Nickel complexes sulfur-containing

Three different classes of compounds form the major and most important commercial categories of photostabilizers for PP. These are based on nickel complexes (those containing sulfur ligands function primarily as peroxide decomposers, PD), UV-absorbers (UVA), e.g. based on 2-hydroxybenzophenone and 2-hydroxyphenylbenztriazole, and sterically hindered amine light stabilizers (HALS). 

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). 

The dissociation kinetics of the nickel chloride complex of the 15-mem-bered, S2N2-macrocycle of type (279) has also been investigated in the presence of hydrochloric acid (Lindoy Smith, 1981). This complex has a similar trans-octahedral structure to that of the 02N2-donor systems just discussed. For the sulfur-containing complex, two consecutive (acid-independent) first-order steps were observed, with the second being slower than the first. The data are in accordance with the scheme ... 

The use of six equivalents of dihydrogen peroxide leads to a clean conversion of the dithiolate complex to the disulfonate compound. Earlier studies on oxidation of nickel thiolates showed that oxidations with dioxygen stop at monosulfinates. Our observation and the characterization of the first chelating bis-sulfonato nickel complex formed from the direct oxidation of a mononuclear nickel dithiolate, may also provide new insight into the chemistry of sulfur-rich nickel-containing enzymes in the presence of oxygen. 

Complex formation between many sulfur-containing ligands andiron, as well as other metals, has been studied in aqueous solution (45). Although pol5muclear complexes have been characterized in nickel (II) systems... 

In the following section we will report on the most recent developments of nickel-sulfur (as well as selenium and tellurium) coordination chemistry, but selected examples of the first reported complexes with classical sulfur-containing ligands which have been extensively reported in the aforementioned article reviews will be also included. 

In Table 108 significant examples of nickel(II) complexes with mixed-donor macrocycles of various denticity are reported. Apart from the nitrogen atoms, the heteroatoms in the macrocyclic rings are usually either O or S, or in a few cases P. Few examples of nickel complexes with macrocycles containing all-sulfur or all-phosphorus donor atoms have been reported to date they are also included in Table 108. In nickel(II) complexes formed by mixed-donor penta- and hexa-dentate ligands the oxygen atoms of the macrocycle are often only weakly coordinated or are not coordinated at all. 

A crystal structure determination of [Pd(dtb)2] showed a distorted tetragonal arrangement of sulfur atoms about the palladium atom. The Pd—S distances in the square plane are 2.32-2.34 A, while the Pd—S (apical) distance is 3.46 A, suggesting some interaction. 47 The nickel complex [Ni(dtb)2] can be readily oxidized to [Ni dtbhSj], which was postulated to be a NiIV complex,136 but it is more likely that the complex contains Ni11 with the structure (42).146... 

Sulfur-Containing Chelating Agents. Perhaps the greatest interest in square planar complexes has arisen in the area of sulfur donors and the resulting discussions concerning multiple oxidation states of nickel (25, 63, 86, 87, 88). 

Polar compounds (water, oxygen-, nitrogen-, and sulfur-containing compoimds). They react with the organoaluminum co-catalyst (water, alcohols, amines, thiols), complex the aluminum center in a Lewis acid/base interaction (ketones, ethers, thioefhers), or coordinate strongly to the nickel catalytic center (amines, sulfur compounds). They reduce the concentration of the active species and may be responsible of the formation of sludges in the reaction section. 

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