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: 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 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 poly cyclic compounds based on norbornadiene-2,5 in the presence of nickel complexes: III. Cyclic dimerization of norbornadiene-2,5 in the presence of organophosphorus additives

The cyclodimerization of norbornadiene-2,5 (NBD) catalyzed by the systems formed on the basis of bis(ηy³-allyl)nickel and organophosphorus compounds and the process kinetics are studied. The formation rate of all products follows the overall second-order rate law: first order with respect to the catalyst and NBD. The addition of phosphines and phosphites substantially decreases the reaction rate compared to that in nickel systems containing no organophosphorus additives. The influence of the phosphine ligand structure and temperature on the ratio of the reaction products is studied. The blocking of one coordination site on the nickel atom changes the process kinetics. The loss of two vacancies results in the loss of the catalytic activity of the system. A mechanism explaining the stoichiometry and composition of the reaction products is proposed.     

Catalytic activity of cycloaurated complexes in the addition of 2‐methylfuran to methyl vinyl ketone

Cycloaurated gold(III) complexes derived from cycloaurated iminophosphorane, triphenylphosphine sulfide or selenide, or pyridylsulfonamide ligands have been assessed for their catalytic activity in the addition of 2‐methylfuran to methyl vinyl ketone. Addition of AgBF₄ was generally needed for high activity, although those with coordinated atoms of high trans influence showed some activity in the absence of added Ag⁺. Copyright © 2011 John Wiley & Sons, Ltd.     

Photodegradation in solution of copolymers of methyl vinyl ketone and methyl isopropenyl ketone with methyl methacrylate

Copolymers of methyl vinyl ketone (MVK) and methyl isopropenyl ketone (MIK) with methyl methacrylate (MMA), have been prepared covering the whole composition range. Reactivity ratios have been estimated as follows: MMA/MVK, r_MMA = 0·63 ± 0·2, r_MVK = 0·53 ± 0·2; MMA/MIK, r_MMA = 0·98 ± 0·2, r_MIK = 0·69 ± 0·2. Number average molecular weights have been measured during the course of photodegradation under 253·7 nm radiation in methyl acetate solution and rates of chain scission calculated. In each system the copolymers are less stable than the corresponding homopolymers, the rate passing through a maximum at 20–30% ketone content. These results have been discussed from a mechanistic point of view.     

Liquid-phase hydrodechlorination of polychloroaromatic compounds in the presence of Pd-promoted nickel catalysts

Liquid phase hydrodechlorination of chlorobenzene, 1,2,4-trichlorobenzene, hexachlorobenzene, polychlorinated biphenyls in the ethanol-containing solution, on Me⁰/C (where Me⁰-Pd, Ni or bimetallic Ni−Pd; C-carbon material “Sibunit”) with H₂ have been studied at 20–70°C and P_{H 2}=1–50 atm. Pd and Pd-promoted Ni catalysts exhibit the highest activity. Kinetic studies show hydrodechlorination of these compounds to be a consecutive reaction, which under the conditions described may produce less chlorinated compounds.     

Copolymerization of methyl vinyl ketone with styrene in the presence of cobalt(II) nitrate

Copolymerization of methyl vinyl ketone (MVK) with styrene was carried out at 50°C in the presence of cobalt(II) nitrate. The resulting monomer reactivity ratios decreased with an increasing concentration of the cobalt salt. This finding suggests that the metal salt participates in the propagation step of the copolymerization. Absolute copolymerization parameters were determined by assuming a three-component system as free MVK (M₁), MVK complexed with cobalt(II) nitrate (M₂), and styrene (M₃): k₁₁/k₁₂ = 0.184, k₁₁/k₁₃ = 0.235, k₂₂/k₂₁ = 7.18 × 10⁻², k₂₂/k₂₃ = 6.79 × 10⁻⁴, k₃₃/k₃₁ = 0.380, and k₃₃/k₃₂ = 2.77 × 10⁻³, and Q₂ = 19.65 and e₂ = 2.83. The complexed MVK monomer is more reactive to the polymer radical with the terminal styrene unit than the free MVK. Very small values for the monomer reactivity ratios, k₂₂/k₂₃ and k₃₃/k₃₂, show the marked alternating tendency for the copolymerization of the complexed monomer with styrene. In practice, however, alternating copolymer could not be obtained because of the poor solubility of cobalt(II) nitrate.     

