Pronounced retention of stereoconfiguration upon sp3 C[sbnd]H bonds hydroxylation of dimethylcyclohexanes and decahydronaphthalenes with m-CPBA oxidant and a Co-phthalocyanine catalyst

Abstract

A series of phthalocyanine (Pc) complexes of general formula [M(Pc)] (M = Mg, V, Mn, Fe, Co, Ni, Cu, Zn) was tested as catalysts for functionalization of sp3 CH bonds, namely in the mild stereoselective oxidation of cyclic alkanes (isomers of dimethylcyclohexane and decahydronaphthalene) using peroxides as oxidants. A high catalytic activity (yield of products up to 75% based on the oxidant) and outstanding retention of stereoconfiguration of substrates (>95% for isomers of dimethylcyclohexane) was disclosed for the cobalt phthalocyanine catalyst [Co(Pc)] using m-chloroperbenzoic acid (m-CPBA) as oxidant and nitric acid as promoter. The phthalocyanine complexes other than Co are much less active with yields of products <10% and low stereo- and bond selectivities. The main reaction mechanism is proposed not to involve high-valent metal species, as evidenced by 18O-labeling and selectivity studies. The [Co(Pc)]/HNO3/m-CPBA system also catalyses chlorination and bromination of cyclohexane with HCl and N-bromosuccinimide as halogen sources.