A hydrogenase catalyses the reversible oxidation of molecular hydrogen in nature. Synthetic biologically inspired complexes exhibiting reactivity similar to hydrogenase enzymes have provided evidence of hydride transfer to the metal and proton transfer to an amine. However, key structural information about the intermediate is not readily discernible with X-rays. The greater sensitivity of neutron to hydrogen makes it ideal for studying the structure and dynamics of catalytic materials. The high resolution neutron structure measured on the SNS TOPAZ single crystal diffractometer at the Oak Ridge National Laboratory for an Fe-based mononuclear electrocatalyst confirms that reaction of [CpFeN-L)](BARF) (1) with H2 under mild conditions leads to a Fe–Hδ-∙∙∙δ+H–N in [1-FeHNH]+, where the ferrous hydridic site {Fe(II)–H-} acts as the H-bond acceptor and the nitrogen of the protic pendant amine {L-N-H+} as the H–bond donor [1]. In this presentation, we will present our recent result showing the dihydrogen complex [1-FeHNH]+ undergoes single-crystal to single-crystal chemical reaction with H2O to form [1-Fe(H2O)N]+ . The neutron structure reveals that the water molecule in reaction product [1-Fe(H2O)N]+ forms classical hydrogen bond with the amine N that acts as a proton acceptor, indicating the displacement of H2 by water under ambient conditions. [Acronyms: Cp = perfluoropyridylcyclopentadienide; N-L= 1, 5-di(tert-butyl)-3,7-di(tert-butyl)-1,5-diaza-3,7-diphosphacyclooctane; BARF = [B[3,5-(CF3)2C6H3]4]−] Reference [1] Liu, T.; Wang, X.; Hoffmann, C.; DuBois, D. L.; Bullock, R. M. Angew. Chem. Int. Ed. 2014, 53, 5300. Aknowledgement: Work performed at the Oak Ridge National Laboratory Spallation Neutron Source’s TOPAZ single-crystal diffractometer was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

Single-crystal to single-crystal structural and chemical transformation of a Fe-based mononuclear electrocatalyst for hydrogen production

249th National Meeting (2015)

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