Nickel complexes aryl phosphines

Aryl and vinyl haiides can be coupled in reactions catalyzed by palladium or nickel complexes bearing phosphine ligands [253], Allylic derivatives that are precursors of tt-allyl palladium complexes can also be coupled with organomagnesium reagents. Asymmetry can be induced by using chiral phosphines as ligands. 

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). 

Nickel complexes also catalyze the coupling of aryl halides with thiolates. In one case, the phosphine ligand on the catalyst was generated in situ from 1,2-dibromobenzene and diphenylphosphine... 

Biaryl synthesis from aryl halides is a more interesting reaction due to the value of these molecules and their difficult access by chemical methods. The first electrosyntheses were simultaneously done in 1979-80 by three groups [21-23] who used NiCljPPha (1-20%) as catalyst precursor in the presence of excess PPhs. Later, several groups investigated the use of bidentate phosphines like dppe associated with nickel in the synthesis of various biaryls, and notably 2,2 -bipyridine and of 2,2 -biquinoline from respectively 2-chloropyridine and 2-chloroquinoline [24], More recently new nickel complexes with l,2-bis(di-2-alkyl-phosphino)benzene have been studied from both fundamental and synthetic points of view [25]. They have been applied to the coupling of aryl halides. 

The effect of tin compounds, especially tetra-alkyl and tetra-aryl tin compounds, is similar to that of phosphine, though lower temperature and pressure are required for the catalyst s optimum activity. Tin can promote the activity of the nickel catalyst to a level that matches that of rhodium under mild conditions of system pressure and temperature e.g. 400 psig at 160 C. The tin-nickel complex is less stable than the phosphine containing catalyst. In the absence of carbon monoxide and at high temperature, as in carbonyl-ation effluent processing, the tin catalyst did not demonstrate the high stability of the phosphine complex. As in the case of phosphine, addition of tin in amounts larger than required to maintain catalyst stability has no effect on reaction activity. 

The carboxylation reaction shown in reaction (11) is catalyzed by both nickel and palladium phosphine complexes. For example, Ni(dppe)Cl2 (where dppe is l,2-bis(diphenylphosphino)ethane) and Pd(PPh3)2Cl2 both catalyze reaction (11) [84-86]. Mechanistic studies have been carried out on these two systems, and the results indicate that two different mechanisms are involved. In the case of the Ni complex, the first step is the reduction of Ni(dppe)Cl2 to a transient Ni(dppe) species [85]. This process occurs in two one-electron steps (reaction 12). Bromobenzene then oxidatively adds to Ni(dppe) to form Ni(dppe)(Br)(Ph), reaction (13). The resulting Ni(II) aryl species is reduced in a one-electron process to form Ni(dppe)(Ph), which reacts rapidly with CO2 to form a Ni—CO2 intermediate as shown in reaction (14). The rate-determining step for the overall catalytic reaction is the insertion of CO2 into the Ni-aryl bond, reaction (15) step 1. This reaction is followed by a final one-electron reduction to regenerate Ni(dppe), the true catalyst in the cycle (reaction 15, step 2). 

PHOSPHINE-NICKEL COMPLEX CATALYZED CROSSCOUPLING OF GRIGNARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Preparations of Ni[P(C6H5)3]3 and trarw-chloro(aryl)bis(triphenyl-phosphine)nickel from NiCl2[P(C6H5)3]2 (12) are reported. Alternatively, the trar s-chloro( aryl) bis (organophosphine) nickel complexes were prepared from Ni(PR3)3 (8, 13). Identical results were obtained from catalysts prepared in different ways. Because all the reactions involved in this work are sensitive to oxygen, all were carried out under N2. 

Carbon-nitrogen bonds can be made using similar coupling reactions. With nickel complexes of chelating phosphines such as l,l -bis(diphenylphosphino)ferro-cene, even the generally unreactive aryl chlorides can be converted to anilines.94... 

Not only noble metal complexes, but also nickel complexes undergo oxidative addition reactions. Fahey found that a variety of vinyl and aryl halides react with (R3P)2Ni(C2H4) to form a stable carbon-metal o-bond 24). Forex-ample, tetrachloroethylene affords /ran. -chloro(trichlorovinyl)bi s(triphenyl-phosphine)nickel. 

P-Donor and As-donor ligands. In order to evaluate further the effect of fluorine substitution on the properties of aryl phosphine ligands, the complexes [PdL X2] [L = (62a X = Cl, Br, I or SCN], [PdL jClO, and [PdL X2] [L = (62b)] have been prepared.Physical measurements indicate that these complexes are generally planar, unlike their nickel analogues, while the potentially... 

Among the nickel-based catalysts, beside the nickel on charcoal [43], mainly the various nickel(0)-phosphine complexes were employed [12,13,44,45]. Several common bidentate phosphine ligands such as dppf, dppe, dppp, dppb and tricyclohexylphosphine (PCys) are the most popular in the nickel-based SM crosscoupling reactions of less reactive aryl chlorides with arylboronic acids [44], While the nickel complexes of electron-rich trialkylphosphines react readily with aryl chlorides. 

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