T‐shaped 14 Electron Rhodium Complexes: Potential Active Species in C‐H Activation

Two T‐shaped 14‐electron rhodium complexes 2a and 2b, "framed" and thus stabilized by PNP pincer ligands have been synthesized. The bis(t‐butyl)phosphine derived PNPtBu‐rhodium 2a was isolated from pentane as the more stable cyclometalated Rh(III) hydrido complex and found to be in equilibrium with the T‐shaped 14e‐Rh(I) complex 2aT which itself could be directly crystallized upon change of the solvent. The cyclometallation is suppressed using an adamantyl substituted PNPAd ligand to give the analogous T‐shaped Rh(I) species 2b, stabilized through an agostic interaction with one of the adamantyl C‐Hs. Depending on the solvent, complex 2a reacted with ethylene either by π‐coordination (4a) or C‐H activation giving a hydrido‐vinyl Rh(III) species 4b, both isomers being in equilibrium in solution. Complex 2b C‐H was found to reversibly activate arenes to form the hydrido‐aryl Rh(III) complexes.