Cationic (η⁵‑C₅Me₄R)Rh^III Complexes with Metalated Aryl Phosphines Featuring η⁴‑Phosphorus plus Pseudo-Allylic Coordination

In this contribution we study experimentally and computationally some electrophilic cationic (η⁵-C₅Me₄R)­Rh^III complexes containing a cyclometalated bis­(aryl) phosphine, PR′Ar₂. The phosphine Ar groups feature methyl substituents at the 2- and 6-positions of the aromatic rings, allowing the formation of the complexes [(η⁵-C₅Me₄R)­Rh­(C^∧P)]⁺ (3⁺), where the metalated phosphine exhibits η⁴ coordination to rhodium through phosphorus and the carbon atoms of the adjoining pseudo-allylic functionality. The solution and solid-state structures of complexes 3⁺ 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 3⁺ has also been addressed, concentrating on reactivity toward CO, H₂ ,and hydrosilanes. Some catalytic Si–H/Si–D exchange and hydrosilylation reactions are also reported.