Asymmetric transfer hydrogenation bifunctional mechanism

Fig. 21. General synthesis of p-CD-linked ruthenium complexes asymmetric transfer hydrogenation is described as a metal-ligand bifunctional mechanism according to 31).

Figure 1.24. Metal-ligand bifunctional mechanism in asymmetric transfer hydrogenation of...

Asymmetric transfer hydrogenation of imines catalyzed by chiral arene-Ru complexes achieves high enantioselectivity (Figure 1.34). Formic acid in aprotic dipolar solvent should be used as a hydride source. The reaction proceeds through the metal-ligand bifunctional mechanism as shown in the carbonyl reduction (Figure 1.24). 

Other chiral diamine-( -arene)ruthenium catalysts were developed by Noyori where the chirality was centred at the metal (see Figure 3.18). These complexes were effective catalysts for asymmetric transfer hydrogenation of carbonyl compounds and a mechanism involving a metal-ligand bifunctional process was proposed. 

Scheme 1.46 A revised catalytic cycle for the asymmetric transfer hydrogenation of aromatic ketones in propan-2-ol by the Noyori-Ikariya (pre)catalyst 2 demonstrates crossover of the reaction pathways the product is obtained via a H"/H+ outer-sphere hydrogenation mechanism and/or step-wise metal-ligand bifunctional mechanism (see text). Formation of the major enantiomeric product is shown. (Adapted from Dub, P. A. et al., /. Am. Chem. Soc., 135, 2604-2619. Copyright 2013 American Chemical Society.)...

Noyori, R., Yamakawa, M. and Hashiquchi, S. Metal-Ligand Bifunctional Catalysis A Nonclassical Mechanism for Asymmetric Hydrogen Transfer between Alcohols and Carbonyl Compounds. J. Org. Chem. 2001, 66, 7931-7944. 

Noyori R, Yamakawa M, Hashiguchi S (2001) Metal-ligand bifunctional catalysis a non-classical mechanism for asymmetric hydrogen transfer between alcohols and carbonyl compounds. J Org Chem 66 7931-7944... 

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