Nickel Catalytic System Research Articles

Influence of a diimine ligand and an activator on the processes taking place in Brookhart-type nickel catalytic systems

Brookhart-type catalytic systems based on zero-valent nickel complexes Ni(COD)2 and Ni(COD)L [where COD is cyclooctadiene and L is bis-2,6-diisopropylphenyl-diazabutadiene (DPP-DAB) or N,N′-bis-2,6- diisopropylphenyl-bis-iminoacenaphthene (DPP-BIAN)] activated with Lewis acids such as methylaluminoxane (MAO) and boron trifluoride etherate BF3·OEt2 were investigated via electron spin resonance (ESR) spectrometry, revealing that presence of diimine ligand results in Lewis acids, formally oxidating Ni(0) to Ni(I). An oxidation mechanism is proposed.

Nickel-Catalyzed Stereoselective Alkenylation of C(sp3)-H Bonds with Terminal Alkynes.

A nickel-catalyzed stereoselective alkenylation of an unactivated β-C(sp3)-H bond in aliphatic amide with terminal alkynes using 8-aminoquinoline auxiliary is reported for the first time. This reaction displays excellent functional group tolerance with respect to both aliphatic amides and terminal alkynes and features a cheap nickel catalytic system. The 8-aminoquinolyl directing group could be smoothly removed, and the resultant β-styrylcarboxylic acid derivatives could serve as versatile building blocks for further transformation.

Preparation of Vinyl Arenes by Nickel-Catalyzed Reductive Coupling of Aryl Halides with Vinyl Bromides.

This work emphasizes the synthesis of substituted vinyl arenes by reductive coupling of aryl halides with vinyl bromides under mild and easy-to-operate nickel-catalyzed reaction conditions. A broad range of aryl halides, including heteroaromatics, and vinyl bromides were employed to yielding products in moderate to excellent yields with high functional-group tolerance. The nickel-catalytic system displays good chemoselectivity between the two C(sp2 )-halide coupling partners, thus demonstrating a mechanistic pathway distinct from other stepwise protocols.

New Copper, Palladium and Nickel Catalytic Systems: An Evolution towards More Efficient Procedures.

Metal-catalysed reactions are a fundamental tool in synthetic chemistry. Increasingly challenging transformations can be accomplished only by means of certain metal catalysts. However, there still remains the need for a substantial decrease of the amount of catalyst, for better reuse or recycling of such active species, and for the avoidance of relatively toxic solvents in favour of environmentally friendly media. These facts apply to copper-, palladium-, and nickel-catalysed cross-coupling reactions, direct arylations, and oxidative processes. This account summarises our research on the last reactions, featuring an evolution towards more sustainable procedures in this field.

ChemInform Abstract: Metal‐Catalyzed Cascade Reactions: Useful Synthetic Tools for the Preparation of Polycyclic Arenes

AbstractReview: [79 refs.

Metal-catalyzed cascade reactions: useful synthetic tools for the preparation of polycyclic arenes.

This account summarizes our recent efforts to synthesize numerous important and interesting polycyclic arenes under mild conditions using metal-catalyzed protocols. The palladium-catalyzed annulations of 2-iodobiphenyls or 2,2'-diiodobiphenyls with alkynes efficiently generated phenanthrene derivatives. This synthetic method was utilized as the key step when preparing phenanthrene-based alkaloids, tetrabenzopyracylenes and persubstituted [8]circulenes. Depending on whether a palladium or nickel catalytic system was used, 1-ethynyl-8-iodonaphthalenes underwent either a cyclodimerization or a nitrile-incorporated cascade reaction to produce zethrenes or pyrroloarenes, respectively. Methylene-bridged polyarenes are generated easily from 2-halo-2'-methylbiaryls through benzylic C-H bond activation and subsequent carbon-carbon bond formation, and palladium complexes promote the arylation of methylene carbons. The palladium-catalyzed annulations of 1,8-bis(arylethynyl)naphthalene derivatives with o-diiodoarenes yielded benzo[k]fluoranthene-based linear acenes, which can be applied to synthesize highly curved fragments of fullerenes. The self-reactions of diarylethynes formed either dihydrocyclopenta[a]indenes or octaaryl-1,3,5,7-octatetraenes through palladium-catalyzed cycloisomerization or nickel-catalyzed tetramerization, respectively. In the presence of palladium catalysts, the hydroalkynylation of terminal arylalkynes directly generated angular trimerization adduct dienynes.

