Molybdenum(VI) complexes with ligands derived from 5-(2-pyridyl)-2H-tetrazole as catalysts for the epoxidation of olefins

abstract

The development of effective catalytic epoxidation processes that are an alternative to stoichiometric non-selective oxidation routes is important to meet environmental sustainability goals. In this work, molybdenum (VI) compounds bearing 5-(2-pyridyl)-2H-tetrazole derivatives as organic components, namely the ionic and neutral mononuclear complexes (H2ptz)[MoO2Cl2(ptz)] (1) and [MoO2Cl2(tBu-ptz)] (2), and the new Lindqvist-type polyoxometalate (POM) [tBu-Hptz]2[Mo6O19] (3), where Hptz = 5-(2-pyridyl)tetrazole and tBu-ptz = 2-tert- butyl-5-(2-pyridyl)- 2H-tetrazole, were studied as epoxidation catalysts using readily available and relatively ecofriendly hydroperoxide oxidants, namely hydrogen peroxide and tert-butyl hydroperoxide (TBHP). The pre-pared catalysts were very active. For example, 100% cis-cyclooctene conversion and 100% epoxide selectivity were reached at 1 h for 1 and 3, and 10 min for 2 (with TBHP). Catalytic and characterization studies indicated that the mononuclear complexes suffered chemical transformations under the reaction conditions, whereas 3 was structurally stable. This POM acted as a homogeneous catalyst and could be recycled by employing an ionic liquid solvent. The POM can be synthesized from 2 under different conditions, including those used in the catalytic process. Moreover, 3 was an effective epoxidation catalyst for a biobased substrate scope that included fatty acid methyl esters and the terpene dl-limonene.

keywords

TERT-BUTYL HYDROPEROXIDE; DIOXOMOLYBDENUM(VI) COMPLEXES; CYCLOOCTENE EPOXIDATION; STRUCTURAL ELUCIDATION; SELECTIVE OXIDATION; LIMONENE OXIDE; TRANSFORMATION; PERFORMANCE; DERIVATIVES; COPPER(II)

subject category

Chemistry; Engineering

authors

Nunes, MS; Gomes, AC; Neves, P; Mendes, RF; Paz, FAA; Lopes, AD; Pillinger, M; Gonçalves, IS; Valente, AA

Groups

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

Projects

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

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

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

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, Portugal) ref. UIDB/50011/2020, UIDP/50011/2020 and LA/P/0006/2020) 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 (Portugal, PIDDAC) and the European Union through the European Regional Development Fund under the Portugal 2020 Partnership Agreement. This study received Portuguese national funds from the FCT through the operational programs CRESC Algarve 2020 and COMPETE 2020 through project EMBRC.PT ALG-01-0145-FEDER-022121. M.S.N. (grant ref. 2021.06403.BD) acknowledges the FCT for Ph.D. grant (State Budget, European Social Fund (ESF) within the framework of PORTUGAL2020, namely through the Centro 2020 Regional Operational Program) . A.C.G. (CEECIND/02128/2017) and R.F.M. (CEE-CIND/00553/2017) thank the FCT/MCTES for funding through the Individual Call to Scientific Employment Stimulus.