Regioselective Gas-Phase n-Butane Transfer Dehydrogenation via Silica-Supported Pincer-Iridium Complexes

The production of olefins via on-purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica-supported pincer-iridium complexes of the form [(equivalent to SiO-(POCOP)-P-R4)Ir(CO)] ((POCOP)-P-R4=kappa(3)-C6H3-2,6-(OPR2)(2)) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 degrees C. However, while solution-phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 degrees C, in open systems at 300 degrees C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes [(equivalent to SiO-(POCOP)-P-tBu4)Ir(CO)] (1) and [(equivalent to SiO-(PCP)-P-iPr4)Ir(CO)] (2) were synthesized via immobilization of molecular precursors. These complexes were used for gas-phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77 %. The results indicate that the active site is conserved upon immobilization.