Nickel aryls

Anionic N,0 ligands have been particularly successful in the search for new oligomerization/polymerization nickel catalysts. Pioneering work by Gavell showed that nickel aryls containing pyridinecarboxylate ligands 170 and 171 are... 

Other catalysts employed in the direct arylation of oxazole include copper and nickel. " Aryl halides can be employed under nonoxidative conditions through benzyne intermediate, and, as with palladium, an oxidant is needed to couple Ar-M species. In all cases, the arylated products are obtained in moderate to good yields. 

In the hydrogenolysis of (diphosphine)aryl methyl ethers catalysed by nickel, a Ni(0) complex featuring Ni-arene interactions adjacent to the aryl-O bond is formed, which on heating leads to a nickel aryl methoxide complex by aryl-O bond activation. Formal -elimination from this species produces a nickel aryl hydride which undergoes reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). Hydrogen is necessary for the formation of the active catalyst but not for the actual catalytic fransformation (Scheme 38). ... 

For these nickel aryl complexes, the marked stability of the ortho-substituted aryls compared with the meta- and /urrci-substituted analogues is believed to result from a combination of steric and electronic factors in the following manner. 

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

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

Several types of nitrogen substituents occur in known dye stmetures. The most useful are the acid-substituted alkyl N-substituents such as sulfopropyl, which provide desirable solubiUty and adsorption characteristics for practical cyanine and merocyanine sensitizers. Patents in this area are numerous. Other types of substituents include N-aryl groups, heterocycHc substituents, and complexes of dye bases with metal ions (iridium, platinum, zinc, copper, nickel). Heteroatom substituents directly bonded to nitrogen (N—O, N—NR2, N—OR) provide photochemically reactive dyes. 

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

ARBUZOV MICHAELIS Phosphonale Synihesis Ni catalyzed phosphonate synthesis from phosphites and aryl halides Reaction of alkyl halides with phosphites proceeds without nickel salts... 

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

Partial reduction of l-aryl-8-chloro-3-methoxy-3//-2-benzazepines, e.g. 8, to their 4,5-dihydro derivatives, e.g. 9, is effected in low yield with Raney nickel and hydrogen at room temperature.78... 

Since these adducts undergo reductive desulfuration with Raney nickel, optically active aryl methyl sulfoxides are versatile reagents for the conversion of imines to optically active amines. 

Combination of nickel bromide (or nickel acetylacetonate) and A. A -dibutylnorephcdrinc catalyzed the enantioselective conjugate addition of dialkylzincs to a./Tunsaturated ketones to afford optically active //-substituted ketones in up to ca. 50% ee53. Use of the nickel(II) bipyridyl-chiral ligand complex in acetonitrile/toluenc as an in situ prepared catalyst system afforded the //-substituted ketones 2, from aryl-substituted enones 1, in up to 90% ee54. 

It has been shown how alkenylcarbene complexes participate in nickel(0)-me-diated [3C+2S+2S] cycloaddition reactions to give cycloheptatriene derivatives (see Sect. 3.3). However, the analogous reaction performed with alkyl- or aryl-carbene complexes leads to similar cycloheptatriene derivatives, but in this case the process can be considered a [2S+2S+2S+1C] cycloaddition reaction as three molecules of the alkyne and one molecule of the carbene complex are incorporated into the structure of the final product [125] (Scheme 82). The mechanism of this transformation is similar to that described in Scheme 77 for the [3C+2S+2S] cycloaddition reactions. 

This is a problem that has been reported by several researchers in other cya-nation methods on heteroaromatic halides. (Hetero)aryl chlorides have also been tackled via in situ halogen exchange to (hetero)aryl bromides followed by sequential cyanation (Scheme 71). For this microwave-assisted process an equimolar amount of NiBr2 and a two-fold excess of NaCN were used. The only heteroaromatic chloride tested was 2-chloropyridine. Although the procedures described involve the use of significant amounts of nickel salts, a clear advantage is that the reactions can be performed in air. Moreover, the cyanat-ing reagents are easily removed since they are water soluble. 

Last, the nickel catalyzed halogen exchange for haloarenes, actually the arylation of halide anions, has been investigated. The equilibrated exchange between the phenyl bromide (60 %) and the phenyliodide (40 %) allows with some... 

As shown in this table, the metal catalysts used in the literature are mostly complexes of Ni or Cu and less often Co or Pd. For soft nucleophiles, on the left of the table, the efficiency of the nickel catalysts was already reported. Here, are presented the investigations concerning the arylation of hard nucleophiles such as amines, alcohols or hydroxide anion, using Ni, Pd and Cu catalysts. 

The mechanism of the nickel (0) catalyzed arylation of nucleophiles corresponds to this catalytic cycle according mostly to the results of Kochi (ref. 70) (Fig. 4). 

This cycle involves, first, a monoelectronic transfer from the nickel (0) complex to the aryl halide affording a Ni(I) complex and then an oxidative addition affording a 16 electron-nickel (II) which undergoes a nucleophilic substitution of Nu-, then a monoelectronic transfer occurs once again with a second aryl halide, and, last, a reductive elimination of the arylated nucleophile regenerates the active Ni(I) species. 

If, instead of a palladium catalyst, a nickel catalyst, such as the bipyridylnickel(II) bromide, is used for the arylation of amines (Fig. 7), the reduction of the aryl halide into the corresponding aromatic hydrocarbon is still present for the primary or secondary benzylamines but, the arylation into substituted anilines is the main reaction even most often the only one, for the other types of amines. 

Therefore, for the arylation of oxygenated nucleophiles, particularly of the alcohols, the investigations were focused on the nickel catalysts (Fig. 8). 

But in the presence simultaneously of a nickel catalyst and of a tertiary amine, the aryl bromide is activated and the bromhydric acid fixed, in such a way to give a very good yield (80 %) in aryl ether in regard to the moderate temperature... 

The comparison of several nickel catalyst for the arylation of alcohols with arylbromide has been performed, in the same conditions of time, temperature and base, using different oxygen, phosphorus and nitrogen ligands. The yields for each catalyst, shown in the table (Fig. 9) range from 5 to 80 %. 

---