Investigation of Iridium ^CF₃PCP Pincer Catalytic Dehydrogenation and Decarbonylation Chemistry

The iridium fluorinated pincer complex (^CF₃PCP)­Ir­(cod) (^CF₃PCP = 2,6-C₆H₃(CH₂P­(CF₃)₂)₂) catalyzes hydrogen transfer from cyclooctane (coa) to <i>tert</i>-butylethylene (tbe) in 1/1 coa/tbe at 200 °C to give cyclooctene (coe) and neohexane (tba) at an initial rate of 40 TO h^–1. In 5/1 coa/tbe, higher initial activity (155 TO h^–1) and higher turnovers (2580 TON’s after 1450 min) are found. Samples of 95% tbe contain significant amounts of isoprene (2-methyl-1,3-butadiene), which reacts with (^CF₃PCP)­Ir­(cod) to initially form (^CF₃PCP)­Ir­(isoprene). Alkene inhibition studies show that (^CF₃PCP)Ir is only modestly inhibited (67% reduced initial activity) in the presence of 800 equiv of added coe. Unlike donor pincer systems, no decrease in activity is noted under 1 atm of N₂ or in the presence of excess water. Hydrogenation of (^CF₃PCP)­Ir­(L) (L = cod, isoprene) did not produce (^CF₃PCP)­Ir­(H)_<i>x</i> but instead afforded the first example of the unusual aryl-bridged bimetallic complex [(μ-1κ²(<i>P</i>,<i>C</i>),2κ²(<i>P</i>′,<i>C</i>)-^CF₃PCP)­Ir­(H)₂]₂(μ-^CF₃PCPH)­(μ-H), which has been isolated and crystallographically characterized. Ir­(I) pincer complexes (^CF₃PCP)­Ir­(L) (L = MeP­(C₂F₅)₂, CO, dfepe (dfepe = (C₂F₅)₂PCH₂CH₂P­(C₂F₅)₂)) also serve as moderately active aldehyde decarbonylation catalyst precursors for 2-naphthaldehyde with similar activities in diglyme (1.7 TO h^–1, 152 °C) and in 1,4-dioxane (0.052 TO h^–1, 94 °C). The catalyst resting states are the corresponding five-coordinate carbonyl complexes (^CF₃PCP)­Ir­(MeP­(C₂F₅)₂)­(CO), (^CF₃PCP)­Ir­(CO)₂, and [(^CF₃PCP)­Ir­(CO)]₂(μ-dfepe). DFT studies indicate that the preferred catalyst resting state for alkane dehydrogenation, (^CF₃PCP)­Ir­(cod), can be ascribed to the lower steric requirements of the CF₃-substituted pincer ligand