Access to Ultra‐High‐Molecular Weight Poly(ethylene) and Activity Boost in the Presence of Cyclopentene With Group 4 Bis‐Amido Complexes

Abstract

ZrIV complexes of the type [Me2Si{(NR)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐yl‐N)}ZrCl2⋅thf] (R=tBu (4), adamantyl (7 a); thf=tetrahydrofuran), [Me2Si{(NAd)(6‐{2‐(diphenylboryl)phenyl}pyridyl‐2‐yl‐N)}ZrCl2] (Ad=adamantyl (7 b)), the nonbridged half‐titanocene complexes of the type [(N‐{6‐(2‐diethylborylphenyl)pyrid‐2‐yl}‐NR)Cp′TiCl2] (R=Me, Cp′=C5H5 (12), Cp′=C5Me5 (13)), and the titanium(IV)‐based metallocene‐type complex [bis{N‐(6‐{2‐(diethylboryl)phenyl}pyrid‐2‐yl)NMe}TiCl2] (14) have been synthesized. The structures of complexes 7 b, 12, and 13 were determined by single‐crystal X‐ray diffraction analysis. In solution, complex 4 slowly rearranges to [Me2Si{(N‐tBu)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐yl‐N)}2Zr] (4 a), the structure of which was unambiguously confirmed by single‐crystal X‐ray crystallography. Similarly, reaction of HfCl4 with Me2Si({RNLi}{6‐[2‐(diethylboryl)phenyl]pyridyl‐2‐ylNLi}) yielded the corresponding HfIV complexes [Me2Si{(NR)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐ylN)}2Hf] (R=tBu (8) and Ad (9)). Upon activation of these complexes with methylalumoxane (MAO), complexes 4, 7 a, 7 b, and 12–14 showed activities up to 750 kg of polyethylene (PE)/molcat. bar h in the homopolymerization of ethylene (E), producing mainly linear PE (high‐density PE, HDPE) with molecular weights in the range of 1 800 000<Mn<4×106 g mol−1. In the copolymerization of E with cyclopentene (CPE), the polymerization activities of complexes 4, 7 a, and 7 b can be enhanced by a factor of 140 up to 7500 kg PE/molcat. bar h, which produced PE‐co‐poly(CPE) containing 3.5 mol % of CPE. This dramatic increase in polymerization activity for E in the presence of CPE can be attributed to an involvement of CPE in the polymerization process rather than to solvent polarity.

Pentamethylcyclopentadienyl Titanium(IV) Amido Pyridylene Phenylene and Pentamethylcyclopentadienyl Titanacyclopropane Amido Complexes and their Behavior in the Polymerization of Ethylene and Cyclic Olefins

“…The diethylboryl group is coordinated to the pyridine N atom (N(2)−B(1)=164.9(9) pm). Compared to that in titanium amido complexes reported previously, the Ti−N bonds in Ti‐1 are substantially longer (201.4(6) pm vs. 186.7–192.59 pm) . By contrast, the Ti−Cl bond lengths in Ti‐1 (225.53(19) pm) are shorter than those in reported for titanium(IV) chloro complexes (226.7–230.3 pm).…”

“…Compared to that in titanium amido complexes reported previously, the Ti−N bonds in Ti‐1 are substantially longer (201.4(6) pm vs. 186.7–192.59 pm) . By contrast, the Ti−Cl bond lengths in Ti‐1 (225.53(19) pm) are shorter than those in reported for titanium(IV) chloro complexes (226.7–230.3 pm). The proposed mechanism for the formation of Ti‐1 from the reaction of 5 b with Cp*TiCl 3 clearly entails the elimination of ClBEt 2 and the formation of the Ti−C bond (Figure S61).…”

“…In contrast to other group 4 metal bisamido complexes that bear the 6‐[2‐(diethylboryl)phenyl]pyridyl‐2‐yl motif, which allowed for a CPE incorporation of <0.5 mol %, the amount of CPE that was incorporated into the copolymers with Ti‐1 /MAO was much higher (5.4 mol %). Along with a higher incorporation of CPE into the copolymer, the T m was decreased to 123 °C.…”

Aminopyridine stabilized group-IV metal complexes and their applications

“…In this polymerization, metal catalyst acts as an active species, while CTA acts as an inactive (dormant) species. In this way, several polymer chains could grow on one catalyst molecule; however, the chain termination process during this polymerization should be negligible [80][81][82]. Thus, polymers of approximately equal chain length with narrow molecular weight distribution are obtained.…”

Group 4 metal complexes bearing the aminoborane motif: origin of tandem ring-opening metathesis/vinyl-insertion polymerization

“…[4][5][6][7][8][9] If successful, this approach would offer an alternative to currently investigated copolymerizations of ethylene with functional monomers such as acrylates. 15,16 Within that context, it also appears desirable to tailor the dissociation temperature of the N-B bond, which is ̴ 60º C for dimethylsilylene-bis(6-[2-(diethylboryl)phenyl]pyrid-2-ylamido)ZrCl 2 (Zr-4) 3 . This proton can then in principle re-add to the metal alkylidene.…”