised by thermogravimetric analysis (TGA), IR and Raman vibrational spectroscopy, and C-13{H-1} CP MAS NMR. The reference complex [MoO2Cl2(H2O)(2)]center dot(diglyme)(2) (1) and compound 2 were studied for the oxidative catalytic conversion of olefins (cis-cyclooctene, cyclohexene and styrene) with aqueous H2O2 as oxidant. Using alcohols as solvents, 2 was employed in a one-pot two-stage strategy for converting olefins to alkoxy products, which involves oxidation (with H2O2) and acid chemistry. Mechanistic studies were carried out using different intermediates as substrates, and the type of solvent and substrate scope were investigated. The results demonstrated the ability of the CB[6]/Mo-VI supramolecular adduct to function as an acid-oxidation multifunctional catalyst, and its recovery and reuse via relatively simple procedures.
- A silicododecamolybdate/pyridinium-tetrazole hybrid molecular salt as a catalyst for the epoxidation of bio-derived olefinsPublication . Nunes, Martinique S.; Neves, Patricia; Gomes, Ana C.; Cunha-Silva, Luis; Lopes, Andre D.; Valente, Anabela A.; Pillinger, Martyn; Goncalves, Isabel S.The hybrid polyoxometalate (POM) salt (Hptz)(4)[SiMo12O40].nH(2)O (1) (ptz = 5-(2-pyridyl)tetrazole) has been prepared, characterized by X-ray crystallography, and examined as a catalyst for the epoxidation of cis-cyclooctene (Cy) and bio-derived olefins, namely dl-limonene (Lim; a naturally occurring monoterpene found in the rinds of citrus fruits), methyl oleate and methyl linoleate (fatty acid methyl esters (FAMEs) obtained by transesterification of vegetable oils). The crystal structure of 1 consists of alpha-Keggin-type heteropolyanions, [SiMo12O40](4-), surrounded by space-filling and charge-balancing 2-(tetrazol-5-yl)pyridinium (Hptz(+)) cations, as well as by a large number of water molecules of crystallization (n = 9). The water molecules mediate an extensive three-dimensional (3D) hydrogen-bonding network involving the inorganic anions and organic cations. For the epoxidation of the model substrate Cy in a nonaqueous system (tert-butylhydroperoxide as oxidant), the catalytic performance of 1 (100% epoxide yield at 24 h, 70 degrees C) was superior to that of the tetrabutylammonium salt (Bu4N)(4) [SiMo12O40] (2) (63% epoxide yield at 24 h), illustrating the role of the counterion Hptz(+) in enhancing catalytic activity. The hybrid salt 1 was effective for the epoxidation of Lim (69%/85% conversion at 6 h/24 h) and the FAMEs (87-88%/100% conversion at 6 h/24 h), leading to useful bio-based products (epoxides, diepoxides and diol products).
- Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0) as precursor to a molybdenum(VI) catalyst for olefin epoxidationPublication . Figueiredo, Sónia; Gomes, Ana C.; Fernandes, José A.; Paz, Filipe A. Almeida; Lopes, Andre D.; Lourenço, J. P.; Pillinger, Martyn; Gonçalves, Isabel S.Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0), cis-[Mo(CO)4(BPM)] (1), was prepared from Mo(CO)6 and the ligand bis(pyrazolyl)methane (BPM), and examined as a catalyst precursor for the epoxidation of olefins using tert-butylhydroperoxide (TBHP) as oxidant. Catalytic activities followed the sequence 1-octene < trans-2-octene < a-pinene < (R)-(þ)-limonene < cis-cyclooctene, and, with the exception of a-pinene and limonene, the corresponding epoxide was always the only reaction product. Turnover frequencies for the epoxidation of cyclooctene were 580 mol molMo 1 h 1 at 55 C and 1175 mol molMo 1 h 1 at 75 C, which compare favourably with those found for other molybdenum carbonyl complexes used as catalyst precursors for the same reaction under similar conditions. Catalytic activities were lower in the presence of organic co-solvents, decreasing in the sequence 1,2-dichloroethane > nitromethane > ethanol > hexane > acetonitrile. It is proposed that the oxodiperoxo complex [MoO(O2)2(BPM)] (2) may be the active catalyst formed in situ by oxidative decarbonylation of 1, since crystals of 2 suitable for structure determination by X-ray diffraction were obtained from the reaction solution recovered after a catalytic run at 55 C with cis-cyclooctene as substrate. In support of this hypothesis, the catalytic performance of 2 for the epoxidation of cyclooctene at 55 C is very similar to that for 1.
