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-Me2Indenyl)2]ZrMe2 with B(C6F5)3 afforded, besides the expected ion pair with outward View the MathML sourceMeB(C6F5)3- anion, also a minor isomer (molar fraction 0.043) with the bulky methylborate anion in the inward site. 2D 1H EXSY experiments revealed exchange between the two isomers, at T > 320 K, through the migration of the View the MathML sourceMeB(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.