Remote Dipole Effects as a Means to Accelerate [Ru(amino alcohol)]-Catalyzed Transfer Hydrogenation of Ketones
作者:Sofia J. M. Nordin、Peter Roth、Tibor Tarnai、Diego A. Alonso、Peter Brandt、Pher G. Andersson
DOI:10.1002/1521-3765(20010401)7:7<1431::aid-chem1431>3.0.co;2-l
日期:2001.4.1
A new generation of 2-azanolbornyl amino alcohol ligands for the catalytic transfer hydrogenation reaction of aromatic ketones was synthesized. Extremely active catalysts were formed by introducing a ketal functionality at the I car end of the ligand, Acetophenone was reduced in 96% cc at low catalyst loading, substrate: to catalyst ratio, S/C 5000, within 90 minutes with isopropyl alcohol as the hydrogen donor. It was round that the dioxolane substituent in the ligand increased the turnover frequency, TOF50 from 1050 h(-1) to 3000 h(-1) at an S/C ratio of 1000, Introduction of a methyl group at the carbinol carbon resulted in TOF50 as high as 8500 h(-1), Transfer hydrogenation of a range of aromatic ketones was evaluated and found to reach completion within 30 minutes at room temperature, and excellent enantioselectivity, up to 99% cc, was obtained. A possible explanation for the enhanced activity was provided by density functional calculations, which showed that the presence of a remote dipole in the ligand lowered the transition state energy.