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

摘要

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}]PF_6, Λ/Δ- [Ir(pq)_2{(S)-1b-H}]PF_6, and Λ/Δ-[Ir(pbt)_2{(S)-1d-H}]PF_6, 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(C~∧N)_2(N~∧N)]PF_6 (C~∧N = cyclometalating ppy, pq, or pbt; N~∧N = 2,2'-bipyridine, 1,10-phenanthroline, or 2,2'-biquinoline) with enantiomeric ratio (er) values of 24:1 to 230:1.