Nickel complexes continued

The most important by-product formed in the reaction of pyridine with degassed Raney nickel is an organonickel complex which has been shown to be a complex of one molecule of 2,2 -bipyridine, two molecules of 2,2 -pyrrolylpyridine (17), and one nickel II ion. It is significant that, although the formation of 2,2 -bipyridine ceases after 50 hr refluxing, the formation of this complex continues for at least another 140 hr. 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

Pipette 25 mL nickel solution (0.01 M) into a conical flask and dilute to 100mL with de-ionised water. Add the solid indicator mixture (50mg) and 10 mL of the 1M ammonium chloride solution, and then add concentrated ammonia solution dropwise until the pH is about 7 as shown by the yellow colour of the solution. Titrate with standard (0.01 M) EDTA solution until the end point is approached, then render the solution strongly alkaline by the addition of 10 mL of concentrated ammonia solution, and continue the titration until the colour changes from yellow to violet. The pH of the final solution must be 10 at lower pH values an orange-yellow colour develops and more ammonia solution must be added until the colour is clear yellow. Nickel complexes rather slowly with EDTA, and consequently the EDTA solution must be added dropwise near the end point. 

Into a Schlenk tube was placed Auf 1,5-cyclooctadiene)-nickeI(0) (2.6 mmol), 2,2 -bipyridyl (2.6mmol), 1,5-cyclooctadiene (0.2ml), DMF (4ml), and toluene (8 ml). The reaction mixture was heated to 80°C for 0.5 h under argon. The dibromide comonomers 623 and 634 dissolved in degassed toluene (8 ml molar ratio of dibromides to nickel complex 0.65) were added under argon to the DMF-toluene solution and the polymerization maintained at 80°C for 3 days in the dark. 2-Bromofluorene (molar ratio of dibromides to monobromide 0.1) dissolved in degassed toluene (1ml) was added and the reaction continued for 12 h. The polymers were precipitated by addition of the hot solution dropwise to an equivolume mixture of concentrated HC1, methanol, and acetone. The isolated polymers were then dissolved in toluene or dichlor-omethane and reprecipitated with methanol/acetone (1 1). The copolymers were dried at 80°C in vacuo. The isolated yields of copolymers 240a-c were 79-85%. 

Another example is butene dimerization catalyzed by nickel complexes in acidic chloroaluminates 14). This reaction has been performed on a continuous basis on the pilot scale by IFF (Difasol process). Relative to the industrial process involving homogeneous catalysis (Dimersol process), the overall yield in dimers is increased. Similarly, selective hydrogenation of diene can be performed in ionic liquids, because the solubility of dienes is higher than that of monoene, which is higher than that of paraffins. In the case of the Difasol process, a reduction of the volume of the reaction section by a factor of up to 40 can be achieved. This new Difasol technology enables lower dimer (e.g., octenes) production costs 14). 

Macrocyclic complexes (continued) nickel(II), 44 93-94 eatalysis, 44 119-125 configurational isomerization, 44 126 electrochemical properties, 44 112-113 electronic absorption spectra, 44 108-112 reactions, 44 118-119 square-planar and octahedral species, 44 116-118... 

NMR spectroscopy (continued) of nickel complexes, 12 305-311 of osmium complexes, 12 276-281... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Using standard anaerobic techniques, a 100-mL Schlenk flask equipped with a stir bar is charged with 50 mL dry benzene and 2 mL (1.96 g, 0.0172 mol) distilled free amine. If crude daco is used, the product will be less pure and of lower yields. The mixture is warmed to 50-60°C under N2. Three 1-mL (0.05 mol) portions of ethylene sulfide are added, allowing 20 min reaction time between additions. The mixture is then heated under N2 for 1 h. Complete reaction is indicated by the formation of a finely divided white precipitate after the final addition. The reaction mixture is filtered anaerobically through a bed of celite in a glass-fritted funnel. Solvent is removed under vacuum while continuing to heat at 50-60°C. The H2-bme-daco is obtained as a colorless to pale yellow oil. Irrespective of color, this material is of suitable quality to be converted to the nickel complex. If distilled daco is used, the product is quite pure. Attempts at vacuum distillation (bpo.immHg = 135°C) resulted in partial decomposition. Yield 3.21 g (80%). 

