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

Abstract

There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2(pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO3(Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 °C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products.

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

“…The corresponding bands appear in the Raman spectrum at 913 and 946 cm -1 with weak and strong intensity, respectively (Figure 4B). For comparison, the complex (H2ptz)[MoO2Cl2(ptz)] displayed a similar pair of bands at 914-915 cm −1 and 945 ± 1 cm −1 [19]. These frequencies are typical for complexes of the type [MoO2Cl2(L)] containing bidentate Lewis-base ligands.…”

“…We previously prepared the complex salt (H 2 ptz)[MoO 2 Cl 2 (ptz)] and the microcrystalline molybdenum oxide/organic hybrid [MoO 3 (Hptz)], which were assessed for their potential as catalysts of the epoxidation of biomass-derived olefins [19]. In the epoxidation of the model olefin cis-cyclooctene, the former acted as a homogeneous catalyst, and the latter as a heterogeneous one.…”

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

“…Limonene has found practical application in biorefineries, where post-production waste generated during the production of, e.g., orange juices, is processed into commercially useful compounds and constitutes a suitable raw material for the production of important products used in the flavor and fragrance industry [16] in the textile industry for the production of fibers [17] or in pharmacy/medicine [18,19]. However, limonene oxidation products are much more valuable than the substrate from which they are obtained and play an important role as an ingredient for the synthesis of fragrances or drugs [20,21], in the production of biodegradable polymers [22][23][24][25][26], or as a solvent/reactive diluent in the production of epoxy resins [26]. The main products of the C 10 H 16 oxidation reactions are demonstrated in Scheme 1.…”

“…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.…”

10th Anniversary of Catalysts: Molecular Catalysis

“…For example, the Special Issue summarizes efforts in the area of homogeneous catalysts concerning iridium catalysts containing NHC ligands applied to the asymmetric transfer hydrogenation of ketones [4], synthesis of quinoxalines from glycerol and diamines [5], cross coupling for natural product synthesis [6], and palladium-catalyzed reductive carbonylation of nitro-styrene [7]. This Special Issue also introduces efforts entitled "Immobilization of Rh(I)-N-Xantphos and Fe(II)-C-scorpionate onto magnetic nanoparticles [8]" and "5-(2-Pyridyl)tetrazolate complex of molybdenum(VI)" as precursors for reusable molybdenum oxide-based hybrid heterogeneous catalyst [9]. Moreover, this Special Issue introduces efforts concerning ring opening polymerization using Al and Zn complex catalysts [10], isospecific propylene polymerization by zirconium catalysts [11], and analysis of catalyst solution for ethylene copolymerization using XAS spectroscopy in solution [12].…”