Nickel bromide NiBr

Allyl bromide reacts with nickel carbonyl in benzene to give the volatile ir-allyl complex [NiBr(ir-C3H6)]2 as a violet-red solid (75). 

Conceptually, the simplest C—X oxidative addition reaction involves a naked metal center. Cocondensation of nickel vapor with pentafluorophenyl bromide yields [NiBr(CgF5)], which can be trapped by reaction with a tertiary phosphine ... 

Spectrophotometric studies have been made on the ligand exchange between the hydrated nickel(II) ion and bromide ions . In those systems which were, however, not anhydrous the species [NiBr]+, NiBr2, [NiBra] and [NiBr4] were detected nickel(II) bromide was observed to have a low stability, thus indicating considerable autocomplex formation . ... 

Thus, addition of <9-tolyl bromide to Ni(tmiy)2 and tmiy at room temperature yields the nickel(ii) complex NiBr(6>-Tol)(tmiy)2 in good yield (70%). An X-ray crystal structure of this complex shows the carbene ligands in a trans-arrangement with a rather long Ni-Ctmiy bond (1.947(3) A). The complex NiIMe(tmiy)2 rapidly decomposes in solution via 1,2,3,4,5-pentamethylimidazolium ion elimination and was only characterized by NMR and MS. The other complexes shown (Equation (14)) were characterized by X-ray diffraction. 

Structural characterization of these species has revealed that complex 69 adopts a trigonal-bipyramidal geometry in which the methylallyl moiety occupies the apical position (Ni-GN 189 pm), whereas complex 71 adopts a square-pyramidal structure with the cyanide ligand at the apical position at a relatively long distance from the Ni center (Ni-CN 199 pm). The latter structure is similar to the bromo analog NiBr(allyl)(dippe), prepared from the reaction of the nickel(i) hydrido dimer [NiH(dippe)]2 and allyl bromide. The involvement of allyl cyano species such as 69 and 71 in the catalytic hydrocyanation of butadiene is supported by the following observations (i) complex 69 catalyzes the isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile (ca. 100 turnovers at 100 °G), (ii) complex 71 decomposes slowly to give Ni(0) complexes of cis- and // 77i--crotonitrile (Scheme 20). 

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