Differentiation of Oxygen Atom Chirality in Copper(II) Complexes with Dipicolylamine‐Derived Ligands

Abstract

AbstractThe ether coordination of the oxygen atom to the copper(II) center supported by dipicolylamine (DPA)‐derived ligands,N‐[2‐(2‐pyridylmethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (LPy), N‐[2‐(2‐quinolylmethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (LQ), N‐[3‐(2‐pyridylmethyloxy)‐1‐propyl]‐N,N‐bis(2‐pyridylmethyl)amine (L′Py), N‐{2‐[1‐(2‐pyridyl)ethyloxy]ethyl}‐N,N‐bis(2‐pyridylmethyl)amine (LPy*1), N‐[2‐(2‐pyridylmethyloxy)‐1‐propyl]‐N,N‐bis(2‐pyridylmethyl)amine (LPy*2), and N‐[2‐(carboxymethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (HLCOO), have been examined. The factors that facilitate the coordination of the ether oxygen atom of these ligands to the copper center and the control of chirality around the copper‐coordinated oxygen atom are discussed. The copper center exhibits a pentacoordinate geometry with these ligands, as evidenced by X‐ray crystallography. The steric effect of the quinoline ring in the LQ complex prevents the coordination of a perchlorate anion to the copper center, which affords the pentacoordinate divalent complex with a shorter copper–oxygen bond than that for the corresponding pyridine ligand (LPy). The six‐membered chelate in the L′Py complex also exhibits a shorter Cu–O distance. The conformation of the oxygen atom of the LPy complex is unstable because of fast lone pair inversion, but this inversion is prevented for the complexes with chiral ligands, LPy*1 and LPy*2. Upon chelation to the metal center, the HLCOO ligand forms a pentacoodinate monomer complex that further affords a 1‐D polymer structure. With respect to the oxygen chirality, the water content of the solvent governs the formation of either a homochiral polymer (R‐R‐R‐R‐ or S‐S‐S‐S‐) or an alternative chirality polymer (R‐S‐R‐S‐). In this case, the isomers with respect to the oxygen chirality were separated and characterized.