OH-substituted tridentate ONO Schiff base ligands and related molybdenum(VI) complexes for solvent-free (ep)oxidation catalysis with TBHP as oxidant

Abstract

Molybdenum complexes with ONO tridentate Schiff base ligands based on salicylideneaminophenolato (SAP) backbone with OH substitution on the salicyl arene ring have been synthesized and characterized. The molecular structures of the full series of OH substituted molybdenum complexes were determined by X-ray crystallography as monomers stabilized by one solvent molecule, [MoO2L(D)]. All dimeric complexes [MoO2L]2 were tested for the epoxidation of cyclooctene and cyclohexene under organic solvent-free conditions using aqueous TBHP as oxidant. The position of the OH on the SAP-modified ligand influenced the catalytic activity of the respective complexes. DFT calculations for the catalytic cycle yield energy spans in agreement with the experimentally observed activity trend.

Efficient Molybdenum Hydrazonato Epoxidation Catalysts Operating under Green Chemistry Conditions: Water vs. Decane Competition

“…Previously, several Mo complexes have been examined through a systematic DFT study. As an example, on the [MoO 2 (SAP)] complexes and different substitutions on ligand showed that the presence of OH group (on a specific position on the aldehyde part) [19] or NO 2 substituent (on aminophenol part) [20] on the ligand provoked higher activity. The presence of 3-and 4-methoxy groups on the ligand was studied several times with other Mo complexes [21].…”

Ligand coordination sphere effect of Schiff base cis‐dioxomolybdenum(VI) complexes in selective catalytic oxidation of alcohols

“…Solvent‐free conditions are one aspect of green chemistry, which are reported for oxidation of primary alcohols to aldehydes 41,42 . Our research group have studied several [MoO 2 L] n (L = ONO, ONS ligands) type cis ‐dioxomolybdenum(VI) Schiff base complexes as catalysts in solvent‐free olefin epoxidation, observing high catalytic activity 24,43–45 . We have to point out that the solvent‐free condition here means organic solvent‐free condition with no further added organic solvent.…”

Replacement of Volatile Acetic Acid by Solid SiO2@COOH Silica (Nano)Beads for (Ep)Oxidation Using Mn and Fe Complexes Containing BPMEN Ligand

“…The use of chlorinated solvents such as dichloroethane (DCE), a highly toxic solvent, has to be avoided [ 15 ]. In the research group, the processes have been found to be active without organic solvent using complexes with tridentate ligands [ 16 , 17 , 18 , 19 , 20 ] or polyoxometalates (POMs) [ 21 , 22 , 23 ], giving a first step towards a cleaner process. The oxidant used in this case is tert -butyl hydroperoxide (TBHP) in aqueous solution.…”