Enantioselective hydrogenation polar factor

Asymmetric hydrogenation of prochiral ketones,s Ketones substituted in the a- or (3-position by diverse polar groups, particularly OH,OR,NR2,COOR, can undergo highly enantioselective hydrogenation catalyzed by BINAP-Ru complexes. A key factor of asymmetric induction is undoubtedly chelation of the carbonyl group and the hetero atom to the Ru atom. 

Another important factor in the hydrogenation of a,p-unsaturated acids was the solvent by increasing the polarity of the solvent used (n-hexane < toluene < methyl acetate < THF < methanol) a progressive decrease in ee was observed. This was probably due to the fact that H2 and the a,p-unsaturated acids were more soluble in the apolar solvents and also that CD was present in the open conformation, the enantioselective conformation (8). In fact, the highest conversion and ee were obtained with n-hexane (Figure 2). 

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