Scanning tunnelling microscopy for characterization of metathesis catalysts based on photogenerated W(CO)(6)/CCl4

Zareie M., KAVAKLI C., Salih B., Piskin E.

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, vol.118, no.2, pp.195-203, 1997 (SCI-Expanded) identifier identifier


We attempted to form a W(CO)(6)/CCl4 catalyst from the gas phase reaction of W(CO)(6) and CCl4 by UV-irradiation and used this catalyst in a model metathesis reaction of 1-heptene. We analyzed both the intermediate volatile compounds using an on-line mass spectrometer and the structure of the solid polymer by FI-MS and DSC. Scanning tunnelling microscopy (STM) was used in order to study the structures of W(CO)(6) and photogenerated W(CO)(6)/CCl4 catalyst on HOPG. Color changes observed during W-irradiation were considered to be an indication of the formation of the W(CO)(6)/CCl4 catalyst. The volatile compounds identified by mass spectrometry supported the formation of the catalyst. The mass spectra obtained with the field ionization mass spectrometer revealed that the catalyst may be in an oligomeric form with [(CO)(4)WC2Cl2](+) repeating units. Thermal transitions observed in the DSC thermograms indicated the existence of oligomeric chains. STM images clearly showed the structure of the W(CO)(6) molecules with some atomic level displacements. The STM images of the catalyst verified that the W(CO)(6)/CCl4 based metathesis catalyst is composed of oligomeric chains with four tungsten atoms.