On the Mechanism of Oligomerization of Propylene by (C5Me5)2MCl2/Methylalumoxane Catalysts (M = Zr, Hf)

Abstract

In the oligomerization of propylene by (C5Me5)2MCl2 (M = Zr,Hf)/methylalumoxane, formation of abnormal oligomers such as 1-pentene(C5), 2,4-dimethyl-1-pentene(C7), 4-methyl-1-heptene(C8), and 2,4,6-trimethyl-1-heptene(C10) besides normal oligomers such as 4-methyl-1-pentene(C6) and 4,6-dimethyl-1-heptene(C9) is indicative of the mixing of unusual β-CH3 and usual β-H transfer terminations from each growing carbon chain which was initiated by insertion of propylene into either M–H or M–Me bond.

Detailed Kinetics of 1‐Hexene Oligomerization Reaction with (n‐Bu‐Cp)2ZrCl2–MAO Catalyst

“…CH 2 ¼CðC 4 H 9 ÞÀ½CH 2 ÀCHðC 4 H 9 Þ nÀ2 ÀCH 2 ÀCH 2 ÀC 4 H 9 þðnÀBuÀCpÞ 2 Zr þ ÀCH 2 ÀCH 2 ÀC 4 H 9 (10) Insertion of a 1-hexene molecule into the ZrÀC bond in the latter produces a dimeric growing chain, ðnÀBuÀCpÞ 2 Zr þ ÀCH 2 ÀCH 2 ÀC 4 H 9 þ CH 2 ¼CHÀC 4 H 9 Àðk p;1 Þ ! ðnÀBuÀCpÞ 2 Zr þ ÀCH 2 ÀCHðC 4 H 9 Þ À CH 2 ÀCH 2 ÀC 4 H 9 (11) which is b-branched with respect to the Zr atom. All subsequent chain growth steps also produce active centers with alkyl chains b-branched with respect to the Zr atom, for example: ðnÀBuÀCpÞ 2 Zr þ À½CH 2 ÀCHðC 4 H 9 Þ nÀ2 ÀCH 2 ÀCH 2 ÀC 4 H 9 þCH 2 ¼CHÀC 4 H 9 Àðk p Þ !…”

“…The chemistry of oligomerization reactions of ethylene and higher 1-alkenes with metallocene and post-metallocene catalysts was described in detail earlier. [5][6][7][8][9][10][11][12][13][14] These data provided the necessary input for the interpretation of the kinetic data presented below.…”

Stereospecific Olefin Polymerization Catalyzed by Metallocene Complexes

“…If chain transfer is negligible or very slow, the polymerization can be "living", as observed in group 5 metallocene-diene complexes [30,31]. b-Methyl elimination is also reported in bis(pentamethylcyclopentadienyl)metallocene catalysts [32,33].…”

Oligomerization of Monoolefins by Homogeneous Catalysts

“…In 1991 Yamazaki et al [28] reported that Cp* 2 MCl 2 (M = Zr, Hf), in presence of methylaluminoxane (MAO), catalyzed the oligomerization of propene to produce mainly 4-methyl-1-pentene as well as other dimers, trimers and higher oligomers.…”