Yu. Yu. Titova

Functions of organoaluminum and proton donor compounds in the formation and functioning of nanosized Ziegler-type nickel-containing hydrogenation catalysts

The turnover frequency (TOF) and turnover number (TON) in styrene hydrogenation have been determined for catalytic systems based on Ni(acac)2 · nH2O (n = 0, 0.5, and 3.0), Ni(COD)2 (COD = cycloocta-1,5-diene), and AlEt3 at different Al/Ni molar ratios. The amount of water of crystallization determines the TON and TOF of the nickel catalysts and their dependence on the Al/Ni ratio. The TON and TOF of the nickel catalysts are markedly increased by the introduction of an optimum amount of a proton donor. The model of the ligand shell stabilizing the nickel nanoparticles has been refined. The refined model provides an explanation for the activating action of proton donor compounds in the formation of the hydrogenation catalysts. The functions of the organoaluminum compounds are not limited to Ni(II) reduction to Ni(0); they are also involved in the stabilization of the nickel-containing nanoparticles.

Formation, nature of activity, and hydrogenation catalysis by nickel bis(acetylacetonate)-lithium tetrahydroaluminate systems

A new approach to synthesis of nickel catalysts under the action of lithium tetrahydroaluminate was proposed which allows preparation of high-performance nanosized catalytic systems with well-reproducible properties. The major stages of formation and the nature of catalytically active species and inhibitors formed in the Ni(acac)2-LiAlH4 system were determined. The catalytic properties of the nickel nanoclusters were studied in relation to the nature and concentration of the proton-containing compounds. Factors responsible for the promoting action exhibited by these compounds were analyzed.

Palladium hydrogenation catalysts modified with aluminum- and phosphorus-containing compounds and with alcohols : Effect of modifiers

The catalytic properties of nanosize catalysts derived from Pd(acac)2 and triethylaluminum in hydrogenation of organic substrates were studied, and the optimal conditions for the catalyst preparation were found. The maximum observed on the plot of the catalyst specific activity vs. Al/Pd ratio was explained by experiments.

The role of phosphine and 1,2-diimine complexes of nickel in the oxidation states 0, +1, and +2 in the catalyzed di-, oligo-, and polymerization of ethylene

The turnover frequency and number have been determined for eighteen catalytic systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene complexes of nickel in the formal oxidation states 0, +1, and +2 in the oligoand polymerization of lower alkenes. The main catalytic characteristics are almost independent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are presented for nickel(I) 1,4-diazo-1,3-butadiene complexes and radical anions resulting from the reactions of the cocatalyst with nickel α-diimine complexes. Reactions describing the formation, functioning, decomposition, and regeneration of the catalytically active nickel hydride complexes are proposed.

Formation of the cobalt hydrogenation catalysts at the action of lithium aluminum hydride and lithium tri( tert -butoxy)aluminohydride and their properties

The interaction of Co(acac)2(3) with LiAlH4 or LiAlH(t-BuO)3 was studied using NMR, UV, IR, ESR spectroscopy, electron microscopy, and volumometry. The basic stages of formation of cobalt catalysts for hydrogenation were suggested. The formation of the nanoparticles that are active in the hydrogenation process is shown to occur at a ratio of reagents 5 ≤ Red/Co ≤ 12. The nanoparticles are stabilized by an excess of LiAlH4 or LiAlH(t-BuO)3, as well as by the products of their catalytic decomposition under the action of cobalt in the reduced state. At the ratio LiAlH4 / Co> 12 to obtain the particles active in catalysis their activation by a proton-donor compound is required.

Catalysis of dimerization and oligomerization reactions of lower alkenes by systems based on Ni(PPh3)2(C2H4) and Ni(PPh3)nCl (n = 2 or 3)

The catalytic characteristics of the individual complex Ni(PPh3)2(C2H4) and Ni(PPh3)nCl (n = 2 or 3) and those of systems based on these complexes in combination with Brönsted and Lewis acids in ethylene and propylene oligomerization have been determined. A correlation between the BF3 · OEt2 solution storage time and the catalytic properties of the nickel systems has been established for the reactions of the lower alkenes. The observed increase in the turnover frequency and turnover number of the catalyst is due to the increase in the Brörsted acid concentration as a result of irreversible conversions of BF3 · OEt2 caused by its interaction with impurity water in the solvent. The formation of the Ni(PPh3)2(C2H4)-BF3 · OEt2 catalytic system in the presence of a substrate dramatically extends the system’s service life. The interaction of the nickel precursors with boron trifluoride etherate has been investigated using a complex of physical methods, and the main reactions yielding catalytically active species have been revealed.

Formation and properties of nickel catalysts for hydrogenation under the action of lithium Di- and tris(tert-butoxy)hydroaluminates

It was demonstrated that systems based on Ni(II) compounds and the alkoxyhydride derivatives LiAlH(tert-BuO)3 and LiAlH2(tert-BuO)2, in contrast to LiAlH4, exhibit high catalytic activity in the reaction of styrene hydrogenation in the absence of activators. The inhibiting effect of an excess of LiAlH2(tert-BuO)2 was found. The analysis of the composition of reaction mixtures by NMR, EPR, and UV spectroscopy and TEM showed that side reactions of the conversion of aluminum-containing components occurred together with the formation of nickel nanoclusters. The most probable reaction schemes of LiAlH(tert-BuO)3 and LiAlH2(tert-BuO)2 disproportionation were proposed. The nature of the stabilizers of nickel nanoparticles was considered.

Preparation method effect on the properties of Ziegler-type hydrogenation catalysts based on bis(acetylacetonato)cobalt

The turnover frequency and turnover number of Ziegler-type systems based on Co(acac)2 · nH2O (n = 0, 0.5, and 2) and AlEt3 or AlEt2(OEt) are reported in relation to the Al: Co molar ratio and to the concentrations of the initial components. Proton donor compounds have an effect on the catalytic characteristics of the systems. ESR data are presented for the interaction of Co(acac)2 with organometallic compounds (AlEt3, AlEt2(OEt), Li(n-Bu), and (C6H5CH2)MgCl) in the presence of various arenes. Seven preparation methods and a formation scheme are suggested for catalytic species that are active in styrene hydrogenation and are based on Co(acac)2 combined with AlEt3 or AlEt2(OEt) and.

Hydrogenation catalysts based on palladium bisacetylacetonate and lithium tetrahydroaluminate: Formation mechanism and reasons for modified effect of water

Mechanism of formation, nature of activity, and properties of species active in hydrogenation catalysis in systems based on Pd(acac)2 and LiAlH4 were studied. The effect consisting in activation of catalytic systems was observed and reasons for the modifying action of water were considered.

Comparison of catalytic properties of systems based on nickel complexes with 1,4-diaza-1,3-butadiene ligands in reactions of styrene hydrogenation and ethylene polymerization

Turnover frequencies of catalytic systems based on nickel complexes with 1,4-diaza-1,3-butadiene (α-diimine) ligands in the reactions of styrene hydrogenation and ethylene polymerization were determined. Results are presented of a study by the electron paramagnetic resonance method and IR spectroscopy of 1,4-diaza-1,3-butadiene complexes of nickel(II) and anion radicals formed in the interaction of the starting components under the conditions of catalysis. It was shown that the paramagnetic Ni(I) complexes are precursors of complexes catalytically active in the hydrogenation and polymerization reactions.