Noncovalent anchoring of asymmetric hydrogenation catalysts on a new mesoporous aluminosilicate: application and solvent effects.
A new Brønsted acidic aluminosilicate, AlTUD-1, with ideal characteristics for catalyst immobilisation (mesoporous structure, high surface area, and high Al(tetrahedral)/Si ratio), was used successfully for the noncovalent anchoring of two well-established asymmetric hydrogenation catalysts: [Rh(I)(cod)[(R,R)-MeDuPHOS]]BF4 (1) and [Rh(I)(cod)[(S,S)-DiPAMP]]BF4 (2). The new heterogeneous catalysts, 1-AlTUD-1 and 2-AlTUD-1, prepared by a straightforward ion-exchange procedure, were highly active and selective in the asymmetric reduction of dimethyl itaconate (3) and methyl 2-acetamidoacrylate (4), giving enantiomeric excesses of up to >98%. The catalysts showed similar behaviour to their homogeneous counterparts. Catalyst 2-AlTUD-1 could be re-used multiple times without loss of enantioselectivity or activity. Leaching of Rh showed a significant dependence on the polarity of the solvent in which the catalysis was performed. By applying tert-butylmethyl ether (MTBE) as solvent, the loss of Rh could be reduced to <0.1%. The solvent also had a noteworthy effect on the enantioselectivity in the hydrogenation of 4 (an effect not seen with 3 as substrate), that is, in MeOH the ee was 92%, in MTBE it dropped to 26% when using 2-AlTUD-1 as catalyst.
Simons
Chrétien
C
Laboratory of Biocatalysis and Organic Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands.
Hanefeld
Ulf
U
Arends
Isabel W C E
IW
Sheldon
Roger A
RA
Maschmeyer
Thomas
T
D000538:Aluminum Silicates / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D016062:Porosity; D012995:Solubility; D012997:Solvents / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D012997:Solvents; C049037:aluminosilicate