Heterogeneous catalysis with an organic-inorganic hybrid based on MoO3 chains decorated with 2,2 '-biimidazole ligands

abstract

The discovery of selective heterogeneous catalytic systems for industrial oxidation processes remains a challenge. Molybdenum oxide-based polymeric hybrid materials have been shown to be oxidation catalysts under mild reaction conditions, although difficulties remain with catalyst recovery/reuse since most perform as homogeneous catalysts or possess low activity. The present study shows that the hybrid material [MoO3(2,2 '-biimidazole)]center dot H2O (1) is a superior catalyst regarding these issues. The structure of 1 was confirmed (by single crystal and synchrotron X-ray powder diffraction) to comprise one-dimensional chains of corner-sharing {MoO4N2} octahedra. Strong Mo = OMIDLINE HORIZONTAL ELLIPSISH-N hydrogen bonds separate adjacent chains to afford parallel channels that are occupied by disordered water molecules. Hybrid 1 was additionally characterised by FT-IR spectroscopy, H-1 and C-13 MAS NMR, scanning electron microscopy and thermogravimetric analysis. The catalytic studies highlighted the versatility of 1 for oxidation reactions with tert-butylhydroperoxide as oxidant. By complementing with characterisation studies, it was verified that the reaction occurs in the heterogeneous phase, the catalyst has good stability and is recoverable via simple procedures. The chemical reaction scope covered epoxidation and sulfoxidation, and the substrate scope included biomass-derived dl-limonene and fatty acid methyl esters to give renewable bio-products, as well as thiophene and thioanisole substrates.

keywords

COMPLEXES; EPOXIDATION

subject category

Chemistry, Physical

authors

Amarante, TR; Neves, P; Paz, FAA; Gomes, AC; Pillinger, M; Valente, AA; Goncalves, IS

Groups

G1 - Porous Materials and Nanosystems
G4 - Renewable Materials and Circular Economy

Projects

Collaboratory for Emerging Technologies, CoLab (EMERGING TECHNOLOGIES)

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Conversao catalitica de olefinas derivadas da biomassa (BiOle_AcidOxCat)

acknowledgements

This work was carried out with the support of CICECO - Aveiro Institute of Materials [FCT (Fundacao para a Ciencia e a Tecnologia) Ref. UIDB/50011/2020 & UIDP/50011/2020] and the COMPETE 2020 Operational Thematic Program for Competitiveness and Internationalization (Project POCI-01-0145-FEDER-030075), co-financed by national funds through the FCT/MCTES and the European Union through the European Regional Development Fund under the Portugal 2020 Partnership Agreement. The positions held by T. R. A. and P. N. were funded by national funds (OE), through FCT, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of article 23 of the Decree-Law 57/2016 of 29 August, changed by Law 57/2017 of 19 July. We thank the FCT and CICECO for specific funding towards the purchase of the single-crystal diffractometer. The European Synchrotron Radiation Facility (ESRF, Grenoble, France) is gratefully acknowledged for approving the experiment CH-4254 (ID22). The authors are grateful to Dr. Zhi Lin (CICECO) for supplying the TS-1 sample.