Nickel synthetic structures

The synthetic route represents a classical ladder polymer synthesis a suitably substituted, open-chain precursor polymer is cyclized to a band structure in a polymer-analogous fashion. The first step here, formation of the polymeric, open-chain precursor structure, is AA-type coupling of a 2,5-dibromo-1,4-dibenzoyl-benzene derivative, by a Yamamoto-type aryl-aryl coupling. The reagent employed for dehalogenation, the nickel(0)/l,5-cyclooctadiene complex (Ni(COD)2), was used in stoichiometric amounts with co-reagents (2,2 -bipyridine and 1,5-cyclooctadiene), in dimethylacetamide or dimethylformamide as solvent. 

At present, synthetic routes to more than 40 metal complexes other than the copper complex are known. Apart from a cobalt phthalocyanine pigment (P.B.75) which was introduced to the market just recently, none of the resulting products, however, has stimulated commercial interest as a pigment. Nickel complexes, however, are found in reactive dyes, while cobalt complexes of this basic structure are employed as developing dyes. 

In these experiments, synthetic zeolites of the faujasite-type without binding substance were used. Calcium and nickel-calcium samples in ionic form were obtained by ion exchange under conditions ensuring stability of the crystal structure (5). Platinum addition was carried out by ion exchange with Pt(NH3)6Cl4 (6). 

Table 1 shows the properties of smectite-type materials prepared. Smectite materials prepared at lower pH had fewer sodium ions, higher surface areas, and larger pore volumes for a series of samples containing the same divalent cation species (nickel and cobalt) in the octahedral sheet. The adsorption of methylene blue on all the synthetic smectites shows that the smectite fragments are negatively charged. The Si M ratios of synthetic smectites were about 8 6, indicating that most of divalent cations exist in octahedral layers and small amount of divalent cations would exist as hydroxide or oxide cluster in smectite materials. However, the amounts of the hydroxide or oxide cluster were small, because only smectite structures were observed in XRD patterns and EXAFS Fourier transforms of synthetic smectites calcined at 873 K. 

Following the aforementioned pioneering work, many other organometallic complexes of nickel(II) were prepared using different synthetic procedures. Complexes containing one molecule of tertiary phosphine were prepared using methods similar to that reported in equations (142) and (143) and Scheme 13.1193-11951219-1223 All of these diamagnetic compounds have the square planar structure exemplified by (155).1193... 

The nickel(II) complexes with bidentate dithiols, starting from those with 1,2-ethanedithiol, are well documented but they still remain far less numerous than those with 1,2-dithiolenes (Section 50.5.6.5.i). In Table 88 selected nickel(II) complexes with some dithiols and related ligands are reported together with synthetic and structural properties. 

Table 88 Synthetic and Structural Properties of Selected Nickel(II) Complexes with Dithiols and Related Ligands...

An interesting use of the nickel-catalyzed allylic alkylation has prochiral allylic ketals as substrate (Scheme 8E.47) [206]. In contrast to the previous kinetic-resolution process, the enantioselectivity achieved in the ionization step is directly reflected in the stereochemical outcome of the reaction. Thus, the commonly observed variation of the enantioselectivity with respect to the structure of the nucleophile is avoided in this type of reaction. Depending on the method of isolation, the regio- and enantioselective substitution gives an asymmetric Michael adduct or an enol ether in quite good enantioselectivity to provide further synthetic flexibility. 

Recently, interest in clays as acidic catalysts has been quickened by the reported high catalytic activity of a synthetic mica-montmorillonite clay and its nickel-containing analogs. Wright et al. (247) have described the structure, thermal modification and surface acidity of the clay, which they designated SMM for synthetic mica-montmorillonite. 

Recent synthetic and spectroscopic work has concentrated on the study of structurally related linear-chain palladium complexes (7, 8), on the possibility of synthesising related nickel complexes, and on the study of mixed-metal mixed-valence complexes of the sort... 

The structure of most of these compounds must be considered as quite well established. Deferrideoxyferrichrome, prepared from the parent compound with Raney nickel and H2 at 50 lbs pressure, is identical to a synthetic cyclic hexapeptide obtained by stepwise addition of three residues of NS-acetyl-L-ornithine to triglycine, followed by cyclization (112). The amino acid sequence in ferrichrome A has been established by degradation (112, 113) and confirmed by crystallography (150). Removal of the a—p unsaturated residue of ferrichrome A, ferrirubin and ferrirho-din followed by re-acylation with acetyl gives, in each case, ferrichrysin (63). All four substances must hence have an identical amino acid sequence and we assume for all of these compounds the configuration shown in Fig. 5. 

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