One-pot Synthesis of 1,3-dinitroalkanes Catalysed by Nickel Species

The reaction of aromatic aldehydes with nitromethane afforded a one-pot preparation of 1,3-dinitroalkanes in the presence of a nickel catalytic system. This efficient and simple method proceeded with moderate to high yields (56–99%) under mild conditions.

ChemInform Abstract: Cobalt‐Catalyzed Cross‐Coupling Reactions of Aryl Halides

AbstractReview: 79 refs.

Cobalt‐Catalyzed Cross‐Coupling Reactions of Aryl Halides

AbstractCobalt‐catalyzed carbon–carbon bond‐forming reactions are an indispensable class of reactions in organic synthesis. This economical and ecologically attractive catalyst could replace, in some cases, the well‐etablished, expensive palladium and toxic nickel catalytic systems that have dominated the field for many years. Cobalt‐catalyzed protocols tolerate various functional groups and present a wide range of reactivity. Moreover, these efficient reactions are very easy to carry out without complex ligands under varied conditions. This review intends to shed light on the fact that cobalt‐catalyzed cross‐coupling reactions offer an excellent alternative to the usual catalysts. Moreover, these methodologies are sometimes superior, especially for reactions involving alkyl halides.

Highly efficient enantio-selective hydrogenation of methyl acetoacetate over chirally modified Raney nickel catalytic system

A new method of preparing a tartaric acid modified Raney nickel (TA-MRNi-NaBr) catalytic system has been studied. Raney nickel was modified with ( R, R)-tartaric acid. Then, methanol, in which an appropriate amount of NaBr dissolved, was used as the hydrogenation reaction medium. This new catalytic system showed high efficiency and high durability in enantio-selective hydrogenation of methyl acetoacetate (MAA). The influence of the important modifying parameter (modifying pH) and reaction variables (solvent type, the types of inorganic salts and their amount, reaction temperature and hydrogen initial pressure) on the hydrogenation rate and optical yield were systematically investigated. The high optical yield of 85% was achieved at pressure (0.6 MPa) nearly 17-fold lower than those previously used to achieve such results, and the hydrogenation rate was enhanced significantly. For comparison, the conventional TA-NaBr-MRNi catalyst was also prepared. Characterization data confirmed that compared with the conventional TA-NaBr-MRNi catalyst, the improved TA-MRNi-NaBr catalyst had lower weight ratio of Al–Ni, higher total surface area and more acid-corrosion on its surface, which could lead to the high efficiency of the TA-MRNi-NaBr catalytic system.

Preparation and formation of nickel-copper catalytic systems on various supports and commercial catalysts based on these systems

Based on the Ni-Cu system, catalysts were developed for low-and high-temperature industrial gas and waste gas purification. It was found that, regardless of the preparation procedure, the formation of a catalytically active structure occurred via the formation of a Ni-Cu solid solution at the stage of activation. The catalytic, physicochemical, and physicomechanical properties of NKO Ni-Cu catalysts can be purposefully regulated by changing the nature and concentration of a liquid reagent. A promoting effect of copper on the activation process and on the catalytic activity of a nickel catalytic system was found. The catalysts developed were commercialized. The catalysts were introduced into various processes of industrial gas and waste gas purification.

