Catalytic syntheses of polycyclic compounds based on norbornadiene-2,5 in the presence of nickel complexes: II. cyclic dimerization of norbornadiene-2,5. Kinetics and mechanism of the process

Kinetics of the cyclodimerization of norbornadiene-2,5 (NBD) is studied in the presence of a catalytic system based on bis(η³-allyl)nickel. The forms of the rate laws characterized by different reaction orders with respect to NBD are determined. The influence of temperature and solvent nature on the process is studied. The thermodynamic parameters are determined. The structure of the products is shown to be determined by the structure of intermediates. The mechanism of the process, consisting of the following main steps, is proposed: (1) the formation of Ni(NBD)₂, which is the true catalyst; (2) the reversible addition of NBD to the indicated complex, resulting in the formation of Ni(NBD)₃ and Ni(NBD)₄ η-complexes and accompanied by a change in ligand coordination; (3) the oxidative addition of coordinated NBD molecules to a nickel atom that gives five and six-membered metallacyclic intermediates; and (4) the reductive elimination of nickel from them to form cyclic dimers. The conditions for the selective formation of individual isomers are proposed.     

Catalytic syntheses of polycyclic compounds based on norbornadiene in the presence of nickel catalysts

The cycloadditions of olefins containing an electron-withdrawing substituent to norbornadiene are reported. The influence of the substituent and solvent nature on the [2+2+2]-cycloadduct yield and stereoselectivity is elucidated. The competitive cycloaddition of pairs of olefins to norbornadiene is discussed. Hypotheses about the structure of key intermediates of the process are considered. The consistent generalized mechanism for the cycloaddition of unsaturated compounds of various classes to norbornadiene is suggested.     

Catalytic syntheses of polycyclic compounds based on norbornadiene in the presence of nickel complexes: V. Codimerization of norbornadiene and methyl vinyl ketone on heterogenized nickel catalysts

A new heterogenized nickel catalyst was developed for the codimerization of norbornadiene and methyl vinyl ketone. This catalyst considerably improved the performance characteristics of the process (selectivity, specific activity, and operating time), as compared with available analogs. A thermogravimetric study of the formation of the active component of the catalyst was performed. Factors affecting the selectivity and productivity of the process were determined.     

Catalytic syntheses of polycyclic compounds based on norbornadiene in the presence of nickel complexes: VI. Heterogenized catalyst for isomerization reactions of norbornene derivatives

The kinetics and mechanism of the thermal izomerization of 5-exo-methyl-tricyclo[3.2.1.0^5,7]octene-2 into 2-methyl-tetracyclo[3.2.1.0^2,7.0^4,6]octane are reported. The use of catalysts based on nickel compounds is demonstrated. As compared to the other catalytic systems, the heterogenized nickel catalyst obtained by thermal treatment of nickel norbornadiene complexes shows much better performance characteristics (selectivity, specific activity, and service life).     

Catalytic characteristics of enzyme-polyelectrolyte complexes based on hexahistidine-containing organophosphorus hydrolase

A number of covalent and non-covalent polyelectrolyte complexes based on enzyme such as hexahistidine-containing organophosphorus hydrolase was developed in this work. Polyanions and polycations were used in the form of block-copolymers with poly(ethylene glycol). To obtain covalent complexes of the enzyme, different coupling agents (glutaric aldehyde, N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide sodium salt) were tried. The best catalytic efficiency of the action of the covalently bound complex ((2.8 ± 0.3) × 10⁸ M^?1 s^?1) was obtained for samples with EDC. The modification of the protein surface was undertaken as an approach to its further biomedical application.     

Catalytic transfer hydrogenation of aromatic nitro compounds in the presence of nickel thiolato-complexes

Summary Transfer hydrogenation of aromatic nitro compounds by hydrazine to the corresponding anilines is catalyzed by (Bu₄N)[Ni(tdt)₂] (tdt=toluene-3,4-dithiolate) and analogous Ni^III complexes in refluxing THF; hydroxylamine derivatives are formed as intermediates.     

