Geometrically Constrained Molybdenum(VI) Metallosupramolecular Architectures: Conventional Synthesis versus Vapor and Thermally Induced Solid-State Structural Transformations

Abstract

This contribution describes the synthesis, characterization, and catalytic implementation of the highly constrained molybdenum­(VI) polymers [MoO2(LR)] n (with R = H (1), 3OMe (2), and 4OMe (3)) and cyclic tetramer [MoO2(L4OMe)]4 ­·0.5MeCN (3′·0.5MeCN) with nicotinoyl hydrazonato ligands (LR) derived from salicylaldehyde (LH), 3-methoxy-2-hydroxybenaldehyde (L3OMe), or 4-methoxy-2-hydroxybenzaldehyde (L4OMe). In order to determine the most stable geometries, conformational analysis of the free and coordinated ligands in these assemblies was carried out through the potential energy surface scans using quantum-chemical methods. The mononuclear analogues [MoO2(HLR)­(MeOH)]Cl (R = H (1a) and 3OMe (2a)), [MoO2(HLR)­Cl] (R = 3OMe (2b) and 4OMe (3b)), and [MoO2(LR)­(MeOH)] (R = H (1c), and 4OMe (3c-α and 3c-β)) were also synthesized and evaluated as potential precursors for reactions in the solid state. Vapor induced transformation of 2a quantitatively afforded complex 2b. The chemometric analysis using principal component analysis was applied to provide insight into the reaction profile. Thermally induced solid-state reactions resulted in the transformation of metallocycle 3′·0.5MeCN and monomeric complexes 1c, 2a, 3c-α, and 3c-β into the corresponding coordination polymers. The structural features responsible for these conversions are discussed in detail. Lastly, the metallosupramolecular architectures were tested as catalysts for cyclooctene epoxidation by using tert-butyl hydroperoxide as an oxidant in water or decane. Compound 3′ is shown to be the most effective and selective catalyst.

Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts

“…A comparison of the PXRD patterns identified them to be a metallosupramolecular species [MoO 2 (L 1–3 )] n , known from our previous investigation. 26,31 Upon standing the filtrate at room temperature, the condensation of the remaining metal oxo-units led to the formation of the Class I assemblies [MoO 2 (HL 1–3 )(D)] 2 [Mo 6 O 19 ]·2CH 3 COCH 3 , where D = acetone in 1H a ·2CH 3 COCH 3 , or water in 2H w ·2CH 3 COCH 3 and 3H w ·2CH 3 COCH 3 . The red crystals deposited after about one to two weeks.…”

“…Further comparison was made considering Mo tetranuclear and polynuclear coordination compounds obtained from H 2 L 1-3 ligands (Table S7, see ESI †). 26,31 With TBHP in decane conversion was 74% and selectivity towards epoxide 85%, while with TBHP in water, the investigated parameters were much lower (27% and 56%, respectively). In this case, it seems that the presence of polyoxomolybdate anion positively inuences the catalytic performance of the tested catalyst, supporting the fact that the Lindqvist-type anion is one active site of the catalyst.…”

“…A comparison of the PXRD patterns identied them to be a metallosupramolecular species [MoO 2 (L 1-3 )] n , known from our previous investigation. 26,31 Upon standing the ltrate at room temperature, the condensation of the remaining metal oxo-units led to the formation of the Class I assemblies Traces of moisture in the solvents are crucial for the polyoxometalate anion formation. The addition of acetic acid during the reactions increased the purity of the compounds, but there was no difference in nal hybrid product formation.…”

“…[26][27][28][29][30] The metallosupramolecular species with long Mo-N ligand bonds were particularly effective. [31][32][33][34] It was, therefore, reasonable to combine Mo VI coordination compounds with POMs into organic-inorganic hybrid architectures. In principle, POMs should be a suitable substitute for any ligand, but due to steric hindrance effects, one might expect their coordination to Mo with a long Mo-O bond.…”

Ligand-Modulated Nuclearity and Geometry in Nickel(II) Hydrazone Complexes: From Mononuclear Complexes to Acetato- and/or Phenoxido-Bridged Clusters

“…have been successfully used for their synthesis [17,18]. Aroylhydrazone ligands ArC=N-NH-(C=O)-R with O-donor atoms have the ability to bridge metallic ions and to build a range of polymetallic arrays [19][20][21]. We have reported the coordination properties of benzhydrazone-related ligands, and conditions for obtaining a number of dinuclear, cubane tetranuclear, and polynuclear copper(II) complexes [22,23].…”