Mechanistic Aspects of Hydrocyanation

Some of the earlier reviews summarizing this extensive chemistry are those of Brown [8, 16], Hubert and Puentes [17], James [18], and Tolman [15]. Low-valent organonickel chemistry was reviewed by Jolly and Wilke [19]. Newer developments, especially the employment of bidentate ligands for the generation of more active catalysts as well as the induction of asymmetry in the product nitriles, are generally reviewed by Casalnuovo and RajanBabu [20] the exploration of water-soluble catalysts for hydrocyanation of butadiene is summarized by Bryndza and Harrelson [21], 

There are common steps in the homogeneously catalyzed reaction of olefins, alkynes, and heteroolefinic substrates with hydrogen cyanide, which facilitate comprehension of the reaction principle. 

Product formation was elucidated by closer examination of the reaction mechanism. The reason for the unavailability, for decades, of more pertinent data was the instability of the reactive intermediates and the lack of suitable precursors for isolable intermediate catalyst species. Mechanistic considerations had to explain the question of the stereoselectivity and to give a valid concept for the dependence between catalyst-olefin intermediate structures and product formation. 

Basically the mechanism of homogeneous hydrocyanation can be separated into four principle steps which are demonstrated in eqs. (2)-(5), in which ligands are omitted for the sake of simplicity [16]. 

These simplified equations concentrate on the main features of the reaction and explain most of the observations made. However, the actual mechanism also includes the equilibrium constants of each reaction step, for most of them are reversible [15]. 

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