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Keywords:

  • Half-sandwich complexes;
  • Ruthenium complexes;
  • η2-Aryl coordination;
  • Phosphoramidite ligands, chiral;
  • Cyclopropanation

Abstract

Chloride abstraction from the half-sandwich complexes [RuCl2(η6-p-cymene)(P*-κP)] (2a: P* = (Sa,R,R)-1a = (1Sa)-[1,1′-binaphthalene]-2,2′-diyl bis[(1R)-1-phenylethyl)]phosphoramidite; 2b: P* = (Sa,R,R)-1b = (1Sa)-[1,1′-binaphthalene]-2,2′-diyl bis[(1R)-(1-(1-naphthalen-1-yl)ethyl]phosphoramidite) with (Et3O)[PF6] or Tl[PF6] gives the cationic, 18-electron complexes dichloro(η6-p-cymene){(1Sa)-[1,1′-binaphthalene]-2,2′-diyl {(1R)-1-[(1,2-η)-phenyl]ethyl}[(1R)-1-phenylethyl]phosphoramidite-κP}ruthenium(II) hexafluorophosphate (3a) and [Ru(S)]-dichloro(η6-p-cymene){(1Sa)-[1,1′-binaphthalene]-2,2′-diyl {(1R)-1-[(1,2-η)-naphthalen-1-yl]ethyl}[(1R)-1-(naphthalen-1-yl)ethyl]phosphoramidite-κP)ruthenium(II) hexafluorophosphate (3b), which feature the η2-coordination of one aryl substituent of the phosphoramidite ligand, as indicated by 1H-, 13C-, and 31P-NMR spectroscopy and confirmed by an X-ray study of 3b. Additionally, the dissociation of p-cymene from 2a and 3a gives dichloro{(1Sa)-[1,1′-binaphthalene]-2,2′-diyl [(1R)-(1-(η6-phenyl)ethyl][(1R)-1-phenylethyl]phosphoramidite-κP)ruthenium(II) (4a) and di-μ-chlorobis{(1Sa)-[1,1′-binaphthalene]-2,2′-diyl [(1R)-1-(η6-phenyl)ethyl][(1R)-1-phenylethyl]phosphoramidite-κP}diruthenium(II) bis(hexafluorophosphate) (5a), respectively, in which one phenyl group of the N-substituents is η6-coordinated to the Ru-center. Complexes 3a and 3b catalyze the asymmetric cyclopropanation of α-methylstyrene with ethyl diazoacetate with up to 86 and 87% ee for the cis- and the trans-isomers, respectively.