Homogeneous catalytic hydrocyanation

Homogeneous catalytic hydrocyanation of mono-olefinic compounds may serve as a simple example. It stands to reason that HCN will add to the olefinic double bond, H going to one of the latter s carbon atoms, and CN to the other ... 

The poor turn-over numbers (TON) in the hydrocyanation reactions are another limitation, because of degradation of the catalyst, which still has to be overcome. The maximum TON reached so far have been in the order of 500-750, which is extremely low compared with other homogenous catalytic reactions. 

Scheme 1. Catalytic loop for the homogeneously catalyzed hydrocyanation of ethylene.

While the hydrocyanation of monoolefins remains under development, the hydrocyanation of butadiene shown in Equation 16.3 is one of the largest-scale homogeneous catalytic processes known. This reaction generates the 1,4-dinitrile called adiponitrile, which is the precursor to the diamine monomer in nylon 6,6. The formation of this regioisomer requires a set of reversible hydrocyanations and isomerizations that are discussed in Section 16.2.4 on hydrocyanation of dienes. 

From what has been discussed so far in this chapter, it is clear that homogeneous catalysis has had spectacular success in imparting high enantioselectiv-ities in the making of new C-H and C-O bonds. An enantioselective method for making new C-C bonds is also potentially very useful. Hydroformylation, hydrocyanation, and carbonylation are reactions that deal with the formation of new C-C bonds. All these have been turned into enantioselective catalytic systems with varying degrees of success. Considerable success has also been... 

Isomerization via homogeneous catalysts occurs, for instance, as 2ui intermediate step in catalytic processes. Thus in Shell s hydroformylation route, which converts internal olefins to primary alcohols, isomerization takes place prior to CO-insertion. Homogeneous isomerization of 2-me-thyl-3-butenenitrile to the linear nitrile is an essential step in du Font s hydrocyanation. Noteworthy is the recent commercial asymmetric isomerization of neryl and geranyl amines [3]. 

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