Synthesis and structure of novel chiral oxazolinylferrocenes and oxazolinylferrocenylphosphines, and their rhodium(I)-complexes

Abstract

A variety of chiral oxazolinylferrocenes are prepared from either ferrocenecarboxylic acid or cyanoferrocene and chiral β-amino alcohols. Highly diastereoselective ortho-lithiation (84 ≈ 99% de) of the oxazolinylferrocenes is accomplished with sec-butyllithium and the treatment of the lithiated compounds with an electrophile such as Mel, Ph 2PCI or (PhSe) 2 gives the corresponding ortho-substituted oxazolinylferrocenes. The molecular structure of ( S, S)[2-(4′-isopropyloxazolin-2′-yl)ferrocenyl]diphenylphosphine ( 10), ( S, S)-2-phenyl-seleno-1-(4′-isopropyloxazolinyl)ferrecene ( 17), ( S, R)-3-methyl-1-diphenylphosphino-2-(4′-isopropyloxazolinyl)ferrocene ( 18), and ( S,S,S)-[2-(4′5′-diphenyloxazolin-2′-yl)ferrocenyl]diphenylphosphine (( S,S,S)-DIPOF; 21) has been fully characterized by X-ray crystal-lography. In connection with their usefulness as chiral ligands for Rh(I)-catalyzed asymmetric hydrosilylation of ketones, the square planar transition metal complexes having oxazolinylferrocenylphosphines, such as [Rh(COD)(P-N)]BF 4 and Rh(CO)(P-N)Cl (P-N = 10 or 21), are prepared by treatment of [Rh(COD) 2]BF 4 and [Rh(CO) 2Cl] 2 with 10 and 21, respectively, and all structures have been characterized spectroscopically and further confirmed by X-ray crystallography.