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 dimers [Ir(C∧N)2Cl]2 (C∧N = cyclometalating ligand) are cleaved in coordinating solvents like acetonitrile
to give neutral Ir(C∧N)2(NCCH3)Cl species which in turn are reacted with AgPF6 to give hexafluorophosphate salts
of the bis-acetonitrile species [Ir(C∧N)2(NCCH3)2]PF6 for C∧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∧N)3 were synthesized with the ligands thpy and ppy at 100 °C in
o-dichlorobenzene from the corresponding [Ir(C∧N)2(NCCH3)2]PF6 complexes. The reaction of [Ir(C∧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)2Cl]2, [Ir(ppy)2Cl]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∧N)2(OH)]2, were synthesized as
starting materials for the selective synthesis of mer-Ir(C∧N)3 complexes at 100 °C in o-dichlorobenzene. A mechanism
is proposed that may account for the selectivity observed in the formation of the mer-Ir(C∧N)3 and fac-Ir(C∧N)3
isomers in previous studies and the studies presented here.