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13. An organic-organometallic CO-releasing material comprising 4,4′-bipyridine and molybdenum subcarbonyl building blocks.

Author

Calhau, Isabel B., Gomes, Ana C., Mendes, Ricardo F., Almeida Paz, Filipe A., Gonçalves, Isabel S., and Pillinger, Martyn

Subjects
MAGIC angle spinning, X-ray powder diffraction, CARBON monoxide, THERMOGRAVIMETRY, ULTRAVIOLET-visible spectroscopy
Abstract

Over the past two decades, following the discovery of the important biological roles of carbon monoxide (CO), metal carbonyl complexes have been intensively studied as CO-releasing molecules (CORMs) for therapeutic applications. To improve the properties of "bare" low molecular weight CORMs, attention has been drawn to conjugating CORMs with macromolecular and inorganic scaffolds to produce CO-releasing materials (CORMAs) capable of storing and delivering large payloads of the gasotransmitter. A significant obstacle is to obtain CORMAs that retain the beneficial features of the parent CORMs. In the present work, a crystalline metal–organic framework (MOF) formulated as Mo(CO)3(4,4′-bipyridine)3/2 (Mobpy), with a structure based on Mo(CO)3 metallic nodes and bipyridine linkers, has been prepared in near quantitative yield by a straightforward reflux method, and found to exhibit CO-release properties that mimic those typically observed for molybdenum carbonyl CORMs. Mobpy was characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and diffuse reflectance (DR) UV-vis spectroscopies, and 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR. The release of CO from Mobpy was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mobpy liberates CO upon contact with a physiological buffer in the dark, leading to a maximum released amount of 1.3–1.5 mmol g−1, after 1.5 h at 37 °C, with half-lives of 0.5–1.0 h (time to transfer 0.5 equiv. of CO to Mb). In the solid-state and under open air, Mobpy undergoes complete decarbonylation over a period of 42 days, corresponding to a theoretical CO-release of 7.25 mmol g−1. [ABSTRACT FROM AUTHOR]

Published
2024
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19. Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5‐cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysis.

Author

Neves, Patrícia, Gomes, Ana C., Monteiro, Rodrigo P., Santos, Mirela J., Valente, Anabela A., Lopes, André D., Gonçalves, Isabel S., and Pillinger, Martyn

Subjects
INCLUSION compounds, EPOXIDATION, FATTY acid methyl esters, MOLYBDENUM, CATALYSTS recycling, COORDINATION polymers
Abstract

There 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)3Me] (1) (Cp = η5‐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, 13C{1H} 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. [ABSTRACT FROM AUTHOR]

Published
2024
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27. A Molybdenum(VI) Complex of 5-(2-pyridyl-1-oxide)tetrazole: Synthesis, Structure, and Transformation into a MoO3-Based Hybrid Catalyst for the Epoxidation of Bio-Olefins

Author

Nunes, Martinique S., primary, Gomes, Diana M., additional, Gomes, Ana C., additional, Neves, Patrícia, additional, Mendes, Ricardo F., additional, Paz, Filipe A. Almeida, additional, Lopes, André D., additional, Pillinger, Martyn, additional, Valente, Anabela A., additional, and Gonçalves, Isabel S., additional

Published
2023
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45. A Molybdenum(VI) Complex of 5-(2-pyridyl-1-oxide)tetrazole: Synthesis, Structure, and Transformation into a MoO 3 -Based Hybrid Catalyst for the Epoxidation of Bio-Olefins.

Author

Nunes, Martinique S., Gomes, Diana M., Gomes, Ana C., Neves, Patrícia, Mendes, Ricardo F., Paz, Filipe A. Almeida, Lopes, André D., Pillinger, Martyn, Valente, Anabela A., and Gonçalves, Isabel S.

Subjects
TETRAZOLES, SULFOXIDES, EPOXIDATION, FATTY acid methyl esters, MOLYBDENUM catalysts, MOLYBDENUM oxides, HETEROGENEOUS catalysts
Abstract

The discovery of heterogeneous catalysts synthesized in easy, sustainable ways for the valorization of olefins derived from renewable biomass is attractive from environmental, sustainability, and economic viewpoints. Here, an organic–inorganic hybrid catalyst formulated as [MoO3(Hpto)]·H2O (2), where Hpto = 5-(2-pyridyl-1-oxide)tetrazole, was prepared by a hydrolysis–condensation reaction of the complex [MoO2Cl2(Hpto)]∙THF (1). The characterization of 1 and 2 by FT-IR and Raman spectroscopies, as well as 13C solid-state NMR, suggests that the bidentate N,O-coordination of Hpto in 1 (forming a six-membered chelate ring, confirmed by X-ray crystallography) is maintained in 2, with the ligand coordinated to a molybdenum oxide substructure. Catalytic studies suggested that 2 is a rare case of a molybdenum oxide/organic hybrid that acts as a stable solid catalyst for olefin epoxidation with tert-butyl hydroperoxide. The catalyst was effective for converting biobased olefins, namely fatty acid methyl esters (methyl oleate, methyl linoleate, methyl linolenate, and methyl ricinoleate) and the terpene limonene, leading predominantly to the corresponding epoxide products with yields in the range of 85–100% after 24 h at 70 °C. The versatility of catalyst 2 was shown by its effectiveness for the oxidation of sulfides into sulfoxides and sulfones, at 35 °C (quantitative yield of sulfoxide plus sulfone, at 24 h; sulfone yields in the range of 77–86%). To the best of our knowledge, 2 is the first molybdenum catalyst reported for methyl linolenate epoxidation, and the first of the family [MoO3(L)x] studied for methyl ricinoleate epoxidation. [ABSTRACT FROM AUTHOR]

Published
2023
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49. 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 Olefins

Author

Nunes, Martinique S., primary, Gomes, Diana M., additional, Gomes, Ana C., additional, Neves, Patrícia, additional, Mendes, Ricardo F., additional, Paz, Filipe A. Almeida, additional, Lopes, André D., additional, Valente, Anabela A., additional, Gonçalves, Isabel S., additional, and Pillinger, Martyn, additional

Published
2021
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