Imre Tóth

Novel chiral water soluble phosphines II. Applications in catalytic asymmetric hydrogenation

Abstract The results of the homogeneous asymmetric hydrogenation of several dehydroamino acids by rhodium-diene complexes of the chiral ligands; 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)butane, 2a ; 2,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)pentane, 3a ; and 2,3-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino) butane, 4a ; and their N-protonated and N-Me quaternized analogues are reported. The ligands comprise a versatile set which can be used both in organic and aqueous solvents. A detailed investigation of solvent and substituent effects is provided. The presence of p-NMe 2 groups enhances the rate of reaction in all cases. For the DIOP derivative, 2a , the presence of the dimethylamino group causes a reversal in the observed dominant product antipode. This is attributed predominantly to a change in preferred ligand conformation rather than to a kinetic difference between the two diastereomers of a single ligand conformation.

Bis[tris(m(sodium sulfonato)phenyl)phosphine] hexacarbonyl dicobalt, Co2(CO)6 (P(m-C6H4SO3Na)3)2, in a supported aqueous phase for the hydroformylation of 1-hexene

Abstract The synthesis of the cobalt carbonyl phosphine complex, Co2(CO)6(P(m-C6H4SO3Na)3)2, is described and the complex is used as a catalyst for the hydroformylation of 1-hexene under two-phase and supported aqueous phase reaction conditions. Under two-phase reaction conditions both with and without excess phosphine substantial quantities of cobalt are leached into the organic phase and the observed activity is consistent with catalysis from HCo(CO)4 in the organic phase. When the complex is supported onto the controlled pore glass CPG-340 in a supported aqueous phase configuration the amount of cobalt lost into the organic phase is minimized and the observed activity appears to come from the complex on the glass. When excess phosphine as well as the complex are supported on the glass cobalt leaching is further reduced under batch reaction conditions.

Novel chiral water soluble phosphines I. Preparation and characterization of amine functionalized DIOP, Chiraphos, and BDPP derivatives and quaternization of their rhodium complexes

Abstract Synthetic details for the preparation of tetra-amine functionalized derivatives of the ligands BDPP, Chiraphos, and DIOP (2,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)pentane; 2,3-bis(-bis(-p-N,N-dimethylaminophenyl)-phosphino)butane; and 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)butane; respectively). The ligands are conveniently quaternized in their rhodium diene complexes with (CH 3 ) 3 OBF 4 . Both the methyl quaternized and proton quaternized versions of the rhodium complexes have unlimited water solubility.

Alternative supported aqueous-phase catalyst systems

Abstract The concept of supported aqueous-phase (SAP) catalysis has been extended to olefin hydroformylations by the use of in situ formed Rh-, Ptue5f8SnCl 3 - and Co-complexes containing HexDPPDS, TAPTS and TPrPTS as ligands, respectively. (HexDPPDS = hexyl-bis(sodium- m -sulfonatophenyl)phosphine; TAPTS = tris(ω-(sodium- p -sulfonatophenyl)alkyl)phosphines, where alkyl ue5fbCH 2 , TBeTS; ue5fbC 2 H 4 , TEtPTS, ue5fbC 3 H 6 , TPrPTs). Furthermore, some data are reported on the SAP asymmetric hydroformylation of styrene by the use of PtCl 2 [( S,S )-BDPP-(( p -NMe 3 )(BF 4 )) 4 ] + SnCl 2 system and on the SAP asymmetric hydrogenation of dehydro-phenylalanine derivatives with Rh(COD)[( S,S )-BDPP-( p -NME 3 ) 4 ](BF 4 ) 5 and Rh(COD)[( S,S )-Chiraphos-( p -NMe 3 ) 4 ](BF 4 ) 5 complexes. (BDPP = 2,4-bis(diphenylphosphino)pentane; Chiraphos = 2,3-bis(diphenylphosphino)butane). For the sake of comparison, the two-phase catalytic results are also given with each alternative SAP catalytic applications, as well as the appropriate (organic) homogeneous values, which were obtained with the analogous complexes containing the respective non-funtionalized ligands. With the exception of the Co-system, the SAP catalytic systems show similar selectivity only to the analogous non-aqueous catalysts. The anomalous behavior of the Co-system in the presence of water is attributed to the presence of sulfonate groups on the ligand which may interact with the cobalt.

Hydroformylation of 1-hexene with Pt(P(m-C6H4SO3Na)3)2Cl2 and its tin chloride analogue on a controlled-pore glass

The compound, bis(trisulfonated triphenylphosphine)platinum dichloride, is supported on a controlled-pore glass to yield an immobilized olefin hydroformylation catalyst. The immobilized complex reacts with excess SnCl2 to yield, in situ, Pt(TPPTS)2Cl(SnCl3), TPPTS = trisulfonated triphenylphosphine. Normal to branch ratios of up to 11.5 are obtained for the hydroformylation of 1-hexene at 100 °C and 1000 psig. The glass-supported catalysts did not show evidence of platinum leaching under batch conditions.

