Catalytic Epoxidations with Peroxides: Molybdenum Trioxide Species as the Origin of Allylic Byproducts

Abstract

Molybdenum(VI)peroxide species, formed in the reaction of Mo(VI) complexes with peroxides, are able to epoxidize >C=C< double bonds heterolytically. In this study, theoretical and experimental evidence is provided for a kinetically competing reaction reaction of such molybdenum(VI)peroxide species with additional peroxide reagent, leading to molybdenum(VI)trioxide species, which easily decompose into radicals. Under epoxidation conditions, those radicals will reduce the selectivity, due to the formation of allylic byproducts. The involved reaction pathways are characterized by DFT calculations, providing kinetic parameters that are in good agreement with the experimental observations.

Oxidation of [CpMo(CO)3R] olefin epoxidation precatalysts with tert-butylhydroperoxide

“…This is a similar situation published by Hermans et al [80], but we neglect the occurrence of radical species as no experimental evidence in this direction has been found. In Scheme 11, the DG values resulting from DG calculations of a similar pathway including trioxide groups are presented.…”

Preparation of γ-Fe2O3@C@MoO3 core/shell nanocomposites as magnetically recyclable catalysts for efficient and selective epoxidation of olefins

“…At the same time, the Mo atom eliminates epoxide and strengthens its interaction with a RO-group, yielding a radical cationic molybdenum complex (metal alkoxide) 7, suggested by Ive Hermans and Werner R. Thiel. 45,46 Then, complex 7, which may actually catalytically activate intermediate, (I) probably undergoes a proton transfer process from the neighboring site Mo-OH to the alkoxy group (RO-), accompanied by the regeneration of the initial catalyst with a molecule of alkyl alcohol released; or (II) proceeds to a new efficient catalytic cycle directly. In this cycle, the radical metal alkoxide intermediate 7, as the catalytically active species, is more conducive for activation of the alkyl peroxide thus avoiding the initial activation of the catalyst.…”

Peroxide intermediates of oxidation processes: Organic trioxides

“…It was assumed and confirmed by DFT calculations that trioxide served as the source of free radicals. Considering the theoretical calculations and kinetic and ESR measurements, Scheme 18 was suggested to describe the process 219 .…”