Destabilizing Predictive Copper-Catalyzed Click Reactions by Remote Interactions with a Zinc-Porphyrin Backbone

In order to obtain new supramolecular ligands that build up around a zinc-porphyrin scaffold, we envisioned to access sulfonyl triazole intermediates by well-known copper-catalyzed click reactions. Unexpectedly, these triazole intermediates do not form due to the presence of the zinc-porphyrin moiety at close proximity of the active copper species. Indeed, the copper catalyst undergoes a different chemo-selective reaction pathway reacting with traces of alcohols or water from the media that behave as effective nucleophiles leading to sulfonyl imidates or sulfonyl amides covalently connected to the zinc-porphyrin. We show that copper-catalyzed click reactions can follow different reaction mechanisms when the catalytic events occur at close proximity of a zinc-porphyrin unit which likely acts as a Lewis acid to stabilize otherwise inaccessible reaction intermediates.

Automated summary

In order to obtain new supramolecular ligands built around a zinc-porphyrin scaffold, we attempted to access sulfonyl triazole intermediates through copper-catalyzed click reactions. Unexpectedly, the presence of the zinc-porphyrin moiety prevents the formation of these triazole intermediates. Instead, the copper catalyst undergoes a different reaction pathway, reacting with trace amounts of alcohols or water in the media, leading to the formation of sulfonyl imidates or sulfonyl amides covalently connected to the zinc-porphyrin. Our study shows that copper-catalyzed click reactions can follow different mechanisms when occurring in close proximity to a zinc-porphyrin unit, which acts as a Lewis acid to stabilize otherwise inaccessible reaction intermediates.