Ni-catalyzed coupling reactions

Pd- and Ni-catalyzed coupling reactions follow a mechanism which is described in Scheme 13. 

Scheme 3 Silyl diene as substrate in Ni-catalyzed coupling reactions with aryl aldehydes...

Chloro- and 2-bromo-pyridines undergo Ni-catalyzed coupling reactions with primary alkyl Grig-nard reagents (equation 3-halopyridines are less reactive and an ortho methyl substituent... 

Reports of catalysis with acyclic carbene-metal complexes first appeared in 2005 [19,22a,38] and dealt with Pd- and Ni-catalyzed coupling reactions for which effective NHC-based catalysts were already known [39]. Gradually, the focus has shifted toward identifying reactions that benefit from the distinct steric and electronic properties of acyclic carbenes. In this section, key examples of catalysts that exhibit imusual stabilities, activities, or selectivities resulting from the presence of acyclic carbene ligands are highlighted. Recent review articles provide more detailed compilations of catalytic applications of this ligand class [9]. 

Formation of multi-substituted arylalkynes was achieved via Ni-catalyzed coupling reaction of zirconacyclopentadienes with two alkynyl halides (Eq. 66) [74]. 

By using Ni-catalyzed coupling reaction, PPP with tetrahydropyrene repeating units 67 was also synthesized from 2,7-dibromo-4,9-di- -octyl-4,5,9,10-tetrahydropyrene (66) (Scheme 26) [67]. This polymer structural... 

Diazonium salts react with various nucleophiles in water (Eq. 11.62).106 In acidic aqueous solution, p-pheny I e ncbis di azo ni um ion reacts with alcohols more rapidly than it does with water.107 In the presence of nucelophiles such as halides, the substitution products are obtained. Furthermore, diazonium salts of aromatic compounds are excellent substrates for palladium-catalyzed coupling reactions such as the Heck-type reactions in water. 

The second fixation reaction that has been the subject of theoretical study is the nickel(0)-catalyzed coupling reaction of C02 with acetylene (equation 1), which was theoretically investigated with the ab initio SD-CI method [25]. The theoretical calculations clearly showed that if the nickel(O) moiety was eliminated from the reaction system, the activation barrier increased very much, and that the C-C bond formation between C02 and acetylene was accelerated by the charge-transfer from the nickel(O) d orbital to the orbital resulting from the combination between n orbitals of acetylene and CO2. Actually, the HOMO contour map of Ni(PH3)(C02)(C2H2) clearly displays this orbital mixing in the transition state. 

One of the first hyperbranched polymers described in the literature was polyphenylenes, which were presented by Kim et al. [30-32] who also coined the term hyperbranched . The polyphenylenes were prepared via Pd(0) or Ni(II) catalyzed coupling reactions of various dihalophenyl derivatives such as di-bromophenylboronic acid. The polymers were highly branched polyphenylenes with terminal bromine groups which could be further transformed into a variety of structures such as methylol, lithiate, or carboxylate (Fig. 5). 

Mulhaupt et al. synthesized novel soluble copoly-arylenes via a Ni(0)-catalyzed coupling reaction of aryl chlorides. Molar ratios of dichlorodiphenyl sulfone (a) to m-dichlorobenzene (y) were used to vary the amount of m-phenylene in the final copolymer. Then these copolymers were dissolved in chloroform and sulfonated with chlorosulfonic acid. The synthe-... 

C-Arylation of indoles can be accomplished by means of palladium-catalyzed coupling reactions, such as the Suzuki coupling (Entry 7, Table 15.7) or Stille coupling with resin-bound 2-bromoindoles [88] or 5-bromoindoles [75]. 2-Iodoindoles have been prepared on polystyrene by iododesilylation of 2-silylindoles with NIS (Entry 8, Table 15.7), and these can be C-arylated with arylboronic acids [73]. 

Pyrans constitute another class of oxygen-containing heterocycles that have been prepared from Ni-catalyzed cycloaddition reactions. The coupling of diynes and aldehydes could be mediated by the combination of a Ni(0)... 

Recent advances of the Negishi cross-coupling reaction have enabled chemists to catalytically couple two sp carbon centres. These reactions provide the coupled alkane as the final product . A remote double bond in primary halides also enabled the Ni-catalyzed crosscoupling reactions between two Csp centres . ... 

The literature has been surveyed up to 1988. Some recent reviews relevant to this section are as follows Ni-, Pd-, " and Cu-catalyzed" coupling reactions. Catalytic asymmetric cross-coupling reactions are not treated in this section, since the subject has recently been well reviewed. ... 

---