Nickel dimerization

The synthesis of a further group of co-facial dimers containing all-nitrogen donor atoms have been described (Busch, 1980). For example, Ni(n) species of type (142 with R = -(CH2)2-,-(CH2)2,-(CH2)4, m-xylene, or Cy-fluorene) have been isolated (Busch et al., 1981 Herron et al., 1983) these nickel dimers contain the metal ions in square-planar environments. 

Optical Spectra. The optical spectra of the nickel dimer (75) shows both the Soret and the Q bands at approximately the same wavelengths as the parent pz (69b)—a Soret band is observed at 340-350 nm, and a Q band at 640-680 (nm) 590-620 nm(sh) however, the Q band of the nickel dimer (75) is split due to decreased symmetry and enhanced n... 

EPR. The frozen solution EPR spectrum of 75 shown in Fig. 13 exhibits rhombic symmetry typical of a Ni(III) bis(dithiolene) complex (126), with g-tensor values of gx = 2.13, gy = 2.04, g, = 1.99. The nickel dimer can thus be viewed as a classical bis(dithiolene) moiety with a 3B3g ground state where the odd electron orbital composed primarily of a metal dyZ orbital and sulfur 2pz orbitals. The Ni(II) in the pz, as expected, is EPR silent (19, 122). 

Gyclopentadienyl nickel dimers with bridging ER groups can be obtained either from nickelocene or from Cp2Ni2(CO)2 (Equation (85),66 Scheme 25).68 For Cp2Ni2 EC(SiMe3)3 2, the Ni-Ni bond distances are 244.85(7) pm for E = Ga and 249.1(1) pm for E = In.68 A tetranuclear cluster is obtained when GaCp is reacted with Ni(GO)4 84.41... 

When the transfer reaction competes successfully with further insertion, as in the case of nickel, dimerization becomes the dominant transformation. When metal hydride elimination, in turn, is slow relative to insertion, polymeric macromolecules are formed. Ligand modification, the oxidation state of the metal, and reaction conditions affect the probability of the two reactions. Since nickel hydride, like other metal hydrides, catalyzes double-bond migration, isomeric alkenes are usually isolated. 

It should also be noted that only close to 50% of the total nickel is present as Ni111. The simplest explanation is that there is a second ESR-undetectable nickel. This nickel centre may have an important role in the activity of hydrogenase. Its structural relationship to the ESR-detectable nickel is of great interest. Some type of nickel dimer cannot be ruled out completely. 

The transformation of P4 in the coordination sphere of 15 VE fragments has been studied by allowing group-6 carbonyls, [M(CO)6] (M=Cr, Mo, W), and nickel cyclopentadienyl carbonyl complexes to react using Scheer s one-pot/three-components practice under thermal or photochemical conditions. Remarkably, the combination of P4, [Cr(CO)6], and the nickel dimer [ Cp Ni (CO) 2] under UV irradiation yields complexes incorporating Pj, P2, and P3 lig-... 

Catalyst 1, [(z7 -crotyl)(cycloocta-l,5-diene)nickel]hexafluorophosphate ( naked nickel ), was prepared following a procedure developed for the methallyl isomer by Tkatchenko and coworkers [35, 37]. Thus bis(cyclo-l,5-octadiene)nickel was reacted with crotyl bromide to yield the bromide-bridged (// -crotyl)nickel dimer. Abstraction of the bromide by thallium hexafluorophosphate in the presence of cyclo-1,5-octadiene yielded 1. The structure of 1 in solution is consistent with its solid state X-ray crystal structure [38]. 

See Refs 118, 190, 272, 273 and 303-312.) The nickel dimer has received considerable attention, at least partially because of the importance of nickel clusters in catalysis. Several ab initio calculations have been perform-gjji9o.272,273,303-308 semiquantitative consensus on the nature of the... 

A typical reaction involving nickel(O) treats an allylic halide such as 3-chloro-2-methyl-l-propene with Ni(CO)4 to form 439,288 a nickel dimer analogous to the palladium chloride dimer discussed in the previous section. This complex reacts with an alkene to form a new complex (440), and subsequent reaction with a variety of electrophilic reagents removes nickel. In this example, the chlorine was converted to an acetate ligand (in 441) and reacted with methanolic carbon monoxide to give the ester (442).288... 

This approach was first accomplished by Ziegler in his early work when nickel was introduced with titanium, either purposely or through autoclave corrosion as part of the investigation of the Aufbau reaction. The nickel dimerized ethylene to butene, while the titanium incorporated it at low levels yielding poly ethylenes with low levels of ethyl branches. We have been told that this work appears in early notebooks from the Ziegler laboratory, but we have been unable to find a reference in the open literature. 

In addition to hydrogenation catalysis, supported IL membranes were also studied for their use as oligomerization catalysts. Such membranes were prepared by loading porous polyethersulfone support membranes with chloroaluminate-based ILs with and without a nickel dimerization catalyst [22]. Although both catalyst types converted ethylene with high activity, the nickel-containing membrane exhibited the higher selectivity for butene production. 

While investigating the oligomerization of ethene by aluminium alkyls (p. 80), Ziegler and coworkers noticed that in the presence of traces of nickel dimerization to 1-butene occurs instead. Very active catalysts can be generated by adding an alkylaluminium halide to [(f/ -CjHJNiCl]. The phosphine complexes NiL are also effective in the presence of acids. A nickel hydrido complex is first formed which adds to ethene to give an ethyl intermediate which can either eliminate 1-... 

Bis(acrylonitrile)-nickel dimerizes norbornadiene at about 60° to (XLVII) and (XLVIII). In addition small amounts of the nitrile (LI) (see Fig. 9) may also be isolated, suggesting that the coordinated acrylonitrile reacted with the norbornadiene as well. The complexes of 1,1-dicyano- and 1,1,2-... 

C3oH36Bi,F8Ni2Ni2f Bis(difluoroboron-dimethylglyoximato)nickel dimer bis(benzimidazole) adduct, 46B, 1122 C3oH36FgN8Ni206S2f Bis((5,7,12,l4-tetramethyl-1,4,8,11-tetraazacyc-lotetradecahexaenato)nickel)(Ni-Ni) trifluoromethanesulphonate,... 

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