2] (Cp* = C₅Me₅; Rf = C₆F₃Cl₂-3,5), General Precursor to Cp*-Diaryl and Cp*-Halo-Aryl RhIII Complexes. Observing and Testing the Effect of Cp*]]>

摘要

The pentacoordinated [RhCp*Rf_(2)] (Rf = C_(6)F_(3)Cl_(2)-3,5) and the octahedral (μ-Cl)_(2)[RhCp*Rf]_(2), obtained by stoichiometric rearrangement with (μ-Cl)_(2)[RhCp*Cl]_(2), are general precursors of [RhCp*RfXL] (X = Rf, Cl; L = ligand) complexes, which were studied by NMR (L dissociation and fluxional processes) and X-ray diffraction (structural effects affecting the Rh–Cp* distances) techniques. The Rh–Cp*_(centroid) distances decrease markedly for identical L in the order [RhCp*Rf_(2)L] > [RhCp*RfClL] > [RhCp*Cl_(2)L] and are further influenced regularly within each family by the trans influence of L (longer distances for higher trans influence of L). The structural effects observed reveal a remarkable capability of Cp* to act as an electron-density buffer, which attenuates the Rh electron density variations induced by the substituents in front of Cp* by releasing toward Rh or polarizing toward Cp*, on demand, the electron density of the Rh–Cp* bonds. This buffer effect explains the easy L dissociation from [RhCp*Rf_(2)L] and the accessibility to formally 16e pentacoordinated [RhCp*Rf_(2)].