Selective Lability of Ruthenium(II) Arene Amino Acid Complexes

A series
of organometallic complexes of the form [(PhH)­Ru­(amino acid)]+ have been synthesized using amino acids able to act as tridentate
ligands. The straightforward syntheses gave enantiomerically pure
complexes with two stereogenic centers due to the enantiopurity of
the chelating ligands. Complexes were characterized in the solid-state
and/or solution-state where the stability of the complex allowed.
The propensity toward labilization of the coordinatively saturated
complexes was investigated. The links between complex stability and
structural features are very subtle. Nonetheless, H/D exchange rates
of coordinated amino groups reveal more significant differences in
reactivity linked to metallocycle ring size resulting in decreasing
stability of the metallocycle as the amino acid side-chain length
increases. The behavior of these systems in acid is unusual, apparently
labilizing the carboxylate residue of the amino acid. This acid-catalyzed
hemilability in an organometallic is relevant to the use of Ru­(II)
arenes in medicinal contexts due to the relatively low pH of cancerous
cells.