Vanadium ethene complexes

The quasi living polymerization of ethene and norbornene has been reviewed, among other topics in living polymerization of alkenes (19). Specifically, arylimido-aryloxo-vanadium(V) complexes with methylaluminoxane or Et2AlCl as co-catalyst have been used as catalyst systems. The polymers exhibit a low polydispersity and a high molecular weight (20). 

Although there are few five-membered metallacycles reported for group 5, there are some examples of metallacyclopentane compounds for niobium and tantalum. The reaction of the labile vanadium naphthalene complex [CpV(Ci0H8)] with ethene provided the unusual binuclear complex [Cp2V2(p-C4H8)2] (34 [Eq. (13)], Fig. 9) in which the two vanadium centres are bridged by two butanediyl groups.38... 

Early transition metal catalysts such as vanadium complexes and zirconocenes effectively copolymerize ethene with norbornene [81]. This capabihty eventually led to the commercial development of the APEL and TOPAS line of cyclic olefin copolymers by Mitsui and Ticona (formerly Hoechst), respectively [82]. Interest in this class of polymers is due to its high glass transition temperatures and transparency that is imparted by the norbornene component. 

In the context of alternative substrates for nitrogenases, in particular alkynes, [Equation (4.27)], model compounds are of interest in which the alkyne is coordinated side-on to vanadium. The side-on or rr coordination implies a weakening of the triple bond by TT-back-donation from vanadium-d into the tt orbitals of the ligand, and hence an activation. The activated siloxyacetylene in the complex [ClVdmpe)2 i7 -(Me3SiOC= COSiMe3)] [dmpe = bis(dimethylphosphino)ethane] is reduced by hydrogen to the respective ethene, [Equation (4.39)]. The precursor acetylene complex is formed by... 

It was reported that one of the trimethylphosphine ligands in the vanadium(III) imido complex [CpV(NAr)(PMe3)2] (Ar = 2,6-C6H3Pr 2) could be substituted with ethene or diphenylethyne to afford complexes of the type [CpV(NAr)(PMe3)(T 2-L)]. Spectroscopic data were consistent with considerable back-donation from the vanadium(m) centres to the alkene and alkyne ligands. Photolysis of a mixture of tri-fcrt-butylcyclopropenium tetrafluoroborate and sodium hexacarbonylvanadate afforded the structurally characterised complex [(C3But3)V(CO)4], which represented the first example of partial insertion of an early transition metal atom into a cyclopropenyl ring. 

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