PHOSPHORUS-BRIDGED METALLOCENES - NEW HOMOGENEOUS CATALYSTS FOR THE POLYMERIZATION OF PROPENE

The synthesis of a new class of metallocenes for the syndiospecific, a specific and isospecific polymerization of propene is reported. This h as been achieved by the incorporation of a phosphorus linking the cycl opentadienyl-type rings. The catalyst precursors, syndiospecific PhP(f luorenyl-Cp)ZrCl2 (2), aspecific PhP(fluorenyl)(2)ZrCl2 (4), and isosp ecific PhP(indenyl)(2)ZrCl2 (5), RP(2-Me,4-Ph-indenyl)(2)ZrCl2 (R = Ph (6); R = Pr-i (7)) were prepared. Compound 2, after activation by met hylaluminoxane (MAO), in LIPP at 67 degrees C affords syndiotactic pol ypropene (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 si milar to that of conventional carbon-bridged systems. Ab initio calcul ations on model compounds assisted in rationalizing the high syndiospe cificity of 2 in contrast to the much poorer stereoreguIarity of close ly related Me2Si(fluorenyl-Cp)ZrCl2. Aspecifrc merallocene 4, after ac tivation with MAO, affords high molecular weight atactic-PP, albeit wi th a low activity. Metallocenes 6 and 7, activated by MAO, afford isot actic poiypropene (i-PP) with extremely high stereoregularity (> 98% m mmm pentads), melting points 156-160 degrees C and molecular weights t unable in the range 250,000-1,100,000. Activities of up to 580 kg i-PP /g Zr . h for 6/MAO (LIPP, 67 degrees C, 37 000 equiv. MAO) and 1265 k g i-PP/g Zr . h for 7/MAO (LIPP, 50 degrees C, 37 000 equiv. MAO) have been obtained. (C) 1998 EIsevier Science B.V.