Investigating the non-classical M-H2 bonding in OsClH3(PPh3)3

Abstract

Dihydrogen ligation to metal centers results in a wide range of metal-hydrogen interactions. Compounds containing non-classical dihydrogen ligands in which the H–H contacts are significantly longer than the 0.74 Å distance found in solid H2 are classified as Kubas-like compounds, stretched dihydrogen ligands, or compressed dihydrides, depending on the H–H contact length. Compounds containing stretched dihydrogen and compressed dihydride ligands are somewhat rare. Developing a more complete understanding of the metal-hydrogen and hydrogen-hydrogen interactions in these species may provide insights into the mechanisms for the oxidative addition reaction and hydrogen storage. Here, we use diffraction and inelastic neutron scattering (INS) measurements, paired with both molecular and solid-state density functional theory (DFT), to fully characterize the nature of the metal-hydrogen and hydrogen-hydrogen interactions in a previously reported compound, OsClH3(PPh3)3. In that report, the H–H distance was measured as 1.48(2) Å by single-crystal neutron diffraction and was described as a “stretched” dihydrogen. The INS-generated phonon density of states is well described by the DFT calculations, including those normal modes dominated by the vibrational motions of the three Os-ligated hydrogen atoms. The resulting calculated electron charge density landscape indicates that there is no remnant bonding character between the Os-ligated hydrogen atoms in the compound. Based on these findings, we update the understanding of the metal-hydrogen bonding in this complex and reclassify it as a compressed dihydride. As such, OsClH3(PPh3)3 represents a rare example of a non-classical compressed dihydride species.