NMR (Nuclear Magnetic Resonance) Evidence for a Planar Arene Intermediate in the Electron-Transfer Induced Eta 6 to Eta 4 Hapticity Change of a Rhodium Arene Complex

摘要

Hydrogen 1 NMR spectra have been obtained for the Rhodium (II) complex (eta-C6Me6)RhCp*)+, Cp* = 5-C5Me5, at 200 MHz, and 470 MHZ. A single resonance was observed for te arene CH3 protons between 298 K and 183 K in Methylene Chloride. The temperature dependence of the resonance was consistent with a doublet state formulation of the Rh(II) complex. At 298 K, the CH3 chemical shifts were 56 ppm for the arene substituents and 123 ppm for the cyclopentadienyl substituents. The magnetic equivalence of the methyl arene resonances is consistent with a planar arene structure in the complex. It is shown that a structural formulation including a highly fluxional bent arene is unlikely. The results demonstrate eta 4-arene hapticity, the one-electron intermediate can retain the planar arene structure, even if this results in a 19 e- metal. (AW)