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

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 Al Me 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] + .