Browsing by Author "Gomes, A. C."
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- Application of an Indenyl Molybdenum Dicarbonyl Complex in the Isomerisation of α-Pinene Oxide to Campholenic AldehydePublication . Bruno, S.; Gomes, A. C.; Gamelas ou Carla A. Gamelas, Carla; Abrantes, M.; Oliveira, M. C.; Valente, A.; Almeida-Paz, Filipe; Pillinger, M.; Romão, C.; Gonçalves, I.The complex [{(Z5-Ind)Mo(CO)2(m-Cl)}2] (1) has been tested for the industrially relevant catalytic isomerisation of a-pinene oxide (PinOx) to campholenic aldehyde (CPA) in the liquid phase. PinOx conversion and CPA selectivity are strongly influenced by the solvent employed. Complete conversion of PinOx was achieved within 1 min at 55 1C or 30 min at 35 1C using 1,2-dichloroethane as solvent, giving CPA in 68% yield. Other products included trans-carveol, iso-pinocamphone and trans-pinocarveol. The stability of 1 under the reaction conditions used was investigated by using FT-IR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS) to characterise recovered solids. In the presence of air/moisture 1 undergoes oxidative decarbonylation upon dissolution to give oxomolybdenum species that are proposed to include a tetranuclear oxomolybdenum(V) complex. Conversely, ESI-MS studies of 1 dissolved in dry acetonitrile show mononuclear species of the type [IndMo(CO)2(CH3CN)n]+. The crystal structure of the ring-slipped dicarbonyl complex [(Z3-Ind)Mo(CO)2Cl(CH3CN)2] (2) (obtained after dissolution of 1 in acetonitrile) is reported.
- Isomerisation of pinene oxide in the presence of an indenyl Molybdenum carbonyl complexPublication . Gamelas ou Carla A. Gamelas, Carla; Bruno, Sofia; Gomes, A. C.; Abrantes, Marta; Oliveira, Maria da Conceição; Valente, Anabela; Almeida-Paz, Filipe; Pillinger, Martyn; Romão, Carlos C.; Gonçalves, Isabel S.
- Isomerization of alfa-pinene oxide in the presence of indenyl allyl dicarbonyl molybdenum(II) and tungsten(II) complexesPublication . Bruno, S. M.; Gamelas ou Carla A. Gamelas, Carla; Gomes, A. C.; Valente, A.; Pillinger, M.; Romão, C.; Gonçalves, I.The indenyl complexes IndM(η3-C3H5)(CO)2 (M=Mo (1), W (2)), (IndMe)Mo(η3-C3H5)(CO)2 (3) and (IndSiMe3)Mo(η3-C3H5)(CO)2 (4) display catalytic activity for the isomerisation of α-pinene oxide. Conversion reached 97% after 3 h at 35 °C in the presence of 1 and 1,2-dichloroethane as solvent, giving campholenic aldehyde in 56% yield. Solvent polarity and basicity appear to affect the reaction rate. Whereas the type of substituent on the indenyl ligand does not appear to have a strong impact on catalytic performance, changing the metal centre from Mo (1) toW(2) gave a significantly more active catalyst.
- Molybdenum(II) Diiodo-Tricarbonyl Complexes Containing Nitrogen Donor Ligands as Catalyst Precursors for the Epoxidation of Methyl OleatePublication . Gamelas ou Carla A. Gamelas, Carla; Neves, P.; Gomes, A. C.; Valente, A.; Romão, C.; Gonçalves, I.; Pillinger, M.The molybdenum(II) tricarbonyl complexes [Mo(CO)3I2L n ] (n = 1, L = 2,2′-bipyridine, 4,4′-di-tert-butyl-2,2′-bipyridine; n = 2, L = pyridine, 4-tert-butylpyridine) have been examined as catalyst precursors for the epoxidation of the biorenewable olefin methyl oleate with tert-butylhydroperoxide. In situ oxidative decarbonylation of the precursors gives highly active and selective molybdenum(VI) catalysts, which were identified as the one-dimensional molybdenum oxide/bipyridine polymer [MoO3(2,2′-bipyridine)], octanuclear [Mo8O24(4,4′-di-tert-butyl-2,2′-bipyridine)4], and the pyridinium β-octamolybdates (LH)4[Mo8O26] for L = pyridine or 4-tert-butylpyridine.
- Molybdenum(VI) Catalysts obtained from eta3-Allyl Dicarbonyl Precursors: Synthesis, Characterization and Catalytic Performance in Cyclooctene EpoxidationPublication . Gamelas ou Carla A. Gamelas, Carla; Gomes, A. C.; Bruno, S.; Almeida-Paz, F.; Valente, A.; Pillinger, M.; Romão, C.; Gonçalves, I.The oxidative decarbonylation of the η3-allyl dicarbonyl complexes [Mo(η3-C3H5)Cl(CO)2(L)] (L = 2,2′- bipyridine (bipy) (1), 4,4′-di-tert-butyl-2,2′-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tertbutylhydroperoxide (TBHP) or H2O2 gave the following compounds in good to excellent yields: the oxobridged dimers [MoO2Cl(L)]2O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH3CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n (4) and the octanuclear complex [Mo8O24(di-tBu-bipy)4] (7) using TBHP(50 equiv.)/H2O/70 °C; the oxodiperoxo complexes MoO(O2)2(L) (L = bipy (5), di-tBu-bipy (8)) using H2O2(10 equiv.)/CH3CN/r.t. The structure of 7·x (solvent) (where solvent = CH2Cl2 and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH2Cl2, the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1–8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H2O2 as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3–5)/TBHP, complex 5 from (1,3–5)/H2O2, and complex 8 from (2,6–8)/H2O2. With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H2O as solvent (28–38% for 1,3–5; 87–98% for 2,6–8), while with H2O2 as oxidant, the highest epoxide yields were obtained using CH3CN as solvent (54–81% for 3–8).
- Oxido-bis¬[chlorido(4,4'-di-tert-butyl-2,2'-bipyridine-2N,N')dioxido¬molybdenum(VI)] 0.2-hydratePublication . Gomes, A. C.; Fernandes, J. A.; Gamelas ou Carla A. Gamelas, Carla; Gonçalves, I. S.; Almeida-Paz, F. A.The title hydrate, [Mo2Cl2O5(C18H24N2)2]·0.2H2O, has been isolated as the oxidation product of [Mo(3-C3H5)Cl(CO)2(di-t-Bu-bipy)] (where di-t-Bu-bipy is 4,4'-di-tert-butyl-2,2'-bipyridine). A -oxide ligand bridges two similar MoCl(di-t-Bu-bipy)O2 units, having the terminal oxide ligands mutually cis, and the chloride and -oxide trans to each other. In the binuclear complex, the coordination geometries of the metal atoms can be described as highly distorted octahedra. Individual complexes co-crystallize with a partially occupied water molecule of crystallization (occupancy factor = 0.20; H atoms not located), with the crystal packing being mediated by the need to effectively fill the available space. A number of weak C-HO and C-HCl interactions are present.