NMR evidence for B(C6F5)(3) attack on the inward position of a highly hindered meso ansa-zirconocene

The reaction of the ansa-zirconocene meso-[C2H4(4,7-Me(2)Indenyl)(2)]ZrMe2 with B(C6F5)(3) afforded, besides the expected ion pair with outward MeB(C6F5)(3)(-) anion, also a minor isomer (molar fraction 0.043) with the bulky methylborate anion in the inward site. 2D H-1 EXSY experiments revealed exchange between the two isomers, at T > 320 K, through the migration of the MeB(C6F5)(3)(-) anion between outward and inward sites. The presence of free B(C6F5)(3) fastened the exchange, suggesting B(C6F5)(3) attack on the zirconium bound methyl ligand of the two ion pairs. (C) 2004 Elsevier B.V. All rights reserved.