The interaction of chromocene with partially and totally dehydroxylated MgO and the reactivity of the adsorbed species towards CO have been studied by IR spectroscopy. Cp+Zr is weakly adsorbed on residual surface MgOH groups, forming hydrogen bonded species and, on the extended (100) faces, forming clustered (Cp,Cr). species. A stronger interaction is observed with the highly unsaturated ions located on the edges and corners of the MgO microcrystals. Upon dosage of CO at room temperature, Cp,CrCO complexes are formed which are stabilized by interaction with the Mg*+ and O*-ions of the surface. The occurrence of an activated process leading to [Cp,Cr]+ and [CpCr(CO),]-charged reaction products is also observed.
THE USE of metallocenes as precursors for the preparation of catalytically active species at the surfaces of oxides has found an important practical application in the silicasupported chromocene catalyst for ethylene polymerization (Union Carbide catalyst) [l, 21. The active centres of this system are thought to be coordinatively unsaturated chromium species formed by reaction of the metallocene molecule with the slightly acidic Briinsted sites (OH groups) of the silica surface following the pathways