Photolabile complexes of the general form rac-[Ru(diimine)2(aa)]ClO4·nH2O (where diimine is either 2,2′-bipyridyl or 1,10-phenanthroline and aa is glycine, N-methylglycine, or N-phenylglycine) have been synthesized and their structures in solution analyzed by using 200-MHz 1H NMR spectroscopy. The results are compared with the solid-state structure of rac-[Ru-(bpy)2(gly)]ClO4·2H2O, which has been determined by X-ray diffraction. This analysis is used to demonstrate the torsional effects of glycine substitution on the structure of the amino acid chelate ring, and on the nature of the diastereomeric ratios in the synthetic product mixtures. Photoequilibration has allowed a quantitative estimate of the discriminatory effects resulting from substitution at the N(amine) chiral centres. In the N-methylglycine chelates those diastereomers that avoid steric interaction between the CH3 group and the diimine molecules are selected, whereas the N-phenylglycine chelates show stereospecific coordination for the same steric reason. Both the amine and methylene protons of the coordinated amino acids exchange for deuterons at high pD. Crystal data: rac-[Ru(bpy)2(gly)]ClO4·2H2O, C22H24N5ClO8Ru, triclinic, space group P1, a = 9.487 (2) Å, b = 12.294 (3) Å, c = 13.041 (3) Å, α = 111.36 (2)°, β = 63.15 (2)°, γ = 113.33 (2)°, U = 1213.77 (10) Å3, Z = 2. The structure was refined by full-matrix least-squares methods to R = 0.033 and R′ = 0.035 for 3752 unique reflections. The molecular structure has Ru-O = 2.105 (3) and Ru-N(amine) = 2.135 (4) Å with the amino acid chelate ring adopting a flattened δ conformation in the Λ enantiomer. The four Ru-N(bpy) bond lengths are not equivalent, the bond trans to Ru-O being significantly shorter (2.008 (4) Å) than the other three (average Ru-N = 2.046 (6) Å).
|Number of pages||5|
|Publication status||Published - 1986|