Novel nickel (II) complexes chelating β‐diketiminate ligands: synthesis and simultaneous polymerization and oligomerization of ethylene

AbstractTwo novel nickel (II) complexes, CH{C(CF3)NAr}2NiBr (1, Ar = 2,6‐iPr2C6H3 and 2, 2,6‐Me2C6H3), were synthesized by the reaction of the lithium salt of fluorinated β‐diketiminate backbone ligands with (1,2‐dimethoxyethane) nickel (II) bromide [(DME)NiBr2]. The solid‐state structure of nickel (II) complex 2 as a dimer reveals four‐coordination and a tetrahedral geometry with bromide bridged by single crystal X‐ray measurement. Both complexes catalyze simultaneous polymerization and oligomerization of ethylene when activated by methylaluminoxane (MAO). It was found that the reaction temperature has a pronounced effect on the activity of ethylene polymerization and the molecular weight of obtained polyethylene. In addition, the nickel catalytic systems predominantly produce linear polyethylene with unsaturated end groups. Copyright © 2006 John Wiley & Sons, Ltd.

Unconventional Allylation of Norbornadiene Catalyzed by Palladium Complexes

A new catalytic system based on palladium complex compounds for the unconventional allylation of norbornadiene with allylic esters of carboxylic acids is developed. The structure of reaction products is determined and the factors affecting their ratio are found. Comparative analysis of the palladium and nickel catalytic systems is performed.

Influence of aluminum Lewis acids on the diastereoselectivity of the nickel-catalyzed [2+2+2] cycloaddition of norbornadiene and electron deficient alkenes

The stereoselective formation of 8-substituted deltacyclanes by homo Diels–Alder (HDA) reaction using a phosphine modified nickel catalyst generated by reduction of Ni(acac) 2 with alkylaluminums is discussed. Depending on the nature of the alkene and on the nickel catalytic system, fair to excellent exo selectivity are observed. A switch in selectivity favoring the endo-cycloadduct is observed when the polar methoxycarbonyl group substituted alkene is activated with aluminum species.

Use of lanthanide shift reagents for analysing the microstructure of polydienes and polyalkenamers by 1H-NMR spectroscopy

A method is proposed for determining the content of the cis- and trans-units and their distribution in the chain of polybutadiene and the trans-polypentanamer by 1H-NMR spectroscopy. It is shown that tris-1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-europium octanedionate combined with AgNO 3 will add at the double bonds of the polymer chain. With the method it is possible to differentiate the diad configurations of cis- ( c) and trans- ( t) units in the chain of the polydienes and polyalkenamers cc, tc(ct) and tt. Statistical analysis of the data on the diad composition of the compounds studied showed that the distribution of the cis- and trans-units in the trans-polypentenamer chain is governed by Bernoulli statistics. Polybutadiene obtained with a nickel catalytic system has a block distribution of the cis- and trans-units along the chain fundamentally differing from the Bernoulli statistics.

Codimerization of ethylene with propylene in the presence of gel-immobilized metallo-complex systems

It was found possible to codimerize ethylene with propylene on gel-immobilized metallo-complex nickel catalytic systems (GCS) under mild conditions (20-80/sup 0/C; p 0.2-0.3 MPa). Maximum pentene yield (46 wt.%) is achieved with a molar ratio of C/sub 2/H/sub 4//C/sub 3/H/sub 6/ of one. The composition of codimers is practically independent of the ratio of monomers. A study was made of the effect of the type of solvent on the efficiency of GCS. In paraffinic hydrocarbons GCS is characterized by high stability in the temperature range studied. It was established that isomerization of ..cap alpha..-pentenes may be inhibited by using GCS containing organic aluminium co-catalysts.

Oligomerization of vinyl- and ethynyl-trimethylsilanes

Oligomerization of vinyl- and ethyl-trimethylsilanes in the presence of homogeneous nickel, cobalt and titanium catalytic systems has been studied. Vinyl-trimethylsilane forms linear dimeric products, 1,4-bis(trimethylsilyl)butenes. Using the titanium catalytic system, in addition to butenyldisilane, a branched dimeric product, 1,3-bis(trimethylsilyl)-3-methylprop-1-ene, and a linear trimer 1,3,6-tris(trimethylsilyl)hex-3-ene are formed. Ethynyltrimethylsilane, in the presence of the nickel catalytic system, is converted into a linear dimer, 1,4-bis(trimethylsilyl)but-3-ene-1-yne, and linear trimer, 1,4,6-tris(trimethylsilyl)hex-3,5-diene-1-yne.