Aryl with nickel complexes

More attention has been devoted to aromatic and heteroaromatic substrates since first reported in 1983 [40]. The results are shown in Table 2 [25, 41-51]. All these reactions were run with nickel complexes associated with a phosphane or bpy ligand. Depending on the experimental conditions, the polymers were either precipitated during the electrolysis or deposited as films at the surface of the electrode. The method is also convenient to prepare copolymers from a mixture of two aryl dihalides. A mechanistic investigation on the nickel-bpy catalyzed polymerisation has been reported very recently [52]. 

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... 

Alkylation of dibromobis(triethylphosphine)nickel(II) has been conducted stepwise using arylmagnesium bromide and methyllithium, leading to unsymmetrical /ra/7.y-aryl(methyl)nickel complex 5 [24], which further reacts with l,2-bis(dimethyl-phosphino)ethane (dmpe) to give ra-aryl(methyl)nickel complex 6 (eq (15)) [25]. 

As an unexpected result of our investigations on the arylation of amines, a new catalysis with nickel complexes was pointed out for the aminolysis of nitriles indeed, in the reaction of the p-bromobenzonitrile with the 4-phenylpyridine in the presence of catalytic amounts of NiBr2, in addition to the expected arylamine, the amide resulting from the aminolysis of the cyano group (and subsequent hydrolysis during the work-up) was isolated (eqn. 8). 

The reaction between aryl halides and cuprous cyanide is called the Rosenmund-von Braun reactionP Reactivity is in the order I > Br > Cl > F, indicating that the SnAt mechanism does not apply.Other cyanides (e.g., KCN and NaCN), do not react with aryl halides, even activated ones. However, alkali cyanides do convert aryl halides to nitrilesin dipolar aprotic solvents in the presence of Pd(II) salts or copper or nickel complexes. A nickel complex also catalyzes the reaction between aryl triflates and KCN to give aryl nitriles. Aromatic ethers ArOR have been photochemically converted to ArCN. 

A useful new method of preparing arylphosphonates (123) involves the reaction of trialkyl phosphites with aryl halides in the presence of a nickel catalyst.The suggested mechanism is via the nickel complex (124), and is non-radical. 

By oxidative addition of aryl sulphides to low-valent nickel complexes, a C—S bond cleavage occurs to form Ni11 thiolate complexes. For example, exposure of diaryl sulphides to [(But3P)3Ni0] leads to oxidative addition, with nickel inserting into the C—S bond (280).814... 

Activated aryl chlorides, which are close in reactivity to unactivated aryl bromides, underwent reaction with the original P(o-tol)3-ligated catalyst.58 Nickel complexes, which catalyze classic C—C bond-forming cross-couplings of aryl chlorides, 9-64 also catalyzed aminations of aryl chlorides under mild conditions.65,66 However, the nickel-catalyzed chemistry generally occurred with lower turnover numbers and with a narrower substrate scope than the most efficient palladium-catalyzed reactions. 

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. 

As mentioned in Sections 3.1.6 and 4.1.3, cyclopropenes can also be suitable starting materials for the generation of carbene complexes. Cyclopropenone di-methylacetal [678] and 3-alkyl- or 3-aryl-disubstituted cyclopropenes [679] have been shown to react, upon catalysis by Ni(COD)2, with acceptor-substituted olefins to yield the products of formal, non-concerted vinylcarbene [2-1-1] cycloaddition (Table 3.6). It has been proposed that nucleophilic nickel carbene complexes are formed as intermediates. Similarly, bicyclo[1.1.0]butane also reacts with Ni(COD)2 to yield a nucleophilic homoallylcarbene nickel complex [680]. This intermediate is capable of cyclopropanating electron-poor alkenes (Table 3.6). 

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. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions).7S2 R may be alkyl or aryl. As in 0-35, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson reaction (0-12), yields are improved by phase-transfer catalysis.753 Instead of RS ions, thiols themselves can be used, if the reaction is run in benzene in the presence of DBU (p. 1023).754 Neopentyl bromide was converted to Me3CCH2SPh in good yield by treatment with PhS in liquid NH3 at -33°C under the influence of light.755 This probably takes place by an SrnI mechanism (see p. 648). Vinylic sulfides can be prepared by treating vinylic bromides with PhS in the presence of a nickel complex,756 and with R3SnPh in the presence of Pd(PPh3)4.757 R can be tertiary if an alcohol is the substrate, e.g,758... 

An important alternative to the Ullmann method is the use of certain nickel complexes,193 This method has also been used intramolecularly.194 Aryl halides ArX can also be converted to Ar—Ar195 by treatment with activated Ni metal,196 with Zn and nickel complexes,197 with aqueous alkaline sodium formate, Pd-C, and a phase transfer catalyst,l9li and in an electrochemical process catalyzed by a nickel complex,199... 

Halogen exchange with aryl and vinyl halidesv This nickel complex is a particularly active catalyst lor exchange between haloarcnes or vinylic halides and inorganic halide salts. In the case of ihe vinylic halides the exchange is particularly... 

Carbonylation of halides with tetramethyltin This nickel complex is the most efficient catalyst for the synthesis of methyl ketones by reaction of aryl halides with carbon monoxide and tetramethyltin in HMPT at 120°. No reaction occurs when tetraphenyltin is used. A typical reaction is formulated in equation (I). 

To date, the tetraazadiene species RN=N—N=NR have not been isolated as free molecules, but they have been found coordinated to a metal centre when aryl azides are reacted with nickel(0) complexes (equations 42 and 43).213 21i... 

---