Nickel bromide complex

TC-Cyclopentadienyl Nickel Complexes. Nickel bromide dimethoxyethane [29823-39-9] forms bis(cydopentadienyl)nickel [1271 -28-9] upon reaction with sodium cyclopentadienide (63). This complex, known as nickelocene, 7T-(C3H3)2Ni, is an emerald-green crystalline sandwich compound, mp 173°C, density 1.47 g/cm. It is paramagnetic and slowly oxidi2es in air. A number of derivatives of nickelocene are known, eg, methylnickelocene [1292-95-4], which is green and has mp 37°C, and bis( 7t-indenyl)nickel [52409-46-8], which is red, mp 150°C (87,88). 

Vinylic copper reagents react with CICN to give vinyl cyanides, though BrCN and ICN give the vinylic halide instead." Vinylic cyanides have also been prepared by the reaction between vinylic lithium compounds and phenyl cyanate PhOCN." Alkyl cyanides (RCN) have been prepared, in varying yields, by treatment of sodium trialkylcyanoborates with NaCN and lead tetraacetate." Vinyl bromides reacted with KCN, in the presence of a nickel complex and zinc metal to give the vinyl nitrile. Vinyl triflates react with LiCN, in the presence of a palladium catalyst, to give the vinyl nitrile." ... 

Activated aryl chlorides, which are close in reactivity to unactivated aryl bromides, underwent reaction with the original P(o-tol)3-ligated catalyst.58 Nickel complexes, which catalyze classic C—C bond-forming cross-couplings of aryl chlorides, 9-64 also catalyzed aminations of aryl chlorides under mild conditions.65,66 However, the nickel-catalyzed chemistry generally occurred with lower turnover numbers and with a narrower substrate scope than the most efficient palladium-catalyzed reactions. 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

The corresponding nickel complexes of these ligands were synthesized through deprotection of the acetyl groups via saponification in methanol, followed by addition of Ni(H20)6Cl2 and air oxidation. The monoanions 4a-e were then precipitated by treatment with tetrabutylammonium bromide, and recrystallized to give shiny, crystalline materials. 7V-Methylpyridinium salts were also produced by substituting A -methylpyridinimn iodide for tetrabutylammonimn bromide. 

The cross-coupling route to allylsilanes is effective with either aromatic or aliphatic a-silylated Grignard reagents16, and palladium catalysts are more reactive and stereoselective than the corresponding nickel complexes. Unsubstituted or i+monosubstituted alkenyl bromides work well but the Z-substituted bromides give lower yields and an inferior enantiomeric excess. The enantiomeric excess increases quite markedly with decreasing temperature, and optimum results are obtained at 0 C or below. 

The competing processes were sufficiently slower than the reaction of interest only in the case of the nickel complex, [Ni(NiL2)2]Cl2. Attempts to determine the rate of reaction of [Pd(NiL2)2]Cl2 with benzyl bromide revealed a very slow process occurring at a rate comparable to, but slightly slower than, the solvolysis of benzyl bromide. It is concluded that the rate of reaction of this complex with benzyl bromide is too slow for accurate rate study in methanol. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions).7S2 R may be alkyl or aryl. As in 0-35, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson reaction (0-12), yields are improved by phase-transfer catalysis.753 Instead of RS ions, thiols themselves can be used, if the reaction is run in benzene in the presence of DBU (p. 1023).754 Neopentyl bromide was converted to Me3CCH2SPh in good yield by treatment with PhS in liquid NH3 at -33°C under the influence of light.755 This probably takes place by an SrnI mechanism (see p. 648). Vinylic sulfides can be prepared by treating vinylic bromides with PhS in the presence of a nickel complex,756 and with R3SnPh in the presence of Pd(PPh3)4.757 R can be tertiary if an alcohol is the substrate, e.g,758... 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

In the case of cyclooctenyl bromide, a reaction proceeding exclusively through a bis(7r-allyl)nickel complex can be excluded, since reaction of bis(7r-cyclooctenyl)nickel in dimethylformamide with carbon monoxide... 

Caeiro and colleagues coupled racemic benzylic bromides 1 with alkynylindium compounds 21 (M=In) catalyzed by a nickel complex generated from 10 mol% NiBivdiglyme and 13 mol% of (S, 5)-5b (entry 30) [74]. Reasonable to good ee values of 77-87% were observed for the benzyl alkyne products. The isolated yields were, however, a rather moderate 35-70%. 

Procedures for the preparation of nickel(II) chloride dihydrate and nickel(II) bromide dihydrate follow. From these, the preparation via the orthoformate ester dehydration route of the anhydrous tetrakis(ethanol) and 1,2-dimethoxyethane complexes is described. The preparation of nickel(II) iodide-bis(l,2-dimethoxyethane) from nickel(II) iodide pentahydrate is also given. 

Similarly, group 10 trigonal nickel complex Cp(PPh3)Ni(c-Pr) was prepared from Cp(PPh3)NiCl and cyclopropylmagnesium bromide". This complex, in analogy with the... 

These cyclophane ligands - featuring two carbene and two pyridine donor groups - do act as tetradentate ligands towards transition metals. Baker et al. [67] reported the respective nickel(II) complex after reaction of the free ligand (bis-imidazolium salt) with nickel(II) bromide in the presence of sodium acetate as base. 

We have also observed that the sensitivity of aryl-methyl-nickel compounds la and b to oxygen is greatly enhanced by the addition of methylllthium. Under these conditions, the presence of la and b as nickelate complexes in is indicated by isotopic excliange studies. These anionic nT el complexes should be even better donors than their neutral counterparts 1,(26) and they are thus expected also to show enhanced reactivity to aryl bromides in those interactions proceeding by electron transfer. Reductive eliminations similar to those presented for 1 can be formulated as ... 

When carbon dioxide was bubbled througlt a solution of the cobalt-nitrogen complex CoHN>(PPhj)s, a cobalt-formate complex and the carbonyl complex Co(CO)(PPhj)3 were isolated (66], and treatment of the nickel complex [CpNi(PPh3)MgBr] with carbon dioxide in the presence of added magnesium bromide led to the nickel carbonyl complex (PPh3)jNi(CO)2. Possible intermediates are shown in F.quation (57). 

The B(5)-acetyl complex [( -Cp )Co(Et2C2B3H4-5-COMe)j (91JA680) can be deprotonated with //-butyl lithium and then react with nickel(II) bromide to yield the tetradecker 7 (ML = = Co(/y -Cp ), M = Ni,... 

A large fraction of the catalysts investigated for this purpose is on the basis of palladium or nickel complexes with chiral ferrocenylphosphine derivatives. This interest was spurred by the early work of Hayashi and Kumada who achieved the asymmetric coupling depicted in equation (5) (R = H) in 68% ee using phosphine (3) to provide chirality at the catalytic center. More recently, Knochel synthesized bisphosphine derivative (4) (R = Ph) which gave results similar to (3) when vinyl bromide was the substrate (equation 5, R = H, 63% ee). However, when the reaction was performed with /3-bromostyrene (R = Ph), the enantioselectivity see Enantioselectivity) increased to 93%. 

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