Hydrocyanation nickel catalysts

Hydrocyanations -nickel catalysts [NICKEL COMPOUNDS] (Vol 17) -use of dimethylacetamide [ACETIC ACID AND DERIVATIVES - DIMETHYLACETAMIDE] (Voll)... 

Hydrogen cyanide smoothly adds to butadiene (BD) in the presence of zero-valent nickel catalysts to give (3PN) and (2M3BN) [1,4- and 1,2-addition products, respectively, Eq. (7)]. A variety of Ni[P(OR)3]4 (R = alkyl or aryl) complexes are suitable as catalysts. The reaction may be carried out neat or in a variety of aromatic or nitrile solvents at temperatures from 50-120°C. Whereas in many olefin hydrocyanations it is desirable to keep the HCN concentration very low to protect the nickel from degradation, with butadiene HCN may be added batchwise as long as the HCN concentration is kept near the butadiene concentration. In the case of batch reactions one must be cautious because of possible temperature rises of 50°C or more over a period of a few minutes. Under typical batch conditions, when Ni[P(OEt)3]4, butadiene, and HCN are allowed to react in a ratio of 0.03 1.0 1.0 at 100°C for 8 hr, a 65% conversion to 3PN and 2M3BN (1.5 1) is observed (7). 

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],... 

The hydrocyanation of alkenes [1] has great potential in catalytic carbon-carbon bond-formation because the nitriles obtained can be converted into a variety of products [2]. Although the cyanation of aryl halides [3] and carbon-hetero double bonds (aldehydes, ketones, and imines) [4] is well studied, the hydrocyanation of alkenes has mainly focused on the DuPont adiponitrile process [5]. Adiponitrile is produced from butadiene in a three-step process via hydrocyanation, isomerization, and a second hydrocyanation step, as displayed in Figure 1. This process was developed in the 1970s with a monodentate phosphite-based zerovalent nickel catalyst [6],... 

Kreutzer, K. A. Tam, W. Hydrocyanation process and multidentate phosphite and nickel catalyst composition therefore. US 5,663,369,1997. 

DuPont manufactures adiponitrile (ADN), a raw material for nylon 6,6, by the hydrocyanation of butadiene using homogeneous nickel catalysts. As shown... 

The mechanism of hydrocyanation by nickel catalysts should proceed through a nickel hydride addition on the double bonds. The nickel hydrides should result from the oxidative HCN addition to the metal, or from the above Lewis acid-assisted dissociation of HCN. The oxidative HCN addition to low-valent metal complexes has been demonstrated, particularly by NMK spectroscopy with Ni(0)(P(OF.t)3 4. 

The active nickel catalyst contains one bidentate phos-phinite ligand and the overall mechanism of the reaction is believed to be similar to butadiene hydrocyanation except that the final reductive elimination step is irreversible under the conditions of the reaction. jr-Allyl intermediates (7) are believed to play an important role in the exclusive formation of the branched nitrile product observed. Formation of the C-CN bond in the final reductive ehmination from the r-allyl intermediate occurs at C(2) and not C(4), because the aromaticity of the naphthalene ring is preserved only when the bond forms with C(2). A a-alkyl complex see a-Bond) with the Ni bound to C(l), which could give the linear (anti-Markovnikov) nitrile product, does not contribute because of the much greater stability of intermediate (7), accounting for the high regioselectivity observed. 

Derivation (1) Condensation of ethylene oxide with hydrocyanic acid followed by reaction with sulfuric acid at 320F (2) acetylene, carbon monoxide, and water, with nickel catalyst (3) propylene is vapor oxidized to acrolein, which is oxidized to acrylic acid at 300C with molybdenum-vanadium catalyst (4) hydrolysis of acrylonitrile. 

Interest in the hydrocyanation of nonactivated olefins with nickel catalysts arose from the discovery that finely divided nickel or nickel cyanide on inert supports gives higher yields of nitrile products at less severe reaction conditions than do cobdt or copper heterogeneous catalysts. ... 

Use of nickel carbonyl to add 1 mol of HCN to 1,3-butadiene may be the first example of hydrocyanation by a homogeneous nickel catalyst. That work also recorded the important observation that substantial improvement in nitrile product yield results from conducting the reaction in the presence of ( 115)3 or (C H5)3As. This work led to extensive studies to develop effective nickel hydrocyanation catdysts. Virtually all subsequent developments have focused on finding the most effective nickel complex and the identification and application of promoters to improve catalyst efficiency and life. ... 

