Thermally Induced Defluorination during a mer to fac Transformation of a Blue-Green Phosphorescent Cyclometalated Iridium(III) Complex

The new homoleptic tris-cyclometalated [Ir((CN)-N-boolean AND)(3)] complexes mer-8, fac-8, and fac-9 incorporating gamma-carboline ligands are reported. Reaction of 3-(2,4-difluorophenyl)-5-(2-ethylhexyl)-pyrido[4,3-b]indole 6 with iridium(III) chloride under standard cyclometalating conditions gave the homoleptic complex mer-8 in 63% yield. The X-ray crystal structure of mer-8 is described. The Ir-C and Ir-N bonds show the expected bond length alternations for the differing trans influence of phenyl and pyridyl ligands. mer-8 quantitatively isomerized to fac-8 upon irradiation with UV light. However, heating mer-8 at 290 degrees C in glycerol led to an unusual regioselective loss of one fluorine atom from each of the ligands, yielding fac-9 in 58% yield. fac-8 is thermally very stable: no decomposition was observed when fac-8 was heated in glycerol at 290 degrees C for 48 h. The gamma-carboline system of fac-8 enhances thermal stability compared to the pyridyl analogue fac-Ir(46dfppy)(3) 10, which decomposes extensively upon being heated in glycerol at 290 degrees C for 2 h. Complexes mer-8, fac-8, and fac-9 are emitters of blue-green light (lambda(em)(max) = 477, 476, and 494 nm, respectively). The triplet lifetimes for fac-8 and fac-9 are similar to 4.5 Its at room temperature; solution On values are 0.31 and 0.22, respectively.