Solution conformation and dynamics of the ion pairs originating from the reaction of B(C6F5)(3) with bisindenyl dimethyl zirconium complexes

The two ion pairs [(4,7-Me(2)indenyl)(2)ZrMe](+)[MeB(C6F5)(3)](-) (1b) and [(indenyl)(2)ZrMe](+) [MeB(C6F5)(3)](-) (2b) have been generated in situ by reaction of stoichiometric B(C6F5)(3) with the corresponding dimethyl zirconocenes. It has been shown that molecular mechanics computations, guided by experimental H-1/H-1 NOE correlations, can provide information on the conformers present in solution. The dynamics of the ion pairs has also been investigated, showing the occurrence of both the processes previously characterized for this class of compounds, namely the B(C6F5)(3) migration between the two methyl groups and dissociation-recombination of the whole [MeB(C6F5)(3)](-) anion, the latter process being much faster than the first one (about three order of magnitude). Moreover, it has been shown that in certain conditions intermolecular processes can occur, which mimic the above-mentioned dissociative exchanges. In particular, the presence of species containing loosely bound [MeB(C6F5)(3)](-) anion fastens the exchange of this anion, while the presence of free B(C6F5)(3) accelerates its exchange between the two methyl sites.