Browsing by Author "Figueiredo, Sónia"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- 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 epoxidation and sulfoxidation activity of a dioxomolybdenum(VI) complex bearing a chiral tetradentate oxazoline ligandPublication . Neves, Patrícia; Gago, Sandra; Pereira, Cláudia C. L.; Figueiredo, Sónia; Lemos, Americo; Lopes, Andre D.; Gonçalves, Isabel S.; Pillinger, Martyn; Silva, Carlos M.; Valente, Anabela A.A dioxomolybdenum(VI) complex bearing a tetradentate anionic N,O oxazoline ligand with four stereocenters has been studied as a catalyst in the liquid-phase epoxidation of 17 different aliphatic and aromatic olefins(including prochiral, racemate or pure enantiomers) using tert-butyl hydroperoxide as the oxidant. Epoxide selectivities of up to 100% and variable epoxide yields (3–100% within 24 h) were obtained. Although the complex generally exhibited low or no chiral induction ability, diastereoselectivity was significant in some cases (in the reaction of limonene, for example). Kinetic studies and recycling tests with the substrates cis-cyclooctene and trans-b-methylstyrene showed that the catalyst is stable and reusable, and recycling is facilitated by immobilization of the complex in a room temperature ionic liquid. Preliminary results show that the complex may have a broad substrate scope, not only for olefin epoxidation, but also for the dehydrogenation of alcohols to carbonyl compounds and the sulfoxidation of sulfides to sulfoxides.
- Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41Publication . Monteiro, Bernardo; Balula, Salete S.; Gago, Sandra; Grosso, Carla; Figueiredo, Sónia; Lopes, Andre D.; Valente, Anabela A.; Pillinger, Martyn; Lourenço, J. P.; Gonçalves, Isabel S.A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17Mo/nm2 was prepared by liquid phase deposition ofMoO2Cl2(dmf)2 (1) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N2 adsorption studies of Mo-MCM-41 indicate that the texture properties of the support were preserved during the grafting experiment. On the basis of evidence from FTIR spectroscopy, 13C and 29Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO2[(–O)3SiO]2(dmf)2} species, with a small contribution from oxo-bridged dimers. Catalysis tests show that complex 1 and Mo-MCM-41 are highly active oxidation catalysts for liquid-phase epoxidation of unfunctionalised olefins using tert-butylhydroperoxide as oxidant, from ambient to 55 ◦C. The high stability and recyclability of the heterogeneous Mo-MCM-41 catalyst is attributed to the strong metal oxide–support interaction. With cyclooctene, 1-octene, trans-2-octene and norbornene substrates, the corresponding epoxides were the only observed reaction products. The reactions of the other substrates gave by-products such as 8,9-p-menthen-1,2-diol from (R)-(+)-limonene, campholenic aldehyde from -pinene, and benzaldehyde from styrene. The addition of dichloromethane as a co-solvent had a beneficial effect on catalytic performance, and in the case of (R)-(+)-limonene allowed the epoxide to be formed as the only reaction product.
- Design de compostos oxometálicos e estudo das suas propriedades catalíticas em reações de oxidaçãoPublication . Figueiredo, Sónia; Lopes, André D.; Gonçalves, Isabel Maria de SousaA presente dissertação tem como objetivo principal contribuir para um maior conhecimento e compreensão das propriedades catalíticas de sistemas baseados em metais de transição com estado de oxidação elevado. O trabalho desenvolvido englobou a síntese e a caracterização de novos compostos de molibdénio, tendo como ponto de partida a síntese de cis-dioxocomplexos do tipo MoO2Cl2Ln (n = 1 ou 2, conforme ligandos bidentados ou monodentados, respetivamente) a partir dos precursores MoO2Cl2, MoO3 e Na2MoO4 com ligandos como dimetilformamida (DMF), tris(benzimidazolil)metano (HC(bim)3). Os compostos MoO2Cl2(DMF)2 (Capítulo2) e [MoO2Cl(HC(bim)3]Y (Y = Cl, BF4 e PF6) (Capítulo 3) foram testados como precursores catalíticos na epoxidação de olefinas, em fase heterogénea. O primeiro foi imobilizado no suporte MCM-41 enquanto os últimos foram heterogeneizados com recurso a líquidos iónicos - [BMIM]Y e [BMPy]Y (BIM = 1-n-butil-3-metilimidazólio, BMPy = 1-n-butil-3-metilpiridina; Y = BF4 ou PF6), como estratégia alternativa à heterogeneização dos catalisadores homogéneos. Por outro lado, aprofundou-se também a epoxidação de olefinas em fase homogénea e, para isso, sintetizaram-se os compostos Mo(CO)3(HC(pz)3) (HC(pz)3 = tris(1-pirazoli)metano), Mo(CO)3(HC(3,5-Me2pz)3 (HC(3,5-Me2pz)3 = tris(3,5-dimetil-1-pirazolil)metano) (Capítulo 4) e Mo(CO)4(BPM) (BPM = bis(pirazolil)metano) (Capítulo 5) a partir do material de partida Mo(CO)6. A descarbonilação oxidativa destes compostos, com TBHP, originaram estruturas cristalinas do tipo dioxo--oxo, [{MoO2(HC(pz)3)}2(2-O)][Mo6O19] e [{MoO2(HC(3,5-Me2pz)3)}2(2-O)][Mo6O19], e oxodiperoxo, MoO(O2)2(BPM), respetivamente. Obtiveram-se os mesmos produtos in situ durante as respetivas reações catalíticas. Todos os compostos foram utilizados como catalisadores ou pré-catalisadores na epoxidação de olefinas, com bons resultados. Por fim e, tendo em conta o crescente interesse em materiais híbridos orgânicos-inorgânicos baseados em óxidos de molibdénio, sintetizou-se o composto MoO2Cl2(pypzEA) (pypzEA = etil[(3-piridin-2-il)-1H-pirazol-1-il]acetato) o qual, ao reagir com água, originou o material híbrido [Mo2O6(HpypzA)] (HpypzA = [3-(piridin-2-il)-1H-pirazol-1-il]acetato) (Capítulo 6). A estrutura deste último composto foi resolvida por difração de monocristal e de raio-X de pós, em conjunto com a informação proveniente de técnicas como FT-IR, RMN 13C CP/MAS e análise elementar. Este material híbrido apresenta um bom desempenho catalítico quando o TBHP é usado como oxidante e continua estável e a comportar-se como um catalisador heterogéneo mesmo após sofrer testes de reciclagem e de filtração. Ainda durante este estudo constatou-se que a reação oxidativa do material de partida, MoO2Cl2(pypzEA), com TBHP, originou o oxo(diperoxo)complexo MoO(O2)2(pypzEA) e o complexo octamérico [Mo8O24(pypzEA)4] obtido previamente pela descarbonilação oxidativa do Mo(CO)4(pypzEA). Todos os catalisadores ou precursores de espécies ativas foram analisados por técnicas de caracterização comuns (AE, FT-IR, Raman, ATR, 1H RMN) bem como por técnicas de caracterização do estado sólido (EXAFS, DRX de pós e de cristal único, 13C e 29Si RMN CP MAS). Os compostos com propriedades catalíticas e pré-catalíticas promissoras foram estudados nas reações catalíticas de epoxidação de diversas olefinas, nomeadamente, cis-cicloocteno, 1-octeno, trans-2-octeno, -pineno, (R)-(+)-limoneno, estireno, norborneno, entre outras.
- Tris(pyrazolyl)methane molybdenum tricarbonyl complexes as catalyst precursors for olefin epoxidationPublication . Gomes, Ana C.; Neves, Patrícia; Figueiredo, Sónia; Fernandes, José A.; Valente, Anabela A.; Almeida Paz, Filipe A.; Pillinger, Martyn; Lopes, Andre D.; Gonçalves, Isabel S.The molybdenum tricarbonyl complexes [Mo(CO)3(HC(3,5-Me2pz)3)] (1) and [Mo(CO)3(HC(pz)3)] (2)(HC(3,5-Me2pz)3 = tris(3,5-dimethyl-1-pyrazolyl)methane, HC(pz)3 = tris(1-pyrazolyl)methane) were obtained in good yields by the microwave-assisted reaction of Mo(CO)6 with the respective organic ligand. Complete oxidative decarbonylation of 1 and 2 was achieved by reaction with excess tert-butylhydroperoxide (TBHP) in 1,2-dichloroethane at 55 ◦C. For complex 1, the (2-oxo)bis[dioxomolybdenum(VI)] hexamolybdate of composition [{MoO2(HC(3,5-Me2pz)3)}2(2- O)][Mo6O19] (3) was obtained in good yield, and its structure was determined by single crystal X-ray diffraction. The compound (4) obtained by oxidative decarbonylation of 2 was not unambiguously identified, but may be chemically analogous to 3. Compounds 1–4 were examined for the first time as homogeneous (pre)catalysts for the epoxidation of olefins with TBHP, using different types of cosolvents at 55 ◦C. During the catalytic reactions 1 and 2 transform in situ into 3 and 4, respectively, and the latter two are fairly stable catalysts. Catalytic tests and characterization studies of the recovered catalysts were carried out in an attempt to understand the kinetic differences observed between the compounds prepared in situ during the catalytic reaction and those prepared prior to the catalytic reaction, from the same precursor complex.
- UALGORITMO, a new instrument of the University of Algarve for scientific outreachPublication . Bragança, José; Figueiredo, Sónia; Rego, Carla Alexandra; dos Reis Conceição, Filomena; Jesus, Saúl Neves deResearchers at Universities generate and convey the knowledge acquired through communications in specialized (inter)national journals and congresses. An effort to share the scientific achievements with the general public is extremely important. For this purpose, we have launched the UALGORITMO, a journal freely accessible online, written in lay Portuguese language by Researchers of the University of the Algarve, to summarize recent communications published in peer reviewed journals. After submission, the manuscripts are revised by High Schools Students of the Algarve, under the guidance of a schoolteacher, for further simplification of the language and general improvement of the manuscript and figures. The revised manuscripts by the authors are edited and published, with an acknowledgment and a presentation of the reviewers at the end of each article. To maximize the outreach, the articles include a summarized biography of the authors, and links to their research centers and teaching courses. We believe that the UALGORITMO is a valuable instrument to promote scientific literacy and culture amongst all communities.