Nickel alkyl and aryl complexes

Nickel Alkyl and Aryl Complexes in Oxidation States 1, iii, and iv 117... 

Table 6 Nickel alkyl and aryl complexes containing anionic chelating ligands, Ni(R)(chelate)(L)...

Nickel alkyl and aryl complexes in olefin polymerization and oligomerization catalysis... 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

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). 

The stability of the alkyl and aryl derivatives increases with the number of phosphines bound to nickel(II). The bis-phosphine derivatives can be prepared according to equations (144)-(146) and using organomagnesium halides or organolithium compounds.1224-1231 A tetrakis phosphine complex was obtained similarly (equation 147). 

Oxidative addition reactions to nickel(O) complexes are another well-developed synthetic method which affords mono and bis alkyl and aryl compounds (equation 148).1232-1239 The oxidative addition of a, ar -dichloro-p-xylene to [Ni(QjH4)(PPh3)2] gives the dinuclear nickel(II) complex t(PPh3)2ClNi(CH2C6H4CH2)NiCl(PPh3)2].124 ... 

Grignard reagents replace halides from the [NiX(L)]+ derivatives by o-bonded alkyl and aryl groups (equation 174), giving a series of diamagnetic organometallic complexes of nickel(H) (189) (Table 74).1444... 

Substituted dithioformate anions as ligands R C(S)S are usually called dithiocarbamates (R = R2N), alkyl and aryl dithiocarbonates or xanthates (R = RO), alkyl and aryl trithiocar-bonates or thioxanthates (R = RS). Dithioacid anions (R = alkyl, aryl) have been rarely used as ligands of nickel(II) because of their instability. Structural properties of selected nickel(II) complexes with substituted dithioformate, dithiolene and related ligands are shown in Table 90. 

Hydrogen cyanide smoothly adds to butadiene (BD) in the presence of zero-valent nickel catalysts to give (3PN) and (2M3BN) [1,4- and 1,2-addition products, respectively, Eq. (7)]. A variety of Ni[P(OR)3]4 (R = alkyl or aryl) complexes are suitable as catalysts. The reaction may be carried out neat or in a variety of aromatic or nitrile solvents at temperatures from 50-120°C. Whereas in many olefin hydrocyanations it is desirable to keep the HCN concentration very low to protect the nickel from degradation, with butadiene HCN may be added batchwise as long as the HCN concentration is kept near the butadiene concentration. In the case of batch reactions one must be cautious because of possible temperature rises of 50°C or more over a period of a few minutes. Under typical batch conditions, when Ni[P(OEt)3]4, butadiene, and HCN are allowed to react in a ratio of 0.03 1.0 1.0 at 100°C for 8 hr, a 65% conversion to 3PN and 2M3BN (1.5 1) is observed (7). 

Nickel-carbon a-bonded complexes with alkyls and aryls, 8, 117 j3-allyls, 8, 105... 

However most organic halides are less easily reduced than Zn(II). So such a process can only be applied if one is able to catalyse the electroreduction of RX. This can be achieved by electrochemically formed zerovalent nickel complexes. Thus Ni(II)-2,2 -bipyridine (Ni-bpy) compounds can catalyse the electroreduction of alkyl and aryl halides1 at potential more positive than... 

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

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