Experimental and Computational Studies of Ruthenium Complexes Bearing Z-Acceptor Aluminum-Based Phosphine Pincer Ligands

[Image: see text] Reaction of [Ru(C(6)H(4)PPh(2))(2)(Ph(2)PC(6)H(4)AlMe(THF))H] with CO results in clean conversion to the Ru−Al heterobimetallic complex [Ru(AlMePhos)(CO)(3)] (1), where AlMePhos is the novel P–Al(Me)–P pincer ligand (o-Ph(2)PC(6)H(4))(2)AlMe. Under photolytic conditions, 1 reacts with H(2) to give [Ru(AlMePhos)(CO)(2)(μ-H)H] (2) that is characterized by multinuclear NMR and IR spectroscopies. DFT calculations indicate that 2 features one terminal and one bridging hydride that are respectively anti and syn to the AlMe group. Calculations also define a mechanism for H(2) addition to 1 and predict facile hydride exchange in 2 that is also observed experimentally. Reaction of 1 with B(C(6)F(5))(3) results in Me abstraction to form the ion pair [Ru(AlPhos)(CO)(3)][MeB(C(6)F(5))(3)] (4) featuring a cationic [(o-Ph(2)PC(6)H(4))(2)Al](+) ligand, [AlPhos](+). The Ru–Al distance in 4 (2.5334(16) Å) is significantly shorter than that in 1 (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 1, 4, and the previously reported [Ru(ZnPhos)(CO)(3)] analogue (ZnPhos = (o-Ph(2)PC(6)H(4))(2)Zn) indicate that the Lewis acidity of these pincer ligands increases along the series ZnPhos < AlMePhos < [AlPhos](+).