Reactivity of a cationic alkyl amino-functionalized cyclopentadienyl aluminum compound with olefins: NMR observation and computational investigation of the single propene insertion product into an Al-C bond

In this study the reactivity of the compound dimethyl [2-(N,N- dmiemylethylen)cyclopentadienyl)]Al(III) toward ionizing species and the subsequent reactivity toward ethylene and propene have been explored. Reactions were studied via NMR tube experiments. Upon methyl abstraction by the Lewis acid B(C6F5)3, the amine donor on the ligand side arm coordinates to aluminum, stabilizing the resulting cationic species versus secondary reactions. The obtained cationic species was able to polymerize ethylene, albeit with low activity. Reaction with propene resulted in the selective 1,2-insertion of one propene molecule into an Al-C bond of the Al-Cp moiety. Density functional and ab initio calculations were used to characterize the energy landscape of the insertion into the Al-Cp bond for both ethylene and propene. The computational results suggest this reaction to be more facile than the insertion into the Al-Me bond. © 2009 American Chemical Society