Cationic (η<sup>5</sup>‑C<sub>5</sub>Me<sub>4</sub>R)Rh<sup>III</sup> Complexes with Metalated Aryl Phosphines Featuring η<sup>4</sup>‑Phosphorus plus Pseudo-Allylic Coordination

In this contribution we study experimentally and computationally some electrophilic cationic (η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>R)­Rh<sup>III</sup> complexes containing a cyclometalated bis­(aryl) phosphine, PR′Ar<sub>2</sub>. The phosphine Ar groups feature methyl substituents at the 2- and 6-positions of the aromatic rings, allowing the formation of the complexes [(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>R)­Rh­(C<sup>∧</sup>P)]<sup>+</sup> (<b>3</b><sup><b>+</b></sup>), where the metalated phosphine exhibits η<sup>4</sup> coordination to rhodium through phosphorus and the carbon atoms of the adjoining pseudo-allylic functionality. The solution and solid-state structures of complexes <b>3</b><sup><b>+</b></sup> have been studied by NMR and X-ray methods and their electronic properties investigated with the aid of DFT calculations. The Lewis acid behavior of complexes <b>3</b><sup><b>+</b></sup> has also been addressed, concentrating on reactivity toward CO, H<sub>2</sub> ,and hydrosilanes. Some catalytic Si–H/Si–D exchange and hydrosilylation reactions are also reported.