2M3BN 2-methyl-3-butenenitrile

A = a Lewis acid such as AICI3, ZnCL, or BR3 ADN = Adiponitrile, NC(CH2)4CN BD = 1,3-butadiene, (CH2=CH)2 ee = Enantiomeric excess ESN = Ethylsuc-cinonitrile, NCCH2CH(CN)CH2Me L = A P-donor ligand such as a phosphite or phosphine 2M3BN = 2-methyl-3-butenenitrile, NCCH(Me)CH=CH2 MGN = 2-methylglutaronitrile, NC(CH2)2CH(CN)Me 2PN = 2-pen-tenenitrile, MeCH2CH=CHCN 3PN = 3-pentenenitrile,... 

The current hydrocyanation process can be broken down into two major steps. In the first, HCN is added to butadiene in the presence of an NiL4 catalyst to give 3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile (2M3BN) [Eq. (7)]. Fortunately the branched 2M3BN may be isomerized to the linear 3PN isomer [Eq. (8)]. In the second step, a Lewis acid promoter is added to the NiL4 (L = a phosphorus ligand) catalyst to effect the double bond isomerization of 3PN to 4-pentenenitrile (4PN) concurrently with the... 

The first HCN addition (eq. 3) occurs at practical rates above 70°C under sufficient pressure to keep butadiene condensed in solution and produces the 1,4- and 1,2-addition products (3-pentenenitrile [4635-87-4 ], 3PN, and 2-methyl-3-butenenitrile [16529-56-9 ], 2M3BN) in a 2 to 1 ratio. Fortunately, thermodynamics favors 3PN (about 20 1) and 2M3BN may be isomerized to 3PN (eq. 4) in the presence of a nickel catalyst. 

The nickel-catalyzed hydrocyanation of butadiene is a two-step process (Figure 3.32). In the first step, HCN is added to butadiene in the presence of a nickel-tetrakis(phosphite) complex. This gives the desired linear product, 3-pente-nenitrile (3PN), and an unwanted branched by-product, 2-methyl-3-butenenitrile (2M3BN). The products are separated by distillation, and the 2M3BN is then isomerized to 3PN. In the second step, 3PN is isomerized to 4PN (using the same nickel catalyst), followed by anti-Markovnikov HCN addition to the terminal double bond. The second step is further complicated by the fact that there is another isomerization product, CH3CH2CH=CHCN or 2PN, which is thermodynamically more stable than 4PN. In fact, the equilibrium ratio of 3PN/2PN/4PN is only 20 78 1.6. Fortunately, the reaction kinetics favor the formation of 4PN [95],... 

Huser et al. have extended Kuntz s work to the isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-PN (isomerization step Eq. (6) 92% yield) [17-19]. 

In the pastfewyears, application of electron-rich phosphine [23-27] and carbene [28] ligands has attracted some attention for the Ni-catalyzed 2M3BN isomerization reaction. These catalyst systems commonly yield 2-pentenenitriles (2PN) and branched 2-methyl-2-butenenitriles (2M2BN). Although the formation of (X,P-unsaturated nitriles 2PN and 2M2BN is of no technical relevance, it has been studied in quite some detail because the transformation is an interesting model reaction to study Ni-catalyzed C-H bond activation (Scheme 8.6). 

It is well know that nickel(O) complexes play a crucial role in the commercial synthesis of adiponitrile (AdN), the major nylon-6,6 precursor. In the global process, the isomerization of the branched 2-methyl-3-butenenitrile (2M3BN) to the linear 3-pentenenitrile (3PN) is a key step. " Such isomerization is obtained through the C-CN bond activation involving a Ni° intermediate. 

The reaction is carried out in two stages. In the first stage, two reactions (5.6.2) and (5.6.3) take place. One molecule of HCN is added to butadiene. This gives 3-pentenenitrile (3PN) and 2-methyl 3-butenenitrile (2M3BN) by anti-Markovnikov and Markovnikov addition of the cyano group. However, under the reaction conditions 2M3BN is isom-erized to 3PN. 

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