Nickel NiBr2

Nickel chloride hexahydrate [7791-20-0] is formed by the reaction of nickel powder or nickel oxide with a hot mixture of water and HCl. Nickel duoride [13940-83-5], 4H2O, is prepared by the reaction of hydroduoric acid on nickel carbonate. Nickel bromide [18721 -96-5], NiBr2 6H20, is made... 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

This is a problem that has been reported by several researchers in other cya-nation methods on heteroaromatic halides. (Hetero)aryl chlorides have also been tackled via in situ halogen exchange to (hetero)aryl bromides followed by sequential cyanation (Scheme 71). For this microwave-assisted process an equimolar amount of NiBr2 and a two-fold excess of NaCN were used. The only heteroaromatic chloride tested was 2-chloropyridine. Although the procedures described involve the use of significant amounts of nickel salts, a clear advantage is that the reactions can be performed in air. Moreover, the cyanat-ing reagents are easily removed since they are water soluble. 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Recently, the heterogenization technique has allowed more-selective reactions to be observed. For example, butadiene gives 95% of 1,3,6-octatriene (example 28 in Table 1) on a catalyst obtained by reduction of NiBr2(supported phenylphosphines)2 with NaBH4 (44). Nickel-carbonyl complexes have also been supported on phosphinated silica (55). 

The square-planar complex (34) NiCI2-(P-/i-Bu3)2 was a better catalyst than the tetrahedral complex NiBr2 (PPh3)2 for hydrosilation of styrene with trichlorosilane at temperatures of 150°-170°C. A nickel(0) complex, Ni[P(OPh)3]4, was as good as NiCl2(NC5H5)4, which was best among known nickel catalysts for this reaction. Addition of copper(I) chloride... 

NiBr2(dipy) [217, 218]. These experimental conditions can probably be applied to many other nickel catalysed reactions... 

When heated with bromine vapors or chlorine gas, nickel catches fire forming nickel bromide, NiBr2, and yellow nickel chloride, NiCb, respectively. 

Nickel(II) salts, such as NiCl2, NiBr2 and Ni(acac)2, are commercially available in anhydrous form as inexpensive compounds (< 200-300/mol), and some others, such as Ni(0Ac)2-4H20 and Ni(N03)2-6H20, are also inexpensive but available only as hydrates. Recently, Ni(II) on C was prepared from Ni(N03)2-6H20 and charcoal and used as needed... 

This last electrochemical process is carried out in an undivided electrolysis cell fitted with a sacrificial magnesium anode and a nickel foam as cathode. The reaction is conducted in dimethylformamide in the presence of both NiBr2(bpy) as the catalyst and dried ZnBr2 (1.1 molar equivalents with respect to bromothiophene), which is used both as supporting electrolyte and as a zinc(II) ion source. The other conditions are the same as those described in the section concerning the aromatic halides. The yield of 3-thienylzinc bromide was roughly 80%, as determined by GC analysis after treatment with iodide (equation 34). 

The coordination geometry of the complexes with the ligands with an NP2 donor set (ligands XXXI, XXXII) is strictly dependent on the nature of the substituents on the nitrogen donor. The (NiX2(R-bda)] complexes are low-spin five-coordinate when R = H or Me and square planar when R = Cy. All of the complexes become square planar, [NiX(R-bda)]+, in solution.1365 The structure of the complex [NiBr2(H-bda)] (165) is typical of low-spin square pyramidal nickel(II) complexes, with the apical Ni—Br distance longer than the basal one and the nickel atom substantially in the basal plane.1299... 

Ni(phenanthrenequinone)2Br2 is the only complex which seems to contain the neutral ligand coordinated to nickel(II). 3 The complex has been synthesized by reacting NiBr2 and the quinone in methanol-acetic acid solution. 

The reaction of trimethyl phosphate, (MeO)3PO, with NiBr2 results in the neutral bis-dimethoxyphosphato complex by elimination of one methyl group from the neutral phosphoric esters (equation 185).1708 But when nickel halides are reacted at higher temperatures with the neutral diisopropylmethylphosphonate, an alkyl elimination and a phosphato condensation occur (equation 186).1709... 

Dunach has reported the insertion of the heterocumulene into N-Boc (Boc = t-butoxycarbonyl) -protected 2-subshtuted aziridines under mild conditions (ambient temperature, atmospheric C02 pressure), using electrochemical methods and dibromo(l,4,8,ll-tetraazocyclotetradecane)-nickel(II), NiBr2(cyclam), as catalyst (10mol%) [68m]. However, the process was poorly selective as a mixture of 4- and 5-regioisomers was obtained in all cases investigated. 

Nickel-Graphite. A highly dispersed nickel on graphite (Ni-Gr 1) is obtained by reduction of NiBr2 2DME dissolved in THF HMPT (15 1) with CSK (2 equiv.) at 20° under argon. This material is slowly oxidized by air to give a less active metal (Ni-Gr 2), which can be stored for several months. 

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