Immobilisation of iron tris(β-diketonates) on a two-dimensional flat amine functionalised silicon wafer: A catalytic study of the formation of urethane, from ethanol and a diisocyanate derivative

A series of immobilised iron tris(beta-diketonato) catalysts on a Si-wafer was prepared, by covalently anchoring the Fe(beta-diketonato)(3) complexes [where beta-diketonato = (RCOCHCORT')(-), with 1 = acac (R = CH3; R' = CH3), 2 = dbm (R=C6H5; R' = C6H5), 3 = tfaa (R = CH3; R' = CF3), and 4 = hfaa (R = CF3; R' = CF3)], onto an aminated functionalised Si-wafer. These new catalysts were characterised by X-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). XPS data revealed that ca. 27-91% of all the amine groups anchored the catalyst, Fe(beta-diketonato)(3 center dot) Different Gaussian peaks could be fitted into the F 1s peak, due to the fluorine either being positioned adjacent to the -C-O-Fe-, or to the -C-N-Fe-. The binding energy of the Fe 2p(3/2) peak varied between ca. 710.4 and 711.0 eV, depending on the electron donating properties of the R-groups on the beta-diketonato ligands, expressed as the sum of the Gordy group electronegativities of the R-groups in the beta-diketonato ligands. The AFM photographs showed that the surface changed dramatically after each treatment: after amination (binding of the aminate silane onto the hydroxylate Si-wafer) the Si-wafer turned from flat with a few spikes, to a very wavy surface with smooth lumps. The surface topography again changed, after covalent anchoring of the iron tris(beta-diketonato) complexes, to a nodular surface with poorly defined grain boundaries. These immobilised iron tris(beta-diketonato) on Si-wafer catalysts, were evaluated for their catalytic activity, during the formation of hexamethylenediurethane from hexamethylenediisocyanate and ethanol. The TOF varied between 15 and 46 s(-1), depending on the electron donating properties of the R-groups on the beta-diketonato ligands. The more electron donating the R groups, the higher the TOF. (C) 2014 Elsevier Ltd. All rights reserved.