Biphosphines catalysts

The reaction pathway for rhodium-catalyzed asymmetric hydrogenation of enamides is described and intermediates are defined in solution by P-31, C-13, and H-l NMR. The stereochemical relationship of bound enamide to rhodium alkyl and to the product of hydrogenation is demonstrated. Experiments involving the addition of HD to a variety of olefins in the presence of rhodium biphosphine catalysts suggest that a concerted addition of hydrogen to olefin and metal may occur in appropriate cases. 

Successively a rhodium chiral biphosphine catalyst ([Rh(l,5-COD)bisphosphine] + BF allowed better selectivity in reducing a-acylaminoacrylic acids (95-96% e.e.)193. 

TABLE I. Hydrogenation of enamides by 5-ring chelate biphosphine catalysts... 

The key intermediate for the antibacterial agent levofloxcin, (,S>( )-7,8-difluoro-2,3-dihydro-3-methyl-4H-l,4-benzoxazin, was prepared by the asymmetric hydrogenation of (442) by the catalyst system made in situ from [Ir(cod)Cl]2, biphosphine and bismuth(III) iodide.703 The product was isolated in 96% yield, with an enantiomeric purity of 90% for the biphosphine (2S,45)-BPPM,(2S,45)-N-( -butoxy-carbonyl)-4-(diphcnylphosphino)-2-[(diphcnylphosphino)mcthyl]-pyrrolidine. 

The above feature of the Brown mechanism that reductive elimination is more difficult than olefin insertion may be related to the nature of catalyst having a chelating bidentate ligand such as DIPHOS. Halpern have also investigated the hydrogenation (Equation 3) (2), where isomerization from the trans- to cis-biphosphine complex is not necessary. 

In addition, a Rh-(R,R)-NORPHOS catalyst has been used to promote enantioselective transfer hydrogenation of the C=C double bond in (Z)-a-(acetylamino)cinnamic acid and in (Z)-a- and ( )-a-(benzoylamino)-2-butenoate by using 80% aqueous formic acid as the source of H2. Optical yields were improved by the addition of sodium formate representative results are presented in Table 2. Comparable, but generally somewhat lower, optical yields were obtained by using other Rh-(biphosphine ligand) catalysts, e.g., biphosphine ligand = (R,S)-(+)-BPPFA (2), (R)-(+)-PROPHOS(3), ot(R,R)-... 

The enantioselective hydrogenation of 3,4-dihydroxy-N-acetylamino dnnamic acid is catalyzed by the cationic Rh-biphosphine complex DIPAMP, in which the enantioselectivity is introduced by the chiral phosphine1104, 105l The hydrogenation proceeds quantitatively with 94% ee. The optically pure L-dopa is separated from the catalyst by crystallization. 

I Ls can also be immobilized by impregnation of an inorganic support. This is a direct transposition of the Supported Aqueous-Phase Catalysis (SAPC) concept to ionic liquids (see Section 2.6). Supported Ionic Liquid Phase (SILP) catalysts containing Rh-biphosphine ligands were applied to perform continuous-flow gas-phase hydroformylation of propene in [BMIMJIPFg] or [BMIMJIRSOJ (R=octyl). 

Allylamines are isomerized by cationic rhodium complexes to the corresponding -enamines.Using the catalyst [Rh( -binap)(COD) containing the optically pure biphosphine ligand -binap, high asymmetric induction in this isomerization can be achieved (Scheme 9). 

In the case of polystyrene-supported catalysts, an additional study explored the influence of the isolation of the catalyst environment on the outcome of the hydroformylation reaction. For this purpose, first- and second-generation dendrons (very similar to those described above) were constructed and the biphosphine-Rh complex was assembled only on... 

Hydrogenation of iV-acyl a-amino acids in 87-91% ee has been accomplished with Rh bound to copolymers (43) with chiral phosphine ligands, as shown in Scheme 16. The same % ee was obtained with Rh catalysts prepared from analogous soluble ligands. Hydrophilic poly(2-hydroxy-ethyl methacrylate) and poly(iV,iV-dimethylacrylamide) provided polar environments for the hydrogenations. The chiral polymeric catalyst can be recycled. Earlier studies with polymers based on chiral biphosphine monomer (44) showed that polar comonomers were required for high % ee catalysis. ... 

Chiral biphosphine Pt" complexes (45) with SnCl2 catalyze hydroformylations of styrene, vinyl acetate and N-vinylphthalimide in 56-65% ee, almost as high as with analogous soluble catalysts, as shown in Scheme 17. The polymer supports can be either soluble or cross-linked. Lower branched-to-normal product ratios were obtained with the polymeric catalysts, especially with the cross-linked ones. Reuse of the catalyst showed no loss in rate or selectivity with precipitated soluble polymer, and slight loss in rate but no loss in selectivity with the cross-linked polymer. 

Hydroformylation reactions of C2-C4 Olefins By applying silica gel-supported BMIm-n-C8Hi70S03 IL phase containing Rh(acac)(CO)2 and xanthene-based biphosphine ligand sulfoxantphos (SX), Scheme 2.21 [89], as catalyst (Rh-1), the hydroformylation of propene was successfully realized under fixed-bed gas-phase reaction conditions. The addition of the ligand SX promoted the formation of linear aldehyde product. Under optimized reaction conditions, the selectivity to linear aldehyde reached 96% with about 1% propene conversion. However, deactivation occurred if the flow reaction was prolonged to 24 h. Subsequently,... 

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