Complex formation of Ndown curve signN-ethylene bridged bis(N′-benzoyl-O-ethyl-isourea) and N-benzoylguanidines with late transition metals

Ndown curve signN-ethylene bridged 3-benzoyl-2-ethyl-1-[2-(3-benzoyl-2-ethyl-isoureido)-ethyl]-isourea 1 and 2-benzoylimino-imidazolidine 2 are easily accessible in good yields and act as N,O donor ligands. After deprotonation 1 and 2 form mononuclear neutral complexes whose molecular structures have been determined by X-ray structure analysis. The metal ions in the 1:1 complexes of 1 with Cu^II, Ni ^II and Co^II are coordinated by the two bridging N atoms and the two carbonyl O atoms of one ligand molecule resulting in one five membered and two six membered chelate rings. The coordination geometry is square planar with cis arrangement of the ligator atoms. In comparison to the free ligand 1 the lengths of the C-O and C-N bonds involved in coordination are changed characteristically. The 2:1 complexes of 2 with Cu^II and Ni^II are isostructural. One deprotonated imidazolidine N and the carbonyl O atom of each ligand molecule coordinate the metal ion in a square planar trans arrangement. The X-ray structure analysis of 2 shows, besides an intramolecular imidazolidine-N-H⋯O hydrogen bridge, two intermolecular hydrogen bonds originating from both imidazolidine N atoms, an N-H⋯N and an N-H⋯O one, leading to the formation of molecular chains in the crystal structure. 2-Benzoylimino-1,3-diaza-6,9-dioxacycloundecane 3 was synthesized from N-dichloromethylene-benzamide and 1,8-diamino-3,6-dioxaoctane using the dilution principle. The crystal structure of 3 reveals again, besides an intramolecular N-H⋯O hydrogen bridge, the formation of molecular chains caused by one intermolecular N-H⋯O hydrogen bridge per molecule. The bulky structure of the 1,3-diaza-6,9-dioxacycloundecane ring in 3 seems to prevent any complex formation of 3 with late transition metal ions.