β-Diketiminate-supported magnesium alkyl: synthesis, structure and application as co-catalyst for polymerizations mediated by a lanthanum half-sandwich complex
Résumé
Mg(n-Bu){η2-HC[C(Me)NMes]2} (2) (Mes = mesityl, 2,4,6-Me3C6H2), a new β-diketiminate-supported magnesium alkyl, has been synthesized and structurally characterized. The X-ray analysis of the lanthanum half-sandwich complex Cp*La(BH4)2(THF)2 (1) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum-catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre-catalyst. The results are compared with those for n-butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4-trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1, 2 and Al(i-Bu)3 leads finally to a 1,4-trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM
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