Haloperoxidase Activity of Oxovanadium(V) Thiobisphenolates

Abstract

By employing the 2,2'-thiobis(2,4-di-tert-butylphenolate) ligand ((S)L(2-)) a novel oxovanadium(V) complex, (PPh(4))(2)[(S)LV(O)(μ(2)-O)(2)V(O)(S)L] (1), was synthesised that exhibits haloperoxidase activity: on addition of H(2)O(2) a sequence of successive peroxide formation and intramolecular thioether oxidation events (sulfoxide and sulfone) led to a mixture of five products, which were all identified unambiguously, partly through an independent synthesis and characterisation. It was shown that internal thioether oxidation proceeds through peroxide formation, but the sulfoxidation of external thioether functions requires further activation of the peroxide function by protons or alkyl cations. Consistently, the employment of tBuOOH instead of H(2)O(2) led to a very active system for the catalytic sulfoxidation of thioethers.

Surface‐Inspired Molecular Vanadium Oxide Catalysts for the Oxidative Dehydrogenation of Alcohols: Evidence for Metal Cooperation and Peroxide Intermediates

“…Dissolved in MeCN, peroxide VII, for instance, only has a half-life of 12 h at room temperature and merely 5 min at 80 8C. [9] With this background our results support the peroxide route for reoxidation.…”

“…As in the case of 1, treatment of 2 with O 2 leads to a colour change from green to violet, and a 51 V NMR spectrum recorded directly afterwards indicated the presence of equimolar amounts of starting compound VI M and known peroxide VII M . [9] Independent reactivity studies with peroxide VII M itself showed that it does not oxidise intermediate 2, but it is capable of oxidising the alcohol, although this reaction proceeds more slowly than oxidation of the alcohol by VI. Hence, this is the route through which the peroxide, formed in the course of reoxidation of the reduced catalyst, re-enters the catalytic cycle after the thio-A C H T U N G T R E N N U N G ether group has been fully oxidised: it oxidises a further alcohol equivalent.…”

“…The latter belonged to peroxide III (Scheme 3 b), which was identified previously as a product of the reaction between II and H 2 O 2 . [9] On storing of the sample at room temperature the peroxide signal decreased in intensity in favour of a new one at d = À512 ppm, characteristic of the monomer of singly S-oxidised compound IV M (Scheme 3 a), generated from III in the course of an intramolecular transfer of a peroxidic oxygen atom to the thioether linker. Like II M , also IV M enters into an equilibrium with a dimeric form, IV D , [9] and it is reasonable to assume that IV D will oxidise a further alcohol equivalent; reoxidation can then be anticipated to lead to IV M and V. Finally, the peroxide group of V will transfer another oxygen atom to the sulfoxide group to yield VI M , which was identified previously as the final product of H 2 O 2 oxidation of II [9] and here represents the monomer of the ultimate catalyst.…”

“…[9] We now report its properties as an ODH catalyst and detailed insight into its function, which at the same time improve and extend the mechanistic view on systems such as Ia.…”

“…Are they beneficial in terms of precoordination of alcohols via H-bonds? We addressed this and other questions by preparing a derivative without these groups: by employing the 2,2'-thiobis(2,4-di-tert-butylphenolate) ligand S L 2À (Scheme 2 a), which can be regarded as the relevant section of the thiacalixarene framework needed for construction of Ia, we managed to prepare analogous complex II (Scheme 2b), [9] which, however, was found to be mainly monomeric in solution.…”