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

(α-Imino acidato)ruthenium(II) complexes, [Ru^II{N(R¹)C(R²)CO₂}L₂]⁺ (R¹ = R² = Me or R¹ = R² = −(CH₂)₃−; L = 2,2‘-bipyridine (=bpy) or 1,10-phenanthroline (=phen)), were obtained by anodic oxidation at a constant potential of the corresponding (α-amino acidato)ruthenium(II) complexes, N-methylalaninato or prolinato complexes, in good to excellent yields. (α-Imino acidato)ruthenium(II) complexes are stable in neutral or acidic aqueous solution. The half-wave potentials of α-imino acidato complexes are 0.73−0.78 V (vs SCE), which are more positive than those of the corresponding α-amino acidato complexes, 0.55−0.59 V. The crystal structure of [Ru(pro-H₂)(bpy)₂]ClO₄·3H₂O (pro-H₂ = 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, β = 114.91(5)°, Z = 8, R = 0.0352. The length of the CN double bond of the α-imino acidate moiety is 1.294(5) Å, and Ru−N(imino nitrogen) = 2.042(3) Å. The chelate ring of the α-imino acidato ligand is planar.