Stereochemistry of Homogeneous Catalysts. Anti-Lock and Key Concept

7 Stereochemistry of Homogeneous Catalysts. Anti-Lock and Key Concept 

Since the BINAP ligand is optically active, the catalytic reaction is enantiomericaUy selective. The rigidity of this phosphine ligand derives from the connectedness of the phosphine groups. 

A successful homogeneous system involves the catalytic hydroaminomethylation of internal alkenes to produce the linear products over an organometallic Rh complex which contains the rigid bulky diphosphorus ligandl . It helps to catalyze the combined sequence of bond isomerization, CO insertion and amination at the Rh center with stereochemical control. The unique feature of this catalyst is that all three of these different 

Interestingly, the major product comes from the very rapid hydrogenation of the less stable diastereomer with H2. This feature that the least-stable intermediate is actually the most reactive has been called anti-lock and key behavior. The enantioselectivity of the reaction is affected by the competition between the rate of hydrogenation and the interconversion of the two diastereomers. 

The results can be best explained as being representative of a loose transition state where the barrier height is dominated by the need to weaken the interaction between catalyst and substrate. The unfavorable adsorption state appears to be the most reactive. It is also the adsorption mode in which the entropy is a maximum. 

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