Dehydrogenation of pyrrolidine based liquid organic hydrogen carriers by an iridium pincer catalyst, an isothermal kinetic study

A previously known homogenous iridium POCOPtBu pincer catalyst and several pyrrolidine based liquid organic hydrogen carriers (LOHCs) were investigated under dehydrogenation conditions and analyzed in a pseudo first order kinetic fashion to determine various kinetic properties. Dehydrogenation onset temperatures (DOT) of 180, 160, and 140 °C; activation energies (EA) of 115, 142, and 166 (kJ/mol); and frequency factor (A) values of 3.56 × 108, 1.05 × 1011, and 2.17 × 1014 (s−1) were found for ethyl perhydro carbazole (EPHC, 2), methyl perhydro indole (MePHI, 3), and butyl pyrrolidine (BuPy, 4) respectively. The dehydrogenation onset temperatures correlate with collision frequency factors rather than the activation energies. This evidence suggests that it is a steric constraint approach of the LOHC rather than a barrier to C-H bond activation at the iridium center which limits the rate of reaction.