Alkylperoxide species

Mimoun and coworkers142 described the first well-defined example of a d° metal alkylperoxidic species 49 which epoxidized simple olefins with high selectivity. Several features of the epoxidation performed by 49 resemble those of the Halcon catalytic epoxidation process240. Novel tungsten complexes containing 2 -pyridyl alcoholate ligands like 50 have been synthesized and tested as catalysts in the epoxidation of cA-cyclooctene with TBHP in the absence of solvent246. The system displayed modest catalytic activity (100% conversion in 60 h) but excellent product selectivity. 

Mimoun proposed a mechanism that is general for both stoichiometric epoxidations with peroxo complexes and for catalytic systems employing alkyl hydroperoxides.292-294 It involves an alkylperoxidic species with the alkene complexed through the metal ... 

In competition with 02-addition [reaction (25)], the (3-alkylperoxide species may undergo radical-induced cleavage of the peroxide function [reaction (26) Bloodworth et al. 1984 Phulkar et al. 1990]. 

This method of preparation was originally reported by Mimoun and coworkers.74 The intermediate hydroperoxy complex is rarely isolated, especially in the presence of hydrogen peroxide, however if an alkylperoxide is employed, then the ring closure reaction does not take place and alkylperoxo species are formed.75 The triangular metal oxirane species formed is of immense importance for the purpose of oxygen transfer to organic substrates. 

Mimoun has given an alternative possibility, suggesting the formation of peroxo metallacyclic adducts following complexafion of the olefin to the metal [171,475]. The reaction sequence (Fig. 1.13) involves a reactive species denoted as Ln-Mo, a Mo(VI) ion with a set of alkoxy ligands. The reaction starts by formation of an alkylperoxo Mo complex by ligand exchange of an alkylperoxide with an alcohol. This is followed by complexafion of the olefin by a coordination bond. A subsequent peroxy metallation of the olefin produces a five-membered... 

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