C(sp3)-F Adsorption Implicated for Reductive Activation at Ag Electrodes.

Abstract

The reductive activation of C-(sp³)-F bonds enables the derivatization of fluorinated motifs with medicinal value as well as the recycling of fluorochemicals. The electrochemical reductive activation of C-(sp³)-Cl, C-(sp³)-Br, and C-(sp³)-I bonds at Ag electrodes is well-documented and commonly attributed to inner-sphere, surface-mediated pathways. In contrast, experimental support for surface-mediated reductive C-(sp³)-F activation at Ag electrodes remains limited. Here, we report evidence for the adsorption of organic fluorides at polarized Ag electrodes. We compare spectroscopic and voltammetric data of nitrile-tagged benzylic bromide, chloride, and fluoride substrate with their non-halogenated congener. Surface-sensitive and in situ spectroscopic data are consistent with their adsorption on polarized Ag surfaces, including the organic fluoride, prior to Faradaic charge transfer. Voltammetric data demonstrate enhanced reductive activation of organic halides at Ag, including the organic fluoride, compared to glassy carbon. Exposing organic fluoride adsorption at electrified surfaces motivates electrode designs that can exploit surface interactions for the development of electroorganic methods beyond outer-sphere modalities.