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Noncovalent Anchoring of Asymmetric Hydrogenation Catalysts on a New Mesoporous Aluminosilicate: Application and Solvent Effects

2004; Wiley; Volume: 10; Issue: 22 Linguagem: Inglês

10.1002/chem.200400528

1521-3765

Chrétien Simons, Ulf Hanefeld, Isabel W. C. E. Arends, Roger A. Sheldon, Thomas Maschmeyer,

Surface Chemistry and Catalysis

Abstract 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}]BF 4 ( 1 ) and [Rh I (cod){( S,S )‐DiPAMP}]BF 4 ( 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.