Additions of carbon nucleophiles to acyclic imine complexes of the chiral rhenium Lewis acid [(eta(5)-C5H5)Re(NO)(PPh3)](+): controlling factors in 1,3-asymmetric induction and syntheses of non-racemic organic amines

摘要

Reactions of the racemic or enantiomerically pure benzaldehyde-derived imine complex [(eta(5)-C5H5)Re(NO)(PPh3)(eta(1)-N-(CH3)=C(H)C6H5)] +TfO- (1(+)TfO(-); 95:5 E/Z N=C isomers) and RLi (THF, -100 degrees C) give amido complexes (eta(5)-C5H5)Re(NO)(PPh3)(N(CH3)CH(R)C6H5) (5) (R = a/CH3, b/C = CSi(CH2CH3)(3), c/CH2Si(CH3)(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 [(eta(5)-C5H5)Re(NO)(PPh3)(NH(CH3)CH(R)C6H5)] +TfO- (6(+)TfO(-)). Reaction of 6a(+)TfO(-) (prepared from (R)-1(+)TfO(-)) and Et4N+CN- yields the cyanide complex (R)-(eta(5)-C5H5)Re(NO)(PPh3)(CN) (85%, >98% ee) and amine (R)-NH(CH3)CH(CH3)C6H5 (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 CH3OTf affording 1(+)TfO(-). Reactions of the acetophenone-derived complex [(eta(5)-C5H5)Re(NO)(PPh3)(eta(1)-N(CH3)=C(CH3)C6H5)]+TfO- (4(+)TfO(-)) with C6H5CH2MgCl and (CH3)(3) SiCH2Li give 41 and >99% deprotonation to the enamido complex (eta(5)-C5H5)Re(NO) (PPh3)(N(CH3)C(C6H5)=CH2). Some addition occurs with C6H5CH2MgCl, and CN-. NMR spectra (-100 degrees C) show Re-N=rotamers of 1,4(+)TfO(-), and mechanisms of 1,3-asymmetric induction are analyzed in detail. (C) 1998 Elsevier Science S.A. [References: 68]