Asymmetric Synthesis of Enantiomerically Pure Mono- and Binuclear Bis(cyclometalated) Iridium(III) Complexes

Chiral precursors
Λ-[Ir­(ppy)2­(l-pro)] (Λ-L, where ppy is 2-phenylpyridine; pro is proline), Λ-[Ir­(ppy)2­(MeCN)2]­(PF6) (Λ-1), Δ-[Ir­(ppy)2(d-pro)] (Δ-D), and Δ-[Ir­(ppy)2­(MeCN)2]­(PF6) (Δ-1) were synthesized
from rac-[(Ir­(ppy)2)2Cl2] and l-pro or d-pro by means of the auxiliary
ligand strategy with 99% de values. The enantiopure mono complexes
Λ/Δ-[Ir­(ppy)2­(L)]­(PF6) (L
is 2,2′-bipyridine, Λ/Δ-2; L is 2,2′-dipyrimidine
(dpm), Λ/Δ-3; L is 2,2′-bibenzimidazole
(H2bbim), Λ/Δ-4) with 99% ee values
and binuclear complexes ΛΛ/ΔΔ-[(Ir­(ppy)2)2­(dpm)]­(PF6)2 (ΛΛ-5 and ΔΔ-5) and ΛΛ/ΔΔ-[(Ir­(ppy)2)2­(bbim)] (ΛΛ-6 and
ΔΔ-6) with 99% de values were synthesized
in one step using the corresponding chiral precursors. The absolute
configurations at Ir­(III) centers of precursor Δ-1, mononuclear Λ-3, and binuclear ΔΔ-6 were confirmed by single-crystal structural analysis and
characterized by circular dichroism (CD) spectroscopy. The correlation
between the absolute configuration at Ir­(III) center and CD spectra
was established. The configurations at Ir­(III) centers are stable
during the reactions, and the chiral precursors can be used for the
asymmetric synthesis of enantiomerically pure mono- and polynuclear
Ir­(III) complexes. Moreover, meso ΛΔ-[(Ir­(ppy)2)2­(dpm)]­(PF6)2 (meso-5) and ΛΔ-[(Ir­(ppy)2)2­(bbim)] (meso-6)
were also synthesized using these precursors.