Investigation of Iridium CF3PCP Pincer Catalytic Dehydrogenation and Decarbonylation Chemistry

The iridium fluorinated pincer complex ( CF 3 PCP)Ir(cod) ( CF 3 PCP = 2,6-C 6 H 3 (CH 2 P(CF 3 ) 2 ) 2 ) catalyzes hydrogen transfer from cyclooctane (coa) to tert -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 ( CF 3 PCP)Ir(cod) to initially form ( CF 3 PCP)Ir(isoprene). Alkene inhibition studies show that ( CF 3 PCP)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 N 2 or in the presence of excess water. Hydrogenation of ( CF 3 PCP)Ir(L) (L = cod, isoprene) did not produce ( CF 3 PCP)Ir(H) x but instead afforded the first example of the unusual aryl-bridged bimetallic complex [(μ-1κ 2 ( P, C ),2κ 2 ( P ′, C )- CF 3 PCP)Ir(H) 2 ] 2 (μ- CF 3 PCPH)(μ-H), which has been isolated and crystallographically characterized. Ir(I) pincer complexes ( CF 3 PCP)Ir(L) (L = MeP(C 2 F 5 ) 2, CO, dfepe (dfepe = (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 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 ( CF 3 PCP)Ir(MeP(C 2 F 5 ) 2 )(CO), ( CF 3 PCP)Ir(CO) 2, and [( CF 3 PCP)Ir(CO)] 2 (μ-dfepe). DFT studies indicate that the preferred catalyst resting state for alkane dehydrogenation, ( CF 3 PCP)Ir(cod), can be ascribed to the lower steric requirements of the CF 3 -substituted pincer ligand.