Optimizing Xanthyliums for Electrocatalytic C-H Activation

<p class="p1">Xanthyliums are promising candidates for C-H bond activation catalysis due to their high hydride ion affinities (HIAs). Further, it has been observed that electrochemical oxidation of xanthenes is irreversible and results in the formation of the parent xanthylium. This makes xanthyliums useable in an electrocatalytic reaction. For this to work, the xanthyliums must have HIAs large enough to abstract hydride from the substrate, and the resulting xanthene must oxidise at a lower potential than the substrates it reacts with. A series of forty-five candidate xanthyliums/xanthenes with various substitutions were proposed, and oxidation potentials and HIAs were calculated. It was shown that oxidation potentials and HIAs can be tuned separately by modifying the xanthene core or 9-phenyl substituent respectively. From this, the most promising xanthenes were synthesised, and oxidation potentials and HIAs measured experimentally to confirm calculations. Experimental data confirmed computation trends leaving 9-(3,5-bis(trifluoromethyl)phenyl)-2,7-dimethoxyxanthylium tetrafluoroborate as the most promising candidate for electrocatalytic C-H activation.