Enantioselective syntheses of sulfoxides in octahedral ruthenium(II) complexes via a chiral-at-metal strategy.
The preparation of chiral 2-(alkylsulfinyl)phenol compounds by enantioselective coordination-oxidation of the thioether ruthenium complexes with a chiral-at-metal strategy has been developed. The enantiomerically pure sulfoxide complexes Δ-[Ru(bpy)2{(R)-LO-R}](PF6) (bpy is 2,2'-bipyridine, HLO-R is 2-(alkylsulfinyl)phenol, R = Me (Δ-1a), Et (Δ-2a), iPr (Δ-3a), Bn (Δ-4a), and Nap (Δ-5a)) and Λ-[Ru(bpy)2{(S)-LO-R}](PF6) (R = Me (Λ-1a), Et (Λ-2a), iPr (Λ-3a), Bn (Λ-4a), and Nap (Λ-5a)) have been synthesized by the reaction of Δ-[Ru(bpy)2(py)2](2+) or Λ-[Ru(bpy)2(py)2](2+) with the prochiral thioether ligands 2-(alkylthio)phenol (HL-R), followed by enantioselective oxidation with m-CPBA as oxidant. The X-ray crystallography was used to verify the stereochemistry of ruthenium complexes and sulfur atoms. The configurations of the ruthenium complexes are stable during the coordination and oxidation reactions. Moreover, the chiral sulfoxide ligands are enantioselectively generated by controlling of the configuration of ruthenium centers in the course of oxidation reaction. That is, the Λ configuration at the ruthenium center generates the S sulfoxide ligand; on the contrary, the Δ configuration of the ruthenium complex originates the R sulfoxide ligand. Acidolysis of Λ-[Ru(bpy)2{(R)-LO-R}](PF6) and Δ-[Ru(bpy)2{(S)-LO-R}](PF6) complexes in the presence of TFA-MeCN afforded the chiral ligands (R)-HLO-R and (S)-HLO-R in 96-99% ee values, respectively. Importantly, the chiral ruthenium complexes can be recycled as Δ/Λ-[Ru(bpy)2(MeCN)2](PF6)2 and reused in a next reaction cycle with complete retention of the configurations at ruthenium centers.
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University , Guangzhou 510275, China.
Zheng-Zheng
ZZ
Li
A-Hao
AH
Wen
Su-Yang
SY
Yao
Bao-Hui
BH
Ye
D015082:2,2'-Dipyridyl / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism; D013454:Sulfoxides / Q000138:chemical synthesis* / Q000737:chemistry*
D008024:Ligands; D009942:Organometallic Compounds; D013454:Sulfoxides; D015082:2,2'-Dipyridyl; D012428:Ruthenium