Rational design of adenine appended synthetic cobalt catalysts via click reaction for electrocatalytic hydrogen production

Green hydrogen has emerged as a critical component in the upcoming renewable energy landscape. Enzyme architecture remains the prime inspiration for designing environment-friendly, efficient, and economical H-2 production catalysts from water. The strategic incorporation of peripheral protic functionalities around synthetic metal cores specifically impacts the electrocatalytic H-2 evolution reactivity. Here, we have deployed a click chemistry methodology to incorporate a 1,2,3-triazole linker in either meta vs. para position to connect a cobaloxime core with nucleobase adenine. The variation in specific positioning (meta vs. para) of the linker creates two isomeric ligands and their corresponding cobaloxime derivatives. The trifunctional ligand motif positively influences the reactivity of the cobaloximes, as the para-substituted complex produces H-2 at a rate of 5350 s(-1) with an overpotential <350 mV in near-neutral aqueous conditions. The meta-substituted complex displayed relatively slower catalysis (rate 3700 s(-1)), albeit with similar energy efficiency under analogous conditions. These robust catalysts also demonstrated substantial H-2 production from water under photocatalytic conditions with an appreciable turnover number (TON) of 150 and 100 for the para- and meta-substituted complexes, respectively. The complementary electrochemical and spectroscopic techniques indicate the designed ligand's dual effect (electronic and peripheral) on the catalytic reactivity, where the para-substituted pyridinyl ligand displayed better reactivity than the meta-derivative.