Nickel couplings

In 1986 Yahalom and Zadok (4) pointed to methods to produce composition-modulated alloys by electrodeposition, initially for the copper-nickel couple. They obtained modulation to thicknesses down to 8 A. The principle of the method is as follows. 

Semmelhack, M. F., Helquist, P. M., Jones, L. D. Synthesis with zerovalent nickel. Coupling of aryl halides with bls(1,5-cyclooctadlene)nlckel(O). J. Am. Chem. Soc. 1971, 93, 5908-5910. 

The copper-nickel couple works well also in the heterodimetallic system based on molecule 15 [37]. Here, a 2, 2,-bipyridine fragment is covalently linked to the carbon backbone of a [Ni(II) (cyclam) ]2+ subunit. Two bpy fragments coordinate a Cu(II) center, giving rise to the trimetallic system 16... 

For the copper couple, increasing the amount of a poor coordinating solvent results in a decrease in the solvation energy of the reduced species, i.e. Cu, whereas the Cu is relatively unaffected so that it becomes more difficult to reduce the Cu to the Cu , i.e. a negative shift in the redox potential. The reverse occurs for the nickel couple with the Ni becoming less stabilized by the poor coordinating solvent and hence easier to reduce, i.e. a positive shift in the redox potential. 

The conventional preparation of the zinc-copper couple is long and tedious Sonication of copper (I) iodide with zinc powder in THF or in alcoholic solvents makes it much easier, and a black suspension is produced in a few minutes The method tolerates up to 40% of water in the organic solvents. Besides the applications for conjugate additions to activated olefins (p. 225), this sonochemically prepared couple was used for the carbonylation of iodoalkanes to aldehydes.52 The zinc-nickel couple prepared from nickel salts and zinc is an excellent catalyst for the hydrogenation of olefinic bonds (p. 187).53 Cementation of cobalt on zinc is achieved in water under sonication.54 The temperature must be adjusted to avoid the reduction of water. 

The authors estimate that sonication is not necessary, but since they used a vibromill stirrer, hydrodynamic cavitation produced by this method is certainly at the origin of the activation (see p. 144 for another case). With an iodoalkyl tetrahydrofuranic diol, only C-I bond reduction was observed. o This imdesired pathway constitutes a frequent minor component in most reactions, which can be reduced in importance by using an indium-nickel couple in pyridine. ... 

HIGH MOLECULAR WEIGHT AROMATIC BIPHENYLENE POLYMERS BY NICKEL COUPLING OF ARYL DICHLORIDES... 

The nickel coupling of aryl chlorides was studied in-depth in our laboratories. It was demonstrated that the corresponding biaryls can be produced in quantitative yields. Hence, it was felt that the method should be appropriate for the preparation of high polymers. Our studies, as herein reported, do indeed show that materials of excellent quality can be prepared via this novel route. Also, proper choice of the starting monomers allows for the synthesis of an almost infinite variety of polymers. In general, these polymers contain biphenyl moieties which contribute excellent thermal, mechanical, impact and alloying characteristics. 

The nickel coupling route which results in the formation of an aromatic carbon-carbon bond, leads to polymers which contain, in the simplest case, a biphenyl group. This is illustrated in an idealized way in equation (I) ... 

The reactions depicted in equation (IV) were studied in detail. The first reaction, i.e. the condensation of p-chlorophenol (16) with 4,4-dichlorodiphenyl sulfone (14) is a classical nucleophilic aromatic substitution it proceeds smoothly in polar aprotic solvents (e.g., DMAC) and yields the dichloro intermediate (17) in quantitative yield. A detailed study was necessary, however, to determine the critical parameters which control the formation of high polymer via the second reaction i.e. via the nickel coupling of (17) to (8). 

Significant Variables in Nickel Coupling to Produce Poly(aryl ether sulfones) as Determined by Experimental Design... 

Properties of Poly(aryl ether sulfone) (8) Produced by Conventional Process and Nickel Coupling... 

Having successfully prepared high polymer via the nickel coupling route, we turned our attention toward developing an integrated two-step process [see equations (IV)] where the isolation and purification of the intermediate (17) [4,4-di(p-chlorophenoxy)diphenyI sulfone] would not be required. The monomer hitherto used was prepared by the reaction of 4,4-dichlorodiphenyl sulfone (14) with two equivalents of p-chlorophenol (16) in N,N-dimethyIacetamide/toluene with potassium carbonate as the base. The monomer was isolated by coagulation in methanol/water, purified by triple recrystallization from isopropanol, and dried in a vacuum oven prior to polymerization. In... 

Further studies have shown that the nickel coupling polymerization is very general and allows for the preparation of a practically infinite number of polymers. This was first demonstrated by copolymerizing the dichloro diphenoxy derivative (17) with a series of comonomers [equation (VI)] ... 

The data in Table IV show that the properties of the two materials, i.e. (30) made via the nickel coupling route [equation (VII)] and (30) made via the nucleophilic route [equation (VIII)] are practically identical. 

Previous studies in our laboratories have established the following key steps for the nickel coupling of aryl chlorides (L represents a ligand, e.g., triphenylphosphine) ... 

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