Organonickel

Other Complexes. Several other classes of organonickel complexes are known. AHyl bromide and nickel carbonyl react to give a member of the TT-aHyl system [12012-90-7], [7T-C3H3NiBr]2 (100). Tris(r -ethene)nickel [50696-82-7] reacts with acetylene and l,2-bis(diisopropylphosphino)ethane to... 

Nickel salts form coordination compounds with many ligands. Dibromobis(tri- -butylphosphine)nickel(Il) [15242-92-9], [( -C4H2)3P]2NiBr2, dicyanoammineaquanickel(11), Ni(NH3)(H20)(CN)2, and bromonitrosobis(triphenylphosphine)nickel(Il) [14586-72-2], are complexes used for syntheses in preparative organonickel chemistry. 

With hydrogen sulfide at 500—600°C, monochlorotoluenes form the corresponding thiophenol derivatives (30). In the presence of palladium catalysts and carbon monoxide, monochlorotoluenes undergo carbonylation at 150—300°C and 0.1—20 MPa (1—200 atm) to give carboxyHc acids (31). Oxidative coupling of -chlorotoluene to form 4,4 -dimethylbiphenyl can be achieved in the presence of an organonickel catalyst, generated in situ, and zinc in dipolar aprotic solvents such as dimethyl acetamide (32,33). An example is shown in equation 4. 

The most important by-product formed in the reaction of pyridine with degassed Raney nickel is an organonickel complex which has been shown to be a complex of one molecule of 2,2 -bipyridine, two molecules of 2,2 -pyrrolylpyridine (17), and one nickel II ion. It is significant that, although the formation of 2,2 -bipyridine ceases after 50 hr refluxing, the formation of this complex continues for at least another 140 hr. 

Some of the factors which affect the relative yields of 2,2 -bipyri-dine and of the organonickel complex are known. For example, the addition of about 1% pyrrole to the pyridine during the reaction causes a 60% increase in the yield of the complex and a 13% decrease in the amount of 2,2 -bipyridine formed (see Table III). When more pyrrole is present the yields of both products are lowered, but the ratio of complex to 2,2 -bipyridine is increased by a factor of about 7. These findings suggest that pyrrole can be incorporated into the complex, presumably by reaction between pyrrole and pyridine to... 

Organonickel derivatives also offer cases of the -coordination of the substituted hydrotrisfpyrazol- l-yl)borate ligand. For the palladium and platinum complexes, the M(II) M(IV) (M = Pd, Pt) transformation is facile. Organopalla-dium chemistry offers anew type of agostic interactions, C—H - - - Pd, where the C—H bond belongs to one of the pyrazolate rings. Cyclopalladation of various pyrazol-l-ylborates and -methanes does not modify their structure. 

Organonickel Chemistry in Organic Synthesis. Some Applications of Alkyl and Metalacyclic Derivatives," Ctopora, J. Paneque, M. Poveda, M.L. Carmona. E. Svnlett 1994, 465... 

The early synthetic processes using organonickel compounds involved the coupling of allylic halides, which react with nickel carbonyl, Ni(CO)4, to give TT-allyl complexes. These complexes react with a variety of halides to give coupling products.255... 

Tamaru Y (2005) Modern organonickel chemistry. Wiley-VCH, Weinheim... 

B2) Metathetical exchange of a nickel(II(-bonded anionic ligand by an anion of a stronger Brdnsted acid. The nickel II) component can be either an organonickel complex or a nickel hydride. 

The primary (7, 47) and most commonly used organonickel compounds have been the dimeric 7r-allyl- (or substituted Tr-allyl-) nickel halides (1) (Scheme 1) or their monophosphine adducts (2) in the presence of Lewis acids such as aluminum halides or alkylaluminum halides (4, 48-53). The... 

Method B2 A modification of method B4 for the preparation of catalysts starting from organonickel halides consists in the exchange of the halide anion by an anion of a strong complex acid, HY. This has been accomplished by reacting 7r-allylnickel halides (1) or their phosphine adducts (2) with silver salts (65) ... 

Reactions leading to the formation of the catalytically active nickel hydride species from organonickel precursors (Section III) can be regarded as model reactions for olefin oligomerization reactions. The reactions described by Eq. (8) and Scheme 3 (Section III) show that RNiX compounds (R = methyl orallyl, X = halide or acetylacetonate) activated by Lewis acids add to double bonds under mild reaction conditions (-40° or 0°C). It follows further from these reactions that under conditions leading to olefin dimerization a rapid nickel hydride /3-hydrogen elimination reaction occurs. The fact that products resulting from olefin insertion into the nickel-carbon bond are only observed when /3-hydride... 

This review is an attempt to rationalize the main reaction patterns observed so far in organonickel chemistry. Synthetic work in organic chemistry has found an exceedingly valuable tool in the use of nickel complexes. The reason for this lies in the fact that nickel possesses a very favorable combination of properties to meet the requirement for an organic reaction to take place via coordination. Let us consider, for example, which basic steps occur when organic ligands react on a transition metal to form C—C bonds. 

The various properties of nickel combine in such a way that all three steps indicated above often occur without difficulty. The main limitations have been found in working with saturated substrates in direct C—H activation. So far the organonickel chemistry mainly relates to unsaturated and aromatic substrates. 

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