Browsing by Author "Bruno, S."
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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.
- Intercalation of a molybdenum eta3-allyl dicarbonyl complex in a layered double hydroxide and catalytic performance in olefin epoxidation.Publication . Gomes, A.; Bruno, S.; Gamelas ou Carla A. Gamelas, Carla; Valente, A.; Abrantes, M.; Gonçalves, I.; Romão, C.; Pillinger, M.A Zn–Al layered double hydroxide (LDH) intercalated by [Mo(η3-C3H5)Cl(CO)2(bpdc)]2− anions (bpdc = 2,2′-bipyridine-5,5′-dicarboxylate) has been prepared by coprecipitation from aqueous solution and characterised by various techniques. The one-pot method gives rise to a highly organised intercalate with an interlayer spacing of 18.3 Å and up to six (00l) basal reflections in the powder X-ray diffraction pattern. Spectroscopic studies (FT-IR, FT-Raman, 13C CP MAS NMR and UV-Vis) confirm the presence of structurally intact [Mo(η3-C3H5)Cl(CO)2(bpdc)]2− anions. The interlayer spacing of 18.3 Å indicates that the material contains a monolayer of guest anions positioned in such a way that the bpdc ligands are arranged with their longest dimension roughly perpendicular to the hydroxide layers of the host. Thermal properties were studied by thermogravimetric analysis and differential scanning calorimetry. The intracrystalline reactivity of intercalated dicarbonyl complexes was probed by using the hybrid nanocomposite as a precatalyst in the liquid phase epoxidation of cis-cyclooctene with tert-butylhydroperoxide as oxidant. Under the reaction conditions used, oxidative decarbonylation of the guest molecules takes place (with release of CO and CO2 as confirmed by on-line gas chromatography experiments) to give intercalated molybdenum oxide/bipyridine species that selectively catalyse the epoxidation reaction. The intracrystalline oxidative decarbonylation reaction is topotactic in nature.
- 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).