Nickel halide compounds

4 Group 17 (halogen) compounds and complexes V.4.1 Nickel halide compounds V.4.1.1 Solid nickel fluoride, Nip2(cr) 

In the present review, a common function is fit to the combined results of the two studies above 250 K. The heat capacity results are weighted using an uncertainty of 0.2 J K mor for measurements between 250 and 270 K, and 0.3 J K mor at higher temperatures. For weighting purposes, the enthalpy differences are assigned an uncertainty of 0.2 kJ-moP. The results are constrained so that // ,(7 )-//°(298.15K) is 

Based on Equation (V.54), the heat capacity of NiF2(cr) at 298.15 K is 63.21 J K mor , whereas the value reported by Catalano and Stout [55CAT/STO] was 64.06 J K mor. Equation (V.54) is accepted in the present review, and as a consequence the reported entropy value at 298.15 K [55CAT/STO] should also be adjusted slightly (by 0.08 J K mol ). 

Several groups have determined values for Af//° (NiFz, cr) from enthalpies of reaction at temperatures between 500 K and 1000 K. Jellinek and Rudat [28JEL/RUD] investigated the reaction  

The enthalpy of formation of NiFz(cr), was measured directly by bomb calorimetry at 298.15 K, and reported as - (657.72 1.67) kJ-mol by Rudzitis et al. [67RUD/DEV]. This complicated experimental work appears to have been carried out with great care. 

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The development of the Grignard-type addition to carbonyl compounds mediated by transition metals would be of interest as the compatibility with a variety of functionality would be expected under the reaction conditions employed. One example has been reported on the addition of allyl halides to aldehydes in the presence of cobalt or nickel metal however, yields were low (up to 22%). Benzylic nickel halides prepared in situ by the oxidative addition of benzyl halides to metallic nickel were found to add to benzil and give the corresponding 3-hydroxyketones in high yields(46). The reaction appears to be quite general and will tolerate a wide range of functionality. 

B,) Treatment of an organo- or a hydrido-nickel(II) compound with a Lewis acid. Organometallic compounds, such as alkylaluminum halides, which have Lewis acid properties, can also be used. 

The primary (7, 47) and most commonly used organonickel compounds have been the dimeric 7r-allyl- (or substituted Tr-allyl-) nickel halides (1) (Scheme 1) or their monophosphine adducts (2) in the presence of Lewis acids such as aluminum halides or alkylaluminum halides (4, 48-53). The... 

Examples of w-allylnickel-X compounds (X = anionic ligand) other than 77-allylnickel halides which have been used in combination with (alkyl)aluminum halides as olefin oligomerization catalysts are 7r-allyl-nickel acetylacetonate (11) (Section III), 7r-allylnickel aziridide (4, 56), and bis(7r-allyl)nickel (6) (59). In addition to ir-allylnickel halides, organo-nickel halides such as tritylnickel chloride (60, 61) and pentafluoro-phenylbis(triphenylphosphine)nickel bromide (62), or hydridonickel halides, e.g., trans-hydridobis(triisopropylphosphine)nickel chloride (12) (Section III), give active catalysts after activation with aluminum halides... 

In the case of orthosubstituted aryl halides the corresponding arylnickel intermediate Ar2Nibpy is stable and should be oxidized to lead to the coupling product and regenerate the nickel(II) compound [27]. 

The indirect electrochemical reduction of alkyl halides is also possible by use of nickel(I) complexes which may be obtained by cathodic reduction of square planar Ni(n)-complexes of macrocyclic tetradentate ligands (Table 7, No. 10, 11) 2 4-248) Comparable to the Co(I)- and Ni(O)-complexes, the Ni(I)-species reacts with the alkyl halide unter oxidative addition to form an organo nickel(III) compound. The stability of the new nickel-carbon bond dominates the overall behavior of the system. If the stability is low, the alkyl group is lost in form of the radical and the original Ni(II)-complex is regenerated. A large number of regenerative cycles is the result. 

Hegedus and Varaprath studied the reactions of various bromodienes with Ni(CO)4 and with bis(cyclooctadiene)nickel. l-Bromo-2,5-hexadiene and 2-bromomethyl-1,3-butadiene give the stable products 62 and 63, respectively, which resemble allyl nickel halides in their properties (217). Similar compounds had been prepared several years previously from geranyl halides (218). l-Bromo-2,4-pentadiene and l-bromo-2,4-hexadiene, however, formed intractable materials which could not be isolated and purified. In these cases the red color of the solution which was first produced faded and NiBr2 was deposited. The desired compounds, however, could be generated in situ at — 30° C and used in coupling reactions with aryl, alkenyl, and allyl halides (217). 

