Reaction mode of catalytic styrene oxidation using a bis-semicarbazide hexaazamacrocyclic Cu complex

Catalytic styrene Ph—CH=CH₂ oxidation is assumed to be a simple reaction procedure; however, its details require further systematic research. Using quantum-chemical treatment, relevant intermediates have been investigated in various charge and spin states of alternative reaction pathways of styrene oxidation by hydroperoxyl using the [CuL]⁻ catalyst, where H2L = trans-2,9-dibutyl-7,14-dimethyl-5,12-di(4-methoxyphenyl)-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-dione. Within reaction pathway A, the neutral hydroperoxyl radical is bonded to Cu to form ²[CuL(OOH)]^–. Subsequent addition of neutral styrene results in the formation of ²{[CuL(OH)](Ph—CH₂—CHO)}^–. Reaction pathway B starts with the initial non-radical formation of the π-complex ¹[CuL(Ph—CH=CH₂)]⁻ which is problematic due to its endothermic character. Subsequent addition of a hydroperoxyl radical leads to ²{CuL[Ph—CH(OOH)—CH₂]}⁻ and its oxidation leads to the separation of Ph—CH(OOH)—CH₂. The exothermic reaction path A is preferred over the endothermic reaction path B.