Oxidative dehydrogenation on the alpha-carbon of 4-pyridylacetonitrile complexes of pentaammineruthenium(II)

The oxidation of Ru(NH3)(5)NCCH(2)py(2+) in 0.10 M HCl turns the solution f rom yellow to greenish blue with an absorption lambda = 791 nm. The absorba nce reaches its maximum value when the complex undergoes a two-electron oxi dation. The IR and H-1 NMR spectra of the product indicate that the metal c enter remains as Ru(II) and that the ligand is oxidized. The C-13 NMR spect ral results suggest that the oxidation product is [(NH3)(5-)RuNCC(pyH)C(pyH )CNRu(NH3)(5)](ClO4)(6). Cyclic voltammetry of the product solution also in dicates that the oxidation proceeds in two one-electron steps corresponding to [Ru(III),Ru(II)] + e(-) reversible arrow [Ru(II),Ru(II)] and [Ru(III),R u(III)] + e reversible arrow [Ru(III),Ru(II)]. The structure of the product in deprotonated form [(NH3)(5)RuNCC(py)C(py)CNRu(NH3)(5)](ClO4)(4)(H2O)(2) was determined crystallogaphically. [(NH3)(5)RuNCC(py)C(py)CNRu(NH3)(5)](C lO4)(4)(H2O)(2) crystallizes in the orthorhombic Pbca space group with cell constants a = 13.7138 (16) Angstrom, b = 15.7553 (18) Angstrom, c = 17.831 (2) Angstrom, 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 concent rations.