Catalytic oxidation of tetralin by dioxomolybdenum complexes: design, synthesis, characterization and DFT investigations

Abstract

Ligands derived from 3,4-dimethoxybenzohydrazide and salicylaldehyde (H₂L¹), 3-methoxysalicylaldehyde (H₂L²), 3,5-di-tert-butylsalicylaldehyde (H₂L³) and 5 chlorosalicylaldehyde (H₂L⁴) react with [MoO₂(acac)₂] salt in an 1 : 1 molar ratio in MeOH to give [MoO₂L¹·H₂O] 1, [MoO₂L²·H₂O] 2, [MoO₂L³·H₂O] 3 and [MoO₂L⁴·H₂O] 4. Single-crystal X-ray diffraction and spectroscopic data confirm that complexes 1a, 2a and 4a adopt the proposed structures, wherein the coordinated water molecule is replaced by DMSO in the crystal. Their structures were thoroughly characterized by many analytical techniques including elemental analysis, FT-IR, UV-vis., ¹H and ¹³C NMR Spectroscopy. Geometry optimizations of the synthesized compounds were also carried out using density functional theory (DFT). Further, the catalytic performance of these complexes was investigated in the oxidation of tetralin using hydrogen peroxide (H₂O₂) as the oxidant. Complex 1 exhibited remarkable activity, affording tetralone with a product selectivity of 95%.