Early Transition Metal Permethylpentalene Complexes for the Polymerization of Ethylene

A series of group 4 permethylpentalene–cyclopentadiene mixed sandwich complexes have been synthesized including the mono- and bis-cyclopentadienyl derivatives Pn*MCp_2–<i>x</i>Cl_<i>x</i> (Pn* = η⁸-C₈Me₆, M = Ti, Zr, Hf, <i>x</i> = 0, 1) and the monopentamethylcyclopentadienyl species Pn*MCp*Cl (Pn* = η⁸-C₈Me₆, M = Ti, Zr, and Hf). The compounds were all characterized via a range of techniques including single crystal X-ray diffraction allowing for comparison of trends descending the group as well as the effect of permethylation of the cyclopentadienyl moiety. The complexes have been tested for their efficacy as catalysts for the solution polymerization of ethylene, and Pn*ZrCpCl was found to give the highest activity of 6993 kg mol^–1 h^–1 bar^–1 at 80 °C with a [MAO]₀/[Zr]₀ ratio of 1000 and 2 bar pressure of ethylene gas in hexane