Asymmetric transfer hydrogenation ATH catalysts

A wide range of metals and ligand combinations have been demonstrated to effect the ATH reaction and in this book we concentrate on the systems that have demonstrated high activities and ees that would be the requirement of an industrial application. The initial breakthrough in this area came in 1995 with the report from Ohkuma et alP on the use of chiral monotosylated diamine complexes for asymmetric transfer hydrogenation. 

The aromatic complex can be a neutral t °-benzene derivative or an anionic ri -cyclopentadienyl ring. Substituents on these aromatic rings can greatly influence the effectiveness of these catalysts. For example, with benzene derivatives the unsubstituted benzene rings give lower ees and the use of hexamethylbenzene results in lower catalytic activities whilst the cumenyl or mesityl rings give optimum catalyst systems. The two types of chiral bifunctional hnkers that have been most practical are anionic ones based on monosulfonated diamines and amino alcohols. 

A detailed review of the mechanisms of the hydrogenation of polar double bonds by ruthenium hydride species have been published by Clapham et alP The article examines the properties of over 100 catalyst systems for transfer and 

The above mentioned catalysts also have the advantage of being robust and they can be attached to scaffolds that allow them to be recycled.  

Another field where ATH catalysts have made an industrial impact is in the area of chiral amine synthesis by stereocontrolled reduction of imines. First demonstrated by Uematsu et the reduction of cyclic imines to yield chiral amines 

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