One-dimensional copper(II) coordination polymers built on 4′-substituted 4,2′:6′,4″- and 3,2′:6′,3″-terpyridines: Syntheses, structures and catalytic properties

Abstract

Divergent ligands containing either 4,2′:6′,4″- or 3,2′:6′,3″-terpyridine domains (1–4) with various 4′-substituents are synthesized. The new ligand 4 was fully characterized by standard spectroscopic and mass spectrometric technique. All ligands were then used to prepare four new copper(II) coordination polymers (5–8) and good quality single crystals were obtained by the layering method. Single crystal X-ray structural analysis reveals that while the structures of compounds 5 and 6 built on 4,2′:6′,4″-terpyridine ligands feature similar zigzag chains composed of paddle-wheel {Cu2(μ-OAc)4} units, the use of 3,2′:6′,3″-terpyridine ligands bearing various 4′-substituents leads to different coordination polymers 7 and 8 in which the ligands adopt remarkably distinct binding modes. The copper(II) coordination polymers were employed to the catalytic aerobic oxidations of alcohols mediated by TEMPO radical (TEMPO=2,2,6,6-tetramethylpiperidinyl-1-oxyl) and the results revealed that the polymers display slightly different catalytic activity towards the oxidation of benzylic alcohol under heterogeneous conditions, and compound 8 was observed to catalyze the reaction in water with almost quantitative yield when a base additive is present.