Aerobic Oxidation of Benzylic Alcohols in Water by 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)/Copper(II) 2‐N‐Arylpyrrolecarbaldimino Complexes

Abstract

Novel copper(II) 2-N-arylpyrrolecarbald-

Oxidovanadium complexes with tridentate aroylhydrazone as catalyst precursors for solvent-free microwave-assisted oxidation of alcohols

“…The previously recognized promoting effect of basic additives, which facilitate the deprotonation of the alcohol [61,62,[69][70][71][72][73][74][75], was not detected for the present systems. In contrast, a strong inhibitor effect of the catalytic activity (Fig.…”

“…It may also proceed via the coordination of the alcohol substrate to an active site of the catalyst, and its deprotonation to form the alkoxide ligand, followed by a metal-centred (and TEMPO assisted) dehydrogenation [68,71,72].…”

Room temperature aerobic oxidation of alcohols using CuBr2 with TEMPO and a tetradentate polymer based pyridyl-imine ligand

“…As shown in Table 2, using L1 a moderate yield can be achieved in neat acetonitrile ( Table 2, entry 1). Recently, Repo and co-workers reported the aerobic oxidation of alcohols using copper(II) 2-N-arylpyrrolecarbaldimino complexes under aqueous conditions (no added organic co-solvent), they achieved 100% yield in 2 hours under an O 2 atmosphere and 17% using air [54]. They also found that upon addition of co-solvents yields decreased.…”

“…For example, under similar conditions to entry 2, Table 1 Encouraged by previous reports that some aerobic oxidation copper catalysts can be easily prepared in situ by mixing the copper salt and ligand in the reaction medium [40,53], we chose an in situ approach to yield copper(II) complexes to be used with TEMPO and t-BuOK in our catalytic system. As revealed in Table 1, the yield of benzyl alcohol to benzaldehyde was very low in the absence of ligand ( tetradentate ligands employed also showed excellent activity (entries 4-7).…”

“…2-furylmethanol) under an oxygen atmosphere [38]. Repo et al recently reported a highly efficient catalytic system based on TEMPO/Copper diimine (10 bar oxygen) and 2-Narylpyrrolecarbaldimino (1 atm oxygen) systems for alcohol oxidation [39][40]. In recent studies, Koskinen et al and Stahl et al have described improved bipyridine-Cu-TEMPO catalytic systems for the effective oxidation of alcohols [41][42].…”