Synthesis and Structural Elucidation of Triazolylmolybdenum(VI) Oxide Hybrids and Their Behavior as Oxidation Catalysts

Abstract

A large family of bifunctional 1,2,4-triazole molecular tectons (tr) has been explored for engineering molybdenum(VI) oxide hybrid solids. Specifically, tr ligands bearing auxiliary basic or acidic groups were of the type amine, pyrazole, 1H-tetrazole, and 1,2,4-triazole. The organically templated molybdenum(VI) oxide solids with the general compositions [MoO3(tr)], [Mo2O6(tr)], and [Mo2O6(tr)(H2O)2] were prepared under mild hydrothermal conditions or by refluxing in water. Their crystal structures consist of zigzag chains, ribbons, or helixes of alternating cis-{MoO4N2} or {MoO5N} polyhedra stapled by short [N-N]-tr bridges that for bitriazole ligands convert the motifs into 2D or 3D frameworks. The high thermal (235-350 °C) and chemical stability observed for the materials makes them promising for catalytic applications. The molybdenum(VI) oxide hybrids were successfully explored as versatile oxidation catalysts with tert-butyl hydroperoxide (TBHP) or aqueous H2O2 as an oxygen source, at 70 °C. Catalytic performances were influenced by the different acidic-basic properties and steric hindrances of coordinating organic ligands as well as the structural dimensionality of the hybrid.

Chemistry and Catalytic Performance of Pyridyl‐Benzimidazole Oxidomolybdenum(VI) Compounds in (Bio)Olefin Epoxidation

“…Various hybrid molybdenum(VI) oxide/organic compounds have been described in the literature as catalysts for the Cy/TBHP reaction, although it is not always possible to clearly compare catalytic performances, due to considerable differences in the reaction conditions used. Focusing on results obtained with PhCF 3 as the cosolvent and a reaction temperature of 70–75 °C, the catalytic results for 3 at 70 °C may be compared with those obtained with molybdenum(VI) oxide hybrid solids with the general compositions [Mo n O 3 n (L) m ] ( n = 1–3; m = 0.5 or 1) and [Mo 2 O 6 (L)(H 2 O) 2 ], where L = triazole‐based ligand, or pzpy . For example, the material [Mo 3 O 9 (pzpy)] led to 60 % Cy conversion after 6 h at 75 °C, and [MoO 3 (1,2,4‐triazole) 0.5 ] led to 35 % conversion at 24 h/70 °C, which is lower than that obtained with 3 at 70 °C (72 %).…”

Metal oxide-triazole hybrids as heterogeneous or reaction-induced self-separating catalysts

“…This system therefore appears to exhibit the features required for a reaction-controlled solid-liquid-solid phase separation procedure. Several triazolylmolybdenum(VI) oxide hybrids recently investigated did not exhibit this behavior [43]. For example, the solid [Mo 2 O 6 (trpzH)(H 2 O) 2 ] (mentioned above) dissolved completely in the reaction mixture but did not selfprecipitate [43].…”

A Linear Trinuclear Oxidodiperoxido‐molybdenum(VI) Complex with Single Triazole Bridges: Catalytic Activity in Epoxidation, Alcoholysis, and Acetalization Reactions

“…The use of the parent 1,2,4‐triazole molecule leads to a rare perovskite‐like hybrid [MoO 3 (trz) 0.5 ] consisting of layers of corner‐sharing MoO 5 N octahedra with the organic subunits projecting into the interlamellar regions . In contrast, 4‐substituted triazole molecules exhibit a tendency to support one‐dimensional (1D) molybdenum(VI) oxide topological motifs (e.g., chains, hydrated chains, ribbons, and helixes), which can be transformed into 2D or 3D frameworks by the use of 1,2,4‐bitriazole ligands . We have been studying these triazolylmolybdenum(VI) oxide hybrids as (pre)catalysts for the oxidation of olefins (epoxidation), sulfides, alcohols, and aldehydes .…”

“…In contrast, 4‐substituted triazole molecules exhibit a tendency to support one‐dimensional (1D) molybdenum(VI) oxide topological motifs (e.g., chains, hydrated chains, ribbons, and helixes), which can be transformed into 2D or 3D frameworks by the use of 1,2,4‐bitriazole ligands . We have been studying these triazolylmolybdenum(VI) oxide hybrids as (pre)catalysts for the oxidation of olefins (epoxidation), sulfides, alcohols, and aldehydes . Layered [MoO 3 (trz) 0.5 ] displayed a truly unique reaction‐induced self‐separating (RISS) catalytic behavior when used with aqueous H 2 O 2 as the oxidant .…”