Dicationic ethylene complex

In 1982, Casey and co-workers reported the first reactions that could be considered hydrocarbations because they involved the direct C-H bond addition across the C-C double bond of alkenes. They showed that the cationic bridging iron methylidyne complex undergoes this type of reaction with alkenes with anti-Markovnikov regioselectivity. No other hydrocarbation reactions had been reported until recently, when Kubiak and co-workers reported hydrocarbation reactions of a nickel carbene complex with alkenes. Thus, the dicationic aminocarbene complex 31 reacts with ethylene, resulting in a complete conversion to the ethylcarbene complex (Scheme 1). 

The remainder of the work on Ni(II) complexes involves the use of chelating ligands in which the carbene is functionalised with pendant heteroatom donor(s). The picolyl-functionalised NHC dicationic complex 29 (Fig. 4.11) was tested for ethylene polymerisation after treatment with MAO [34]. This complex was found to be highly active in a preliminary test (330 kg moF bar h" ), giving predominantly linear polyethylene. Unfortunately this work does not seem to have been followed up. The same system was active for norbomene polymerisation (TOF = 24 400 h" over 1 h). Maximum activity was achieved at 80°C whereafter thermal deactivation became significant, although the nature of this deactivation was not studied. The phenoxide-functionalised carbene complex 30 (Fig. 4.11) was also... 

Figure 8.24 The structure of the dication [YMe(THF)6] + [78]. (Reproduced with permission from S. Arndt, etal., Homogeneous Ethylene-Polymerization Catalysts Based on Alkyl Cations of the Rare-Earth Metals Are Dicationic Mono(aUcyl)Complexe s the Active Species , Angewanrffe Chemie International Edition, 2003, 442, 5075-5079 (Eigure 2). Wiley-VCH Verlag GmbH Co. KGaA.)...

In recent years, a large number of mono- and dicationic lanthanide alkyl complexes have been found to be efficient catalysts for ethylene polymerization, and in some cases, the dicationic lanthanide derivatives show higher activity and selectivity than their monocationic counterparts. Ionic radii of lanthanide metals also affect the catalytic behavior, and polymerization activity often increases with ionic radius [5, 76],... 

Dicationic NHG chelate complexes of Pd have been employed in the catalytic co-polymerization of ethylene and GO with modest activity under mild conditions of temperature and pressure. It was concluded that only a very small percentage of the palladium pre-catalyst is active in the co-polymerization reaction, although no suggestion of what the actual active species might be was provided. This is an interesting report chain-growth reactions (oligomerization... 

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