Nickel Dibromides

The corresponding Ni(II) species (6a-c) are accessible by in situ reaction of (DME)NiBr2 with the ligands 3a-c [31]. The activation was performed by treatment of 6a-c wifh MAO at ambient temperature in order to avoid decomposition of the active catalyst form as observed for 5a-c/NaB(Ar )4. The catalysts 6a-c/ MAO were found to be highly active for efhene homopolymerizations (Tab. 2.3). 

For the 2,6-diphenyl-substituted 6a/MAO yields are obtained that rival those found for Brookharfs catalyst 6d/MAO (Tab. 2.3, entries 1 and 6). 

1-Reinsertions after //-hydride abstraction from the growing chain is effectively suppressed and reduces the probability of the formation of a secondary Ni-C 

3) clearly results from a reaction with MAO (probably through coordination via the methoxy units) indicated by the formation of an insoluble precipitate directly after MAO addition. 

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The reagent is prepared by sodium amalgam reduction of bis(triphenylphosphine)-nickel dibromide in acetonitrile or benzene. 

Benzoyl peroxide (dibenzoyl peroxide), (CjHjCOO>2 (mp 104-106 °C dec), and /r-nitrobenzoyl peroxide (p-02NCgH4COO)2 (mp 156 °C dec), which is synthesized from p-nitrobenzoyl chloride and sodium peroxide [229], are rarely used as oxidants, and if so, they do not offer appreciable advantages over other organic oxidation agents. The anti addition of benzoyl groups to double bonds and the benzoxylation of aromatic rings are achieved in the presence of iodine [230], and alcohols are oxidized to carbonyl compounds in the presence of nickel dibromide [231],... 

Britovsek et al. [38] reported a bidentate imino quinolinyl nickel dibromide complex (Fig. 3.9) for the polymerization of ethylene, but it showed moderate activity toward the formation of oligomers rather than polymers [37]. 

Late-transition metal (Ni, Pd, Fe, and Co) olefin polymerization catalysts are particularly stable to Lewis bases and water in contrast to the vast majority of olefin polymerization catalysts. Miilhaupt et al. used both Pd- and Ni-based catalysts, [ iPr2C6H3N=C(Me)C(Me)=NC6H3iPr2-2,6 Pd(CH3)(N=CCH3)]dBArJ- and N,N-bis(2,6-diisopropylphenyl)- , 4-diaza-2,3-dimethyl-l,3-butadiene nickel dibromide, for preparing highly branched PE-clay nanocomposite. They found that they were much less sensitive to the addition of non-modified and modified layered silicates than metallocene catalysts. 

Bardi G, Brunetti B, CiccarieUo E, Piacente V (1997) Vapour pressures tmd sublimation enthalpies of cobalt and nickel dibromides. J Alloys Comp 247 202-205... 

In contrast to the transition metal catalysts above, nickel complexes have been studied intensely for the polymerization of CHD and its derivatives. jr-Allylnickel-based complexes were employed by Dolgoplosk et al. for CHD polymerization. They used n-alkenylnickel halides, for example, K-metallyl nickel dichloride and it-allyl nickel dibromide, combined with electron acceptors such as chloranil (tetrachloro-/ -quinone) or nickel trichloroacetate. Unfortunately, the true propagating species of the above catalytic systems are not clear, but they were moderately active for CHD polymerization and the polymer obtained appeared to have a predominantly 1,4-linked structure. However, the stereoregularity of the polymer was not very high based on its Tm (270 °C). 

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