Selective low-temperature syntheses of facial and meridional tris-cyclometalated iridium(III) complexes

We have developed a selective low-temperature synthesis of fac and mer tris-cyclometalated Ir(III) complexes. The chloro-bridged dinners [Ir(C boolean AND N)(2)Cl](2) (C boolean AND N = cyclometalating ligand) are cleaved in coordinating solvents like acetonitrile to give neutral Ir(C boolean AND N)(2)(NCCH3)Cl species which in turn are reacted with AgPF6 to give hexafluorophosphate salts of the bis-acetonitrile species [Ir(C boolean AND N)(2)(NCCH3)(2)]PF6 for C boolean AND N = 2,2'-thienylpyridine (thpy) and 2-phenylpyridine (ppy). These bis-acetonitrile complexes are excellent starting materials for the synthesis of tris-Ir(III) complexes. The complexes of the general formula fac-Ir(C boolean AND N)(3) were synthesized with the ligands thpy and ppy at 100 degrees C in o-dichlorobenzene from the corresponding [Ir(C boolean AND N)(2)(NCCH3)(2)]PF6 complexes. The reaction of [Ir(C boolean AND N)(2)(NCCH3)(2)]PF6 with thpy at room temperature did not give the expected tris complex but instead gave [Ir(thpy)(2)(N,S-thpy)]PF6, with the third chelating ligand complexed through the sulfur atom of the thiophene ring. [Ir(thpy)(2)Cl](2), [Ir(ppy)(2)Cl](2), Ir(thpy)(2)(NCCH3)Cl, [Ir(thpy)(2)(NCCH3)(2)]PF6, [Ir(ppy)(2)(NCCH3)(2)]PF6, and [Ir(thpy)(2)(N,S-thpy)]PF6 were structurally characterized by X-ray crystallography. Additionally, hydroxy-bridged dimers, [Ir(C boolean AND N)(2)(OH)](2), were synthesized as starting materials for the selective synthesis of mer-Ir(C boolean AND N)(3) complexes at 100 degrees C in o-dichlorobenzene. A mechanism is proposed that may account for the selectivity observed in the formation of the mer-Ir(C boolean AND N)(3) and fac-Ir(C boolean AND N)(3) isomers in previous studies and the studies presented here.