Diene complexes hydrocyanation

Nickel is frequently used in industrial homogeneous catalysis. Many carbon-carbon bond-formation reactions can be carried out with high selectivity when catalyzed by organonickel complexes. Such reactions include linear and cyclic oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions [1], Many of the complexes that are active catalysts for oligomerization and isomerization reactions are supposed also to be active as hydrogenation catalysts. 

Hydrocyanation of aliphatic conjugated dienes in the presence of Ni(0) complexes gives diene rearrangement products and /i.y-unsaUiratcd nitriles in 10-90% yields10. Dienes other than 1,3-butadiene do not produce terminal nitriles, implying that the more highly substituted jr-allyl nickel complex is favored. Thus, reaction of 1-phenylbuta-l,3-diene (1) affords ( )-2-methyl-4-phenylbut-3-enenitrile (2) as the sole product (equation 5). The... 

Hydrocyanation of olefins and dienes is an extremely important reaction [32] (about 75 % of the world s adiponitrile production is based on the hydrocyanation of 1,3-butediene). Not surprisingly, already one of the first Rhone Poluenc patents on the use of water soluble complexes of TPPTS described the Ni-catalyzed hydration of butadiene and 3-pentenenitrile (Scheme 9.10). The aqueous phase with the catalyst could be recycled, however the reaction was found not sufficiently selective. 

In a proton NMR experiment in which 1,4-pentadiene was added to a solution of HNi[P(OMe)3]4, it was possible to watch the isomerization of 1,4- to 1,3-pentadiene, followed by formation of l,3-dimethyl-7t-allyl complexes (53). The observation of 7t-allyl products in the reaction of the hydride with the conjugated diene, but not in the ff-alkyl intermediates involved in isomerization, illustrates the much greater stability of zr-allyl complexes of nickel compared to tr-alkyls, a feature which is also observed in the hydrocyanation reactions. 

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... 

Hydrocyanation is also catalyzed by [Pd(PPh3)4] (103) and [Pd P(OPh), 4] (132), again in both cases in the presence of excess ligand.604 Complex (132) is an effective catalyst for the addition of hydrogen cyanide to cyclic monoenes and dienes such as norbomene and norbornadiene 605-606 ethylene also reacted readily. The product obtained from norbornene was the exo isomer (equation 165). When norbornadiene was the substrate, some of the endo product was formed.605... 

The most outstanding example for the applieation of homogeneously catalyzed hydrocyanation is the DuPont adiponitrile process. About 75 % of the world s demand for adiponitrile is covered by hydrocyanation of butadiene in the presence of nickel(O) phosphite species. This process is discussed for the addition of HCN to dienes as an example, because in this case a well-founded set of data is available. Though it was Taylor and Swift who referred to hydrocyanation of butadiene for the first time [45], it was to Drinkard s credit that this principle was fully exploited for the development of the DuPont adiponitrile process [18]. The overall process is described as the addition of two equivalents of HCN to butadiene in the presence of a tetrakisphosphite-nickel(O) catalyst and a Lewis acid promoter. A phosphine-containing ligand system for the catalyst is not suitable, since addition of HCN to the tetrakisphosphine-nickel complex results in the formation of hydrogen and the non-aetive dicyano complex [67], In general the reaction can... 

In the first stage Lewis acids are absent and further hydroeyanation of the monoolefm products 3-PN 40 and 2M3BN 41 does not readily oeeur. The monoeyanation of butadiene is similar to HCN addition to olefins. An individual feature of hydrocyanation of conjugated dienes is the intermediate appearance of TT-allylic complexes 43, which participate in the successive carbon-carbon coupling. Equations (12) and (13) demonstrate the reaction of butadiene with the hydrido-nickel complex 42 leading to formation of nitrile 40 (a) and explain the generation of byproducts, i.e., the branched nitrile 41 via an alternative pathway (b) [68-70]. 

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 alkenes and dienes has similarly provided an exceptionally useful process for the conversion of simple feedstocks into more complex structures. [Caution Hydrogen cyanide is a highly toxic gas.] The process is best known as a key step in the DuPont adiponitrile process, which involves the dihydrocyanation of 1,3-butadiene (Scheme 3-95). The overall sequence first involves butadiene hydrocyanation to afford a mixture of 3-pentenenitrile and 2-methyl-3-butenenitrile. The unwanted branched isomer 2-methyl-3-butenenitrile is isomerized to 3-pentenenitrile under different conditions, and then 3-pentenenitrile is isomerized to 4-pentenenitrile in a subsequent nickel-catalyzed process in the presence of Lewis acidic additives. Finally, hydrocyanation of the remaining alkene generates the desired product adiponitrile, which serves as a precursor for nylon. A vast number of studies describing the optimization and mechanistic study of this process has appeared, and the interested reader is referred to the many excellent studies describing the details of this process. " ... 

The kinetics and mechanism of nickel-catalysed olefin hydrocyanation have been reported , and the addition of DCN to cyclohexa-1,3-diene catalysed by [Ni (p 0Ph 3 )i ] is found to occur with cis-stereochemistry indicating cis-migration of coordinated cyanide in the intermediate ir-allyl complex. The reactions of various organic bromides RBr (R Ph, PhCH=CH, allyl, MeCH=CHCH2) with a mixture of bicycloheptene or bicycloheptadiene and alkynes R C=CH (R =Ph, hexyl, etc) catalysed by Ni(0) or Pd(0) complexes produce bicyclic compounds such as (55) . PhCH=CHBr reacts with bicyclo [2.2.1]hept-2-ene and R2NH (R2 = (CH2), (CH2)5,... 

Allyl complexes have contributed significantly to the development of the organometallic chemistry of nickel and the applications of nickel complexes in organic synthesis, for example, nucleophilic attack on coordinated allyl ligands. In addition, allylnickel complexes have been identified as key intermediates in the oligomerization and cyclization of olefins and dienes. For example, the Ni(0)-catalyzed hydrocyanation of butadiene to adiponitrile, the main component of a major commercial process for the production of nylon, involves Ni (7r-allyl) intermediates. Moreover, the 77-rearrangements of allylnickel species have helped explain the facile isomerization of olefins in the presence of nickel complexes. The Ni-catalyzed homoallylation of carbonyl compounds with 1,3-dienes also involves Ni(7r-allyl) complexes this subject has been reviewed recently. New applications include the cleavage of G-G bonds in the deallylation of malonates, the preparation of cyclopentenones by carbonylative cycloaddi-... 

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