Rene Ernst

Phosphorus-bridged metallocenes: New homogeneous catalysts for the polymerization of propene

Abstract The synthesis of a new class of metallocenes for the syndiospecific, aspecific and isospecific polymerization of propene is reported. This has been achieved by the incorporation of a phosphorus linking the cyclopentadienyl-type rings. The catalyst precursors, syndiospecific PhP(fluorenyl–Cp)ZrCl2 (2), aspecific PhP(fluorenyl)2ZrCl2 (4), and isospecific PhP(indenyl)2ZrCl2 (5), RP(2-Me,4-Ph-indenyl)2ZrCl2 (R=Ph (6); R= i Pr (7)) were prepared. Compound 2, after activation by methylaluminoxane (MAO), in LIPP at 67°C affords syndiotactic polypropene (s-PP) with an activity of 155 kg s-PP/g Zr·h. The physical properties of the s-PP (stereoregularity and molecular weight) are similar to that of conventional carbon-bridged systems. Ab initio calculations on model compounds assisted in rationalizing the high syndiospecificity of 2 in contrast to the much poorer stereoregularity of closely related Me2Si(fluorenyl–Cp)ZrCl2. Aspecific metallocene 4, after activation with MAO, affords high molecular weight atactic-PP, albeit with a low activity. Metallocenes 6 and 7, activated by MAO, afford isotactic polypropene (i-PP) with extremely high stereoregularity (>98% mmmm pentads), melting points 156–160°C and molecular weights tunable in the range 250,000–1,100,000. Activities of up to 580 kg i-PP/g Zr·h for 6/MAO (LIPP, 67°C, 37 000 equiv. MAO) and 1265 kg i-PP/g Zr·h for 7/MAO (LIPP, 50°C, 37 000 equiv. MAO) have been obtained.