Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C¹^C^C¹) or 1,3-bis(3-butylbenzimidazolin-2-ylidene) phenyl anion (C²^C^C²) and aromatic diimine (2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4'-dimethyl-2,2'-bipyridine (Me₂bpy), or dipyrido-[3,2-f:2',3'-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]⁺ have been prepared. Crystal structures for these complexes show that the Ir-C_NHC distances are 2.043(5)-2.056(5) Å. The hydride chemical shifts for complexes bearing C¹^C^C¹ (-20.6 to-20.3 ppm) are more upfield than those with C²^C^C² (-19.5 and-19.2 ppm), revealing that C¹^C^C¹ is a better electron donor than C²^C^C². Spectroscopic comparisons and timedependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340-530 nm (∈ ≤ 10³ dm³ mol^-1 cm^-1)) originate from a dπ(Ir^III) → π∗(N^N) metal-to-ligand charge transfer transition, where the dp(Ir^III) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellowspectral region (553-604 nm in CH₃CN and CH₂Cl₂) upon photo-excitation with quantum yields of 10^-3-10^-1.