Gordon, Benjamin Maxwell. A combined experimental and computational approach to the development of alkane dehydrogenation catalysts. Retrieved from https://doi.org/doi:10.7282/t3-vmd5-tx22
DescriptionPincer-iridium catalyzed alkane dehydrogenation is a selective and relatively mild route to the functionalization of an abundant and otherwise inert feedstock. Significant developments have been made since the initial reports of their use in dehydrogenation, however, they suffer from notable limitations that prevent them from being adopted on industrial scale. In this thesis, we identify the origin of regioselectivity for two prototypical pincer catalysts, (tBuPCP) and (tBuPOCOP), and find it to be the result of differing trans-influences in the aryl ring. This varying trans-influence destabilizes a trans-hydride pincer geometry, changing the rate-determining step from beta-hydride transfer to olefin dissociation which favors the formation of 2-olefin. This kinetically disfavored trans-hydride geometry was further explored. The high energy was determined to be the result of a series of hydride reorganization energies, as no such kinetic barrier to dissociation was found with the similar cis-dihydride geometry. We next examine an asymmetric pincer geometry that favors the formation of a cis-hydride geometry during its catalytic cycle. This geometry leads to a high regioselectivity in alkane dehydrogenation reactions. Unexpectedly, this also leads to an orders of magnitude increase in activity due to resting state destabilization. Finally, we explore of a series of new pincer-molybdenum complexes.