Iridium Water Oxidation Catalysts Based on Pyridine‐Carbene Alkyl‐Substituted Ligands

Iridium complexes bearing pyridine triazolylidene ligands with variable steric hindrance, derived by the presence of an R group (R=H, Me, Et, nPr, iPr, Bu, and Oct) onto the N1-nitrogen, have been synthesized, fully characterized and tested as water oxidation catalysts (WOCs), using chemical sacrificial oxidants (CAN and NaIO4) or in photocatalytic experiments ([Ru(bpy)(3)]Cl-2 as phosensitizer and Na2S2O8 as an electron acceptor). The catalytic activity is barely affected by the nature of R when WO is driven by NaIO4 (1min(-1)= Et, hampers transfer of the hydroperoxo or peroxo moiety from iridium active species to cerium, a process that could slow down kinetics of O-2 evolution.