Hydrocyanation of 1,3-Dienes

The isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile is thought to occur by elimination and re-addition of HCN. A number of labeling experiments have been conducted to reveal the order and reversibility of the steps of hydrocyanation an experiment that addresses the mechanism of isomerization of the branched nitrile is depicted in Equation 16.8. As shown on the left of this equation, allylic transposition of the nitrile group without elimination would lead to 5-deuterio-3-pentenenitrile as the only isotopomer of 3-PN-iij. However, elimination to form an H-Ni-CN complex and free 1-deuteriobutadi-ene would lead to a mixture of two labeled 3-PN-iij isotopomers after re-insertion of the labeled butadiene and reductive elimination of the free labeled 3-PN. A mixture of the two isotopomers was formed, and this result indicates that isomerization occurs by elimination and re-addition of HCN. 

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Hydrocyanation of dienes, a process of industrial importance (see Section 6.2.4), yields 1,4-addition products when conjugated dienes are reacted. The addition involves ri3-allyl intermediates (19) ... 

The hydrocyanation of butadiene is an important industrial route to adiponitrile (equation 163).602 Again, complex (131) is used as the catalyst for the reaction. The hydrocyanation of dienes proceeds mainly by 1,4-addition and r/ -allyl complexes are believed to be intermediates (Scheme 59).603 The l-cyano-2-butene is then isomerized to l-cyano-3-butene which undergoes further hydrocyanation to give adiponitrile.601"603... 

Besides the class of traditional phosphines ligands, the related class of phosphite ligands has been utilized as ancillary ligation in various industrially relevant processes such as the hydrocyanation see Hydrocyanation) of dienes or hydroformylation see Hydroformylation) or the copolymerization of CO and olefins.The thermochemistry of ligand substitution of a variety of phosphite ligands has... 

Keim, W., Behr, A., Luehr, H.O., and Weisser, J. 1982. Catal3ftic hydrocyanation of dienes and trienes. Journal of Catalysis, 78 209-216. 

In the metal catalyzed hydrocyanation area, the stage is set for major improvements in enantioselectivity for simple styrene derivatives. Asymmetric hydrocyanation of dienes and functionaUzed olefins is another exciting area ripe for further explorations. 

Mechanistic studies on the reductive elimination of square-planar type aryl(j7 -allyl)palladium complexes demonstrated occurrence of bond formation between the aryl carbon and one of the allyl termini that are located cis to each other (Scheme 8.53) [91]. The allyl ligand remained 17 -coordinated during the coupling. Similar reductive elimination between 17 -allyl and cyano ligands may be a key step in the industrially important nickel catalyzed hydrocyanation of dienes (Scheme 8.54) [92]. 

Ni(0) complexes of TPPTS have been employed as catalysts for the hydrocyanation of dienes and unsaturated nitriles. Product linearity and catalyst lifetimes can be improved if the catalysis is performed in a xylene/water biphasic system by using TPPTS as co-catalyst [33]. The Ni(0)/TPPTS complexes employed may be obtained by electrochemical reduction of Ni(CN)2 in water in presence of TPPTS [34]. 

The hydrocyanation of alk5mes provides a direct method for preparing a,p-unsaturated nitriles such as 67. The reactions proceed at 120 °C in an autoclave with hydrogen cyanide and catal3hic tetrakis(triphenyl phosphite)nickel(O) (Scheme 51). Lower temperatures may be employed if the aUq ne and hydrogen cyanide are added very slowly. The hydrocyanation of dienes and aUcenes (Sections 1.1.1.6 and 1.1.4.5) are much more widely used procedures than the hydrocyanation of alkynes. 

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. 

The asymmetric hydrocyanation of dienes with substantial enantioselectivities has also been reported (Equation 16.10). Like the reactions of vinylarenes, these reactions have been reported with catalysts containing carbohydrate-derived phosphinites. Reactions of aryl-substituted dienes occur to form the products from 1,2-hydrocyanation. In addition to the reactions of purely acyclic dienes, such as 1-phenyl-l,3-butadiene, dienes containing an exocyclic vinyl group have been studied. These are substrates for products possessing... 

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