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

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 PNPtBu‐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 PNPAd 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. [ABSTRACT FROM AUTHOR]