Mechanism of chloramine-T oxidation of methyl vinyl ketone and isopropyl methyl ketone in aqueous alkaline media

The oxidation kinetics of methyl vinyl ketone and isopropyl ketone by chloramine-T in aqueous alkaline solutions show first-order dependence on chloramine-T, both substrates and alkali. No effect of p-toluenesulphonamide was evident. Observed stoichiometry, negligible effect of ionic strength and a positive dielectric effect point to a mechanism involving interaction of enolate anions with chloramine-T in the rate determining step. Activation parameters and the isolation of the product formaldehyde are in agreement with the proposed mechanism.     

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.     

Codimerization of ethylene with isoprene and 1,3-cyclohexadiene in presence of catalytic systems based on cyclopentadienyl complexes of titanium

Conclusions Isoprene and 1,3-cyclohexadiene react with ethylene under the influence of catalytic systems based on the mono- and dicyclopentadienyl complexes of titanium to give linear codimerization and oligomerization products. The reaction of isoprene with ethylene in the presence of Cp₂TiCl₂-C₂H₅MgBr proceeds selectively on the type of 3,4-addition to give 2,3-dimethylpentadienes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 907–910, April, 1979.     

[2 + 2] Dimerization of norbornadiene and its derivatives in the presence of nickel complexes and zinc metal

Norbornadiene undergoes [2 + 2] reaction in THF in the presence of NiX₂ and zinc metal powder to give an exo-trans-exo dimer and an exo-trans-exo-trans-exo trimer. In these products, the norbornadiene molecules are linked to each other by forming cyclobutane rings with all cyclobutane carbons occupying exo positions relative to the bridging carbons on the two norbornadiene fragments. Polymerization of norbornadiene occurs if the catalyst NiX₂ is replaced by Ni(PPh₃)₂Cl₂. 1,4-Dihydro-1,4-epoxynaphthalene, 5,8-dimethoxy-1,4-dihydro-1,4-epoxynaphthalene, 5-methoxy-1,4-dihydro-1,4-epoxynaphathalene and methyl 1,4-dihydro-1,4-iminonaphthalene-9-carboxylate also dimerize to give exo-trans-exo products in excellent yields in toluene in the presence of Ni(PPh₃)₂Cl₂ and Zn powder. For the dimerization products of 5-methoxy-1,4-dihydro-1–4-epoxynaphthalene, cis and trans isomers with respect to the orientation of methoxy groups in about 1 : 1 ratio were oberved. Under similar reaction conditions for the dimerization of norbornadiene, norbornene undergoes reductive dimerization to afford a product which consists of two norbornyl groups. The structure of this product is also exo-trans-exo.     

Regioselective silylphosphination of methyl vinyl ketone with complexes containing cyclic and linear iron-silicon-phosphorus reacting sites

Treatment of Cp*(CO)Fe{kappa2(Si,P)-SiMe2PPh2} with methyl vinyl ketone gave a 1,2-addition product, Cp*(CO)Fe{kappa2(Si,P)-SiMe2OCMe(CH=CH2)PPh2}. A linear-type Cp*(CO)2FeSiMe2PPh2 also reacted with the ketone to yield a 1,4-addition product, Cp*(CO)2Fe{kappa1(Si)-SiMe2OC(Me=CHCH2PPh2}, which was further converted to a seven-membered metallacycle, Cp*(CO)Fe{kappa2(Si,P)-SiMe2OC(Me)=CHCH2PPh2}, upon photolysis.     

Styrene polymerization by ziegler-natta catalysts based on bis(salicylaldiminate)nickel(II) complexes and methyl aluminoxane

The homopolymerization of styrene by using different catalytic systems based on bis(salicylaldiminate)nickel(II) and methylaluminoxane was investigated. In particular, the effect on catalyst activity and polymer characteristics by electron withdrawing groups located on the phenolic moiety was studied. The influence of the bulkiness of the substituents on the N-aldimine ligand was also ascertained. Finally the catalytic performances were investigated as a function of the main reaction parameters, such as temperature, Al/Ni molar ratio and duration.