Proline and α-Methylproline as Chiral Auxiliaries for the Synthesis of Enantiopure Bis-Cyclometalated Iridium(III) Complexes
Melanie Helms, Chuanyong Wang, Barbara Orth, Klaus Harms, Eric Meggers
European Journal of Inorganic Chemistry
A convenient proline- and α-methylproline-mediated method for the synthesis of enantiomerically pure bis-cyclometalated iridium(III) complexes is reported. The reactions of l-proline or l-α-methylproline with [Ir(µ-Cl)(C^N)2]2 (C^N = cyclometalating 2-phenylpyridine, 2-phenylbenzoxazole, or 2-phenylbenzothiazole ligand) afforded diastereomeric mixtures of intermediate prolinatoiridium(III) complexes from which the Λ-(S) diastereomers were isolated with excellent diastereomeric purity by washing, precipitation, or crystallization. A subsequent trifluoroacetic acid (TFA) induced substitution of the prolinate ligands with 2,2′-bipyridine with the retention of configuration provided the chiral-only-at-metal complexes with >99 % ee.
Circular dichroism, Stereochemistry, Inorganic chemistry,