Phosphane nickel complex

More attention has been devoted to aromatic and heteroaromatic substrates since first reported in 1983 [40]. The results are shown in Table 2 [25, 41-51]. All these reactions were run with nickel complexes associated with a phosphane or bpy ligand. Depending on the experimental conditions, the polymers were either precipitated during the electrolysis or deposited as films at the surface of the electrode. The method is also convenient to prepare copolymers from a mixture of two aryl dihalides. A mechanistic investigation on the nickel-bpy catalyzed polymerisation has been reported very recently [52]. 

It was shown that room-temperature molten salts derived from the combination of 1,3-dialkylimidazolium chloride and A1C13 can be used as solvents in two-phase catalytic dimerization of propene to give hexenes catalyzed by Ni(II) compounds (125). The effects of phosphane ligands coordinated to nickel and operating variables were also investigated (126). The dimerization products separate as an organic layer above the molten salt. This reaction has been carried out with n-butenes as the reactant and cationic nickel complex catalysts dissolved in organochloroaluminate liquids (127). 

When aqueous solutions of sodium arenetellurolatcs and cyclopentadienylbis[tributyl-phosphane]nickel chloride were mixed at 20° under an atmosphere of nitrogen, oils were formed immediately. The oils were extracted with benzene, the extracts dried over anhydrous calcium chloride, and the dried extracts evaporated. The residues were recrystallizcd from pentane3. The complexes were obtained in yields ranging from 76 to 88%. 

By systematic variation of the phosphane ligands it was found that catalysts formed from basic phosphanes with small cone angles gave the highest activity and selectivity. The optimum ligand to metal ratio lies between 1 1 and 2 1. Excess phosphane decreases the catalytic activity drastically, possibly due to the formation of stable coordinative saturated nickel complexes. The catalytic system works in a temperature range between 20 and 120°C, most effectively at 60°C with a low but constant reaction rate over a long time. Furthermore,... 

Ditertiary phosphane complexes of nickel were found to be effective in the formation of pyrone 108 by cyclocotrimerization of alkynes with carbon dioxide. The formation of the nickelacyclopentadiene 105 from two moles of alkyne and a nickel complex is followed by CO2 insertion into a nickel-carbon bond to give the oxanickelacycloheptadienone 106, which then eliminates 108 with intramolecular C—O coupling. Another route involving [4 + 2] cycloadditions of 105 with CO2 in a Diels - Alder reaction to give 107 cannot be ruled out but is less probable because CO2 does not undergo [4 + 2] cycloaddition with dienes. Addition of another alkyne to 105 results in the formation of a benzene derivative (Scheme 38). ... 

When phosphane-free nickel complexes, such as bis(cycloocta-l,5-diene)nickel(0) or te-tracarbonylnickel, are employed in the codimerization reaction of acrylic esters, the codimer arising from [2-1-1] addition to the electron-deficient double bond is the main product. The exo-isomer is the only product in these cyclopropanation reactions. This is opposite to the carbene and carbenoid addition reactions to alkenes catalyzed by copper complexes (see previous section) where the thermodynamically less favored e Jo-isomers are formed. This finding indicates that the reaction proceeds via organonickel intermediates rather than carbenoids or carbenes. The introduction of alkyl substituents in the /I-position of the electron-deficient alkenes favors isomerization and/or homo-cyclodimerization of the cyclopropenes. Thus, with methyl crotonate and 3,3-diphenylcyclopropene only 16% of the corresponding ethenylcyc-lopropane was obtained. Methyl 3,3-dimethylacrylate does not react at all with 3,3-dimethyl-cyclopropene, so that the methylester of tra 5-chrysanthemic acid cannot be prepared in this way. This reactivity pattern can be rationalized in terms of a different tendency of the alkenes to coordinate to nickel(O). This tendency decreases in the order un-, mono- < di-< tri- < tet-... 

In summary, prominent features of ylide nickel complexes versus phosphane complexes have been identified an electron-rich nickel center, energetically destabilized nickel-localized occupied orbitals, a significant weakening of the Ni-O bond, the phosphoms moiety being located outside the nickel coordination plane, thus opening one axial position in the nickel coordination sphere for easy monomer landing . 

