Substituent effect on the coordination ability of the amide group of N-protected amino acids

Abstract

The binary system Cu(II)-hydantoic acid (hydaH) and the corresponding ternary systems with 2,2′-bipyridine(bpy) and 1,10-phenanthroline (ophen) were investigated both in the solid state and solution. The crystal and molecular structure of the complex [Cu(ophen)(hyda) 2]·H 2O was also determined. The crystal of the compound C 18H 20CuN 6O 7 is monoclinic, space group P2 1/ c, a=7.601(5), b=14.647(2), c=19.714(3) Å, β=96.57(3), Z=4, R=0.049, R w=0.053. The structure consists of discrete [Cu(ophen)(hyda) 2] units and lattice water molecules. The Cu(II) atom is coordinated in the equatorial plane by two nitrogens from the ophen molecule and two oxygens from two hydantoate anions; the nitrogen atom of the neutral NH group of a hydantoate anion occupies the more distant fifth position (CuN(1)=2.541(5) Å) giving rise to elongated square-pyramidal geometry. In solution the carboxylate species [CuL 2] is formed in the binary system and the species [CuAL 2], [CuAL(OH)] in the ternary systems with bpy and ophen. Spectroscopic data indicate that any possibility of the NH group being coordinated in solution can be excluded.