Synthesis, Structure, and Reactivity of (C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>Y{(μ-FC<sub>6</sub>F<sub>4</sub>)(μ-Me)B(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>}:  Tight Ion Pairing in a Cationic Lanthanide Complex

The reaction of [Cp‘<sub>2</sub>YMe]<sub>2</sub> (Cp‘ = C<sub>5</sub>H<sub>5</sub>, C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>) with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> affords the complexes Cp‘<sub>2</sub>Y{MeB(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>}. The anion is coordinated in a chelating fashion via one <i>ortho</i>-fluorine atom and agostic interactions to two of the methyl hydrogens; the complexes are highly fluxional in solution. They act as initiators for the carbocationic polymerization of isobutene.