Chiral bis(oxazoline) ruthenium complexes with bipyridyl-type N-heteroaromatics: Comparative stereochemical and photochemical characterization of their ∇- And Δ-diastereomeric geminate isomers

Diastereomeric geminate pairs of chiral bis(2-oxazoline) ruthenium complexes with bipyridyl-type N-heteroaromatics, λ- and Δ-[Ru(L-L)₂(iPr-biox)]²⁺ (iPr-biox=(4S,4′S)-4, 4′-diisopropyl-2,2′-bis(2-oxazoline); L-L=2,2′-bipyridyl (bpy) for 1 λ and 1 Δ, 4,4′-dimethyl-2,2′-bipyridyl (dmbpy) for 2 λ and 2 Δ, and 1,10-phenanthroline (phen) for 3 λ and 3 Δ), were separated as BF₄ and PF₆ salts and were subjected to the comparative studies of their stereochemical and photochemical characterization. DFT calculations of 1 λ and 1 Δ electronic configurations for the lowest triplet excited state revealed that their MO-149 (HOMO) and MO-150 (lower SOMO) characters are interchanged between them and that the phosphorescence-emissive states are an admixture of a Ru-to-biox charge-transfer state and an intraligand excited state within the iPr-biox. Furthermore, photoluminescence properties of the two λ,Δ- diastereomeric series are discussed with reference to [Ru(bpy)₃] ²⁺.