Additions of carbon nucleophiles to acyclic imine complexes of the chiral rhenium Lewis acid [( η5-C 5H 5)Re(NO)(PPh 3] +: controlling factors in 1,3-asymmetric induction and syntheses of non-racemic organic amines

Abstract

Reactions of the racemic or enantiomerically pure benzaldehyde-derived imine complex [(η 5- C 5 H 5) Re( NO)( PPh 3) (η 1- N-( CH 3)= C( H) C 6 H 5] + TfO −; ( 1 + RFO −; 95.5 E/Z N= C isomers) and RLi (THF, − 100°C) give amido complexes (η 5-C 5H 5)Re(NO)-(PPh 3)(N̈(CH 3)CH(R)C 6H 5) ( 5) ( R= a/CH 3, b / C CSi( CH 2 CH 3) 3 , e/CH 2Si(CH) 3) 3 ) in quantitative NMR yields as 74-72:26–28 mixtures of Re,C configurational diastereomers. These labile adducts and TfOH react to give amine complexes [(η 5-C 5H 5)Re(NO)(PPh 3)- (NH(CH 3)CH(R)C 6H 5)] +TfO− ( 6 +TFO −). Reaction of 6a +TfO − (prepared from (R)- 1 + TfO − ) and Et 4N +CN − yields the cyanide complex ( R)-( η 5-C 5H 5)Re(NO)(PPh 3)(CN) (85%, >98% ee) and amine ( R)-NH(CH 3)CH(CH 3)C 6 H 5 (81%, 46% ee). Reactions of 1 +TfO − and CN − give similar amido complexes (85-84:15-16 Re,C diastereomers), but appear reversible, with additions of CH 3OTf affording 1 +TfO −. Reactions of the acetophenone-derived complex [( η 5-C 5H 5)Re(NO)(PPh 3)( η 1-N (CH 3)=C(CH 3)C 6H 5)] +TfO − 4 +TfO −) with C 6H 5CH 2MgCl and (CH 3) 3SiCH 2Li give 41 and >99% deprotonation to the enamido complex (η 5-C 5H 5)Re(NO)(PPh 3) ( N ̈ ( CH 3) C( C 6 H 5= CH 2 . Some addition occurs with C 6H 5CH 2MgCl, and CN −, NMR spectra (− 100°C) show ReN=rotamers of 1,4 +TfO −, and mechanisms of 1,3-asymmetric induction are analyzed in detail.