Facile Dehydrogenation of α-Amino Acids Chelated to a Ruthenium(II) Ion: (α-Imino acidato)ruthenium(II) Complexes

(alpha-Imino acidato)ruthenium(II) complexes, [Ru(II){N(R(1))=C(R(2))CO(2)}L(2)](+) (R(1) = R(2) = Me or R(1) = R(2) = -(CH(2))(3)-; L = 2,2'-bipyridine (=bpy) or 1,10-phenanthroline (=phen)), were obtained by anodic oxidation at a constant potential of the corresponding (alpha-amino acidato)ruthenium(II) complexes, N-methylalaninato or prolinato complexes, in good to excellent yields. (alpha-Imino acidato)ruthenium(II) complexes are stable in neutral or acidic aqueous solution. The half-wave potentials of alpha-imino acidato complexes are 0.73-0.78 V (vs SCE), which are more positive than those of the corresponding alpha-amino acidato complexes, 0.55-0.59 V. The crystal structure of [Ru(pro-H(2))(bpy)(2)]ClO(4).3H(2)O (pro-H(2) = 1,2-didehydroprolinato) has been determined by single-crystal X-ray analysis. Crystallographic data: space group C2/c, a = 21.73(1) Å, b = 19.33(1) Å, c = 14.58(1) Å, beta = 114.91(5) degrees, Z = 8, R = 0.0352. The length of the C=N double bond of the alpha-imino acidate moiety is 1.294(5) Å, and Ru-N(imino nitrogen) = 2.042(3) Å. The chelate ring of the alpha-imino acidato ligand is planar.