Phosphorescent Cationic Heterodinuclear IrIII/MI Complexes (M=CuI, AuI) with a Hybrid Janus‐Type N‐Heterocyclic Carbene Bridge

• Published in: Chemistry : a European journal 2020-09, Vol.26 (51), p.11751-11766
• Main Authors: Bonfiglio, Anna, Pallova, Lenka, César, Vincent, Gourlaouen, Christophe, Bellemin‐Laponnaz, Stéphane, Daniel, Chantal, Polo, Federico, Mauro, Matteo
• Format: Article
• Language: English
• Subjects: Bimetals; Cations; Charge transfer; Chelation; Chemistry; Computer applications; Congeners; cyclometalating ligands; density functional calculations; Electrochemistry; Emission analysis; Energy gap; hybrid ligand; iridium; Ligands; N-heterocyclic carbenes; Phosphorescence; Rate constants; Spin-orbit interactions
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202002767

A novel class of phosphorescent cationic heterobimetallic IrIII/MI complexes, where MI=CuI (4) and AuI (5), is reported. The two metal centers are connected by the hybrid bridging 1,3‐dimesityl‐5‐acetylimidazol‐2‐ylidene‐4‐olate (IMesAcac) ligand that combines both a chelating acetylacetonato‐like and a monodentate N‐heterocyclic carbene site coordinated onto an IrIII and a MI center, respectively. Complexes 4 and 5 have been prepared straightforwardly by a stepwise site‐selective metalation with the zwitterionic [(IPr)MI(IMesAcac)] metalloproligand (IPr=1,3‐(2,6‐diisopropylphenyl)‐2H‐imidazol‐2‐ylidene) and they have been fully characterized by spectroscopic, electrochemical, and computational investigation. Complexes 4 and 5 display intense red emission arising from a low‐energy excited state that is located onto the “Ir(C^N)” moiety featuring an admixed triplet ligand‐centered/metal‐to‐ligand charge transfer (3IL/1MLCT) character. Comparison with the benchmark mononuclear complexes reveals negligible electronic coupling between the two distal metal centers at the electronic ground state. The bimetallic systems display enhanced photophysical properties in comparison with the parental congeners. Noteworthy, similar non‐radiative rate constants have been determined along with a two‐fold increase of radiative rate, yielding brightly red‐emitting cyclometalating IrIII complexes. This finding is ascribed to the increased MLCT character of the emitting state in complexes 4 and 5 due to the smaller energy gap between the 3IL and 1MLCT manifolds, which mix via spin–orbit coupling. Complex battle: A novel class of phosphorescent cationic heterobimetallic IrIII–CuI and IrIII–AuI complexes featuring a hybrid ambidentate N‐heterocyclic carbene bridge is reported. In comparison with their mononuclear counterparts, the bimetallic species displayed enhanced photophysical properties that have been thoroughly elucidated also by means of electrochemical and computational investigations.