Synthesis and Metal Complexes of Thiourea Ligands Containing Carbohydrate-Derived Substituents

Two glucose-derived thiourea derivatives, 2a and 2b, were prepared by addition of the corresponding amino sugars to a solution of 4-nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation, elemental analysis, and also by single-crystal X-ray diffraction. Attempts to obtain Cu-II and Ni-II bis(chelate) complexes with these thioureas failed. However, the C(1)-protected thiourea derivative 2a reacted with orthopalladated acetato-bridged dimers to afford the corresponding monomeric Pd-II complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as monoanionic O,S chelate ligand, which was confirmed by X-ray crystallography.