Photon-Driven Catalytic Proton Reduction with a Robust Homoleptic Iridium(III) 6-Phenyl-2,2′-bipyridine Complex ([Ir(C/\N/\N)2]+)

Abstract

The improved stability of a photocatalytic proton reduction system is accomplished when a heteroleptic bis-cyclometalated diimine iridium(III) photosensitizer ([Ir(ppy)(2)(bpy)](+), ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine) is replaced with a novel iridium complex, [Ir(phbpy)(2)](+) (phbpy = 6-phenyl-2,2'-bipyridine). The decomposition of [Ir(ppy)(2)(bpy)](+) analogs in photocatalytic systems has been previously shown to result from 2,2'-bipyridine dissociation, which will be hindered by the improved architecture. Although desirable for reasons beyond stability, syntheses of bis-tridentate iridium complexes of 6-phenyl-2,2'-bipyridine are uncommon, with no previous examples having an analogous coordination sphere to the well-studied [Ir(C--N)(2)(N--N)](+) architecture (where C--N = cyclometalating ligand and N--N = neutral diimine ligand). Ligand modification has proven a successful strategy in tuning the photophysical properties of [Ir(C--N)(2)(N--N)](+) complexes and can now be employed for the more robust [Ir(C--N--N)(2)](+) framework (where C--N--N = cyclometalating diimine ligand). Characterization of the novel complex reveals similar electrochemical properties and calculated orbital densities to the parent [Ir(ppy)(2)(bpy)](+) species, while there are notable differences between the absorption and photophysical properties of the two complexes.