Revisiting ruthenium scorpionate chemistry: Reactivity of bis(3,5-dimethylpyrazol-1-yl)acetic acid toward organoruthenium(II) precursors.

The reactivity of the scorpionate ligand bis(3,5-dimethylpyrazol-1-yl)acetic acid (L1H) toward organoruthenium(II) precursors was investigated. Reactions of chlorido and bromido p-cymene ruthenium dimers afforded the corresponding complexes in which L1H acts as a neutral κ2-N,N' donor. In the presence of acetonitrile and base, ligand deprotonation was accompanied by displacement of the p-cymene ligand, yielding a tris(acetonitrile)ruthenium(II) complex containing a κ3-N,N',O-coordinated scorpionate ligand.  Under ethanol-containing reaction conditions, in situ esterification of the coordinated carboxylic acid group was observed, yielding crystals of a new ruthenium complex 4 containing the ethyl ester derivative of the ligand. The compounds 1-3 were characterized by NMR, IR, HRMS, while the crystal structures of compounds 1·H2O, 3·MeOH, and 4 were determined by single-crystal X-ray diffraction. The results demonstrate the influence of reaction conditions on the coordination mode and transformation of bis(pyrazolyl)acetate ligands in ruthenium chemistry.