Nickel complexes triphenylphosphine

Hydride transfer from organic substrates to olefins (219) or halides (220), catalyzed by halogeno(triphenylphosphine)nickel complexes, and halide replacement reactions (example 13, Table VIII) by hydrolytic cleavage of nickel complexes have also been described. 

Therefore it seems reasonable to assume that cyanation of aryl halides involves two fundamental processes oxidative addition of the tris(triphenylphosphine)nickel complex on the aromatic halide (Reaction 2) and cyanation of the arylnickel(II) complex 1 (Reaction 8). A further proof of the validity of this scheme is that both Ni[P(C6H5)3]3 and arylnickel (II) complexes 1 have an equal catalytic activity, these latter being intermediates of the catalytic process. Recent studies (22) on the influence of substituents on the aromatic halide in the oxidative addition reaction with Ni[P(C6H5)3]3 have given the results shown in Figure 4. 

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. 

A complex reaction takes place when dichlorobis(triphenylphosphine)-nickel (5) is treated with excess methylmagnesium bromide in ether. Detectable amounts of benzene, toluene, and biphenyl are formed, together with mixed phosphines. Nickel appears to be necessary for the substitution reaction since triphenylphosphine alone does not react with the Grignard reagent. 

Although the copper mediated Ullmann reaction is a well known method for biaryl synthesis, drastic conditions in the range of 150-280 °C are required. Zerovalent nickel complexes such as bis(l,5-cyclooctadiene)nickel or tetrakis(triphenylphosphine)nickel have been shown to be acceptable coupling reagents under mild conditions however, the complexes are unstable and not easy to prepare. The method using activated metallic nickel eliminates most of these problems and provides an attractive alternative for carrying out aryl coupling reactions(36,38). 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

The nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

Tris (triphenylphosphine) nickel, tris (tri-p-tolylphosphine) nickel, and bis (1,3-diphenylphosphinepropane) nickel proved to be good catalysts, the first being slightly more effective. The tricyclohexylphosphine complex was a very poor catalyst, and bis (cyclooctadiene) nickel did not catalyze cyanation. Cyanation of several substituted aromatic halides in the presence of Ni[P(C6H5)3]3 prepared by reducing dichlorobis (triphenylphosphine) nickel (II) 2 with a powdered manganese iron (80 20) alloy (Reaction 3) is reported in Table II. 

Cyanation Catalyzed by trans-CHLORO ( aryl ) bis ( triphenylphos-phine) nickel (II) Complexes. In Table III cyanation of aryl halides catalyzed by the Ni(II) complexes obtained by reaction between aryl halides and Ni[P(C6H5)3]3 (Reaction 2) is shown. In general the trans-chloro (1-naphthyl) bis (triphenylphosphine) nickel (II) complex was used. Ortho substituted aryl halides were allowed to react in dimethylformamide... 

The reactions were carried out by using trans-chloro( 1-naphthyl)-bis(triphenylphosphine)nickel(II) (l, Ar = Ci0H7) complex as catalyst in the presence of various phosphorus ligands. We observed that aromatic phosphines in arylnickel(II) complexes 1 are easily replaced by aliphatic phosphines. In fact in the presence of alkylphosphines, such as P( C6Hn )3 and P(C4H9)3, cyanation did not occur. Moreover phosphites such as... 

Table IX. Cyanation of trans-Chloro(aryl)bis(triphenylphosphine)-nickel(II) Complexes, IR Absorptions...

G. Wilke, and G. Herrmann, Ethylenebis(triphenylphosphine)nickel and Analogous Complexes, Angew. Chem. 74, 693-694 (1962). 

Under remarkably mild conditions aromatic cyanides can be prepared from halogen compounds with alkali metal cyanides in the presence of transition metal complexes. Complexes of palladium and nickel are particularly useful, for instance tetrakis(triphenylphosphine)palladium(0) (6), tris(triphe-nylphosphine)nickel(O) (7) or trun -dichlorobis(triphenylphosphine)nickel(II) (8 Scheme 7). 

The relatively weak Ar-Br and especially Ar-I bonds would readily dissociate, giving rise to the Ni(I) paramagnetic complex and free aryl radical. This decomposition path is normally disfavored for aryl chlorides with considerably stronger Ar-Cl bonds. As a result, no Ni(I) species formed in the reactions of all chlo-roarenes studied, the only exception being [p-Me3NC6H4Cl]+. The p value of 5.4 obtained by Tsou and Kochi [33] is close to that (8.8 see above) previously reported by Foa and Cassar [32], suggesting that SET (Scheme 1) may play a certain role in some of the reactions of triphenylphosphine nickel(O) complexes with chloroarenes. It is still unclear if every reaction between any chloroarene and Ni(0) always involves the SET step. However, the excellent selectivity of the o-aryl Ni(II) complex formation from ArCl and highly reactive Ni(0) makes chloroarenes especially attractive substrates for various arylation reactions catalyzed by Ni complexes. 

For the metal—alkyne fragmait, nonlinearity also increases upon increasing valence electron count [14 valence electron (triphenylphosphine) gold alkynyl compounds <18 valence electron (cyclopentadienyl) (triphenylphosphine)nickel, and (cyclopentadienyl) bis(triphenylphosphine) ruthenium alkynyl compounds] and increasing ease of oxidation (less easily oxidizable (cyclopentadienyl)(tri-phenylphosphine)nickel alkynyl complexes < more easily oxidizable (cyclopen-tadienyl)bis(triphenylphosphine)ruthenium alkynyl complexes). 

Tetrakis(triphenylphosphine)nickel(0), [(C6Hs)3P]4Ni. Mol. wt. 1107.89, reddish brown sohd, m.p. 123-128°. The complex decomposes rapidly upon exposure to air as a soUd or in solution. 

Closely related to the dimerization of biphenylene (36) to tetraphen-ylene (37, Scheme XV) is the dimerization of an aryl-substituted cyclobutadiene to octadienes or cyclooctadienes by way of nickel complexes. A useful source of the cyclobutadiene group is its air-stable complex with NiBr2. Reduction of this complex with tert-butyllithium (electron-transfer agent) gives the tetraphenylcyclobutadiene-nickel(0)-triphenylphosphine complex (38), which isomerizes to the nickelole (39). The dimerization of 39 leads to 40, whose protonation yields the octadiene. Alternatively, at higher temperatures, 40 can extrude Ni(0) to produce 41 (26, Scheme XVI). 

OPSijCiiHj, Phosphine, [2,2-dimethyl-l-(trimethylsiloxy)propylidene](tri-methylsilyl)-, 27 250 OP3RhC55H44, Rhodium(I), carbonylhy-dridotris(triphenylphosphine)-, 28 82 0SC,2H (, Diphenyl sulfoxide, nickel complex, 29 116... 

---