Impact of the Alkali Metal on the Structural and Dynamic Properties of the Anionic Pentahydride Ruthenium Complexes [M(THF)_<i>x</i>][RuH₅(PCy₃)₂] (M = Li, Na, K)

A series of anionic ruthenium pentahydride complexes with the general formula [M­(THF)x]­[RuH5(PCy3)2] (M = Li, Na, K) were synthesized. Their characterization by multinuclear NMR, IR, X-ray diffraction, and DFT techniques show that these complexes can adopt different structural features (monomer/dimer, cis/trans phosphines, hydride/dihydrogen ligands) depending on the countercation, the solvent, and/or the temperature. While the X-ray diffraction analyses offer snapshots of three out of five isomeric structures found by DFT, the solution and solid-state NMR analysis proved that these complexes exhibit a highly dynamic behavior. Rapid H–D exchange was found between Ru–H and D2, which was attributed to the presence of Ru–H·····M interactions in the absence of crown-ether.