The Lewis acid tris(pentafluorophenyl)borane adds to the (butadiene)group 4 metallocenes 1a-d (metallocene = Cp2Zr, Cp2Hf, (MeCp)(2)Zr, (Me3CCp)(2)Zr) to give the metallocene-(mu-C4H6) -borate-betaine complexes 2a-d. (Isoprene)zirconocene (1e) and (2-phenylbutadiene)zirconocene (1f) add the B(C6F5)(3) reagent regioselectively at the carbon atom C-4 to give the complexes 2e and 2f, respectively. The complexes 2 all show a pronounced M ... F-C interaction with one of the six ortho-B(C6F5)(3) fluorine atoms. The resulting metallacyclic structures were characterized by X-ray diffraction of the complexes 2c and 2e (Zr ... F approximate to 2.40 Angstrom, angle Zr-F-C approximate to 140 degrees). The bridging fluorine atom of the complexes in solution is characterized by an extreme upfield shift of its F-19 NMR resonance (delta approximate to -210 to -220 ppm) relative to the signals of the remaining five o-F resonances of the B(C6F5)(3) moiety (average delta approximate to -135 ppm). The F-19 NMR spectra of the complexes 2 are dynamic even in the noncoordinating solvent toluene-d(8). All six o-fluorine signals equilibrate with coalescence temperatures around 240 K at 564 MHz to give a single resonance signal at high temperature. This fluorine equilibration process of the -B(C6F5)(3) end of the metallocene-borate-betaine complexes 2 is very likely to proceed via a rate determining cleavage of the coordinative M ... F-C interaction, From the activation barrier of this process, obtained from the dynamic fluorine NMR spectra, Zr ... F bond dissociation energies of ca. 8.5 kcal/mol were estimated for the complexes 2. This magnitude of the M ... F-C bond dissociation energy makes the internal fluorocarbon coordination a very suitable tool for protecting active electrophilic metal catalyst centers. The Zr ... F-C bond of the complexes 2 is cleaved by the addition of the donor solvent THF with formation of acyclic 1,2-eta(2)-allyl metallocene complexes.