The design of chiral ligands is the key to attaining high asymmetric induction in transition-metal-catalyzed reactions. Subtle changes in the conformational, steric, and/or electronic properties of the chiral ligand can often lead to dramatic variation of the reactivity and enantioselectivity. As a result of strong substrate dependence in most cases, tunable and readily synthesized ligands are desirable to obtain high enantioselectivities.Nowadays, asymmetric copper-catalyzed conjugate addition and allylic substitution are well-developed methodologies for creating CÀC bonds. Many efforts have been made in designing efficient systems and identifying new ligands to improve enantioselectivities.

A study of the secondary interactions involving a pendant phenethyl group (NCH(CH 3 )Ph) of (S a ,R C ,R C )-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenylethyl]phosphoramidite (1) in d 8 and d 6 metal complexes is reported. A 1,2-η-phenyl interaction is found in [Pd(η 3 -allyl)(1,2-η-Ph-1-κP)] + (3), as indicated by NMR spectroscopy and by an X-ray study. The Rh(I) complexes [RhCl(NBD)(1-κP)] (4a) and [RhCl(COD)(1-κP)] (4b) were prepared, and their X-ray structures were determined. Chloride abstraction from 4a and 4b gave the corresponding cations [Rh(NBD)(1,2-η-Ph-1-κP)] + (5a) and [Rh(COD)(1,2η-Ph-1-κP)] + (5b), which were fully characterized. Besides NMR spectroscopic data, the 1,2-η-phenyl interaction is supported by an X-ray study of 5a. Upon standing in MeOH solution, 5b undergoes loss of the COD and forms [Rh(1-κP)(η 6 -Ph-1-κP)] + (6), whose η 6 -arene coordination was studied by NMR spectroscopy and by X-ray diffraction. For the sake of comparison with the d 8 complex 6, the crystal structure of the previously reported d 6 analogue [RuCl 2 (η 6 -Ph-1-κP)] + (7) was determined. This study shows that secondary π-arene-metal interactions turn phosphoramidite 1 to a four-, six-, or eight-electron donor, with increasing bond strength in this order.

The design of chiral ligands is the key to attaining high asymmetric induction in transition-metal-catalyzed reactions. Subtle changes in the conformational, steric, and/or electronic properties of the chiral ligand can often lead to dramatic variation of the reactivity and enantioselectivity. As a result of strong substrate dependence in most cases, tunable and readily synthesized ligands are desirable to obtain high enantioselectivities.Nowadays, asymmetric copper-catalyzed conjugate addition and allylic substitution are well-developed methodologies for creating CÀC bonds. Many efforts have been made in designing efficient systems and identifying new ligands to improve enantioselectivities.

No 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.