Nickel complexes isomerism

Shell Higher Olefin Process) plant (16,17). C -C alcohols are also produced by this process. Ethylene is first oligomerized to linear, even carbon—number alpha olefins using a nickel complex catalyst. After separation of portions of the a-olefins for sale, others, particularly C g and higher, are catalyticaHy isomerized to internal olefins, which are then disproportionated over a catalyst to a broad mixture of linear internal olefins. The desired fraction is... 

The Ni1 complexes may exist in different isomeric forms, and the form obtained may depend upon whether pulse radiolysis of electroreduction are employed to synthesize them.2323 Usually, isomeric integrity of tmc nickel complexes is not maintained upon going from Ni11 to Ni1 ... 

Nickel complexes are also active catalyst for the isomerization of allylic alcohols. Ni(dppb)2, prepared by mixing Ni(cod)2/2dppb (2equiv.), catalyzed the isomerization of geraniol to citronellal in the presence of CF3C02H (4equiv.) in toluene at 80 °C (Equation (10)).34... 

The next five transition metals iron, cobalt, nickel, copper and zinc are of undisputed importance in the living world, as we know it. The multiple roles that iron can play will be presented in more detail later in Chapter 13, but we can already point out that, with very few exceptions, iron is essential for almost all living organisms, most probably because of its role in forming the amino acid radicals required for the conversion of ribonucleotides to deoxyribonucleotides in the Fe-dependent ribonucleotide reductases. In those organisms, such as Lactobacilli6, which do not have access to iron, their ribonucleotide reductases use a cobalt-based cofactor, related to vitamin B12. Cobalt is also used in a number of other enzymes, some of which catalyse complex isomerization reactions. Like cobalt, nickel appears to be much more extensively utilized by anaerobic bacteria, in reactions involving chemicals such as CH4, CO and H2, the metabolism of which was important... 

In order to obtain adiponitrile, 2 should isomerize to 4, and not to the thermodynamically more stable 3 (stabilised by the energy of conjugation). The thermodynamic ratio is 2 3 4 = 20 78 1.6 [6], The isomerization of 2 to 4 happens to be favorably controlled by the kinetics of the reactions the reaction 2 to 4 reaches equilibrium, but the reaction 2 to 3 does not. Note that the nickel complex not only is responsible for the addition of HCN but that it is also capable of catalysing selectively the isomerisation. The final step is the addition of HCN to 4 to give 5, adiponitrile. 

The reaction of planar Ni ([14]aneN4) + represented as shown in (2.10) with a number of bidentate ligands (XY) to produce c -octahedral Ni ([14]aneN4) XY + is first-order in nickel complex and [OH ] and independent of the concentration of XY.In the preferred mechanism, the folding of the macrocycle (base-catalyzed tmns — cis isomerization) is rate determining, and this is followed by rapid coordination of XY ... 

As seen from Scheme 7.2, the epoxy-ring cleavage and nickel oxidation proceed simultaneously. The nickel-oxygen bond is formed. This results in the formation of the carbon-nickel biradical in which Ph-CH fragment can rotate freely. The cleavage of the (NiO)-C bond leads to the formation of a mixture of styrenes. At early reaction stages (30 min), cis and trans olefins are formed in 50 50 ratio. After a prolonged contact (30 h), when all possible transformations should be completed, the trans isomer becomes the main product and cis trans ratio becomes 5 95. Such enrichment of the mixture with the trans isomer follows from the formation of the di-P-(trimethylsilyl)styrene anion-radical and its isomerization. The styrene formed interacts with an excess of the nickel complex. 

Insertion of 1,3-diynes into NiXMe(PMe3)2 (X = Cl, Br, I) gives the corresponding 1-alkynylalkenyl-nickel complexes 293, which undergo E/Z isomerization in solution, the former predominating. ... 

