Oxidative Dehydrogenation on the α-Carbon of 4-Pyridylacetonitrile Complexes of Pentaammineruthenium(II)

The oxidation of Ru(NH3)5NCCH2py2+ in 0.10 M HCl turns the solution from yellow to greenish blue with an
absorption at λ = 791 nm. The absorbance reaches its maximum value when the complex undergoes a two-electron oxidation. The IR and 1H NMR spectra of the product indicate that the metal center remains as Ru(II)
and that the ligand is oxidized. The 13C NMR spectral results suggest that the oxidation product is [(NH3)5RuNCC(pyH)C(pyH)CNRu(NH3)5](ClO4)6. Cyclic voltammetry of the product solution also indicates that the
oxidation proceeds in two one-electron steps corresponding to [Ru(III),Ru(II)] + e- ⇌ [Ru(II),Ru(II)] and [Ru(III),Ru(III)] + e- ⇌ [Ru(III),Ru(II)]. The structure of the product in deprotonated form [(NH3)5RuNCC(py)C(py)CNRu(NH3)5](ClO4)4(H2O)2 was determined crystallographically. [(NH3)5RuNCC(py)C(py)CNRu(NH3)5](ClO4)4(H2O)2 crystallizes in the orthorhombic Pbca space group with cell constants a = 13.7138 (16) Å, b =
15.7553 (18) Å, c = 17.831(2) Å, and Z = 4. A mechanism for the oxidation has been proposed on the basis of
the kinetic studies in the region of 0.01−0.20 M acid concentrations.