Ethene Polymerization at Cationic Aluminum Amidinate and Neutral Aluminum Alkyl. A Theoretical Study

The effect of substituent variation on olefin insertion and chain transfer in cationic aluminum amidinate alkyls [R 1 C(NR 2 ) 2 AlEt] + was studied by theoretical methods. Introduction of bulky substituents at C ( t -Bu) and N ( i -Pr) favors insertion more than chain transfer, but the system still keeps a clear preference for chain transfer, and even the full system [ t -BuC(N i -Pr) 2 AlEt] + is predicted not to polymerize ethene. Changing to a neutral analogue (as in H 2 C(NH) 2 AlEt) and relieving the geometric constraints (in Me 2 AlEt) favor insertion even more, so that trialkylaluminum is finally predicted to have a clear preference for oligomerization.