AbstractSoluble halogen free polymerisation catalysts have been prepared by reacting tetrabenzyl zirconium and related compounds with silanols. The combination of tetrabenzyl zirconium and 1,1,3,3‐tetraphenyldisiloxane‐1,3‐diol (VI) was found to be particularly active. Structural analysis of VI shows that the SiOSi angle is linear, which may account for this compound behaving as a monodentate ligand. The relationship between structure and activity in these soluble systems and the transition metal polymerisation centres, prepared by reacting transition metal alkyls with silica and alumina, is