Nickel cyanide Ni

Nickel Monocyanide.—Reduction of potassium nickelo-cyanide, K2Ni(CN)4, with potassium amalgam yields a red salt, K2Ni(CN)3, in which nickel appears to be monovalent. Upon acidifying, an orange-yellow precipitate of the monocyanide is obtained, NiCN. It readily oxidises to nickel cyanide, Ni(CN)a.4... 

Cyanide ions yield a green precipitate of nickel cyanide Ni(CN)2 soluble in excess of cyanide ions by the formation of the tetracyanonickelate(II) complex (or nickelo-cyanide anion) [Ni(CN)4] . The complex is moderately stable. It is decomposed by adding mineral acids, which liberate hydrocyanic acid and precipitate nickel cyanide. In a second stage, nickel cyanide itself decomposes into Ni + and hydrocyanic acid ... 

If nickel(II) cyanide, Ni(CN)2, is dissolved in excess potassium cyanide, the orange-red complex salt K2Ni(CN)4. HjO can be crystallised out this contains the stable square-planar [Ni(CN)4] anion. 

In addition to the tetrahedral and octahedral complexes mentioned above, there are two other types commonly found—the square planar and the linear. In the square planar complexes, the central atom has four near neighbors at the corners of a square. The coordination number is 4, the same number as in the tetrahedral complexes. An example of a square planar complex is the complex nickel cyanide anion, Ni(CN)4-2. 

When acetylene is heated with nickel cyanide, other Ni(II) or Ni(0) compounds, or... 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

Hydrocyanation of butadiene is more complicated than that of ethene it requires two hydrocyanation steps and several isomers can be observed. The isomers obtained in the first step of the HCN addition to butadiene are shown in Figure 11.3. The addition first leads to compounds 1 and 2, in a 1 2 ratio, but they equilibrate to a favourable 1 9 ratio via the retro-reaction. The retro reaction involves a C-C bond breaking reaction, which is rare, but in this case the intermediate is a Tt-allyl species and a stable, anionic cyanide group. Electron-rich nickel species (Ni-dippe) can cleave aromatic nitrile C-C bonds... 

Alkali metal salts of such tetracyanonickelate(II) anion may be crystallized from such solutions as hydrates, K2 [Ni(CN)4 3H2O upon evaporation of the solution. In strong cyanide solution, a pentacyano complex anion, red penta-cyanonickelate(ll), [Ni(CN)5] forms. Strong acids decompose cyanonickelate salts, precipitating nickel cyanide. 

Otherwise, unusual valency states are often observed in cyanide complexes. A Mn complex K5Mn(CN)6 has been reported here the stable 18-electron configuration causes the valency of manganese to take the very unusual value of one, and the compound is formed in spite of the extremely unfavourable cation anion ratio. Still more remarkable are the complex nickel cyanides. KGN and Ni(CN)2 form a complex K2Ni(CN)4, in which sixteen electrons are involved in the bond formation. The diamagnetism and the square structure of the Ni(CN)4 ion show that the bonding is due to dsp2 hybridization. 

Because of its low acidity, hydrogen cyanide seldom adds to nonactivated multiple bonds. Catalytic processes, however, may be applied to achieve such additions. Metal catalysts, mainly nickel and palladium complexes, and [Co(CO)4]2 are used to catalyze the addition of HCN to alkenes known as hydrocyanation.l67 l74 Most studies usually apply nickel triarylphosphites with a Lewis acid promoter. The mechanism involves the insertion of the alkene into the Ni—H bond of a hydrido nickel cyanide complex to form a cr-alkylnickel complex173-176 (Scheme 6.3). The addition of DCN to deuterium-labeled compound 17 was shown to take place... 

In a covalent complex of bivalent nickel such as the nickel cyanide ion [Ni(CN)4] — the 26 inner electrons of the nickel atom can be placed in pairs in the Is, 2s, three 2p, 3s, three 3p, and four of the 3d orbitals. This leaves available for use in bond formation the fifth 3d orbital as well as the 4s and three 4p orbitals. It is found on hybridizing these orbitals that four strong bond orbitals directed to the corners of a square can be formed.4 The four orbitals (written with the bonds directed along +x, —x, and — y) are... 

The reaction of nickel cyanide with aqueous ammonia affords compounds of the type Ni(CN)2-NH3 tH20. The structure of the complex where x = 0.25 closely resembles that of... 

Clathrates of the type Ni(CN)2NH3-solv (solv = benzene, aniline, etc.) have also been reported. In general, the host molecules are arranged perpendicularly to the layers of nickel cyanide.635... 

