A set of eight-coordinate rhenium(V) pentahydride complexes supported by either a bidentate amine with a pendant functional group (1,2-diaminoethane, 1,3-diaminopropane, 2-aminoethanol) or by an unsymmetrically-substituted aromatic amine (3-aminopyridine or 3-picoline) were prepared from reactions with ReH7(PPh3)2. Low temperature two-dimensional 1H NMR exchange spectroscopy indicates an exchange of hydrogen between the unique hydride ligand residing in a dodecahedral B site and the ortho protons of the triphenylphosphine ligands plus the usual fluxional behavior of the hydride ligands of rhenium(V) pentahydride complexes. Values of ΔG‡ for the two fluxional processes ranged from 8.5 to 10.4 kcal/mol while ΔG‡ for the intramolecular hydrogen exchange ranged from 10.4 to 10.8 kcal/mol. Isomer interconversion for the two complexes supported by the aromatic amines had values of ΔG‡ of 11.2 and 11.7 kcal/mol. The activation entropies for the several processes suggested the fluxional hydride exchanges are unimolecular while the intramolecular hydrogen exchange and isomer interconversion entropies of activation are significantly positive, suggesting an elimination step. Amine ligand exchange occurs for the complexes. The rate law for the amine exchange indicates a dependence only on the concentration of the rhenium complex.

Intramolecular hydrogen exchange and topological rearrangements at rhenium(V) pentahydride complexes supported by two triphenyl phosphine ligands and an amine

256th National Meeting (2018)

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