Convenient Synthesis and Characterization of the Chiral Complexes cis- and trans-[Ru((SS)-Pr(i)pybox)(py)(2)Cl]PF(6) and [Ru((SS)-Pr(i)pybox)(bpy)Cl]PF(6).

Abstract

The chiral oxazoline complexes cis- and trans-[Ru((SS)-Pr(i)pybox)(py)(2)Cl]PF(6) were prepared from the common precursor trans-[Ru((SS)-Pr(i)pybox)(py)Cl(2)], and all three complexes were spectroscopically and structurally characterized. The complex cis-[Ru((SS)-Pr(i)pybox)(py)(2)Cl]PF(6) crystallized in P2(1)2(1)2(1) with Z = 4, a = 8.396(2) Å, b = 18.396(3) Å, c = 20.954(3) Å, and R = 0.039 for 4131 reflections. The complex trans-[Ru((SS)-Pr(i)pybox)(py)(2)Cl]PF(6) crystallized in P2(1) with Z = 2, a = 10.110(2) Å, b = 13.566(2) Å, c = 12.043(2) Å, beta = 106.10(2) degrees, and R = 0.039 for 3869 reflections. The precursor trans-[Ru((SS)-Pr(i)pybox)(py)Cl(2)] crystallized in P2(1)2(1)2(1) with Z = 8, a = 15.856(2) Å, b = 17.216(1) Å, c = 17.768(1) Å, and R = 0.030 for 5826 reflections. A related reagent, [Ru((SS)-Pr(i)pybox)(bpy)Cl]PF(6), was prepared by a more direct route and was also characterized. Aqua complexes were formed by hydrolysis of the chloride ligand in the bis(pyridine) complexes with retention of the stereochemistry. Electrochemical oxidation of the aqua complexes yielded oxo species which are formally ruthenium(IV). Reactions of the oxo complexes with the prochiral reductant, methyl p-tolyl sulfide led to stereoselective formation of the sulfoxide with enantiomeric excess of the R isomer ranging from 7% to 13%.