High-valent oxovanadium metallosupramolecular species as catalysts for the oxidation of benzyl alcohol derivatives

Abstract

Coordination-driven synthesis has been successfully utilized to prepare vanadium-based metallosupramolecular species. By systematically varying synthesis methods and reaction conditions, two series of isostructural oxovanadium(V) coordination polymers [VO(SIH)(OR)]_n (where SIH²⁻ represents salicylaldehyde isonicotinoylhydrazonate, and R corresponds to CH₃ (1β·0.25CH₃OH), C₂H₅ (2α and 2β·0.25C₂H₅OH), C₃H₇ (3α), C₄H₉ (4α and 4β), and C₅H₁₁ (5β)), were synthesized. Additionally, a phase-pure tetranuclear compound [VO(SIH)(OCH₃)]₄·4CH₃OH (1t·4CH₃OH) was also prepared. In these compounds the [VO(SIH)] units, featuring the isonicotinoylhydrazonate heterocyclic moiety, are interconnected through V–N_{isonicotinoyl} coordination bonds. This linkage enables formation of the one-dimensional (1D) zig–zag chain compounds and zero-dimensional (0D) metallocycle, as determined by single crystal X-ray crystallography. This study further explored the formation and transformation of the assemblies, thereby emphasizing the influence of the ancillary OR⁻ ligand. The compounds were also characterized by powder X-ray diffraction, chemical analysis, thermogravimetric (TGA) measurements, and spectroscopic methods (IR-ATR, UV-Vis, and NMR). The catalytic activity of vanadium coordination entities 1t and 1β was tested for the oxidation of benzyl alcohol and its derivatives, including 2-nitrobenzyl, 2-chlorobenzyl, and 2-methylbenzyl alcohol. Several oxidizing agents were used, including tert-butyl hydroperoxide (TBHP) in aqueous and decane solutions, as well as hydrogen peroxide (H₂O₂). The study also assessed the impact of different solvents, such as toluene, acetonitrile, and methanol, thereby enhancing the understanding of these systems.