A Molybdenum Trioxide Hybrid Decorated by 3-(1,2,4-Triazol-4-yl)adamantane-1-carboxylic Acid: A Promising Reaction-Induced Self-Separating (RISS) Catalyst

Abstract

3-(1,2,4-Triazol-4-yl)­adamantane-1-carboxylic acid (tradcH), a heterobifunctional organic ligand in which carboxylic acid and 1,2,4-triazole groups are united through a rigid 1,3-adamantanediyl spacer, was employed for the synthesis of a MoVI oxide organic hybrid. The ligand crystallized from water as tradcH·H2O (1), possessing a two-dimensional hydrogen-bonding network, and from ethanol as a cyclic molecular solvate with the composition (tradcH)3·2EtOH (2). Treatment of tradcH with MoO3 under hydrothermal conditions afforded a new Mo trioxide hybrid, [MoO3(tradcH)]·H2O (3), which was structurally characterized. In 3, the molybdenum atoms form a polymeric zigzag chain of {μ2-O-MoO2} n which is supported by double triazole bridges, while the carboxylic acid termini are left uncoordinated. The coordination environment of the Mo centers appears as distorted cis-{MoN2O4} octahedra. The hybrid exhibits high thermal stability (up to 270 °C) and was employed for a relatively broad scope of catalytic oxidation reactions in the liquid phase. Its catalytic behavior may be compared to a reversible mutation, featuring the best sides of homogeneous and heterogeneous catalysis. The original solid material converts into soluble active species, and the latter revert to the original material upon completion of the catalytic reaction, precipitating and allowing straightforward catalyst separation/reuse (like a heterogeneous catalyst). This catalyst was explored for a chemical reaction scope covering sulfoxidation, oxidative alcohol dehydrogenation, aldehyde oxidation, and olefin epoxidation, using hydrogen peroxide as an eco-friendly oxidant that gives water as a coproduct.

Hydrophobic/Hydrophilic Interplay in 1,2,4‐Triazole‐ or Carboxylate‐Based Molybdenum(VI) Oxide Hybrids: A Step Toward Development of Reaction‐Induced Self‐Separating Catalysts

“…The structural motif in 2 is identical to that of the recently described hybrid [MoO 3 (tradcH)] • H 2 O. [18] The Mo(VI) atoms are in a distorted octahedral arrangement cis-{N 2 O 4 }. They participate in vertex-sharing through opposite O atoms to form a zig-zag chain (Figure 2).…”

“…[11,12,17,22] Hybrid 2 led to somewhat comparable (e. g. entries 8, 12, 14) [12,18,23] or superior (e. g. entries 6, 9-11, 15) [11,22,23] results to most of the organo-oxomolybdenum(VI) oxide polymeric hybrids reported in the literature; exceptionally, hybrids possessing tr, trpzH and tradcH ligands (entries 5, 7, 13) led to superior results. [17,18,23] Catalyst Recyclability. An important aspect is the recovery and reuse of the catalyst, which may be an issue for most homogeneous catalytic systems studied, including nearly all studies listed in Table 2.…”

“…Recently, it was found that two-dimensional [MoO 3 (1H-1,2,4-triazole) 0.5 ] and one-dimensional [MoO 3 (tradcH)] • H 2 O (where tradcH = 3-(1,2,4triazol-4-yl)adamantane-1-carboxylic acid) coordination hybrids behaved as efficient recoverable catalysts for oxidation of alcohols to aldehydes/carboxylic acids, sulfides to sulfoxides/ sulfones and epoxidation of olefins using aqueous H 2 O 2 as oxidant. [17,18] Apparently, the RISS behavior requires the finetuning of catalyst solubility in the continuously changing reaction medium (including, on the one hand, the factors of reagent concentrations and reactivity, and, on the other, polarity, diffusivity and viscosity of reaction solution). We presuppose that it can be rationalized on the basis of the previously described hybrid [MoO 3 (tradcH)] • H 2 O.…”

“…We presuppose that it can be rationalized on the basis of the previously described hybrid [MoO 3 (tradcH)] • H 2 O. [18] The rigid structure of the tradcH module employed unites two hydrophilic donor functions separated through a hydrophobic hydrocarbon core of adamantanediyl. In this respect, angular 1,2,4triazolecarboxylic acids, derived from natural alpha-amino acids, represent an attractive series of heterofunctional ligands with a suitable choice of hydrophilic-hydrophobic termini for the preparation and rational design of MoO 3 -coordination hybrids with the desired chemical behavior for further catalytic applications.…”

Crystal structure and Hirshfeld surface analysis of 4,4′-(propane-1,3-diyl)bis(4H-1,2,4-triazol-1-ium) pentafluoridooxidovanadate(V)

“…A similar effect is known for the isoelectronic neutral pyrazole ring (Gospodinov et al, 2020). The protonation also results in a certain shortening of the N-N bonds [1.362 (2) Å ], as may be compared with N-N = 1.3918 (15) Å for the neutral and non-coordinated triazole rings in the adamantane derivative (Lysenko et al, 2019). The methylene linkage adopts a transgauche conformation with the corresponding torsion angles C5-C6-C7-N6 of À171.58 (12) and N3-C5-C6-C7 of À63.73 (17) .…”