Nickel complexes acrylonitrile

If, in an early stage of the reaction, a second cyclopropene molecule is coordinated to the nickel, homo-cyclodimerization leading to tricyclic dimers of type 28 may also occur. To prevent the formation of 28, the stationary concentration of the cyclopropene in the reaction mixture must be small, i.e. the cyclopropene must be added slowly. This is especially critical if the electron-poor alkenes are only weakly bound, as is the case with methyl acrylate and the 3-alkyl-substituted acrylates. When acrolein or acrylonitrile are employed, the cycloaddition reaction is inhibited due to the formation of stable bis(alkene)nickel complexes. 

Belokon and coworkers introduced chiral nickel complexes formed from imine 1.109, and these are good Michael donors [383, 861], In the presence of catalytic amounts of base and under thermodynamic control, these complexes give 1,4-adducts with a,p-unsaturated ketones, -esters and acrylonitrile with a good... 

An example of the variation of the character of the carbon metal bonds is the 7r-allyl complexes of palladium and nickel. They are similar in structure. However, the nickel complex reacts with electrophiles such as aldehydes, ketones, and acrylonitrile 28,36,37)... 

The acrylonitrile coordinated diethyldipryridyl nickel complex was isolated as an unstable intermediate 133>. 

Addition of cyclopropane to activated olefins to form cyclopentanes is catalyzed by a zero-valent nickel complex, S41. Thus methylenecyclopropane and methyl acrylate react in the presence of a catalytic amount of bis(acrylonitrile nickel) to give methyl 3-methylenecyclopentanecarboxylate in 82% yield. 

Associative path (c) has been mainly observed for nickel(II) complexes [BOSS], This is because nickel(II) has a higher propensity to make five-coordinate species than palladium(II) and platinum(II). A steric condition is another important factor. Thus the reductive elimination from bipyridine-coordinated dialkyl-nickel complexes is known to be effectively accelerated by addition of n-acceptor olefins such as maleic anhydride and acrylonitrile to the systems (Scheme 9.8)... 

Nickel complexes containing acrylonitrile and acrolein, i.e., [Ni(AN)2] and [Ni(CH2CHCHO)2], are rapidly oxidized in air. Depending upon dispersion, their color may be light yellow to red for the weakly dispersed forms. IR spectra, as well as chemical and physical properties such as nonsolubility, nonvolatility of [Ni(AN)2], and readiness to react with Lewis bases, show that this compound is polymeric in the solid state. It is not possible to exclude that acrylonitrile constitutes a bridge which coordinates through the double bond and the nitrile group. 

Since cyclooctadiene has no suitable low-lying unoccupied orbitals some of the 3d electrons of nickel are expected to have a relatively high antibonding character. It is therefore not surprising that the nickel complex is extremely reactive, air-sensitive, and very unstable in solutions even in the absence of oxygen. Carbon monoxide at room temperature completely displaces the cyclooctadiene molecules and yields nickel carbonyl (99). Acrylonitrile reacts with (LII) under similarly mild conditions, forming bis(acrylo-nitrile)-nickel 101), while duroquinone, well below room temperature, affords cyclooctadiene-duroquinone-nickel 101). These reactions uniquely demonstrate the close interrelationship between all complexes of zero-valent nickel. 

It has been found that bis-acrylonitrile nickel also acts as a precursor of catalytic nickel complexes and some of its reactions are shown in Figure 86. 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

The stability of the olefin complexes seems to be determined by the steric and electronic characters of both the phosphorus ligand and the olefin (22). For example, ethylene complexes have only been isolated for the cases with sterically large ligands such as P(0-o-tolyl)3 and PPh3 however, maleic anhydride forms a stable isolable complex with the smaller P(0-p-tolyl)3 ligand. The nickel-ethylene bond strength is estimated to be 39 kcal/mol based on values of 36 kcal/mol for 1-hexene and 42 kcal/mol for acrylonitrile [when L = P(0-o-tolyl)3] (22). 

Pandarus and Zargarian developed propane-1,3-diol-based diphosphinite pincer nickel(III) complex 135 as a catalyst for Kharasch additions of olefins with CCI4 [154,155]. Only 0.1 mol% of the complex catalyzed the reaction of several olefins, such as styrene, methyl (meth)acrylate, acrolein, or acrylonitrile, in 65-97% yield. 

Bicyclo[2.1.0]pentane (7 equation 3) readily undergoes a cycloaddition across carbon-carbon double bonds in the presence of nickel(O) complexes. The mode is formally analyzed as a thermally forbidden [2 + 2] process and is in striking contrast to that of the lower homolog, bicyclo[1.1.0]butane, which suffers cleavage of two o -bonds and affords formal allylcarbene addition products. When a solution of bi-cyclo[2.1.0]pentane (7) and [Ni(AN)2] in excess methyl acrylate is heated at 40 C for 36 h under a nitrogen atmosphere, the stereoisomeric cycloadducts exo- and c/ product methyl 3-(cyclopent-2-enyl)propionate (10a 22%). Reaction of (7) with acrylonitrile affords the corresponding adducts (8b), (9b) and (10b). 

The complexes [Ni(acrylonitrile)2] and [Ni(COD)2] catalyze [3 + 2] cycloadditions of (26) with electron deficient l,2 isubstituted alkenes to afford 2,3- or 3,4-disubstituted methylenecyclopentanes such as (32) and (33). Similar reactions have been reported by use of tertiary phosphine complexes of nickel(0) and palladium(0) (equation 13 and Table 1). The reaction proceeds regioselectively to give (32) or (33) depending on both the alkene stmcture and catalytic system. Reactions catalyzed by phos-phine-palladium(0) complexes afford only products of the type (32), via selective cleavage of the C(2)— C(3)bondof(26). 

Acrylonitrile and related compounds displace all the carbonyl groups from nickel carbonyl to form [(RCH CHCN)2Ni], in which the nitrile bonds through the olefinic double bond 222, 418). The bis(acrylonitrile) complex catalyzes many reactions, including the conversion of acrylonitrile and acetylene to heptatrienenitrile and the polymerization of acetylene to cyclooctatetraene 418). Cobalt carbonyl gave a brown-red amorphous material with acrylonitrile, which had i cn absorptions typical of uncoordinated nitrile groups, but interestingly, the presence of C=N groups was also indicated 419). In acidic methanol, cobalt carbonyl converts a,j8-unsaturated nitriles to saturated aldehydes 459). 

Until about 1957, only metals toward the end of the transition series, such as Pd, Pt, Cu, Ag, and Hg, were known to form mono-olefin complexes. In 1959 Schrauzer 219, 220) prepared the first olefin complex of nickel, starting with nickel carbonyl and acrylonitrile ... 

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

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