- Catalytic alcoholysis of epoxides using metal-free cucurbituril-based solidsPublication . Bruno, Sofia M.; Gomes, Ana C.; Oliveira, Tânia S. M.; Antunes, Margarida M.; Lopes, Andre D.; Valente, Anabela A.; Gonçalves, Isabel S.; Pillinger, MartynMetal-free cucurbit[7]uril (CB7) solid-state assemblies promote acid-catalysed alcoholysis of aliphatic and aromatic epoxides under mild conditions to give beta-alkoxy alcohols, which are important intermediates for the synthesis of a vast range of compounds such as bioactive pharmaceuticals. The catalytic process is heterogeneous and the catalyst can be reused in consecutive runs without any reactivation treatment. The acid species responsible for the catalytic activity of CB7 may be entrapped hydronium ions.
- Chemistry and catalytic performance of pyridyl-benzimidazole oxidomolybdenum(VI) compounds in (bio)olefin epoxidationPublication . Neves, Patricia; Nogueira, Lucie S.; Gomes, Ana C.; Oliveira, Tânia S. M.; Lopes, Andre D.; Valente, Anabela A.; Gonçalves, Isabel S.; Pillinger, MartynThe chemistry and catalytic performance of the dichlorido complex [MoO2Cl2(pbim)] (1) [pbim = 2-(2-pyridyl)benzimidazole] in the epoxidation of olefins is reported. Complex 1 acts as a precatalyst and is more effective with tert-butyl-hydroperoxide (TBHP) as the oxidant than with aq. hydrogen peroxide: the cis-cyclooctene (Cy) reaction with TBHP gave 98 % epoxide yield at 70 degrees C/24 h. Catalyst characterization showed that 1 is transformed in situ to the oxidodiperoxido complex [MoO(O-2)(2)(pbim)] (2), with H2O2 and a hybrid molybdenum(VI) oxide solid formulated as [MoO3(pbim)] (3) with TBHP. The hybrid material 3 was prepared on a larger scale and explored for the epoxidation of the biorenewable olefins methyl oleate, methyl linoleate, and (R)-(+)-limonene. With TBHP as the oxidant, 3 acts as a source of soluble active species of the type 2. A practical method for recycling oxidodiperoxidomolybdenum(VI) catalysts for the Cy/TBHP reaction is demonstrated by using an ionic liquid as the solvent for the molecular catalyst 2.
- Desulfurization of diesel by extraction coupled with Mo-catalyzed sulfoxidation in polyethylene glycol-based deep eutectic solventsPublication . Juliao, Diana; Gomes, Ana C.; Pillinger, Martyn; Lopes, Andre D.; Valenca, Rita; Ribeiro, Jorge C.; Goncalves, Isabel S.; Balula, Salete S.Oxidative desulfurization (ODS) is a method of removing sulfur from diesel fuel that has the potential to complement or even replace conventional hydrodesulfurization processes in oil refineries. One of the most promising variants of ODS is extractive and catalytic ODS (ECODS) in which the organic sulfur compounds in the liquid fuel are oxidized and extracted in situ from the oil phase into an extractant phase. In this study, the desulfurizalion of model and real diesel fuel has been performed in ECODS systems employing two different types of deep eutectic solvents (DESs), prepared by combining polyethylene glycol (PEG) as hydrogen bond donor with tetrabutylammonium chloride (TBACl) or choline chloride (ChCl) as hydrogen bond acceptor. The ECODS systems were evaluated with the complexes [MoO2Cl2(DMB)(2)] (1) and [MoO2Cl2(DEO)] (2) (DMB - N,N-dimethylbenzamide, DEO = N,N'-diethyloxamide) as catalysts and 30 wt% H2O2 as oxidant. The effects of different reaction conditions, such as the amount of catalyst, H2O2 and DES, and reaction temperature, were investigated. The combination of complex 1 with the DES ChCl/PEG showed the best performance for the removal of dibenzothiophene, 4-methyldibenzothiophene and 4,6-di methyldibenzothiophene from a high-sulfur (3000 ppm) model diesel, allowing a desulfurization efficiency of 99.6% to be attained at 70 degrees C within 2 h. By applying the optimized model diesel ECODS systems to the treatment of a commercial untreated diesel with a sulfur content of 2300 ppm. 82% of sulfur compounds could be eliminated. These promising results indicate that DESs are a viable alternative to ionic liquids as extraction solvents in ECODS processes. (C) 2020 Elsevier B.V. All rights reserved.
