Ion pair symmetrization in metallocenium cations partnered with diborane derived borate counteranions

The thermodynamics of ion pair symmetrization in a series of metallocenium species generated from View the MathML sourceCp2″ZrMe2(Cp″=1,2-Me2C5H3) were studied using a variety of solution dynamic techniques including line broadening, 2D-EXSY, and 1D-DPFGSE-NOE. Ion pairs were generated by methide abstraction using the corresponding trityl salts [1-A] to yield View the MathML source[Cp2″ZrMe]+[A]- (A = {C6F4-1,2-[B(C6F5)2]2(μ-O(C6F5))}−, 2-O(C6F5); {C6F4-1,2-[B(C6F5)2]2(μ-OPh)}−, 2-OPh; {C6F4-1,2-[B(C6F5)2]2(μ-OMe)}−, 2-OMe; and [B(C6F5)4]−, 2-B(C6F5)4). The observed activation parameters were interpreted on the basis of a solvent-assisted mechanism of ion pair symmetrization.