Bellows Sarina M, Chakraborty Sumit, Gary J Brannon, Jones William D, Cundari Thomas R
Department of Chemistry, University of Rochester , Rochester, New York 14627, United States.
Center for Enabling New Technologies through Catalysis, Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
Inorg Chem. 2017 May 15;56(10):5519-5524. doi: 10.1021/acs.inorgchem.6b01800. Epub 2017 Apr 28.
The mechanism of the dehydrogenation of N-heterocycles with the recently established bifunctional catalyst (PNP)Fe(CO)(H) was investigated through experiments and density functional theory calculations (PNP = PrPCHCHNCHCHPPr). In this system, the saturated N-heterocyclic substrates are completely dehydrogenated to the aromatic products. Calculations indicate that dehydrogenation barriers of the C-C bonds are very high in energy (ΔG = 37.4-42.2 kcal/mol), and thus dehydrogenation only occurs at the C-N bond (ΔG = 9.6-22.2 kcal/mol). Interestingly, substrates like piperidine with relatively unpolarized C-N bonds are dehydrogenated through a concerted proton/hydride transfer bifunctional transition state involving the nitrogen on the PNP ligand. However, substrates with polarized C-N bonds entail stepwise (proton then hydride) bifunctional dehydrogenation.
