This thesis describes the synthesis of novel ligands bearing chiral benzylamine moieties for use in asymmetric catalysis.
The lithiation of 1-dimethylamino-1-phenylethane with tBuLi and subsequent reaction with aminochlorophosphites leads to the novel enantiopure aminophosphonites (R)-1 and (S)-1or the aminophosphinites (R,R)-7 and (S,S)-7. The chiral aminophosphonite (R)-1reacts with (R)-2,2´-binaphtol to yield the novel cyclic phosphonite (R,R)-4. Reaction of (R>,R)-4 with [CODRhCl]₂ yields the Rh-(I)-COD complexe (R,R)-5. The structure of (R,R)-5 is investigated by 2D-NOE spectroscopy.
The both enantiomeres of o-(1-dimethylaminoethyl)-phenylphosphine (R)-3 and (S)-3 are prepared in high yields by a two step synthesis starting from (R)-1 and (S)-1, respectively. The subsequent reaction of (R)-3 or (S)-3 with the cyclic sulfate of (S,S)-2,5-hexanediol leads to two novel diasteromeric P,N-ligands (R,RR)-6 and (S,RR)-6 (DuPHAMIN).
The enantiomers of the novel enantiopure secondary phosphines (R,R)-8 and (S,S)-8 with two amino-groups are prepared by reduction of the aminophosphinites (R,R)-7 or (S,S)-7. The corresponding C₂-symmetrically phosphanides (R,R)-8a and (S,S)-8a are used to prepare a novel type of enantiopure multidentate hemilabile PₙNₘ-ligands 9, 10, 11 by using different electrophiles as α,ω -dihaloalkanes or diphenylvinylphosphine. The reaction of (R,R)-8a with a Merrifield resin leads to the chiral hemilabile polymer-supported ligand (R,R)-12.
A formerly unknown fluorinated derivative of the chiral P,N-ligand AMPHOS [o-(1-dimethylaminoethyl)-phenyl)-diphenylphosphine] was prepared and converted to the Rh-(I)-COD complexe (R)-18 and the PdCl₂ complexe (R)-19. The crystal structures of the Rh-(I)-COD complexe (R)-18 and the nonfluorinated AMPHOS-Rh-(I)-COD complexe (R)-18a were compared. Dynamic processes of (R)-18 and (R)-19 were investigated by low-temperature NMR spectroscopy.
Hydrophilic chiral pnictogenanes bearing amino acid moieties 29a,b and 30a,b were prepared in both enantiomeric forms by the reaction of enantiopure α-(2-fluorophenyl)-alanine (S)-21 or (R)-21 with KPPh₂ and KAsPh₂.The α-(2-fluorophenyl)-alanine 21 has been resolved by fractional crystallisation using enantiopure (S)- or (R)-prolinol. The absolute configuration of 21 was determined by X-ray structural analysis of the (S)-prolinolium salt (S,R)-24.
The two diastereomeres of DuPHAMIN 6 were used to prepare Rh-(I) and Pd-(II) complexes. The X-ray structural analysis of the Rh-(I)-COD complexes (R,RR)-31, (S,RR)-31, the η³-allyl-Pd-(II) complex (R,RR)-33, and the PdCl2 complex (S,RR)-34 were performed. A detailed comparison of these X-ray-structures and the structural informations obtained by 2D-NOE spectroscopy is also described here. Differences of the DuPHAMIN-Rh-(I) diolefine moiety in the solid-state structures and the solution structures have been found and should be described as an inversion of the distorted Rh-(I) diolefine chelate. The orientations of the allyl ligand in the DuPHAMIN- η³-allyl-Pd-(II) complexes (R,RR)-33 and (S,RR)-33 in solution are determined also by 2D-NOE spectroscopy.
The EXSY spectra of the Rh-(I)-diolefine complexes 31and 32 and the η 3 -allyl-Pd-(II) complexes 33 gave a detailed insight in dynamic processes in these complexes. In the case of the Rh-(I)-COD complexes (R,RR)-31 and (S,RR)-31 the different reactivity of these two diastereomeres towards hydrogen is explained by their EXSY and NOESY spectra.
Complex (R>,RR)-32 shows good selectivity as catalyst. Asymmetric hydrogenation of MAC using (R,RR)-32 yields the (R)-N-acetyl-phenylalanine-methylester in 96 % ee. The DuPHAMIN-Rh-(I)-COD complexe (R,RR)-31 was used for mechanistic investigations of the hydrogenation. The reaction was monitored by NMR-spectroscopy. The detection of substrate-complexes (R,RR)-35b in absence of hydrogen shows the expected manifold of discrete intermediates. PHIP-NMR investigations were used for the selective detection of Rh-hydrido intermediates. The solvent dihydrido complexes (R,RR)-35aH₂ and substrate-dihydrido complexes (R,RR)-35c were detected by using PHIP-NMR spectroscopy.