Control of the Mutual Arrangement of Cyclometalated Ligands in Cationic Iridium(III) Complexes. Synthesis, Spectroscopy, and Electroluminescence of the Different Isomers

Synthetic control of the mutual arrangement of the cyclometalated ligands (C boolean AND N) in Ir(III) dimers, [Ir(C boolean AND N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C boolean AND N)(2)-(L boolean AND L)](+) (L boolean AND L = neutral ligand), is described for the first time. Using I-benzy1-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 degrees C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C boolean AND N ligands is isolated. In contrast, at higher temperature (140 degrees C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C boolean AND N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvent complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C boolean AND N arrangement of the parent dimers. Controlling the C boolean AND N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir-(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C boolean AND N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C boolean AND N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C boolean AND N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.