Vanadium and molybdenum peroxides: synthesis and catalytic activity in oxidation reactions

Abstract

Catalysis by transition metal ions in oxidation reactions with hydrogen peroxide and alkyl hydroperoxides is a leading topic in the pursuit of more sustainable and selective processes, to obtain compounds with high added value. The most recent achievements concerning the synthesis and characterization, as well as the key aspects of reactivity, of V(V) and Mo(VI) peroxo complexes have been collected here.

Salophen and salen oxo vanadium complexes as catalysts of sulfides oxidation with H2O2: Mechanistic insights

“…The IR spectrum of the yellow precipitate showed no signals in the range of 918-954 cm −1 were the O O stretching is usually present for side-on monoperoxo vanadium complexes [12], thus supporting the hypothesis that salen and salophen oxovanadium complexes form an end-on hydroperoxidic species in the presence of H 2 O 2 (see Section 3 below).…”

“…An alternative pathway (not represented in Scheme 4), where water elimination from the LV V (OH)(OOH) + leads to the formation of a LV V (OO) + species was found to be endothermic by 5.4 kcal mol −1 in the case of L = salen, confirming that vanadium complexes without oxo or hydroxo moieties are not stable [12]: Therefore, calculations suggest that a vanadium oxohydroperoxo species, LV V (O)(OOH), is the most plausible intermediate formed upon H 2 O 2 addition to vanadium Salen and Salophen complexes, followed by one proton removal. A Scheme 3.…”

“…Typical electrophilic processes are the oxidation of sulfides and tertiary amines and the epoxidation of allylic alcohol or simple alkenes [11][12][13]. The oxidation of alcohols and the hydroxylation of aliphatic and aromatic hydrocarbons are examples of homolytic reactivity [5,12,14].…”

Mechanistic aspects of vanadium catalysed oxidations with peroxides

“…Recent book chapters [9,[19][20][21] and reviews [8,22,23] have been dedicated to this topic. Furthermore, this general behaviour applies also to vanadium catalysis [21,24]…”

“…The most active d 0 metal peroxo complexes toward nucleophilic substrates, like amines, phosphines, thioethers, double bonds, etc., are molybdenum, tungsten and rhenium derivatives [19,21,25,26]; vanadium [23,24,75] and titanium [33,34] catalysis is also important in particular for enantioselective processes. Numerous studies have been carried out in the last decades, with all the d 0 metals involved in this type of catalysis, to clarify the mechanism of the oxygen transfer step and also to understand the transfer of chirality in enantioselective processes.…”