Stepwise Access of Emissive Ir(III) Complexes Bearing a Multi-Dentate Heteroaromatic Chelate: Fundamentals and Applications

Three multi-dentate coordinated chelates LnH2 (n = 1, 2, and 3), comprising a linked 1-(pyridin-2-yl)ethylbenzene and one pyrazolyl pyridine unit and showing either tridentate or tetradentate coordination modes, are successfully designed and synthesized. Dinuclear Ir(III) complexes [Ir(κ4-Ln)(μ-Cl)]2 bearing tetradentate coordinated κ4-Ln chelate (2a, n = 1; 2b, n = 2; 2c, n = 3) were next obtained en route from the respective intermediate [Ir(κ3-LnH)Cl(μ-Cl)]2 bearing the tridentate coordinated κ3-LnH chelate (1a, n = 1; 1b, n = 2; 1c, n = 3). Next, mononuclear Ir(III) complexes Ir(κ4-Ln)(thd) (3a, n = 1; 3b, n = 2; 3c, n = 3) with the tetradentate chelate were obtained upon treatment of 2 with 2,2,6,6-tetramethyl-3,5-heptanedione (thd)H in the presence of K2CO3. Concurrently, methylation of 2c in the presence of MeI and nBu4NCl afforded tridentate Ir(κ3-L3HMe)Cl3 (4) and, next, can be converted to tetradentate Ir(κ4-L3Me)Cl2 (5) by further cyclometalation and HCl elimination in refluxing diethylene glycol monoethyl ether solution. The Ir(III) complexes 3a, 4, and 5 were unambiguously identified using spectroscopic methods, together with single-crystal X-ray structural analyses on Ir(III) derivatives 3a, 4, and 5. Their photophysical and,electrochemical properties and device fabrication properties were also investigated and compared with results from theoretical studies.