A chelating diphosphite prepared from biphenol and PCI3 provides a very stable Ni(0) complex that catalyzes the hydrocyanantion of butadiene without excess ligand. Although the stability of this catalyst is enhanced, the amount of butadiene dimerization byproducts is significant. A related nickel catalyst prepared using a chiral chelating diphosphite based on I -2,2 -binaphthol provides enantioselectivity in the hydrocyanation of norbomene. The major product, J -exo-2-cyanonorbomane, was obtained in an enantiomeric excess of up to 38%. 

Nickel catalysts for hydrocyanation are poisoned by the formation of dicyanide complexes, LjNifCN). The formation of this material is second order in HCN. Thus, hydrocyanation reactions are t57pically nm under conditions in which HCN is dilute. The presence of added phosphite also helps to minirnize deactivation of the catalyst. 

More success has been achieved with the enantioselective hydrocyanation of vinylar-enes. For reasons described below, the hydrocyanation of vinylarenes tends to generate the branched, chiral, a-aryl nitrile product, instead of the linear, achiral, P-aryl nitrile product. Much research has focused on the hydrocyanation of 6-methoxyvinylnaphtha-lene because hydrolysis of the nitrile product would lead to the profen drug Naproxen. As shown in Equation 16.9, the hydrocyanation of this vinylarene occurs with high enanti-oselectivity in the presence of a nickel catalyst containing a phosphinite derived from a... 

Scheme 5.15 Hydrocyanations of various 1,3-dienes with in situ generated nickel catalysts from D-glucose-derived diaiyldiphosphinite ligands.

Scheme 5.16 Hydrocyanation of cyclohexa-1,3-diene with an in situ generated nickel catalyst derived from a diphosphite ligand.

The mechanism and the scope of the hydrocyanation and 2-methyl-3-butenenitrile isomerization reaction has been studied at DuPont in great detail for nickel catalysts featuring monodentate phosphite ligands, such as P(Otolyl)3. The results of these studies have been published in a review by Tolman and coworkers [9]. Later advances in the field have been summarized in recent reviews [10, 11], and book chapters [12, 13]. The aim of this chapter is to give an account of those developments that have not been covered in these reviews yet or are directly relevant to our own SFB-based research conducted in the field. 

Nickel plays a role in the Reppe polymeriza tion of acetylene where nickel salts act as catalysts to form cyclooctatetraene (62) the reduction of nickel haUdes by sodium cyclopentadienide to form nickelocene [1271 -28-9] (63) the synthesis of cyclododecatrienenickel [39330-67-1] (64) and formation from elemental nickel powder and other reagents of nickel(0) complexes that serve as catalysts for oligomerization and hydrocyanation reactions (65). 

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. 

Isomerisation is also an important step in the DuPont process for making adiponitrile (Chapter 11) in which internal pentenenitriles must be converted to the terminal alkene. The catalyst is the same as that used for the hydrocyanation reaction, namely nickel(II) hydrides containing phosphite ligands. 

First we will describe the hydrocyanation of ethene as a model substrate. The catalyst precursor is a nickel(O) tetrakis(phosphite) complex which is protonated to form a nickel(II) hydride. Actually, this is an oxidative addition of HCN to nickel zero. In Figure 11.1 the hydrocyanation mechanism in a simplified form is given the basic steps are the same as for butadiene, the actual substrate, but the complications due to isomer formation are lacking. 

In the presence of a large excess of cyanide, the catalyst prepared from [Ni(COD)2] and TPPTS was also active in the hydrocyanation of allylbenzene however, at low cyanide/nickel ratios isomerization to propenylbenzene became the main reaction path (Scheme 9.9) [5]. 

Because of its low acidity, hydrogen cyanide seldom adds to nonactivated multiple bonds. Catalytic processes, however, may be applied to achieve such additions. Metal catalysts, mainly nickel and palladium complexes, and [Co(CO)4]2 are used to catalyze the addition of HCN to alkenes known as hydrocyanation.l67 l74 Most studies usually apply nickel triarylphosphites with a Lewis acid promoter. The mechanism involves the insertion of the alkene into the Ni—H bond of a hydrido nickel cyanide complex to form a cr-alkylnickel complex173-176 (Scheme 6.3). The addition of DCN to deuterium-labeled compound 17 was shown to take place... 

The unpromoted hydrocyanations of monoolefins discussed so far generally involved only a few catalytic cycles on nickel. The development of a practical commercial process depended on getting many cycles. Certain Lewis acids are quite remarkable in increasing (1) catalyst cycles, (2) the linearity of products obtained, and (3) the rates of reaction. The effects depend on the Lewis acid, the phosphorus ligand used, and the olefin substrate (72). 

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