Immobilization of rhodium complexes with chiral cationic water soluble ligands on Nafion-H and other strongly acidic cation exchange resins

Abstract Rhodium complexes of the chiral cationic water soluble ligands, [(S, S)-2,4-bis[-bis(-p-N, N-dimethylammoniumphenyl)phosphino]pentane]4+, [(S, S)-2,3-bis[-bis(-p-N, N-dimethylammoniumphenyl)phosphino]butane]4+, and [(S, S)-2,4-bis[-bis(-p-N, N, N-trimethylammoniumphenyl)phosphino]pentane]4+, were immobilized on several cation exchange resins. All of these supported complexes catalyze the asymmetric hydrogenation of dehydroaminoacid derivatives at the appropriate conditions with no detectable loss of rhodium into the substrate phase. The rates and enantioselectivities of these hydrogenations depend not only on the ligand used but also on the nature of the exchange resin upon which the complex is immobilized. When the complexes were supported onto the acidic Nafion-H cation exchange resin the resulting catalysts were easy to handle and gave optical yields comparable to those obtained with the non-supported complexes in homogeneous solution. The results presented here show that ion exchange resins may be used in the immobilization of asymmetric catalysts with no detectable rhodium leaching under batch conditions.

Enantioselective two-phase hydrogenation of α-amino acid precursors with water soluble rhodium complexes of the cationic ligand (S,S)-2,4-bis[bis-(p-N,N,N-trimethylammoniumphenyl)phosphino]pentane, [CH3CH(P(p-C6H4NMe3)2CH2CH(P(p-C6H4NMe3)2CH3]4+

Rhodium complexes of the chiral cationic phosphine, (S,S)-2,4-bis[bis-(p-N,N.N-trimethyl-ammoniumphenyl)phosphino]pentane show excellent enantioselectivity for the hydrogenation of the DOPA precursor. (Z)-3-OMe,4-OAcC6H3CHC(COOH)(NHCOCH3), and dehydro-phenylalanineacetamide as slurries in water. The catalytic reactions may be done in either a two-phase system with the catalyst in the aqueous phase or as a slurry in water provided the substrates have some water solubility. Enantioselectivities of as high as 95% can be obtained.

Immobilization of rhodium complexes of amine-functionalized BDPP and chiraphos on a soluble form of the strongly acidic Nafion-H cation exchange resin

Abstract The soluble form of the superacid exchange resin, Nafion®-NR-50, is used for the first time as a precursor to a solid supported asymmetric hydrogenation catalyst. Addition of the resin to solutions containing [BDPP(NMe 2 ) 4 RhNBD] + or [chiraphos(NMe 2 ) 4 RhNBD] + leads to the precipitation of a finely divided form of Nafion which contains the rhodium complexes protonated at the amine nitrogens. Rates for the hydrogenation of dehydroamino acids with the catalysts prepared here are much faster than previously obtained with the identical complexes immobilized on large Nafion beads. The rates obtained are nearly as large as those observed for the corresponding homogeneous catalysts in methanol.

Immobilization of HRh(CO)(P(m-C6H4SO3Na)3)3 on an anion exchange resin for the hydroformylation of higher olefins

The anion exchange resin Amberlyst, A-26, forms an efficient matrix for the immobilization of the water soluble complex, HRh(CO)(m-C6H4SO3Na)3)3. Catalysis proceeds in anhydrous alcohol solvents which allows the conversion of water insoluble olefins to aldehydes. Activities and selectivities are similar to both supported aqueous phase catalysts and to the neutral complex, HRh(CO)(PPh3)3 in non-aqueous solvents. The catalyst preparation minimizes the quantity of water in the supported catalyst; the lack of water is thought to be responsible for an increase in catalyst stability toward oxidation.

Immobilization of rhodium complexes in aqueous HBF4. The enantioselective hydrogenation of prochiral olefins with {[CH3CHP(p-C6H4NMe2H)2CH2CHP(p-C6H4NMe2H)2CH3]RhNBD}5+

The complex {[CH3CHP(p-C6H4NMe2H)2CH2CHP(p-C6H4NMe2H)2CH3]RhNBD}5+ is active for the enantioselective hydrogenation of cinnamic acid derivatives at low pH in aqueous solutions of the noncoordinating acid HBF4. Analytical data are consistent with protonation occurring exclusively at the dimethylamino groups and not at the metal. Enantiomeric excesses of 67 to 97% are obtained for the hydrogenation of Z-(4-OMe, 3-OAcC6H3CHue5fbC(NHC(O)Me)COOH in aqueous HBF4 at 14 bar H2. The use of aqueous acidic solutions allows for the convenient workup of the product and recycling of the catalyst.