Nickel complexes carbonylation

Reaction of l,3-bis(phenylmethyl)imidazol-2-ylidene with nickel tetra carbonyl gives [(t (C)-1,3-bis(phenylmethyl)imidazol-2-ylidene)Ni(CO)3] (970M2472). Complexes of composition [Ni(CO)2L2] with imidazol-2-ylidenes are also known (93JOM(459)177). Another species to be mentioned in this respect is bis(l,3-dimesitylimidazol-2-ylidene)nickel(0) (94JA4391). 1,3-Dicyclohexylimidazol-2-yUdene substitutes triphenylphosphine or THF from [NiX LJ (X = Cl, Br L PPhj, THF) to yield the stable nickel(II) complexes 69 (X = C1, Br R = Cy) (97OM2209). Another preparation of nickel(II) derivatives is the interaction of... 

Reactions of alcohols, ethers, and aliphatic halides with carbon monoxide were described as far back as 1948-1953 (173, 195). High pressure and temperature were required, however, for these processes. The use of alkaline media allowed carbonylation of alkyl iodides under mild conditions (example 22, Table VII). More recently, carbonylation of alkyl-nickel complexes was reported (example 26, Table VII). 

Not only do palladium complexes catalyze reactions of Eq. (58), but nickel complexes were also effective (51) and formed the same products. Complexes such as Fe(CO)5 and Fe2(CO)8 were ineffective. Cobalt carbonyl, and tris-triphenylphosphinerhodium chloride were effective even at room temperature, but no 2 1 adducts were made. With both palladium and nickel, the activity of the catalyst and the distribution of products between 1 1 and 2 1 adducts is greatly dependent on the nature of the donor ligands on the metal. 

As a further illustration of the dependence of n i 7t pi-backbonding interactions on metal and ligand character, we may compare simple NiL complexes of nickel with carbonyl (CO), cyanide (CN-), and isocyanide (NC-) ligands, as shown in Fig. 4.41. This figure shows that the nNi 7rL pi-backbonding interaction decreases appreciably (from 28.5 kcal mol-1 in NiCO to 6.3 kcalmol-1 in NiNC-, estimated by second-order perturbation theory) as the polarity of the 7Tl acceptor shifts unfavorably away from the metal donor orbital. The interaction in NiCO is stronger than that in NiCN- partially due to the shorter Ni—C distance in the... 

Recently, four-component coupling reactions of aldehydes, alkynes, dienes, and dimethylzinc catalyzed by a nickel complex have been reported (Equation (78)).435 Similarly, l,c< -dienynes react with carbonyl compounds and dimethylzinc in the presence of an Ni catalyst to afford the corresponding cyclized products. 

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCF2COOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel-complex catalyst [26], The catalytic cycle is shown in Scheme 3.11 and nickel zinc exchange is a key step. 

Nickel forms a large number of complexes with various anions (monoden-tate, bidentate, and polydentate) and many neutral ligands. The most common coordination numbers of the metal in these complexes are six and four while the metal is usually in +2 oxidation state, Ni2+. Also, some complexes of three and five coordinations exist. Several zero valent nickel complexes, such as nickel tetracarbonyl, and a number of substituted carbonyl complexes are well known. 

In the case of phosphine, especially tri-n-butyl and triphenyl phosphines, an active phosphine complex is formed in the reaction medium via reaction with nickel carbonyl. This complex is a very active species provided that the optimum concentration of phosphine is used. Low phosphine concentration results in a loss of the effective nickel concentration through the formation of nickel tetra-carbonyl, nickel metal or nickel iodide. The absolute concentration of phosphine is less important than the P/Ni ratio. In addition to form the stable Ni-P catalyst, the phosphine has to compete with other ligands in the reaction mixture for nickel. With high carbon monoxide partial pressure, there is more CO in solution to compete with phosphine favoring the formation of the carbonyl, which is inactive under the reaction conditions. Hence with high carbon mon-... 

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 ability of nickel complexes, e.g., nickel carbonyl and its phosphine derivatives, to catalyze polymerization and other reactions of olefins and acetylenes has been studied extensively (46, 53), particularly by Reppe. 

Isoelectronic with nickel carbonyl are the anions, Ni(CN)44- and Pd(CN)44-, which are obtained as their potassium salts by reduction of the corresponding cyanides of oxidation state +2 with potassium in liquid ammonia (32, 65, 186). The infrared spectrum of the nickel complex has been reported (67) to show only one band at 1985 cm-1, in the triple-bond... 

Carbonyl Vibrational Frequencies and Carbon Monoxide Binding Constants for Nickel(I) Carbonyl Complexes of Macrocycuc Ligands... 

CjHjS, Thiophene, tetrahydro-gold complexes, 26 85-87 C4H,NO, 2-Propenamide, 2-methyl-nickel complex, 26 205 C4H1()02, Ethane, 1,2-dimethoxy-solvates of chromium, molybdenum, and tungsten carbonyl cyclopentadienyl complexes, 6 343 tungsten complex, 26 50 ytterbium complex, 26 22 C4H i02.NaC5H5, Ethane, 1,2-dimethoxy-compd. with cyclopentadienylsodium, 26 341... 

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). 

The nickel(II) complexes with the ligand diars (XVIII) were first reported by Nyholm. The NiX2(diars)2 complexes were prepared from the reactants in hot ethanol.1318 The 1 1 complexes were originally prepared by oxidation of the nickel(O) carbonyl complex with gaseous hydrogen halides under anaerobic conditions (equation 161).1283 Other complexes with diars were subsequently prepared according to equations (162)-(164).1319-1321... 

The oxidation of a nickel(O) carbonyl compound with halogens was employed by Chatt and Hart to prepare nickel(II) complexes with the diphosphine ligand (XVII R = Et equation 165) 1311 2 1 complexes were subsequently prepared by the direct synthesis of the reactants in acetone.1287... 

The square planar [NiX(bdppm)]+ complex was found to react with CO at room temperature and atmospheric pressure in EtOH—H20 solution according to equation (168). The nickel(O) carbonyl complex containing the protonated ligand Hbdppm reacts in turn with acids with evolution of H2 (equation 169). Thus the complex [NiX(bdppm)]+ acts as an effective homogeneous catalyst of the water-gas reaction.1373... 

This process is an example of the ability of nickel complexes to catalyze substitution reactions of aromatic halides under very mild conditions. A further example of their catalytic activity is the carbonylation of aromatic halides at the atmospheric pressure of carbon monoxide (6). 

Examples of nickel complexes are rare and are confined to three reported nickel carbonyl clusters containing interstitial germanium or tin atoms (90). The reaction between [Ni6(CO)l2]2 and GeCl4 affords two species, [Ni10Ge(CO)2o]2 , 79, and [Ni12Ge(CO)22]2, 80. The former structure is based on a pentagonal antiprismatic framework of nickel atoms with an... 

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