Nickel-catalyzed reactions formation

Mori has reported the nickel-catalyzed cyclization/hydrosilylation of dienals to form protected alkenylcycloalk-anols." For example, reaction of 4-benzyloxymethyl-5,7-octadienal 48a and triethylsilane catalyzed by a 1 2 mixture of Ni(GOD)2 and PPhs in toluene at room temperature gave the silyloxycyclopentane 49a in 70% yield with exclusive formation of the m,//7 //i -diastereomer (Scheme 14). In a similar manner, the 6,8-nonadienal 48b underwent nickel-catalyzed reaction to form silyloxycyclohexane 49b in 71% yield with exclusive formation of the // /i ,// /i -diastereomer, and the 7,9-decadienal 48c underwent reaction to form silyloxycycloheptane 49c in 66% yield with undetermined stereochemistry (Scheme 14). On the basis of related stoichiometric experiments, Mori proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of dienals involving initial insertion of the diene moiety into the Ni-H bond of a silylnickel hydride complex to form the (7r-allyl)nickel silyl complex li (Scheme 15). Intramolecular carbometallation followed by O-Si reductive elimination and H-Si oxidative addition would release the silyloxycycloalkane with regeneration of the active silylnickel hydride catalyst. 

General Comments. The formation of deoxy sugars by hydrogenation over Raney nickel often leads to the abnormal isomer (namely, that formed by diequatorial opening of the oxirane ring) as the major product, in contrast to the product afforded by lithium aluminum hydride this suggests that a different mechanism is involved in the nickel-catalyzed reaction. 

Discussion Point DPS The previously unexpected observation of side-chain branches in diimine-nickel catalyzed polyethylene formation is explained by the reaction scheme represented in Figure 15. Propose related chain migration schemes which explain i) the chain straightening , i.e. the incorporation of propylene methyl substituents into the backbone of polypropylene chains produced by these catalysts, ii) the 2,co-concatenation of higher a-olefins by some Ni-based catalysts, and Hi) the introduction of stereoerrors in isotactic polypropylene by chain-migration of chiral ansa-zirconocene catalysts. 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-catalyzed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity7 to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] catalyzed reaction, methyl acetate carbonylation is considered to go through formation of etliylidene diacetate (33) ... 

The requirement for sodium borohydride in the nickel-catalyzed reactions with amines is presumably owing to its ability to prevent complex formation between Ni(acac)2 and the amine. Even in cases where the borohydride is not essential, its addition results in some enhancement of the rate. The role of the phosphine is to reduce Ni(ll) to Ni(0). 

Negishi, E., Van Horn, D. E. Selective carbon-carbon bond formation via transition metal catalysis. 4. A novel approach to cross-coupling exemplified by the nickel-catalyzed reaction of alkenylzirconium derivatives with aryl halides. J. Am. Chem. Soc. 1977, 99, 3168-3170. 

Formation of n-alkylnickels by addiction of Ni hydride to an alkene is important in many nickel-catalyzed reactions such as alkene dimerization and isomerization. However, stoichiometric formation of alkylnickels from alkenes and Ni hydrides is not synthetically useful because of the reactivity of alkylnickels. The regiochemistry of the addition of HNiX(PR3)2 to propene is affected by the nature of the trialkylphosphine group used in the Ni hydride complex. The observed ratios of n-propyl- to isopropyl-nickel found after the insertion step vary from 82 18 to 82 20 to 19 81 as the phosphine is changed from P(OC6Hs)3 to P(c-C6Hu) to P(t-C4H9)2(i-C3H7). ... 

In recent decades much effort has been devoted to extending the scope of palladium, copper, and nickel-catalyzed reactions proceeding via aryl or vinyl metal intermediates [12]. These coupling reactions have enabled the formation of many kinds of carbon-carbon and carbon-heteroatom connections that were previously very difficult to realize. Metal-mediated transformations have proven especially valuable for introduction of substituents to aromatic core structures. They allow the presence of a wide variety of functional groups and perform equally well in both inter and intramolecular applications. Furthermore, in homogeneous catalysis,... 

Formation of poly(benzoyl-l,4-phenylene) with the aid of a nickel-catalyzed reaction was reported [247] ... 

Before 1970, the reactions of aryl halides (ArX) with nucleophiles were restricted to electron-deficient aryl halides via S Ar mechanisms. The reactivity of aryl hahdes in S Ar reactions decreases in the order ArF>ArCl>ArBr ArI [1]. The range of reactive nucleophiles was narrow, and reactions of alkenes or alkynes were not known. The discovery in 1968 of oxidative additions of palladium(O) (Fitton [2a]) and then nickel(O) (Kochi [2b]) with aryl hahdes (ArI>ArBr>ArCl) that generate ArM XL (M=Pd, Ni) paved the way to new palladium- and nickel-catalyzed reactions of aryl hahdes with C-nucleophiles, leading to the formation of C—C bonds. Palladium- or nickel-catalyzed cross-couphng reactions are described herein, following the historical order of discovery. 

Ananikov VP, Orlov NV, Kabeshov MA, Beletskaya IP, Starikova ZA. Stereoselective synthesis of a new t)fpe of 1, 3-dienes by ligand-controlled carbon-carbon and carbon-heteroatom bond formation in nickel-catalyzed reaction of diaryldichalcogenides with alkynes. Organometallics 2008 27 4056 061. 

In the presence of 1,3-butadiene, nickel-catalyzed reactions of alkyl halides (Br, Cl, or OTs) with Grignard reagents yield the corresponding cross-coupling products. An anionic Ni(II) intermediate is suggested to be involved in the overall transformation leading to the formation of carbon-carbon bonds [92]. 

Development of new methodologies for formation of carbon-carbon bonds has been one of the major tasks in organic chemistry. Obviously, organometallic compounds, particularly zinc derivatives, have found great use in such reactions. During the past several years, there have been several significant reports of nickel- and palladium-catalyzed reactions of dialkylzincs and alkylzinc halides with alkyl halides of diverse structure. A detailed account of most of these studies can be found in a recent review by Knochel et al,246... 

In the course of investigation into new C-C bond formation processes, Hiyama has developed an efficient nickel-catalyzed arylcyanation of alkynes.67 The addition reaction of an aryl-CN bond to alkyne affords aryl-substituted alkene nitrile in good yield. Good regioselectivity is reported in the case of unsymmetrical alkynes with two sterically different substituents. 

While transition metal-catalyzed hydroboration is a well-established reaction, the same cannot be said for the transition metal-catalyzed hydroalumination. The synthetic utility of this reaction is only just beginning to emerge. Lautens has led the way in the use of hydroaluminations as the key step in the total synthesis of complex natural products. The synthesis of the anti-depressant sertraline130 involved the formation of the tetrahydronaphthalene core, and this is best achieved using the nickel-catalyzed hydroalumination of oxabicyclic alkenes (Table 16). 

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