Distinct methylalumoxane(MAO)-derived Me–MAO⁻anions in contact with a zirconocenium cation—a¹³C-NMR study

Abstract

Zirconocenium cations of the type [(MeC5H4)2ZrMe]+, formed by excess methylalumoxane (MAO) from (MeC5H4)2ZrCl2 or (MeC5H4)2ZrMe2 with 13C-labelled ring ligands, are found to form ion pairs with two types of anions, Me-MAO(A)- and Me-MAO(B)-, which differ in their coordinative strengths: More strongly coherent ion pairs [(MeC5H4)2ZrMe+...Me-MAO(B)-] are converted to more easily separable ion pairs [(MeC5H4)2ZrMe+...Me-MAO(A)-] by a sufficient excess of MAO. These react with Al2Me6 to form outer-sphere ion pairs containing the cationic AlMe3 adduct [(MeC5H4)2Zr(mu-Me)2AlMe2]+; formation of the more easily separable ion pairs might be required also for polymerisation catalysis.