The Union Carbide catalyst (Cp2Cr + SiO2), studied by solid-state NMR

The Union Carbide catalyst, that can be synthesized by reaction of chromocene (Cp₂Cr) with silica (SiC₂), allows the polymerization of olefins at low pressure and low temperature without any cocatalyst. Despite the interest in this heterogeneous catalyst, the nature of the active species is still unknown. In this contribution it is demonstrated that ¹H solid-state NMR serves as a powerful method for the investigation of the surface species. The spectra are evidence for the presence of one mononuclear and two dinuclear surface-attached complexes. The nature of these species is discussed on the basis of molecular model compounds and their NMR characteristics.