Synthesis, characterization and study of the catalytic properties of Zn(II) camphor derived complexes

•Eighteen camphor derived Zn(II) complexes were synthetized and characterized.•Some of the Zn camphor complexes catalyse the cyclization of 4-pentyn-1-ol.•The dinuclear camphor Zn(II) compounds are better catalysts than the mononuclear.•XPS studies and SEM images allow an insight into the surface of Zn complexes.

Zinc(II) complexes of general formula [ZnX2(YNC10H14O)], [ZnX2(YNC10H13NSO2)], [ZnX2(H2NNC10H14O)2], [{ZnX2}2(YNC10H14O)] and [{ZnX2}2(YNC10H13NSO2)] were obtained from zinc halides (chloride or bromide) by reaction with the suitable camphor ligands.In most of the complexes, the camphor ligands remain unchanged upon coordination, except in [{Zn(MeNNC10H14O)}2(μ-Cl)2] where proton loss from MeHNNC10H14O occurs. The new complexes and camphor derivatives were characterized by IR, NMR (1H, 13C{H}, DEPT, 2D) and elemental analysis. In some cases the surface composition was studied by X-ray photoelectron spectroscopy (XPS) and imaged by Scanning Electron Microscopy (SEM). Images of [ZnCl2(Me2NNC10H14O)] and [ZnCl2(Me2NNC10H13NSO2)] obtained by SEM show the solid particles have tubular structures capped in one or both extremities. The coordination of THF in [ZnCl2(YNC10H14O)THF] was confirmed by X-ray diffraction analysis. The camphor derivatives YNC10H14NSO2 (Y = NMe2; NHMe) and p-C6H4(NC10H14O)2 were structurally characterized by X-ray diffraction analysis.The ability of selected Zn(II) camphor complexes to catalyse the cyclization of 4-pentyn-1-ol was evaluated showing that the binuclear complex [{ZnX2}2(YNC10H14O)] performs better than the mononuclear Zn(II) complexes.

Graphical abstractCamphor derived ligands coordinate Zn(II) forming complexes with different metal to ligand ratios. The binuclear complexes with bi-camphor type ligands are efficient catalysts for cyclization of 4-pentyn-1-ol with further addition of a second alkynol molecule.Figure optionsDownload full-size imageDownload as PowerPoint slide