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

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.

Ionic liquid-stabilized metal oxoclusters: from design to catalytic application

“…Recently, the Lindqvist-type POM [tBu-Hptz] 2 [Mo 6 O 19 ] (tBu-Hptz = 2-tert-butyl-5-(2-pyridyl)tetrazole) was studied as epoxidation catalysts using readily available and relatively ecofriendly hydroperoxide oxidants (hydrogen peroxide and tertbutyl hydroperoxide). 87 This POM acted as a homogeneous catalyst and could be recycled by employing an IL solvent. It was found that the type of anion of the IL could affect the catalytic performance.…”

Oil‐based epoxy and their composites: A sustainable alternative to traditional epoxy

“…A bidentate NO coordination with molybdenum (VI) is formed during catalyst formations. Catalytic study is done on epoxidation of several compounds such as cis‐cyclooctene (90% yield at 6 h), biobased olefins (linolenates, limonene diol, and monoepoxide), sulfide (methylphenylsulfide and diphenylsulfide) 112 . Zhang et al synthesized vitrimers from castor oil by introducing an epoxy group with a CC double bond.…”

DFT Studies of the Activity and Reactivity of Limonene in Comparison with Selected Monoterpenes

“…For HOOH, the following complexes were used: cobalt sandwich-type polyoxometalates [39], tungstophosphates [2], polyoxotungstates [11], Schiff base complexes with Co(II) and Cu(II) and the same compounds but immobilized in zeolite-Y [40], manganese(II) acetylacetonate on MCM41 [41], Al 2 O 3 [42], the ions of non-transition metal [1], methyltrioxorhenium with different ligands [43], activated carbon where the active phase was the magnetite Fe 3 O 4 [44] or MoO 2 [45], complexes of VO and copper(II) with Schiff base ligands entrapped in the supercages of zeolite-Y [46], homogeneous and heterogeneous VO and iron(II) with Schiff base ligands [47], γ-Fe 2 O 3 /SiO 2 -NHFeP prepared from nanospheres and 5,10,15,20-tetrakis (pentafluorphenylporphyrin) iron(III) [48], heterogeneous Mn(III), Fe(III), and Co(III) porphyrin-based complexes immobilized on zeolite [49] or others complexes based on zeolite-Y [50][51][52] in which enclosing the catalyst in the porous structure of the support prevents the dimerization of the complexes, ensuring their catalytic activity. Catalysts used with t-butyl hydroperoxide as the oxidant are also zeolites, e.g., zeolite-Y with entrapped VO with Schiff base ligands [50], organic hybrid materials [26,53], Ti-MCM-41, and Ti-MWW compounds [54], iron(II) [55], molybdenum(II) complexes [56], salen-like Jacobsen's catalysts with manganese(III) [57] or carbon-based complexes with cobalt(II) acetylacetonate [58]. Jacobsen's compounds with manganese(III) [59,60] with Mn(II), Ni(II), Co(II) [61], or VO(Salten) anchored on SBA-15 (Salten-3-[N,N ′ -bis-3(salicylidenamino)ethyltriamine]) [62] were also used with other oxidants such as KHSO 5 (used as ozone), iodosylbenzene, sodium hypochlorite, or urea hydroperoxide.…”