Does the Facile Inter and Intramolecular C-H Bond Activation by Tp~*-Rh Complexes Proceed via Rh~I or Rh~(III) Intermediates?

摘要

the majority of C-H activation processes in arenes that are induced by Rh or Ir complexes of cyclopentadienyl or related ligands involve low-valent, electron-rich Rh~I or Ir~I centers as the reactive intermediates. Recent work from our laboratory andfrom Bergman's group has shown that more electrophilic Ir~(III) species are able to promote C-H activation under very mild conditions. In our case, as in a similar example reported by Graham et al. the use of a hard, N-donor ligand, the tris (3,5-dimethylpyrazol-1-y) hydroborate (Tp~*), which is in addition known to enforce sixfold coordination, contributes to the stabilization of the Ir~(III) oxidation state and drives, for example, the conversion of [Tp~*Ir(C_2H_4)_2] into the thermodynamically more stable hydridovinyl Ir~(III) isomer [Tp~*Ir(H)(CH=CH_2)(C_2H_4)]. We have now prepared the Rh analogue [Tp~*Rh(C_2H_4)_2] (1) and would like to report preliminary studies which reveal intriguing and unexpected reactivity patterns in the thermal C-H activation.