Chloro(<i>η</i>⁶‐<i>p</i>‐cymene)(phosphoramidite)ruthenium(II), a 16‐Electron Fragment Stabilized by an <i>η</i>²‐Aryl–Metal Interaction, and Its Use in Asymmetric Cyclopropanation

Abstract

Abstract Chloride abstraction from the half‐sandwich complexes [RuCl 2 ( η 6 ‐ p ‐cymene)(P*‐ κP )] ( 2a : P* = ( S a ,R,R )‐ 1a = (1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1 R )‐1‐phenylethyl)]phosphoramidite; 2b : P* = ( S a ,R,R )‐ 1b = (1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1 R )‐(1‐(1‐naphthalen‐1‐yl)ethyl]phosphoramidite) with (Et 3 O)[PF 6 ] or Tl[PF 6 ] gives the cationic, 18‐electron complexes dichloro( η 6 ‐ p ‐cymene){(1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1 R )‐1‐[(1,2‐ η )‐phenyl]ethyl}[(1 R )‐1‐phenylethyl]phosphoramidite‐ κP }ruthenium(II) hexafluorophosphate ( 3a ) and [ Ru ( S )]‐dichloro( η 6 ‐ p ‐cymene){(1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1 R )‐1‐[(1,2‐ η )‐naphthalen‐1‐yl]ethyl}[(1 R )‐1‐(naphthalen‐1‐yl)ethyl]phosphoramidite‐ κP )ruthenium(II) hexafluorophosphate ( 3b ), which feature the η 2 ‐coordination of one aryl substituent of the phosphoramidite ligand, as indicated by 1 H‐, 13 C‐, and 31 P‐NMR spectroscopy and confirmed by an X‐ray study of 3b . Additionally, the dissociation of p ‐cymene from 2a and 3a gives dichloro{(1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1 R )‐(1‐( η 6 ‐phenyl)ethyl][(1 R )‐1‐phenylethyl]phosphoramidite‐ κP )ruthenium(II) ( 4a ) and di‐ μ ‐chlorobis{(1 S a )‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1 R )‐1‐( η 6 ‐phenyl)ethyl][(1 R )‐1‐phenylethyl]phosphoramidite‐ κP }diruthenium(II) bis(hexafluorophosphate) ( 5a ), respectively, in which one phenyl group of the N ‐substituents is η 6 ‐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.