Journal of the Chemical Society - Faraday Transactions p. 5093 - 5101 (1996)
Update date:2022-08-29
Topics:
Hunter, Geoffrey
Rochester, Colin H.
Wilkinson, Anthony G.
Paton, John
IR spectra are reported of Cr(CO)6, (C6H6)Cr(CO)3 and (Me4C6H2)Cr(CO)3 adsorbed on silica which had been pretreated in vacuum at temperatures in the range 250-800°C or in H2O or D2O vapour at 700°C. Surface isolated silanol groups formed hydrogen bonds with arene rings in Cr complexes which also interacted with the surfaces via ligation involving carbonyl groups. The generation of active adsorption sites was promoted by increasing pretreatment temperature. Several types of site were involved and resulted from dehydroxylation of the silica surface. Adsorbed bridging carbonyl species resulted from interactions with active Siδ+Oδ- surface sites. There was negligible evidence for the loss of CO ligands from adsorbed molecules and the supported complexes were inactive for the polymerisation of ethene. However, some loss of benzene occurred for (C6H6)Cr(CO)3 on silica pretreated at 800°C. Pretreatment of silica in H2O or D2O at 700°C promoted hydrothermal surface reorganisation of silica and destroyed a high proportion of the active adsorption sites generated at 700°C on silica in vacuum.
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