Dihalosalicylaldehyde based molybdenum(VI) complexes: Synthesis, spectral characterization, crystal structures, and catalytic activities for the selective oxidation of benzylic alcohols.

[Display omitted] • New cis -dioxo Mo(VI) complexes incorporating ONO donor Schiff base ligands derived from dihalosalicylaldehyde and nicotinic hydrazide were synthesized and characterized. • X-ray crystallographic study has confirmed the structures of the H 2 Cl 2 SN ligand and two Mo(VI) complexes (2 & 3). • All complexes were successfully screened as catalysts for the selective oxidation of benzylic alcohols employing ethanol and hydrogen peroxide. Three ONO donor Schiff base ligands were obtained by the condensation of 3,5-dihalosalicylaldehydes with nicotinoylhydrazide (H 2 Cl 2 SN: (E)-N'-(3,5-dichlorosalicylaldehyde) nicotinoylhydrazone, H 2 Br 2 SN: (E)-N'-(3,5-dibromosalicylaldehyde) nicotinoylhydrazone, and H 2 I 2 SN: (E)-N'-(3,5-diiodosalicylaldehyde) nicotinoylhydrazone on refluxing in ethanol. The treatment of [MoO 2 (acac) 2 ] (acac = acetylacetonato) with these ligands in methanol afforded cis -dioxidomolybdenum(VI) complexes [MoO 2 (Cl 2 SN)(CH 3 OH)] (1), [MoO 2 (Br 2 SN)(CH 3 OH)] (2), and [MoO 2 (I 2 SN)(CH 3 OH)] (3). Various techniques like NMR (1H and 13C), FT-IR, Mass, TGA, elemental (CHN), and single-crystal X-ray diffraction analysis (for H 2 Cl 2 SN · H 2 O , 2a , [MoO 2 (Br 2 SN)(C 2 H 5 OH)], and 3a , [MoO 2 (I 2 SN)(H 2 O)].DMF) were utilized to characterize the synthesized compounds. The data collected from diffraction studies revealed that the geometry around Mo(VI) ions was distorted octahedral. Additionally, all complexes were successfully screened as catalysts for the selective oxidation of benzylic alcohols employing ethanol and hydrogen peroxide. [ABSTRACT FROM AUTHOR]