Nickel chloro complexes

Absorption spectra of solutions of Ni(II) in the LiNOg-KNOg eutectic to which excess Cl has been added are shown in Fig. 37.The results in this case are not as clear-cut as for the corresponding Co(II) system, partly because of the lower solubility of nickel chloro complexes in the nitrate melt. By increasing the temperature, a higher concentration of nickel complexes could be stabilized and the resulting spectrum closely resembled that of Ni(II) in pure LiCl. The spectral changes shown in Fig. 37 may be due to a conversion to an octahedral chloro complex. 

Nickel and Cobalt. Often present with copper in sulfuric acid leach Hquors are nickel [7440-02-0] and cobalt [7440-48-4]. Extraction using an organophosphoric acid such as D2EHPA at a moderate (3 to 4) pH can readily take out the nickel and cobalt together, leaving the copper in the aqueous phase, but the cobalt—nickel separation is more difficult (274). In the case of chloride leach Hquors, separation of cobalt from nickel is inherently simpler because cobalt, unlike nickel, has a strong tendency to form anionic chloro-complexes. Thus cobalt can be separated by amine extractants, provided the chloride content of the aqueous phase is carefully controUed. A successhil example of this approach is the Falcon-bridge process developed in Norway (274). 

Primary separation occurs in the leaching procedure, where the metals copper, zinc, and nickel are dissolved as metal ammonium chlorides or chloro complexes, while iron and chromium remain in the solid residue as hydroxides. 

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. 

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... 

Stoichiometric Cyanation Reaction. To elucidate the mechanism, the stoichiometric cyanation reaction of tram-chloro (aryl) bis (triphenylphos-phine) nickel (II) complexes 1 was studied. Arylnickel (II) complexes... 

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

A secondary, more subtle, effect that can be utilized in the achievement of selectivity in cation exchange is the selective complexation of certain metal ions with anionic ligands. This reduces the net positive charge of those ions and decreases their extraction by the resin. In certain instances, where stable anionic complexes form, extraction is suppressed completely. This technique has been utilized in the separation of cobalt and nickel from iron, by masking of the iron as a neutral or anionic complex with citrate350 or tartrate.351 Similarly, a high chloride concentration would complex the cobalt and the iron as anionic complexes and allow nickel, which does not form anionic chloro complexes, to be extracted selectively by a cation-exchange resin. 

The first compound containing carbon monoxide as a ligand was another platinum chloro complex, reported in 1867. In 1890, Mond6 reported the preparation of Ni(CO)4, a compound that became commercially useful for the purification of nickel. Other metal CO ( carbonyl ) complexes were soon obtained particularly notable was the work on iron carbonyls beginning around 80 years ago by Hieber.7... 

Table 2. Molecular second-order NLO results for nickel alkynyl and chloro complexes ...

The method of frontal analysis on an ion-exchange column was used to study the formation of weak chloro complexes of nickel(II), cobalt(II) and copper(II). Although, the reported dissociation constant for the complex NiCr (X iss = (4.6 0.1), which can be converted to log,) X, = - (0.66 0.01)) is close to other reported values, some experimental data, such as the temperature of the measurements, were not published. Therefore, the reported constant is rejected in this review. 

The formation of nickel(II) chloro complexes in aqueous solution has been studied using a cation-exchange method at 20°C, in a solution of 0.691 M H(C104,C1). The distri-... 

An attempt to determine the stability constants of the nickel bromo complexes was complicated by the slow formation of bromine from oxidation of bromide by the nitrate ion. However, the results indicated that the bromo and chloro complexes of nickel(II) have similar stability. 

The hydrolysis of aqueous nickel(II) chloride solutions ([NiCl2]tot = 0.03 to 1.5 M) has been studied by potentiometric titrations at 25°C. The ionic strength was not controlled instead, the activity coefficients, based on literature values, were taken into account. The formation of a single hydroxo complex was assumed. The evaluation of experimental data indicated the presence of the Ni COH) tetrameric species. A value of logic Paa (27.0 0.1) was reported for its thermodynamic hydrolysis constant. The formation of chloro complexes was not taken into account, although these may only have made a small contribution to the total solution concentration of nickel at [NiCl2]iot <0.1 M. Therefore, the reported value is accepted for use in this review, but with an increased uncertainty log, = - (27.0 0.3). 

This type of cationic nickel complex can be generated directly in acidic chloro-aluminate starting from an air-stable nickel(II) salt and in the presence of an alkylaluminum derivative [6]. When an alkylaluminum derivative such as EtAlCl2 is added in acidic chloroaluminates (BMIMJlClJ/AlClj, mixed alkylchloroaluminate anions are formed, as characterized by Raman spectroscopy [Eq. (2)] [7]. The resulting IL plays the dual role of solvent and nickel activator (or cocoordinating chloride anions to afford an anionic inactive nickel chloride complex. 

With Compounds of Ni", Pd", and Pt. The removal of PH3 from inert gases with nickel oxide on activated carbon [113] and with Pd" chloro complexes on kieselguhr [114] was described. Acidic solutions of H2PtCl6 oxidize PH3 to H3PO4 with formation of Pt" which activates PH3 [115]. The rate of the reaction increases with increasing acidity of the solution and with increasing concentration of Cl", Br", I" [23, pp. 305/7], or SCN" [116]. 

It can be attributed to the effect of the donor strength of the solvent, for instance, that the equilibrium stabilities of chloro complexes are considerably higher in acetonitrile (which has a lower donicity than water) than in aqueous solution [Ba 63, Ma 65] that complexes of lower stability are formed in dimethyl sulphoxide than in dimethylformamide, the former solvent having the larger donor strength [Ga 67] and that nickel bromide is in a fully dissociated state in dimethyl sulphoxide, whereas in dimethylformamide it dissociates only partially [Gu 68a]. 

Besides of ethene also other alkenes react with carbon dioxide in the presence of nickel(0) complexes. Some examples are given in Figure 6. Hexenes lead to different isomeric heptanoic acids, styrene reacts to cynnamic acid and norbornene (bicyclo 2.2.1 heptene) gives the exo-norbornane-2-carboxylic acid in 95 % yield [5,12,13]. Nor-bornadiene which contains two isolated double bonds reacts to a monoaddition product whose decomposition with hydrochloric acid yields a mixture of six chloronorbornanecarboxylic acids with the chloro-and carboxy-substituents both in exo- and in endo-positions [14]. 

---