Synthesis Of Chiral Cyclopalladated Ferrocenylimines And α-ferrocenyl-α-aminophosphine Oxides And Their Application In Asymmetric Catalysis

In this thesis, both the asymmetric addition and cyclopalladation of chiral ferrocenylaldimines were investigated: five pairs of racemicα-ferrocenyl-α-aminophosphine oxides were synthesized from ferrocenylaldimines; four pairs of novel chiralα-aminophosphine oxides and two ferrocenyl amino alcohols were synthesized from amino alcohol derived imines. These chiral ligands were further applied in asymmetric reactions; four pairs of novel diastereomeric di-α-chloro-bridged dimers and four pairs of diastereomeric monomers of cyclopalladated ferrocenylimines were designed and synthesized; In addition, the application of these planar chiral cyclopalladated ferrocenylimines to asymmetric aza-Claisen rearrangement of allylic imidates have been preliminarily investigated.1. Synthesis, structural characterization and application of novel racemic and chiralα-ferrocenyl-α-aminophosphine oxidesStarting from ferrocenylaldimines, five pairs of racemicα-ferrocenylα-aminophosphine oxides 2a-2e were synthesized (Scheme 1). The products wereR=H(a), p-CH₃(b), p-Cl(c), p-OCH₃(d), p-OC₂H₅(e)Scheme 1characterized by elemental analysis, IR, ¹H NMR and ³¹p NMR spectra. The molecular structure of complex 2e was further determined by single-crystal X-ray diffraction. It was founded that the P(O)Ph₂ group in complex 2e is trans to the unsubstituting Cp ring, which suggested that the PPh₂ group attacked the C=N far away from the unsubstituting Cp ring due to the steric hindrance. The asymmetric addition reactions of chiral imines 3 and 6 were investigated: four pairs of optically active aminophosphine oxides with two chiral centers were obtained (Scheme 2). The products were characterized by elemental analysis, IR, ¹H NMR and ³¹p NMR spectra. The structure of (S, S)-4b was further determined by single-crystal X-ray diffraction. Complexes (S, S)-4b and (R, S)-Sb were isolated byScheme 2fractional crystallization from dichloromethane-petroleum in 41% and 16% yields. The d.e.% of 4a, 5a and 7a, 8a are 100%, while the d.e.% of 7b, 8b is 33%. The results suggested that the steric hindrance of ferrocenyl group and substituting groups of original chiral center in imines played very important roles in the asymmetric addition of chiral imines. In addition, a plausible transition state for the asymmetric addition of chiral imines was proposed.In order to study the effect of P(O)Ph₂ group in the application of chiral ligands 4, 5, 7 and 8 to asymmetric reactions, two ferrocenyl amino alcohols 9a and 9b wereScheme 3synthesized from chiral amino alcohol derived imines 3 (Scheme 3) and applied in the same asymmetric reactions. The products were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR spectra and specific rotations.The chiral ligands 4, 5, 7, 8 and 9 were used in the asymmetric addition of diethylzinc to aldehyde and the asymmetric reduction of acetophenone using NaBH₄/I₂. In ruthenium-catalyzed asymmetric transfer hydrogenation reactions, the best result was given by 9b, and the corresponding (R)-1-phenyl-1-ethanol was isolated in 99.1% yield with 74.2% e.e. But theα-ferrocenyl-α-aminophosphine oxide 4b gave (R)-1-phenyl-1-ethanol in 51.5% yield with 41.1% e.e. due to the steric hindrance of P(O)Ph₂ group.2. Synthesis, structural characterization and application of novel chiral cyclopalladated ferrocenyliminesThe asymmetric cyclopalladation of chiral ferrocenylimines were investigated: Cyclopalladation of ferrocenylimines (S)-10 with Li₂PdCl₄ in the presence of sodium acetate gave four pairs of novel diastereomeric di-μ-chloro-bridged dimers 11 and 12, 16 and 17 were not obtained (Scheme 4); Treatment 11 and 12 with PPh₃ gave four pairs of diastereomeric monomers 14 and 15 respectively; In the same way, cyclopalladation of 10a and 10c, subsequently treated with PPh₃ gave a 1:1 mixture 13 of 14a and 15a, while 14c and 15c were obtained respectively by fractional crystallization. The products were characterized by elemental analysis, IR, NMR and specific rotations. The molecular structures and absolute configurations of complexes 13, (Rp, So, Rp, Sc)-12c, (Sp, Sc)-14a and (Rp, Sc)-15c were determined by single-crystal X-ray diffraction. In 12c, 14a, 15c and 13, the N-Pd distances are 2.080--2.187 A, which is much shorter than the sum of the van der Waals radius of N and Pd (about 3.18 A).This indicated there are intramolecular coordination between N and Scheme 4Pd. In addition, Me N-Pd distance of 12c (2.080--2.083 A) is shorter than that of 15c (2.159 A). These suggested that the coordination of N and Pd is stronger in dimer. In 12c, O-Pd distance (4.226 A) is much longer than the sum of the van der Waals radius of O and Pd (about 3.15A), it showed that 16 and 17 were not formed.It was shown that intramolecular chiral inducement can afford diastereomeric planar chiral palladacycle, but in poor d.c. value. When R₁ is phenyl, the d.c.% is higher (up to 63% d.e.).The application of these planar chiral cyclopalladated ferrocenylimines in the asymmetric aza-Claisen rearrangement of allylic imidates have been preliminarily investigated (Scheme 5). But no 22 was obtained, only 21 and a small amount of 23 were isolated. The application of these planar chiral cyclopalladated ferrocenylimines in asymmetric aza-Claisen rearrangement is still in process in our group. Ar=C₆H₅(a), p-CH₃C₆H₄(b), p-OCH₃C₆H₄(c), p-ClC₆H₄(d)Scheme 5...