Method for the Preparation of Nonracemic Bis-Cyclometalated Iridium(III) Complexes



A practical strategy for the generation of virtually enantiomerically pure bis-cyclometalated iridium(III) complexes is reported. Accordingly, the reactions of [Ir(μ-Cl)(ppy)2]2 (ppy = cyclometalating 2-phenylpyridine) with (S)-4-tert-butyl-2-(2′-hydroxyphenyl)-2-oxazoline [(S)-1a], [Ir(μ-Cl)(pq)2]2 (pq = cyclometalating 2-phenylquinoline) with (S)-2-(2′-hydroxyphenyl)-4-isopropyl-2-oxazoline [(S)-1b], and [Ir(μ-Cl)(pbt)2]2 (pbt = cyclometalating 2-phenylbenzothiazole) with (S)-2-(2′-hydroxyphenyl)-4-isopropyl-2-thiazoline [(S)-1d] afforded diastereomeric mixtures of salicyloxazolinato or salicylthiazolinato complexes Λ/Δ-[Ir(ppy)2{(S)-1a–H}]PF6, Λ/Δ-[Ir(pq)2{(S)-1b–H}]PF6, and Λ/Δ-[Ir(pbt)2{(S)-1d–H}]PF6, respectively, which could be resolved by silica gel flash chromatography. With the individual diastereomers in hand, an acid-induced substitution of the chiral auxiliaries by achiral bidentate ligands with retention of configuration afforded several iridium complexes Λ- or Δ-[Ir(CN)2(NN)]PF6 (CN = cyclometalating ppy, pq, or pbt; NN = 2,2′-bipyridine, 1,10-phenanthroline, or 2,2′-biquinoline) with enantiomeric ratio (er) values of 24:1 to 230:1.