Mechanistic Insights into the ortho-Defluorination-Hydroxylation of 2-Halophenolates Promoted by a Bis(μ-oxo)dicopper(III) Complex.

Abstract

C-F bonds are one of the most inert functionalities. Nevertheless, some [Cu2O2]2+ species are able to defluorinate-hydroxylate ortho-fluorophenolates in a chemoselective manner over other ortho-halophenolates. Albeit it is known that such reactivity is promoted by an electrophilic attack of a [Cu2O2]2+ core over the arene ring, the crucial details of the mechanism that explain the chemo- and regioselectivity of the reaction remain unknown, and it has not being determined either if CuII2(η2:η2-O2) or CuIII2(μ-O)2 species are responsible for the initial attack on the arene. Herein, we present a combined theoretical and experimental mechanistic study to unravel the origin of the chemoselectivity of the ortho-defluorination-hydroxylation of 2-halophenolates by the [Cu2(O)2(DBED)2]2+ complex (DBED = N,N'-di-tert-butylethylenediamine). Our results show that the equilibria between (side-on)peroxo (P) and bis(μ-oxo) (O) isomers plays a key role in the mechanism, with the latter being the reactive species. Furthermore, on the basis of quantum-mechanical calculations, we were able to rationalize the chemoselective preference of the [Cu2(O)2(DBED)2]2+ catalyst for the C-F activation over C-Cl and C-H activations.