Chemistry of tripodal ligands. Part III.: Copper complexes of tris(benzimidazol-2-ylmethyl)amine and of its N- n-propyl derivative

Abstract

The reactions of copper (I or II) salts with ligands Rntb (tris( N-alkylbenzimidazol-2-ylmethyl)amine) gave complexes [Cu(II)(ntb)Cl]Cl·3H 2O ( 1), [Cu(I)(ntb)(PPh 3)](NO 3)·1.5H 2O ( 2), [Cu(II)(Prntb)I]Cl ( 3) and [Cu(I)(Prntb)I] ( 4), depending on the reaction conditions. X-ray single crystal diffraction analyses showed the copper atom to be tetrahedrally coordinated in 2 and 4, but square pyramidal in 1 and trigonal bipyramidal in 3. Structural characteristics were revealed for the complexes and compared, and complex 3 was shown to be the best model compound among the four for the active center of blue copper proteins. CV studies showed the electrochemical behaviors of the complexes: 1 has two redox couples, phosphine ligation stabilizes 2 towards redox reactions, while 3 and 4, with the same cationic formula [Cu(Prntb)I] 1+,0 have very similar complicated redox patterns, indicating the reversibility of the two species. IR and UV–Vis spectroscopic studies were also reported.