Nickel 2 complex

Nickel complexes (156-159) used as ATRP catalysts for polymerization of (meth)acrylates are shown in Table 9.8. 

Tlie complex 157 is more soluble than 156 in organic solvents it is more thermally stable and can be used at higher temperatures. Moreover, it can be used without the Al((OiPr)i cocatalyst that is required with 156.  

In addition to the usual Ni(II) (d8) oxidation state, the other common oxidation states for nickel in its complexes are III and I (d7 and d9, respectively). Also the oxidation state IV (d6) is not completely uncommon. 

In both cases the N2O2 coordination of the Ni(II) ion is essentially planar, though there is a slight tetrahedral distortion. However, the diamagnetism displayed by these complexes confirms that they are planar. 

Electrochemical studies show that [Ni(salen)] in dmso undergoes a Ni(II)/Ni(III) oxidation (Ep= +0.71 V vj. SCE), complicated by fast chemical reactions, and a chemically reversible Ni(II)/Ni(I) reduction ( ° = -1.61 V).151 152 

The oxidation product obtained by controlled potential electrolysis, [Ni(3,5-Cl2saloph)] +, shows an EPR spectrum typical of a Ni(III) ion (d7 - low spin) having an octahedral coordination, which is attributed to the axial coordination of two solvent molecules.153 Therefore, from a speculative viewpoint, it could be assumed that the electrochemical quasireversibility is due to the change in coordination from square planar to octahedral. 

The geometry becomes essentially tetrahedral (dihedral angle between the two planes formed by the Ni atom and the two P atoms of each dmpp ligands = 87°) and a significant shortening of the Ni-P distances (by about 0.06 A) occurs. Since within a given geometry reduction processes 

As can be seen, the molecule undergoes two separate one-electron oxidations, reversible in character. The first has been assigned to electron loss from the ferro-cenyl unit, the second to the Ni redox change. As summarized in Table 7-28, coupling the ferrocenylsulfonamide fragment to the azacyclam-nickel(ii) unit makes electron removal slightly more difficult with respect to the corresponding free molecules. 

The same electronic effects hold as far as the complex [NiL ] is concerned. In aqueous solution it undergoes two distinct one-electron oxidations, centered on the ferrocenyl and open poly amine-nickel (ii) fragments, respectively [145]. As shown 

Finally, Fig. 7-46 shows the redox behavior of the trinuclear complex [NiL ] in acetonitrile solution [147]. 

A first single-step two-electron oxidation is followed by a second one-electron oxidation. The first step is assigned to the simultaneous removal of one electron from the two non-interacting ferrocenyl fragments, whereas the second step involves the Ni(ii)/Ni(iii) redox changes. The first process has features of chemical reversibility, whereas the second nickel-based step is complicated by subsequent decomposition reactions. 

It has been briefly reported that in 1,2-dichloroethane solution [Fe(C5H4PPh2)2]-NiCl2 undergoes an irreversible oxidation [151]. In this context, it must be kept in mind that the free ligand l,T-bis(diphenylphosphino)ferrocene itself undergoes a one-electron oxidation followed by fast chemical complications [53]. 

The direct preparation of the iodides may be accomplished in the same manner as the bromides, with the use of 5.5 ml. of reagent-grade hydriodic acid (47-50%) in place of the hydrobromic acid. The diethylenetriamine complex was found to be 

Complex Amine, ml. %Yieid Concn. 0.01 =M Concn. = 0.005 M Analyses  

All the nickel(II) complexes are obtained as fine violet crystals. They are insoluble in acetone, and all but the [Ni(chxn)3 ] I2 complex are water-soluble. The spectral properties, elemental analyses, and yields obtained for the various complexes are reported in Table II. 

Schlessinger, Inorganic Laboratory Preparations, pp. 189 ff., Chemical Publishing Company, Inc., New York, 1962. 

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Cyclization with various nickel complex catalysts gives up to 97% selectivity to a mixture of cyclooctatetraene derivatives, with only 3% of benzene derivatives. The principal isomer is the symmetrical l,3,5,7-cyclooctatetraene-l,3,5,7-tetramethanol (29). 

