Diruthenium Phenylacetylide Complexes Bearing para-/meta-Amino Phenyl Substituents

Presented herein is the synthesis and characterization of four diruthenium(II,III) compounds of formulas Ru-2(Xap)(4)(C C-C6H4-4-NH2) (Xap is 2-anilinopyridinate, la; and 2-(3,5-dimethoxy)-anilinopyridinate, lb) and Ru-2(Xap)(4)(C C-C6H4-3-NH2) (2a/2b). X-ray structural studies of compounds 1b and 2a revealed minimal changes in the coordination sphere of the Ru-2 core. Voltammetric measurements showed that compounds 1 exhibit three one-electron redox processes: a reversible reduction of Ru-2, a reversible oxidation of Ru-2, and a quasi-reversible oxidation of an amino group. Compounds 2 display the same Ru-2-based redox processes but not the -NH2 oxidation. Compounds 1a/1b were successfully converted to the corresponding diazonium salts [Ru-2(Xap)(4)-(C C-C6H4-4-N-2)](BF4) (3a/3b) via oxidation by nitrosonium tetrafluoroborate, which was generated in situ from t-BuONO and BF3. However, the attempt to convert compounds 2 to the corresponding diazonium salts was unsuccessful. DFT calculations of model compounds were performed to rationalize some unusual structural and electrochemical characteristics observed for compounds 1/2.