Experimental and Computational Studies of Ruthenium Complexes Bearing <i>Z</i>‑Acceptor Aluminum-Based Phosphine Pincer Ligands

Reaction of [Ru(C₆H₄PPh₂)₂(Ph₂PC₆H₄AlMe(THF))H] with CO results in clean conversion to the Ru−Al heterobimetallic complex [Ru(AlMePhos)(CO)₃] (<b>1</b>), where AlMePhos is the novel P–Al(Me)–P pincer ligand (<i>o</i>-Ph₂PC₆H₄)₂AlMe. Under photolytic conditions, <b>1</b> reacts with H₂ to give [Ru(AlMePhos)(CO)₂(μ-H)H] (<b>2</b>) that is characterized by multinuclear NMR and IR spectroscopies. DFT calculations indicate that <b>2</b> features one terminal and one bridging hydride that are respectively <i>anti</i> and <i>syn</i> to the Al<i>Me</i> group. Calculations also define a mechanism for H₂ addition to <b>1</b> and predict facile hydride exchange in <b>2</b> that is also observed experimentally. Reaction of <b>1</b> with B(C₆F₅)₃ results in Me abstraction to form the ion pair [Ru(AlPhos)(CO)₃][MeB(C₆F₅)₃] (<b>4</b>) featuring a cationic [(<i>o</i>-Ph₂PC₆H₄)₂Al]⁺ ligand, [AlPhos]⁺. The Ru–Al distance in <b>4</b> (2.5334(16) Å) is significantly shorter than that in <b>1</b> (2.6578(6) Å), consistent with an enhanced Lewis acidity of the [AlPhos]⁺ ligand. This is corroborated by a blue shift in both the observed and computed ν_CO stretching frequencies upon Me abstraction. Electronic structure analyses (QTAIM and EDA-ETS) comparing <b>1</b>, <b>4</b>, and the previously reported [Ru(ZnPhos)(CO)₃] analogue (ZnPhos = (<i>o</i>-Ph₂PC₆H₄)₂Zn) indicate that the Lewis acidity of these pincer ligands increases along the series ZnPhos < AlMePhos < [AlPhos]⁺.