Upon treatment with suitable cobalt complexes, methylbutynol cyclizes to a 1,2,4-substituted benzene. Nickel complexes give the 1,3,5-isomer (196), sometimes accompanied by linear polymer (25) or a mixture of tetrasubstituted cyclooctatetraenes (26). 

Shell Higher Olefin Process) plant (16,17). C -C alcohols are also produced by this process. Ethylene is first oligomerized to linear, even carbon—number alpha olefins using a nickel complex catalyst. After separation of portions of the a-olefins for sale, others, particularly C g and higher, are catalyticaHy isomerized to internal olefins, which are then disproportionated over a catalyst to a broad mixture of linear internal olefins. The desired fraction is... 

TC-Cyclopentadienyl Nickel Complexes. Nickel bromide dimethoxyethane [29823-39-9] forms bis(cydopentadienyl)nickel [1271 -28-9] upon reaction with sodium cyclopentadienide (63). This complex, known as nickelocene, 7T-(C3H3)2Ni, is an emerald-green crystalline sandwich compound, mp 173°C, density 1.47 g/cm. It is paramagnetic and slowly oxidi2es in air. A number of derivatives of nickelocene are known, eg, methylnickelocene [1292-95-4], which is green and has mp 37°C, and bis( 7t-indenyl)nickel [52409-46-8], which is red, mp 150°C (87,88). 

Plastics Additives. Many claims have been made for the use of nickel chemicals as additives to various resin systems. By far the most important appHcation is as uv-quenchers in polyolefins (173,174). Among the useful nickel complexes in these systems are dibutyldithiocarbamate nickel [13927-77-0], nickel thiobisphenolates, and nickel amide complexes of bisphenol sulfides (175). The nickel complex of... 

Other Specialty Chemicals. In fuel-ceU technology, nickel oxide cathodes have been demonstrated for the conversion of synthesis gas and the generation of electricity (199) (see Fuel cells). Nickel salts have been proposed as additions to water-flood tertiary cmde-oil recovery systems (see Petroleum, ENHANCED oil recovery). The salt forms nickel sulfide, which is an oxidation catalyst for H2S, and provides corrosion protection for downweU equipment. Sulfur-containing nickel complexes have been used to limit the oxidative deterioration of solvent-refined mineral oils (200). 

Metal chelation is also a means of insoliihilizing organic molecules. For example. Cl Pigment Green 10 [51931 -46-5] (138) (Cl 12775) is a 2 1 nickel complex of a bidentate o-hydroxyazo ligand. 

Additive inhibitors have been developed to reduce the contaminant coke produced through nickel-cataly2ed reactions. These inhibitors are injected into the feed stream going to the catalytic cracker. The additive forms a nickel complex that deposits the nickel on the catalyst in a less catalyticaHy active state. The first such additive was an antimony compound developed and first used in 1976 by Phillips Petroleum. The use of the antimony additive reportedly reduced coke yields by 15% in a commercial trial (17). 

Porphyrin, octaethyl-, nickel complex cyclic voltammetry, 4, 399 <73JA5140)... 

Radical pertluoroalky lation of anilines occurs in the presence of a sufur dioxide radical anion precursor, such as Zn-S02 or sodium dithionite [154, 755], or of a nickel complex [756] (equation 134)... 

However, with the application in the 19, iOs of crystal held theory to transition-metal ehemistry it was realized that CFSEs were unfavourable to the lormation of tetrahedral d complexes, and previous assignments were re-examined. A typical ca.se was Ni(acac)i. which had often been cited as an example of a tetrahedral nickel complex, but which was shown - in I9. I6 to be trimeric and octahedral. The over-zealous were then inclined to regard tetrahedral d" as non-existent until Hrst L.. M. Venanz.i and then N., S. Gill and R. S. Nyholm" demonstrated the existence of discrete tetrahedral species which in some cases were also rather easily prepared. 

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Synthesis, characterization, and chemistry of core-modified porphyrins and their nickel complexes 97NJC691. 

The nickel and cohalt aqua complexes were even more effective, both for catalytic activity and enantioselectivity, than the corresponding anhydrous complexes (Scheme 7.5). Addition of three equivalents of water to the anhydrous nickel complex recovered the catalytic efficiency. DBFOX/Ph complexes derived from manga-nese(II), iron(II), copper(II), and zinc(II) perchlorates, both anhydrous and vef. 

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