Nickel-catalyzed coupling

The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

Colquhoun at ICI first reported the synthesis of macrocyclic monomers containing ether and ketone linkages through nickel-catalyzed coupling of... 

Recent discoveries have expanded the utility of nickel-catalyzed coupling reactions. Inclusion of butadiene greatly improves the efficiency of the reactions.268... 

Aryl carbamates are also reactive toward nickel-catalyzed coupling.270 Since the carbamates can be readily prepared from phenols, they are convenient starting materials. 

In 1979, the reaction of styrenyl and hexenyl halides with an alkali metal thiophenolate and ethanethiolate was reported (Equation (40))130 Reaction yields exceeded 90%, and the products retained the geometry of the starting olefin. In contrast to the stereospecificity of palladium-catalyzed couplings involving vinyl halides, nickel-catalyzed couplings of vinyl halides with thiolates gave mixtures of stereoisomeric products 131... 

By means of nickel-catalyzed couplings of vinyl zirconocenes, Schwaebe et al. succeeded in obtaining fluorinated materials using a-bromo esters as electrophiles (Scheme 4.62) [113]. The yields achieved, albeit modest (24—65%), were far better using Ni(0) than those obtained in experiments based on several palladium(O) sources (no product observed). Isopropyl esters appear to be crucial, as competing 1,2-addition occurs with both ethyl and n-butyl analogues. Curiously, t-butyl esters were found to completely inhibit both modes of reaction of the zirconocene. 

Scheme 72 Nickel-catalyzed coupling of aryl halides and alkenes.

Oxidative nickel-catalyzed coupling of aldehydes and alkynes to generate allylic alcohols. Intermolecular and intramolecular examples are both effective, and the transmetalating agent (MR" ) may be an organosilane, organoborane, organozinc, or alkenylzirconium. ... 

The recent applications of NHCs in ruthenium-catalyzed olefin metathesis and palladium/nickel-catalyzed coupling reactions show the value of such a profound understanding about ligand properties before using them for specific catalytic transformations. 

In addition, the reaction is very chemoselective and even a keto group is tolerated (Table 5). It should be underlined that this procedure compares advantageously to the corresponding palladium- or nickel-catalyzed coupling reactions. 

Similarly, decreasing the electron density on the metal will enhance its willingness to undergo reductive elimination and become more electron rich. A typical demonstration of this tendency is the nickel catalyzed coupling of sp3 hybridized carbon atoms. Here, if a nickel-phosphine catalyst is used, the catalytic cycle is very slow, due to disfavoured reductive elimination. The use of additives that deplete the electron density of the nickel atom through coordination (e.g. fluorostyrenes) leads to a marked increase of the turnover frequency.18... 

An analogous nickel catalyzed coupling was also reported recently, where 3-, and 4-cyanopyridine were coupled with different ethynylzinc derivatives in the presence of a nickel-phosphine catalyst system (7.43.),61 Although this reaction is not a Sonogashira coupling, it constitutes an efficient alternative approach to ethynylpyridines. It is also interesting to... 

In certain cases, when the palladium or nickel catalyzed coupling is not efficient or fails completely, an alternate solution is provided by the use of copper based catalyst systems. The 5-iodouracil derivative shown in 7.77. was unreactive towards imidazole using either the Buchwald-Hartwig conditions or the copper(I) triflate promoted the carbon-nitrogen bond formation reported by Buchwald98 These latter conditions, however, were effective in coupling the iodouracil with a series of other amines (7.77.), The optimal catalyst system consisted of copper(I) triflate, phenantroline and dibenzylideneacetone (dba).99... 

Nickel-Catalyzed Coupling of Aryl O-Carbamates with Grignard Reagents, Synthesis of 2,7-Dimethylnaphthalene and Derivatives. 

An elegant synthesis method which is specific to sulfone polymers containing phenyl—phenyl linkages (such as PPSF) is the nickel-catalyzed coupling of aryl dihalides. The scheme for this synthesis involves a two-step process. First, an aromatic dihalide intermediate is formed which carries the backbone features of the desired polymer. This aromatic dihalide intermediate is then self-coupled in the presence of zero-valent nickel, triphenylphosphine, and excess zinc to form the biphenyl- or terphenyl-containing polymer. Application of this two-step scheme to PPSF can be depicted as follows ... 

An important advancement for the synthesis of well-defined PPPs was the site-controlled nickel-catalyzed coupling of Grignard reagents, derived from dihalobenzenes, to yield linear PPP as shown in Scheme 19 [63,64]. The PPPs obtained by Yamamoto chemistry range from yellow to brown infusible solids of low molecular weights typically with degrees of polymerization ranging from 10-12. 

Allylsilanes. A regio- and stereoselective synthesis of allylsilanes involves nickel-catalyzed coupling of enol phosphates with trimethylsilylmcthylmagnesium chloride... 

Fig. 3 Hiyama, Kumada-Corriu, Stille, Sonogashira, and other nickel-catalyzed coupling reactions...

The nickel-catalyzed coupling reaction is relatively unaffected by the steric congestion of the reaction partners, as exemplified in Eq. (150) [351], In addition, it shows reasonable compatibility of functional groups that are susceptible to the Grignard addition. An example is shown in Eq. (151) [187]. 

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