Molybdenum Schiff Base Complexes: Synthesis, Structural Analysis, and Catalytic Performance in Benzyl Alcohol Oxidation

Molybdenum, a transition metal, is widely recognized for its ability to exhibit multiple oxidation states and form diverse complexes, including molybdenum Schiff base complexes. These complexes, formed by coordinating molybdenum with Schiff base ligands derived from primary amines and carbonyl compounds, possess unique properties and have garnered attention for their roles in biological and industrial applications. They are particularly important in catalytic processes, such as petroleum refining and chemical manufacturing. A key application of molybdenum Schiff base complexes is in the catalytic oxidation of benzyl alcohol to benzaldehyde, an essential industrial chemical. Benzaldehyde is valued for its almond-like aroma, making it a key ingredient in fragrances and cosmetics. It also serves as a precursor in the synthesis of pharmaceuticals, dyes, and agrochemicals, and its reactivity supports its role as an intermediate in organic synthesis. This highlights the industrial significance of molybdenum-based catalysts.

In this study, a Schiff base ligand was synthesized via the condensation of salicylaldehyde or 2-hydroxy-5-nitrobenzaldehyde with 2-furoic hydrazide and subsequently coordinated to the [MoO₂]²⁺ core. Reactions in methanol yielded the complex [MoO₂(L^1or2)(MeOH)], whereas reactions in acetonitrile produced [MoO₂(L^1or2)(H₂O)]. Characterization was performed using IR-ATR spectroscopy and thermogravimetric analysis, while molecular and crystal structures were determined by X-ray diffraction. These complexes were evaluated as catalysts for the oxidation of benzyl alcohol, demonstrating significant potential for catalytic applications, while the effect of varying oxidant quantities on selectivity and conversion was also investigated.