Browsing by Author "Monteiro, Rodrigo P."
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- Host-guest complexes of cucurbit[8]uril and [(η5-C5H4R)Mo(CO)3CH3] (R = H, CO2CH3) for controlled release of carbon monoxidePublication . Gomes, Ana C.; Monteiro, Rodrigo P.; Calhau, Isabel B.; D. Lopes, André; Gonçalves, Isabel S.; Pillinger, MartynThe monosubstituted cyclopentadienyl half-sandwich molybdenum(II) tricarbonyl complex [(eta 5-C5H4CO2CH3) Mo(CO)3CH3] (1) and its 1:1 inclusion compound with cucurbit[8]uril (1@CB8) have been prepared and characterised by elemental and thermogravimetric analyses, powder X-ray diffraction, diffuse reflectance UV-vis, solid-state 13C{1H} MAS NMR, FT-IR, and Raman spectroscopies. The CO-releasing behaviours of 1, 1@CB8 and, for comparison, [(eta 5-C5H5)Mo(CO)3CH3] (2) and its 1:1 inclusion complex with CB8, were assessed using a deoxymyoglobin-carbonmonoxymyglobin assay. For assays performed in the dark at 37 degrees C, complex 1 undergoes thermally assisted spontaneous CO release, with ca. 0.5 equivalents of CO being released after 6 h. The half-life (t1/2) of 325 min identifies 1 as a slow releaser when compared to complex 2 bearing the unsubstituted cyclopentadienyl ligand (t1/2 = 25 min). CO release from 1 was promoted by exposure to UV light (t1/2 = 85 min), establishing the complex as a photochemically activated CO-releasing molecule (photoCORM). For 1@CB8, t1/2 for photo-assisted CO release increased to ca. 7 h, and for 2@CB8 the dark-release t1/2 increased to 165 min, showing that molecular acceptors like cucurbiturils can be used effectively as second-sphere ligands to modulate the CO release profile of CORMs.
- Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5 -cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysisPublication . Neves, Patrícia; Gomes, Ana C.; Monteiro, Rodrigo P.; Santos, Mirela J.; Valente, Anabela A.; D. Lopes, André; Gonçalves, Isabel S.; Pillinger, MartynThere are very few known examples of supramolecular compounds comprising molybdenum species hosted inside the portals/cavities of cucurbit[n]urils (CBn). In this work, CB7 and CB8 macrocycles have been studied as hosts for the carbonyl complex [CpMo(CO)(3)Me] (1) (Cp = eta(5)-C5H5). Compounds were isolated in the solid state and characterized as genuine 1:1 inclusion complexes (1@CBn) by elemental and thermogravimetric analyses, powder X-ray diffraction, scanning electron microscopy, C-13{H-1} cross-polarization magic-angle spinning NMR, FT-IR, Raman, and diffuse reflectance UV-Vis spectroscopies. The host-guest structures can act as supramolecular precatalysts for olefin epoxidation. Based on the model reaction of cis-cyclooctene with hydroperoxide oxidants (tert-butylhydroperoxide or hydrogen peroxide), the structural features of 1@CBn as well as the operating conditions influence the catalytic process. The metal species in 1@CBn undergo oxidative decarbonylation in situ, giving oxidized metal species that are catalytically active for olefin epoxidation. The type of oxidant and solvent influences the catalytic activity and stability. 1@CB8 was more stable than 1@CB7 with regard to catalyst recycling and reuse. Based on the substrate scope investigation, for relatively large olefins, such as the fatty acid methyl ester methyl oleate, the size of the macrocyclic host may be a determining factor for catalytic activity.
- β-Cyclodextrin and cucurbit[7]uril as protective encapsulation agents of the CO-releasing molecule [CpMo(CO)3Me]Publication . Monteiro, Rodrigo P.; Calhau, Isabel B.; Gomes, Ana C.; D. Lopes, André; Da Silva, José Paulo; Gonçalves, Isabel P.; Pillinger, MartynThe CO releasing ability of the complex [CpMo(CO)3Me] (1) (Cp = eta 5-C5H5) has been assessed using a deoxymyoglobin-carbonmonoxymyoglobin assay. In the dark, CO release was shown to be promoted by the reducing agent sodium dithionite in a concentration-dependent manner. At lower dithionite concentrations, where dithionite-induced CO release was minimised, irradiation at 365 nm with a low-power UV lamp resulted in a strongly enhanced release of CO (half-life (t1/2) = 6.3 min), thus establishing complex 1 as a photochemically activated CO-releasing molecule. To modify the CO release behaviour of the tricarbonyl complex, the possibility of obtaining inclusion complexes between 1 and beta-cyclodextrin (beta CD) or cucurbit[7]uril (CB7) by liquid-liquid interfacial precipitation (1@beta CD(IP)), liquid antisolvent precipitation (1@CB7), and mechanochemical ball-milling (1@beta CD(BM)) was evaluated. All these methods led to the isolation of a true inclusion compound (albeit mixed with nonincluded 1 for 1@beta CD(BM)), as evidenced by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR and FT-Raman spectroscopies, and 13C{1H} magic angle spinning (MAS) NMR. PXRD showed that 1@beta CD(IP) was microcrystalline with a channel-type crystal packing structure. High resolution mass spectrometry studies revealed the formation of aqueous phase 1 : 1 complexes between 1 and CB7. For 1@beta CD(IP) and 1@CB7, the protective effects of the hosts led to a decrease in the CO release rates with respect to nonincluded 1. beta CD had the strongest effect, with a ca. 10-fold increase in t1/4 for dithionite-induced CO release, and a ca. 2-fold increase in t1/2 for photoinduced CO release.