Nickel-complex-catalyzed reactions

In the nitrone cycloaddition reactions catalyzed by the l ,J -DBFOX/Ph transition metal complexes also, the diastereo- and enantioselectivities were found to depend upon the presence of MS 4 A [71]. Thus, both the selectivities were much lowered in the iron(II) or nickel(II) complex-catalyzed reactions without MS 4 A,... 

Not only do palladium complexes catalyze reactions of Eq. (58), but nickel complexes were also effective (51) and formed the same products. Complexes such as Fe(CO)5 and Fe2(CO)8 were ineffective. Cobalt carbonyl, and tris-triphenylphosphinerhodium chloride were effective even at room temperature, but no 2 1 adducts were made. With both palladium and nickel, the activity of the catalyst and the distribution of products between 1 1 and 2 1 adducts is greatly dependent on the nature of the donor ligands on the metal. 

Sugimura, H. Takei, H. Synthesis of 6-Alkylpurine Derivatives by Nickel Complex Catalyzed Coupling Reaction of 6-(Meth-ylthio)purine derivatives with Grignard Reagents. Bull. Chem. Soc. Jpn. 1985, 58, 664-666. 

Interestingly these complexes showed high activity without addition of alkyl aluminum compounds in the ionic liquid while they are almost inactive in toluene. These results are interpretable in terms of catalyst stabilization by the imidazolium-based ionic liquid. Reductive elimination of imidazolium is also possible as in toluene as in the ionic liquid but in the ionic liquid, a rapid reoxidation via addition of the solvent imidazolium cation seems possible and may prevent the formation of Ni deposits associated with catalyst deactivation. The carbene complex with R = n-Bu showed the highest activity with a dimer yield of 70.2% (TOF = 7020 h ). The preferred product of the nickel-catalyzed reaction is methylpentene. Additional phosphine ligand had no significant influence on the distribution of the products in this case. 

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

Stable enolates such as diethyl malonate anions react with allyl sulfones (or acetates) in the presence of nickel complexes to give a mixture of the a- and /-product83. The regioselectivity is generally poor in the nickel-catalyzed reaction, but the molybdenum-catalyzed reaction is selective for alkylation at the more substituted allylic site, thereby creating a quaternary carbon center84. 

The reaction between aryl halides and cuprous cyanide is called the Rosenmund-von Braun reactionP Reactivity is in the order I > Br > Cl > F, indicating that the SnAt mechanism does not apply.Other cyanides (e.g., KCN and NaCN), do not react with aryl halides, even activated ones. However, alkali cyanides do convert aryl halides to nitrilesin dipolar aprotic solvents in the presence of Pd(II) salts or copper or nickel complexes. A nickel complex also catalyzes the reaction between aryl triflates and KCN to give aryl nitriles. Aromatic ethers ArOR have been photochemically converted to ArCN. 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

The disilanickela complex 21 was also found to be a good catalyst for the dehydrogenative double silylation of aldehydes. The nickel-catalyzed reactions of 1,2-bis(dimethylsilyl)carborane 11 with aldehydes such as isobutyraldehyde, trimethylacetaldehyde, hexanal, and benzaldehyde afforded 5,6-carboranylene-2-oxa-l,4-disilacyclohexane.32 34 36 The dehydrogenative 1,4-double silylation of methacrolein and tram-4-phenyl-3-buten-2-one in the presence of a catalytic amount ofNi(PEt3)4 also took place under similar conditions. In contrast, the reaction of 11 with a-methyl-tran.s-cinnamaldehyde and irans-cinnamaldehyde under... 

Most studies on nickel-catalyzed domino reactions have been performed by Ikeda and colleagues [287], who observed that alkenyl nickel species, obtained from alkynes 6/4-41 and a (jr-allyl) nickel complex, can react with organometallics as 6/4-42. If this reaction is carried out in the presence of enones 6/4-43 and TM SCI, then coupling products such as 6/4-44 are obtained. After hydrolysis, substituted ketones 6/4-45 are obtained (Scheme 6/4.12). With cyclic and (5-substituted enones the use of pyridine is essential. Usually, the regioselectivity and stereoselectivity of the reactions is very high. On occasion, alkenes can be used instead of alkynes, though this is rather restricted as only norbornene gave reasonable results [288]. 

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