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Ionic liquid-phase asymmetric catalytic hydrogenation: hydrogen concentration effects on enantioselectivity

2001; Elsevier BV; Volume: 12; Issue: 13 Linguagem: Inglês

10.1016/s0957-4166(01)00341-x

1362-511X

Alexsandro Berger, Roberto Fernando de Souza, Marcelo R. Delgado, Jaı̈rton Dupont,

Chemical and Physical Properties in Aqueous Solutions

Molecular hydrogen is almost four times more soluble in the ionic liquid 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF4) than in its hexafluorophosphate (BMI·PF6) analogue at the same pressure. The Henry coefficient solubility constant for the solution BMI·BF4/H2 is K=3.0×10−3 mol L−1 atm−1 and 8.8×10−4 mol L−1 atm−1 for BMI·PF6/H2, at room temperature. The asymmetric hydrogenation of (Z)-α-acetamido cinnamic acid and kinetic resolution of (±)-methyl-3-hydroxy-2-methylenebutanoate by (−)-1,2-bis((2R,5R)-2,5-diethylphospholano)benzene(cyclooctadiene)rhodium(I) trifluoromethanesulfonate and dichloro[(S)-(−)-2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl]ruthenium(II) complexes immobilised in BMI·PF6 and BMI·BF4 were investigated. Remarkable effects in the conversion and enantioselectivity of these reactions were observed as a function of molecular hydrogen concentration in the ionic phase rather than pressure in the gas phase.