Nickel reduction cross-coupling reactions

Reductive elimination of 5 and 6 has been studied in detail in connection with the nickel-catalyzed cross-coupling reaction of aryl halides (ArX) and alkylmagnesium halides (RMgX) (eq (18)). The reaction of tram-5 is induced by addition of aryl halides (ArX) to the system, where the reductive elimination process involving para-... 

One of the challenges is to extend the reaction from triflates to less reactive arylsulfonates. The palladium-catalyzed reaction of aryl mesylates results in low yields because of their slow oxidative addition to a palladium(O) complex, but they readily participate in the nickel-catalyzed cross-coupling reaction at 80°-100 °C. A nickel(O) species incorporating dppf ligand, obtained by in situ reduction of 10 mol% of NiCljCdppf) with zinc dust, is recognized as the most effective catalyst (Eq. 43). However, again the reaction needs to be optimized because a... 

Knochel and co-workers developed the Ni(acac)3-catalyzed cross-coupling reaction between polyfunctional primary iodoalkanes and a variety of primary diorganozinc compounds in the presence of w-trifluoromethylstyrene as a promoter. " The addition of this unsaturated promoter is required in order to coordinate to the nickel center and remove electron density from the metal atom, to facilitate the reductive elimination step. " " The scope of the reaction is extended, when Ni(acac)2 is used in the presence of BU4NI and fluorostyrene (Scheme With these... 

The Mechanism of the cross coupling reaction can be accommodated by an oxidative addition of 1-bromopropene to iron(l) followed by exchange with ethylmagnesium bromide and reductive elimination. Scheme 3 is intended to form a basis for discussion and further study of the catalytic mechanism. In order to maintain the stereospecificity, the oxidative addition of bromo-propene in step a should occur with retention. Similar stereochemistry has been observed in oxidative additions of platinum(O) and nickel(O) complexes.(32)(33) The metathesis of the iron(lll) intermediate in step b is ixp icted to be rapid in analogy with other alkylations.(34) The formation of a new carbon-carbon bond by the redilcTive elimination of a pair of carbon-centered ligands in step c has been demonstrated to occur... 

Enal-derived nickel-Jt-allyl complexes are efficient partners in cross-coupling reactions with alkenyl- and arylstannanes leading to products such as 39 (Scheme 23).P 1 As described for the aUylic ether derived complexes, the mechanism of the coupling process involves transmetalation followed by reductive elimination. The reaction is catal hic in nickel, unlike couplings of enals with allstoichiometric quantities of nickel. Many other variants of nickel-catalyzed conjugate additions may involve Ji-allyl complexes, but these are treated separately in a section on alkenes (Section 1.1.4.2) because the mechanism is poorly defined in most nickel-catalyzed conjugate additions. 

Applications of NHC - nickel in cross-coupling of organic halides with a range of organometallic reagents as well as reductive coupling reactions have been reviewed in Chinese. ... 

The latter process can even provide enantioselectivities over 99% in 1,4-additions to enones [437]. Very recently, cinnamaldehydes were found to give an anomalous selfconjugate reduction/cross-coupling tandem reaction [438], and arylboroxines reportedly undergo a catalytic asymmetric addition to N-tosylaryHmines [439]. Palladium and nickel catalysts promote similar additions of boronic adds onto unactivated alkynes [440], allenes [441], and 1,3-butadienes [442]. These new reactions of boronic acids are reviewed in detail in Chapter 4. 

The nickel-catalyzed cross-coupling of boronic acids with secondary phosphine oxides is an attractive approach for the preparation of arylphosphine oxides (Scheme 4.208) [346], After some experimentation, the authors found that nickel(II) bromide was the most effective nickel source. A mineral base was needed and potassium carbonate was effective. The substrate scope of this reaction was exceptionally high, and a range of functionalized boronic acids as well as secondary phosphine oxides were successfully cross-coupled. One drawback to this system was the use of 1,2-dichloroethane as the solvent for this reaction. It was noteworthy that the chemistry could be carried out under an atmosphere of air for some examples with only a minor reduction in the yields of the arylphosphine oxides. Thus, this reaction is very attractive as no glovebox or vacuum manifold was needed. This chemistry has the potential to generate a large number of different arylphosphine oxides due to the vast array of boronic acids that are readily available. 

Among the various oxidation states of nickd (0-IV), Ni(II) and Ni(0) are the most stable, which enables the C-C bond forming cross-coupling reactions via the oxidative addition and reductive elimination process in organic chemistry such as cross-coupling reactions. Since the nickel chemistry often... 

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