It has previously been shown that the oxazines (169) can isomerize by ringopening to the Schiff bases (170). The reactions of the oxazines with Ni , Co", and Cu" have now been examined in the hope of yielding chelates of the Schiff bases. However, the products were not the expected ones in the case of nickel, two kinds of chelate were obtained. Those formed in the absence of air were (171), in which proton migration from the original ligand had occurred, and, in the presence of air, (172) was formed in which dehydration had taken place on the original oxazine. The Co" and Cu" chelates are structurally analogous to the nickel complexes. ... 

A number of workers have examined enantioselective isomerizations as a desym-metrization strategy. Frauenrath and coworkers have been interested in the isomerization of dihydrooxepins using nickel complexes.More recently, these workers reported that a Me-DUPHOS-Nil2 complex in the presence of LiEt3BH provides high enantioselectivity in the isomerization of dihydrooxepins ... 

Homogeneous nickel complexes proved to be versatile catalysts in dimerization and trimerization of dienes to yield different oligomeric products.46-55 Depending on the actual catalyst structure, nickel catalyzes the dimerization of 1,3-butadiene to yield isomeric octatrienes, and the cyclodimerization and cyclotrimerization to give 1,5-cyclooctadiene and all-trans-l,5,9-cyclododecatriene, respectively46 56 [Eq. (13.13)]. Ziegler-type complexes may be used to form cis,trans,trans-1,5,9-cyclododecatriene37,57 58 [Eq. (13.14)], which is an industrial intermediate ... 

With the addition of 1,3-butadiene, the initially yellow hydride solutions turn red with the formation of relatively stable l-Me-it-allyl-nickel complexes, and olefin isomerization activity stops. By measuring the rate of formation of the rc-allyl complexes in the presence of added P(OEt)3, it was possible to measure the rate constant for dissociation of L from HNiL4 and show that this is the rate-determining step (42). 

Copper and nickel Chromium and cobalt N -Np Na-Np Meridional/facial coordination Azo/hydrazone tautomerism Non-planarity due to azo/hydrazone tautomerism Formation of two copper and two nickel complexes by unsymmetrical o.o -dihydroxyazobenzenes78 Detection of isomeric 2 1 chromium complexes 79 proton magnetic resonance80 Isolation of isomeric 2 1 chromium and cobalt complexes 86 87 limited X-ray crystallographic89 90 Proton magnetic resonance80 Detection of five isomeric 2 1 chromium complexes of symmetrical o.o -dihydroxydiarylazo compounds... 

Hydrothermal methods, for molecuarlar precursor transformation to materials, 12, 47 Hydrotris(3,5-diisopropylpyrazolyl)borate-containing acetylide, in iron complex, 6, 108 Hydrotris(3,5-dimethylpyrazolyl)borate groups, in rhodium Cp complexes, 7, 151 Hydrotris(pyrazolyl)borates in cobalt(II) complexes, 7, 16 for cobalt(II) complexes, 7, 16 in rhodium Cp complexes, 7, 151 Hydrovinylation, with transition metal catalysts, 10, 318 Hydroxides, info nickel complexes, 8, 59-60 Hydroxo complexes, with bis-Cp Ti(IV), 4, 586 Hydroxyalkenyl complexes, mononuclear Ru and Os compounds, 6, 404-405 a-Hydroxyalkylstannanes, preparation, 3, 822 y-Hydroxyalkynecarboxylate, isomerization, 10, 98 Hydroxyalkynes, in hexaruthenium carbido clusters, 6, 1015 a-Hydroxyallenes... 

The isomeric distribution in the catalyzed reaction is apparently not influenced by the stability of the various CDT-nickel complexes. All four... 

The formation of both DVCB and COD directly from butadiene requires that the intermediate nickel complex exist in at least two isomeric forms. 

The condensation of o-aminobenzamide and pyridine-2-carbaldehyde produced the terdentate ligand (129) which partially isomerizes in methanol, in the presence of nickel(n) nitrate, to form the cyclic ligand (130). The nickel complex [Ni( 129)(130)-(H20)](N03)2,4H20 has been X-rayed, and the results show that (129) bonds as a terdentate N20 donor, and (130) as a bidentate N2 ligand, the co-ordinated water molecule completing the irregular octahedron about the nickel.575... 

