Beta-Diketone and beta-Ketoenamine based molecular squares

Abstract

This dissertation focuses on synthesis of β-diketone and β-ketoenamine ligands for molecular polygons. Previous work with the bis(β-diketone) m-pbaH2 showed that it can be converted to a copper molecular square, Cu4(m-pba)4, but its use in host-guest reactions was limited by its low solubility in most organic solvents. Accordingly, in the present work, the mpbhxH2 ligand, with pentyl chains replacing the methyl groups in the β-diketone moieties of mpbaH2, was successfully prepared beginning with 6-dodecyne. This ligand reacts with Cu2+ to make the molecular square Cu4(m-pbhx)4, which is soluble in a wider range of solvents. Hostguest reactions of Cu4(m-pbhx)4 with a variety of guest molecules were studied. The structures of the “empty” square, [Cu4(m-pbhx)4(CH3OH)2], and its adducts with several guest molecules, were determined by single crystal X-ray analysis. In these host-guest adducts, the Cu---Cu distances range from 13.7-15.1 Å. As part of a study of the effects of substituents on the properties of the resulting molecular squares, the 2-MeO-m-pbaH2 ligand had been prepared previously. This dissertation reports an improved synthesis of 2-MeO-m-pbaH2, and its larger homolog 2-MeO-m-pbprH2 was synthesized as well. Treatment of 2-MeO-m-pbprH2 with Cu2+ afforded a molecular square that is soluble in chloroform and dichloromethane. Treatment of the square with guest molecules did not yield adducts, most likely because of steric interference from the internal methoxy groups. The two ligands m-pbaH2 and m-pbprH2 were converted to their ketoenamine analogs mpbiH2 and m-pbpriH2 through microwave-assisted synthesis. The molecular squares Cu4(m-pbi)4, xi Cu4(m-pbpri)4, and Ni4(m-pbpri)4 were prepared from these ligands and characterized by single crystal X-ray analysis, UV-Vis spectroscopy, and cyclic voltammetry. Two new bis(β-diketone) ligands based on triphenylamine were prepared for the first time. The new ligands were designed to make Cu(II) molecular squares that are larger (Cu---Cu ca. 21 Å) than Cu4(m-pba)4 and its derivatives.