Selective functionalization of C(sp 3 )-H bonds: catalytic chlorination and bromination by Iron III -acacen-halide under ambient condition.

The oxidative catalytic halogenations of the C(sp 3 )-H bond of alkanes promoted by Fe III (acacen)Cl (1III-Cl) and Fe III (acacen)Br (1III-Br) in the presence of trifluoroacetic acid (TFA) were investigated. Four major steps were involved: (i) formation of [Fe V (acacen)(oxo)X] species (X = Cl or Br), (ii) hydrogen-atom transfer, (iii) halogen atom rebound, and (iv) regeneration of 1III-Cl or 1III-Br. TFA played a significant role in (i) forming the high-valent iron-oxo intermediate and (ii) generating the reaction selectivity.