Thiocarbonyl derivatives of 1,3-dioxolanes and 1,3-oxathiolanes are readily isomerized to the 2-carbonyl compounds as shown in Scheme 20. Alkylation of the sulfur atom with alkyl halides usually leads to ring-opened products (Scheme 21) (69JOC3011). Most of the other chemistry of the sulfur derivatives has focused on desulfurization and subsequent generation of alkenes. The reaction is shown in equation (20) and proceeds with cis elimination via carbene intermediate (see Section 4.30.2.2.5) and is usually carried out with a phosphine (73JA7161) or a zero-valent nickel complex (73TL2667). 

The oligomerization catalyst is a homogeneous nickel complex of a phosphi-nocarboxylic acid. The other catalysts are fixed bed catalysts a Co/Mo oxide for the metathesis reaction and a solid catalyst for the isomerization. 

Subjecting 2 or 3 to strongly acidic conditions (e.g. 1 M CF3CO2H or concentrated HQ) leads to rapid demetalation and the production of two isomeric free-base macrocycles 10 and 11 [11, 12]. The structure of 10 was conflrmed by its spectral properties and its remetalation to form the nickel complex 5. On the other hand, the structure of 11 was determined solely by its spectral properties. For instance, the NMR spectrum of 11 demonstrated the presence of a fully unsaturated system. Typical also was the presence of pyrrolic proton signals in the 6-7 ppm range of the NMR spectrum [12]. Compound 11 was very unstable... 

The coordination chemistry of the hexaphyrin system has provided a number of surprises [190]. The addition of nickel chloride to the isomeric mixture of hexaphyrins 250 leads to a single product. The proposed structure of the resulting nickel complex is shown as compound 254 in Scheme 44. Other metals were also found to react with this and other isomeric mixtures of hexaphyrins to give rise to only one isomeric product. For instance, treatment of either 250 or 252 with zinc chloride gives the bimetallic complexes 255 or 256 as one isomer, respectively (Scheme 45). In contrast, the reaction of 253 under identical conditions gives rise to a similar complex 257, wherein, the positions of the ter substituents are different from those reen in the previous examples (Scheme 46). The reactions of hexaphyrins with zinc would appear to indicate that the two isomers normally... 

Allylic malonate 100 completely isomerizes to the thermodynamically favored linear isomer 101 on treatment with a palladium catalyst [119]. Formation of a stabilized carbanion and Jt-(allyl)palladium species facilitates the C-C bond cleavage. Analogous isomerization is also catalyzed by a nickel complex [120]. These results demonstrate that the transition metal-catalyzed nucleophilic substitution of an allylic substrate with a carbon nucleophile is reversible, if the cleaved nucleophile is sufficiently stabilized. 

When phosphane-free nickel complexes, such as bis(cycloocta-l,5-diene)nickel(0) or te-tracarbonylnickel, are employed in the codimerization reaction of acrylic esters, the codimer arising from [2-1-1] addition to the electron-deficient double bond is the main product. The exo-isomer is the only product in these cyclopropanation reactions. This is opposite to the carbene and carbenoid addition reactions to alkenes catalyzed by copper complexes (see previous section) where the thermodynamically less favored e Jo-isomers are formed. This finding indicates that the reaction proceeds via organonickel intermediates rather than carbenoids or carbenes. The introduction of alkyl substituents in the /I-position of the electron-deficient alkenes favors isomerization and/or homo-cyclodimerization of the cyclopropenes. Thus, with methyl crotonate and 3,3-diphenylcyclopropene only 16% of the corresponding ethenylcyc-lopropane was obtained. Methyl 3,3-dimethylacrylate does not react at all with 3,3-dimethyl-cyclopropene, so that the methylester of tra 5-chrysanthemic acid cannot be prepared in this way. This reactivity pattern can be rationalized in terms of a different tendency of the alkenes to coordinate to nickel(O). This tendency decreases in the order un-, mono- < di-< tri- < tet-... 

It is known that in the dimerization of ethylene in the presence of homogeneous nickel complexes, 1-butene is initially formed, its major part being isomerized into c/s-2-butene. The... 

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