Volumetric Methods.—Nickel may be conveniently estimated volu-metrically in the absence of cobalt, copper, silver, gold, and the platinum metals by means of potassium cyanide.4 The solution containing the nickel is, if acid, neutralised with ammonia and some ammonium sulphate is added to render the indicator more sensitive. A little ammonia is now added, and a few drops of potassium iodide and silver nitrate. The solution becomes turbid in consequence of the precipitation of silver iodide. The liquid is now titrated with potassium cyanide solution until the turbidity just disappears. The reaction consists in converting the nickel salt into the double cyanide, Ni(CN)a.2KCN, after which any excess of potassium cyanide attacks the silver iodide, yielding the soluble double cyanide, AgCN.KCN. The disappearance of the turbidity therefore indicates the complete conversion of the nickel salt. A slight correction is necessary for the silver introduced. 

Detection of traces of nickel in cobalt salts. The solution containing the cobalt and nickel is treated with excess concentrated potassium cyanide solution, followed by 30 per cent hydrogen peroxide whereby the complex cyanides [Co(CN)6]3- and [Ni(CN)4]4 respectively are formed. Upon adding 40 per cent formaldehyde solution the hexacyanocobaltate(III) is unaffected (and hence remains inactive to dimethylglyoxime) whereas the tetracyanato-nickelate(II) decomposes with the formation of nickel cyanide, which reacts immediately with the dimethylglyoxime. 

A drawback connected with the tendency of Ni(0) to undergo oxidative addition of HCN is the formation of inactive nickel cyanide complexes. Such inhibition can be overcome, however, by keeping the HCN concentration low. This also has the further advantage of preventing sudden temperature increases arising from the high exothermicity of the reactions with HCN. 

Vinyl sulfides have been prepared by the catalytic addition of the S—H bond of thiols (85) to terminal alkynes (86) under solvent-free conditions using the nickel complex Ni(acac)2 (47). High alkyne conversions (up to 99%) were achieved after 30 min at 40 °C in favor of the corresponding Markovnikov products (87) (equation 23). Other metal acetylacetonate complexes were examined for this reaction, but none showed any improvement over the nickel catalyst. Mechanistic details suggest that alkyne insertion into the Ni—S bond is important to the catalytic cycle and that nanosized structural units comprised of [Ni(SAr)2] represent the active form of the catalyst. Isothiocyanates and vinyl sulfides have been produced in related Rh(acac)(H2C=CH2)2 (6) and VO(acac)2 (35) catalyzed sulfenylation reactions of aryl cyanides and aryl acetylenes, respectively. 

Some iron and nickel cyanide and carbonyl complexes have been reported as models of the [FeNi]-hydrogenase enzymes. The preparation and structures of the trigonal bipyramidal nickel and iron complexes with the tetradentate ligands tris(2-phenylthiol)phosphine (PS3) and tris(3-phenyl-2-thiophenyl)phosphine (PS3 ) have been reported [70, 71]. The nickel carbonyl complex [Ni(PS3 )(CO)] exhibits vco at 2029 cm compared with the value of 1940 em" for the iron earbonyl complex [Fe(PS3 )(CO)]. Both of these complexes lose CO upon oxidation. The use of cyanide in place of carbon monoxide allows for the preparation of both [Fe (PS3)(CN)] and [Fe (PS3 )(CN)] eomplexes. The IR properties of... 

When acetylene is heated with nickel cyanide, other Ni(ll) or Ni(0) compounds, or similar catalysts, it gives benzene and cyclooctatetraene. It is possible to get more of either product by a proper choice of catalyst. Substituted acetylenes give substituted benzenes.This reaction has been used to prepare very crowded... 

An ammoniacal solution of nickel cyanide produces a pale mauve clathrate when shaken vigorously with benzene. The formula is Ni(CN)2NH3.CgHg and the structure as shown in Fig. 88. 

The entrance into the catalytic cycle from complex 5 may occur via a small equilibrium concentration of Ni-(la)-(MVN) complex6 (pathA, Schemes) and/or via oxidative addition of HCN to generate the species Ni-[la]-HCN, 7 (pathB). In either event, formation of the hydridoalkene complex Ni-[1]-(MVN)(H)(CN), 8, occurs and is followed by an insertion reaction to produce the (ri -benzyl)nickel cyanide intermediate 9. Although this allyl-type species has not been directly detected, the exclusive formation of the branched nitrile supports its intermediacy. Analogous intermediates have been postulated in the hydrocyanation of 1,3-butadiene with NilPlO-o-tolylljjj or Ni[P(OEt)3]4 and in the hydrocyanation of styrene with Ni[P(0-p-tolyl)3]4. Examples of other nick-el-benzyl complexes exhibiting similar allylic interactions in the solution and solid state are also known. 

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