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

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