Jörn Karl, and Gerhard Erker, R. Fröhlich
Nov 19, 1997
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0
Influential Citations
64
Citations
Journal
Journal of the American Chemical Society
Abstract
The Lewis acid tris(pentafluorophenyl)borane adds to the (butadiene)group 4 metallocenes 1a−d (metallocene = Cp2Zr, Cp2Hf, (MeCp)2Zr, (Me3CCp)2Zr) to give the metallocene−(μ-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 ≈ 2.40 A, angle Zr−F−C ≈ 140°). The bridging fluorine atom of the complexes in solution is characterized by an extreme upfield shift of its 19F NMR resonance (δ ≈ −210 to −220 ppm) relative to the signals of the remaining five o-F resonances of the B(C6F5)3 moiety (average δ ≈ −135 ppm). The 19F NMR spectra of the complexes 2 are dynamic even in the noncoordinating solvent toluene-d8. All six o-fluorine ...