FTIR study of the active ethene polymerisation catalyst, alumina-supported C6H6Cr(CO)3

Abstract

IR spectra are reported for C₆H₆Cr(CO)₃ adsorbed on alumina which had been pretreated in vacuum at 500, 700 and 800 °C. Two dominant modes of adsorption involved H-bonding of surface hydroxy groups to benzene nuclei and O-ligation of CO groups to Lewis acidic Al³⁺ surface sites. Displacement of both benzene and CO ligands occurred and led to adsorbed subcarbonyl species. Ligand loss was enhanced by evacuation at 25 °C, mild heating or contact with ethene. Sub-carbonyl surface species contained coordinatively unsaturated Cr sites which were active for the polymerisation of ethene to give highly linear polyethene.