The selectivity of butadiene cyclooligomerization in the presence of bis(l,5-cyclooctadiene)-nickel(0) varies with the phosphane added, e.g., monophosphanes, such as (S)-ter/-butyl(iso-propyl)phenylphosphane and (- )-dimethyl(phenyl)phosphane, or diphosphanes, such as Diop. In all cases, 1,5-cyclooctadiene is preferentially formed, along with 4-vinylcyclohexene, ill a 4.5-6 1 ratio. The optical purity of the 4-vinylcyclohexene reaches 12% at a monophosphane/ nickel ratio of about 8 1 and is much lower with Diop57. The use of various 1,3,2-dioxaphospho-lanes with bulky substituents leads to a significant improvement in product selectivity (favoring 4-vinylcyclohexene over 1,5-cyclooctadiene in a ratio of up to 1 0.3) and in the enantioselectiv-ity. The best Optical yield (35% ee, later corrected to 24% ee58) was obtained with a nickel complex of diethyl 2-toT-butyl-l,3,2-dioxaphospholane-4,5-dicarboxylate (1) at 20 C57. 

The chiral iron(III) Lewis acid 3, derived from an oxazoline ligand, catalyzes Diels-Alder reactions of A -acryloyl-l,3-oxazolidinone (1) and cyclopentadiene (2) with good enantiomeric excess30. Nickel complexes of chiral phosphanes also catalyze Diels-Alder reactions albeit with low enantiomeric excess, not exceeding 15% cc31. Much better results are achieved for cobalt complexes with chiral phosphanes in the presence of a Lewis acid31,32. 

Similar work was reported by Liang etal. [166] in 2012 by using an amido phosphane chelate with a pendant amine arm as a ligand to form a nickel complex. A variety of alkyl and arylmagnesium chlorides were coupled with iodoarenes, bromoarenes, and chloroarenes using these nickel complexes under mild conditions. 

The chemical shift differences of the diastereotopic hydrogens are listed in Table 17 they depend strongly on solvent effects, as expected for an ionic product. They are in the range of 8 = 0.01 -0.1, well suited for measurement of the enantiomeric purity of the phosphanes. An alternative method for the measurement of Horner phosphanes is by 13C-NMR spectroscopy of diastereomeric complexes formed with [>/3-( + )-0 7 ,57 )-pinenyl]nickel bromide dimer73. 

Recently, several diamagnetic nickel(II) complexes were reported with 18-membered potentially hexadentate macrocydes containing four phosphane groups and two additional... 

With 1,1-difluorocyclopropabenzene and a range of nickel(O) complexes, nickelabicy-clobutanes 118 (84—93%) are formed by loss of olefin or phosphane ligands and addition of the nickel atom across the bridge bond (Scheme 20)256-266. The products appear to be stable at ambient temperatures but are oxygen sensitive the majority revert to cycloproparene in solution even below -20 °C. With (j -allyl)( s-cyclopentadienyl(palladium in the... 

Metal complex chemistry, homogeneous catalysis and phosphane chemistry have always been strongly connected, since phosphanes constitute one of the most important families of ligands. The catalytic addition of P(III)-H or P(IV)-H to unsaturated compounds (alkene, alkyne) offers an access to new phosphines with a good control of the regio- and stereoselectivity [98]. Hydrophosphination of terminal nonfunctional alkynes has already been reported with lanthanides [99, 100], or palladium and nickel catalysts [101]. Ruthenium catalysts have made possible the hydrophosphination of functional alkynes, thereby opening the way to the direct synthesis of bidentate ligands (Scheme 8.35) [102]. 

Alkyl phenyl telluriums and diaryl telluriums react with Grignard reagents in THF or diethyl ether in the presence of catalytic amounts of nickel- or cobalt-phosphane complexes. Tellurium is precipitated. The organic groups combine to form in most cases all three possible coupling products in ratios determined by reaction conditions . The reaction of ( Z,)-phenylethenyl phenyl tellurium and phenyl magnesium bromide formed almost exclusively ( Zj-stilbene in quantitative yield. ( ZJ-Ethoxycarbonylethenyl phenyl tellurium and phenyl magnesium bromide reacted differently ( Fj-ethoxycarbonyl-(phenyl)-ethene and diphenyl tellurium were produced. Tellurium was not formed. ... 

They confirmed the reaction mechanism and underlined the effect of tertiaiy phosphanes on the regioselectivity of the linking of propene molecules. This complex is soluble only in chlorinated hydrocarbons. Many other systems based on nickel catalyze the dimerization reaction and have been described in many publications and patents. 

In contrast to stoichiometric conversions, phosphane-modified nickel(O) complexes catalyze the trimerization of methylenecyclopropane in 95% overall yield. Linear and cyclic trimers, all containing cyclopropane units, were formed with ratios depending on the phosphane used. According to the structure of some of the products, ring opening of the methylenecyclopropane is involved. 

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