Kinetics of propylene dimerization in the presence of a phosphite-modified, nickel based catalytic system

Propylene dimerization by a catalytic system consisting of nickel(II)acetylacetonate, triphenylphosphite and diethylaluminium chloride has been studied. A kinetic analysis shows a first order dependence on catalyst and a second order dependence on propylene. This revised version was published online in June 2006 with corrections to the Cover Date.     

Studies on the syntheses of heterocyclic compounds. Part DCXLIV . Catalytic reduction of homoproaporphine related compounds

Hydrogenation of the homoproaporphine (IV) over platinum oxide gave a mixture of the cyclohexanols VIIa and VIIb. In contrast, reduction of IV on palladium provided the cyclo-hexanone VI, which was also obtained from VIIb by oxidation. Treatment of the cyclohexanols VIIa and VIIb under hydrogen on platinum oxide afforded the same mixture of VIIa and VIIb.     

Redox conversions in crystalline compounds based on macrocyclic complexes of nickel(II)/(III) and aromatic carboxylates

It is shown that conversion of nickel(II) complexes, in the composition of crystalline compounds of various structures, into nickel(III) leads to the preparation of new redox-active metal-organic skeletons. The structure of the chromophore of the metal ion and the chemical properties of the compounds formed by this process (thermal stability, reactivity) depend to an important extent on the nature of the construction blocks which makes possible the creation of new materials with controlled properties.     

Cyclic organophosphorus compounds. XVIII—the mass spectroscopy of some 2-amino-1,3,2-dioxaphosphorinans,cyclic phosphorodiamidates and phosphorodiamidothionates

Stepwise replacement of O in 1,3-dioxa-2-phospha(V)-cyclohexanes (or related ring systems) by NR (R=H or Me) leads to an increase in the stability of the hetero-ring ions produced under electron impact conditions. In the case of the 2-phenoxy derivatives, there is also an increased abundance of [M? PhO]⁺ or [M? PhOH]⁺ ions, and, for the 2-sulphides, a reduction in the abundance of [M-S]^+˙ and [M-SH]⁺ ions, with a concurrent increase in that of [M-PhS]⁺ ions. Such trends have been correlated with ultraviolet photoelectron spectral data on a qualitative basis.     

Catalytic deoxygenation of organic compounds by carbon monoxide: III. The reaction under pressure of aromatic nitro compounds in the presence of o-phthalaldehyde

The reaction of o-phthalaldehyde with several aromatic nitro compounds in the presence of carbon monoxide and catalytic quantities of hexarhodium-hexadecacarbonyl eventuated in the formation of the corresponding N-substituted isoindolinone as the major product. A reaction mechanism has been suggested incorporating deoxygenation of the nitro compound by carbon monoxide to a nitrene intermediate and the subsequent interception of the latter by o-phthalaldehyde.     

Transformation of organic compounds in the presence of metal complexes: III. Transfer hydrogenation of alkylcyclohexanones. Effect of phosphine basicity on stereoselectivity

The transfer hydrogenation of 2- and 4-alkylcyclohexanones (alkyl = Me or t-Bu) was studied in alkaline i-PrOH with catalyst systems prepared in situ from [Rh(COD)Cl]₂ + phosphine (Ph₃P, Bu₃P). The stereoselectivity depends on the basicity of the phosphine and on the bulk and position of the alkyl substituent.     

Tail-to-tail dimerization of methyl acrylate in the presence of triphenylarsine ruthenium complexes

Catalytic dimerization of methyl acrylate by homogenous ruthenium catalysts was investigated. The effect of the addition of acidic additives, supporting ligands, polymerization inhibitor, and reaction conditions on the selectivity of dimerization was studied, and possible reaction mechanism was discussed. Conversion and selectivity were significantly affected by using triphenylarsine as supporting ligand. Under mild conditions, conversion up to 98% with good selectivity to tail-to-tail product was achieved.