β-Hydride Elimination and C-H Activation by an Iridium Acetate Complex, Catalyzed by Lewis Acids. Alkane Dehydrogenation Cocatalyzed by Lewis Acids and [2,6-Bis(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl]iridium.

NaBAr (sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate) was found to catalyze reactions of (Phebox)Ir(acetate) (Phebox = 2,6-bis(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl) complexes, including (i) β-H elimination of (Phebox)Ir(OAc)(n-alkyl) to give (Phebox)Ir(OAc)(H) and the microscopic reverse, alkene insertion into the Ir-H bond of (Phebox)Ir(OAc)(H), and (ii) hydrogenolysis of the Ir-alkyl bond of (Phebox)Ir(OAc)(n-alkyl) and the microscopic reverse, C-H activation by (Phebox)Ir(OAc)(H), as indicated by H/D exchange experiments. For example, β-H elimination of (Phebox)Ir(OAc)(n-octyl) (2-Oc) proceeded on a time scale of minutes at -15 °C in the presence of (0.4 mM) NaBAr as compared with a very slow reaction at 125 °C in the absence of NaBAr. In addition to NaBAr, other Lewis acids are also effective. Density functional theory calculations capture the effect of the Na cation and indicate that it operates primarily by promoting κ-κ dechelation of the acetate anion, which opens the coordination site needed to allow the observed reaction to proceed. In accord with the effect on these individual stoichiometric reactions, NaBAr was also found to cocatalyze, with (Phebox)Ir(OAc)(H), the acceptorless dehydrogenation of n-dodecane.