Solvent is removed under vacuum while continuing to heat at 50-60°C. The H2-bme -daco which remains is a colorless to pale yellow oil, and is of suitable quality to be converted to the nickel complex. If distilled daco is used, the product is pure. Yield 3.3 g (65%). 

The field of nickel complexes with macrocydic ligands is enormous and continuous interest in this area in recent years has resulted in innumerable publications. A number of books and review articles are also available covering the general argument of the bonding capability of the various macrocydic ligands towards transition and non-transition metals. 22 2627 Synthetic procedures for metal complexes with some tetraaza macrocycles have been reported.2628 Kinetics and mechanism of substitution reactions of six-coordinate macrocydic complexes have also been reviewed.2629... 

Nickel(ii) and cobalt(ii) complexes continue to be the most widely studied first-series transition metal complexes. The well resolved NMR spectra arise from the very rapid electron-spin relaxation which occurs as a result of modulation of the zero-field splitting of these ions. In the case of 4-coordinate nickel(ii), only tetrahedral complexes (ground state Ti) are of interest since the square-planar complexes are invariably diamagnetic. Many complexes, however, undergo a square-planar-tetrahedral dynamic equilibrium which can be studied by standard band-shape fitting methods (Section B.l). 

As with thermal stabilizers, photostabilizers must satisfy basic chemical and physical requirements (see the section titled ""Antioxidant permanence effects of chemical and physical factors ). In addition, they must be photo-stable, i.e., stable to UV-light, to withstand continuous periods of UV-exposure, without being prematurely destroyed or effectively transformed into sensitizing products. There are essentially three classes of compounds that are categorized as photostabilizers/ photoantioxidants UV-absorbers and pigments, peroxide decomposers including nickel complexes, and sterically hindered amine light stabilizers. 

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

The trimethylsilylated silicic acids formed in this instance are soluble in conventional organic solvents, and their volatility is sufficiently high for them to be analysed by gas chromatography. Carzo and Hoebbel [411] carried out a comprehensive study of the chromatographic retention of various trimethylsilylated silicic acids on different stationary phases Apiezon L and silicone OV-1 and OV-17. The analysis of metals in the form of volatile complexes continues to attract attention, and have been described for analysing sodium [412], potassium [412], radium [413], caesium [413], barium [414], calcium [414], strontium [415], beryllium [416, 417], magnesium [418], zinc [419, 420], nickel [419], mercury [421], copper [422, 423], silver [424, 425], cadmium [421], indium [426, 427], g ium [428], scandium [217], cobalt [421], thallium [426], hafnium [429, 430], lead [431, 432], titanium [430], vanadium [433], chromium [434-436], manganese [426], iron [437], yttrium [438], platinum [439,440], palladium [439, 441, 442], zirconium [430], molybdenum [443], ruthenium [444], rhodium [445], rare earths [446—449], thorium [221, 450, 451] and uranium [221, 452]. The literature on GC analysis of metal chelates was reviewed by Sokolov [458]. 

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and dispose of wastes. One way to optimize catalyst consumption and waste disposal is to operate the reaction in a biphasic system. The first difliculty was to choose a good solvent. N,N-Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. They are liquid at the reaction temperature, butenes are reasonably soluble in them (Table 5.4-3), and they are poorly miscible with the products (Table 5.4-2, case (a)). The chloroaluminate eSiciently dissolves and stabilizes the nickel catalyst in the ionic medium without the addition of special ligand. The ionic liquid plays the role of both catalyst solvent and co-catalyst. Its Lewis acidity can be adjusted to get the best performance. The catalytically active nickel complex is generated directly in the ionic liquid by reaction of a commercialized tiickel(II) salt, as used in the Dimersol process, with an alkylaluminum chloride derivative. 

Interest in metal complexes containing polyfluoroalkyl- and polyfluoro-aryl-acetylenes as ligands has continued to be high, and has included compounds of platinum, palladium, gold, iridium, rhodium, - ruthenium, cobalt, - - nickel, molybdenum, and iron. These are reviewed in detail elsewhere in the Report (see Chapter 5). Such complexes may acquire usefulness for organic synthesis in due course thus significant amounts of hexakis(trifiuoromethyl)benzene are formed when perfluorobut-2-yne is incorporated into certain cobalt and nickel complexes. Similarly, the interesting compound hexakis(pentafluorophenyl)benzene was isolated in 40—70% yield hy trimerization of perfluorodiphenylacetylene over 7C-cyclopentadienylrhodium dicarbonyl in toluene. ... 

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