Promoting N−N Bond Formation of Ammonia Oxidation by a Dangling Carboxylate Proton Relay

Inspired by enzymatic proton-coupled electron transfer (PCET) control, introducing proton relays into catalysts' second coordination sphere accelerates proton-transfer reactions, yet this strategy remains underexplored for N–H bond cleavage in ammonia oxidation reaction (AOR). Here, we report ammonia oxidation catalyzed by [Ru(pdc-κ-N 1 O 1 )(tpy)(NH 3 )] ( Ru(pdc-t)(NH 3 ) ; H 2 pdc = 2, 6-pyridinedicarboxylic acid; tpy = terpyridine), featuring a pendant carboxylate group, and its structural analog [Ru(pic)(tpy)(NH 3 )](PF 6 ) ( Ru(pic-t)(NH 3 ) ; Hpic = picolinic acid). Such a structural design creates a dangling carboxylate group as a proton relay, assisting the proton transfer during N− bond formation. Ru(pdc-t)(NH 3 ) exhibits superior AOR performance relative to Ru(pic-t)(NH 3 ) and previously reported [Ru(pdc-κ-N 1 O 2 )(bpy)(NH 3 )] ( Ru(pdc-b)(NH 3 ); bpy = bipyridine), with a catalytic rate of 209.7±12.2 s −1 (11.1-fold increase) and a turnover number (TON) of 319 for N 2 (4.2-fold increase). The calculated barrier for N−N bond formation for Ru(pdc-t)(NH 3 ) is +0.8 kcal/mol, which is significantly lower than the +7.8 kcal/mol barrier for Ru(pic-t)(NH 3 ) . This work demonstrates the promotional effect of a proton relay on the catalytic oxidation of ammonia to N 2 .