- Dichlorodioxomolybdenum(VI) complexes bearing oxygen-donor ligands as catalysts for oxidative desulfurization of simulated and real dieselPublication . Juliao, Diana; Gomes, Ana C.; Cunha-Silva, Luis; Pillinger, Martyn; Lopes, Andre D.; Valenca, Rita; Ribeiro, Jorge C.; Goncalves, Isabel S.; Balula, Salete S.The complexes [MoO2Cl2(DMB)(2)] (1) and [MoO2Cl2(DEO)] (2) (DMB = N,N-dimethylbenzamide, DEO = N,N'-diethyloxamide) have been evaluated as catalysts in extractive-catalytic oxidative desulfurization (ECOD) of a simulated diesel fuel. Using the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) as extraction solvent and H2O2 as oxidant, ultra-deep desulfurization (S-content from 3000 ppm to < 10 ppm) was possible within a reaction time of 1-3 h, and the systems Catalyst/[BMIM]PF6 could be recycled for five times without significant decrease in activity. The S-content of a real untreated diesel was lowered by 94.4% from 2300 ppm to 129 ppm after only 2 h of reaction using the ECOD process with 2 as catalyst.
- Dichlorodioxomolybdenum(VI) complexes bearing oxygen-donor ligands as olefin epoxidation catalystsPublication . Oliveira, Tânia S. M.; Gomes, Ana C.; Lopes, Andre D.; Lourenço, J. P.; Almeida Paz, Filipe A.; Pillinger, Martyn; Gonçalves, Isabel S.Treatment of the solvent adduct [MoO2Cl2(THF)2] with either 2 equivalents of N,N-dimethylbenzamide (DMB) or 1 equivalent of N,N'-diethyloxamide (DEO) gave the dioxomolybdenum(vi) complexes [MoO2Cl2(DMB)2] () and [MoO2Cl2(DEO)] (). The molecular structures of and were determined by single-crystal X-ray diffraction. Both complexes present a distorted octahedral geometry and adopt the cis-oxo, trans-Cl, cis-L configuration typical of complexes of the type [MoO2X2(L)n], with either the monodentate DMB or bidentate DEO oxygen-donor ligands occupying the equatorial positions trans to the oxo groups. The complexes were applied as homogeneous catalysts for the epoxidation of olefins, namely cis-cyclooctene (Cy), 1-octene, trans-2-octene, α-pinene and (R)-(+)-limonene, using tert-butylhydroperoxide (TBHP) as oxidant. In the epoxidation of Cy at 55 °C, the desired epoxide was the only product and turnover frequencies in the range of ca. 3150-3200 mol molMo(-1) h(-1) could be reached. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the cosolvent. Complexes and were also applied in liquid-liquid biphasic catalytic epoxidation reactions by using an ionic liquid of the type [C4mim][X] (C4mim = 1-n-butyl-3-methylimidazolium; X = NTf2, BF4 or PF6] as a solvent to immobilise the metal catalysts. Recycling for multiple catalytic runs was achieved without loss of activity.
- Ferrocene and ferrocenium inclusion compounds with cucurbiturils: a study of metal atom dynamics probed by Mossbauer spectroscopyPublication . Magalhães, Clara I. R.; Gomes, Ana C.; Lopes, Andre D.; Gonçalves, Isabel S.; Pillinger, Martyn; Jin, Eunyoung; Kim, Ikjin; Ko, Young Ho; Kim, Kimoon; Nowik, Israel; Herber, Rolfe H.Temperature-dependent 57Fe Mossbauer effect (ME) spectroscopic studies were carried out on ferrocene (Fc), 1,10-dimethylferrocene (1,10'(CH3)(2)Fc) and ferrocenium hexafluorophosphate (FcPF(6)) guest species in cucurbit[n] uril (n = 7, 8) inclusion complexes. The solid inclusion complexes were isolated by freeze-drying of dilute aqueous solutions and/or microwave-assisted precipitation from concentrated mixtures. The presence of genuine 1 : 1 (host : guest) inclusion complexes in the isolated solids was supported by liquid-state H-1 and solid-state C-13{H-1} MAS NMR, elemental and thermogravimetric analyses, powder X-ray diffraction, FTIR spectroscopy, and diffuse reflectance UV-Vis spectroscopy. The ME spectra of the complexes CB7.Fc and CB7.11'(CH3)(2)Fc consist of well-resolved doublets with hyperfine parameters (isomer shift and quadrupole splitting at 90 K) and temperature-dependent recoil-free fraction data that are very similar to those for the neat parent compounds, Fc and 1,10(CH3)(2)Fc, suggesting that the organometallic guest molecules do not interact significantly with the host environment over the experimental temperature range. The ME spectra for CB7.FcPF(6) and CB8.FcPF(6) consist of a major broad line resonance attributed to a paramagnetic FeIII site. From the temperature-dependence of the recoil-free fraction it is evident that the charged guest species in these systems interact with the host environment significantly more strongly than was observed in the case of the neutral guest species, Fc and 1,10(CH3)(2)Fc. Moreover, the ME data indicate that the vibrational amplitude of the ferrocenium guest molecule is significantly larger in the CB8 host molecule than in the CB7 homologue, as expected on the basis of the different cavity sizes.