The synthesis of nickel organic compounds often requires a source of organic-solvent-soluble anhydrous nickel halide. 

With the tripod ligand np3 an entire series of compounds with tbp structures Ni(np3)X (X = Cl, Br, I, CN, CO, and H) can be prepared by reaction of nickel halides with the np3 ligand in the presence of borohydride, followed, if necessary, by metathesis with other X groups. The comproportionation of the Ni complex Ni2(CO)2(/i.-CO)(/i.-dppm)2 with NiG2(dppm)2 (dppm = Ph2PCH2PPh2) gives the iluxional A-frame compound (17-G-XIX).18... 

The bis-triphenylphosphine nickel halides are not activated by tin (II) halides. However, the iodide, (03P)2Nil2, is an effective catalyst for the hydrogenation of methyl linoleate to the monoene stage. The bromide is less effective, and the chloride has very little catalytic power. None of these nickel compounds has much ability to bring about isomerization. The nickel compounds are unstable in alcoholic solutions, and the experiments reported in Table III were carried out in either benzene, tetrahydro-furan, or toluene. 

The dimeric allylic nickel halide complexes are simpler in that no problems of reaction with organo-aluminium compounds are involved. They are of low activity and give polymer of low molecular weight owing to a rapid monomer transfer reaction [61]. The active centre is formed by dissociation of the complex in the presence of monomer and since the rate is proportional to [Ni] and [M] the extent of dissociation is small and the complex with monomer of low stability. 

TT-Allylnickel halides are more stable, and thermal disproportionation is not observed even at higher temperatures. Recently, we found that TT-allylnickel halides can be disproportionated easily by treating them in solution with excess gaseous ammonia (2). Bis(7r-allyl)nickel and ammonia adducts of nickel dihalides are obtained in quantitative yields and can be separated easily. In fact, the disproportionation reaction represents at the moment the easiest way to synthesize bis (7r-allyl) nickel type compounds since as mentioned, all types of 7r-allylnickel halides can be prepared easily. The advantage of the new method lies in the fact that bis (TT-allyl) nickel type compounds can be prepared without prior preparation of organometallic allyl compounds, such as Grignard compounds, which are sometimes diflBcult to prepare. The disproportionation of TT-allylnickel halides has an analog in the chemistry of alkyl-mercuric halides, some of which disproportionate under the influence of ammonia (12). 

Dichlorodifluoromethane reacts with WO at 525 C mainly to give CO, WOF and WOCl. Small amounts of phosgene and carbonyl difluoride are also formed, but these compounds may arise from the reactions of the CO with the nickel halide films formed on the inside surfaces of the nickel reactor [2159]. 

The reactions of metal complexes of monoterpenes continue to be actively explored and many specific examples will be found in later sections. Of general interest are the dimerization of 7r-allyl-Pd complexes of a- and p-pinenes and of carvone that are effected by irradiation at 366 nmM and the thermal decompositions of (TC-allyl)nickel halide complexes of, e.g., isoprene (33), to form myrcene.95 Hydrosilylation of 1,3-dienes e.g. isoprene, myrcene, ocimene) was found to be a regiospecific 1,4-addition for Pd complexes but followed the alternative route for Rh compounds a good discussion is appended.96 A series of dimers of isoprene... 

Many examples of alkene and alkyne insertion into metal-carbon bonds can also be found in the section on homogeneous catalysis. Other recent examples include the insertion of conjugated dienes into palladium-allyl bonds, olefin arylation in the presence of palladium acetate, and the reaction of ethylene with arylmagnesium halides in the presence of nickel chloride. Reaction of isocyanates with nickel-ethynyl compounds... 

As described in Section VI, D, tetraphenylcyclobutadienepalladium halides react with terf-phosphines to liberate the organic ligand which is obtained as the dimer, octaphenylcyclooctatetraene (XLIII) (72). The phosphines in bis(ferNphosphine)nickel halides are quite labile and on reaction of these compounds with tetraphenylcyclobutadienepalladium halides exchange of the ligands occurs (69). A suggested mechanism is as shown. 

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