DOI: 10.1002/cplu.201300378 Access to Ultra-High-Molecular Weight Poly(ethylene) and Activity Boost in the Presence of Cyclopentene With Group 4 Bis-Amido Complexes Gurram Venkata Narayana, [a] Guangjuan Xu, [a] Dongren Wang, [a] Wolfgang Frey, [b] and Michael R. Buchmeiser* [a, c] Introduction Olefin polymerization by homogeneous transition-metal com- plexes is considered to be a mature field of polymer chemistry, especially when using early-transition metals. [1–6] Over the past twenty years it has emerged that Group 4 transition-metal complexes containing amide ligands are promising systems in olefin polymerization catalysis. [2] In particular, a large number of metallocene complexes have been developed for the co- polymerization of ethylene (E) with cycloolefins. [7, 8] Metallocene catalysts, particularly zirconium complexes, are effective cata- lytic systems for the copolymerization of E with different cyclo- olefins such as norborn-2-ene (NBE) or cyclopentene (CPE). [1] The copolymerization of E with NBE has been investigated with various metallocene catalysts, and the resulting polymers were found to be amorphous solids with high transparency. [2–7] Compared to C 2 -symmetric catalyst systems, for example, [Me 2 Si(Ind) 2 ZrCl 2 ] or [Ph 2 Si(Ind) 2 ZrCl 2 ] (Ind = indenyl), C s -sym- metric catalyst systems, for example, [Me 2 C(Flu)(C 5 H 5 )ZrCl 2 ] or [Ph 2 C(Flu)(C 5 H 5 )ZrCl 2 ] (Flu = 9-fluorenyl), are well suited for the synthesis of amorphous copolymers with high glass-transition temperatures (T g  1808). [8] Nomura et al. [9, 10] reported on non- bridged (anilido)(cyclopentadienyl)titanium(IV) complexes of the type [{N(2,6-Me 2 C 6 H 3 )(R)}Cp’TiCl 2 ] (Cp’ = C 5 Me 5 , 1,3-Me 2 C 5 H 3 , (C 5 H 5 )Cp; R = SiMe 3 ) for olefin polymerization, in which [(C 5 Me 5 )TiCl 2 {N(2,6-Me 2 C 6 H 3 )(SiMe 3 )}], in particular, exhibited moderate activity (180 kg PE/mol cat. bar h) in E polymerization. In the copolymerization of E with NBE by various nonbridged (aryloxo)(cyclopentadienyl)TiCl 2 -type complexes of the general formula [Cp’TiCl 2 (OAr)] (Cp’ = indenyl, C 5 Me 5 , tBuC 5 H 4 , 1,2,4- Me 3 C 5 H 2 ; OAr = O-2,6-(2-Pr) C 6 H 3 ) the catalytic activity and in- corporation of NBE was found to be highly dependent on the substituent on the cyclopentadienyl ring. In particular, indenyl- based Ti complexes showed high activity and efficient incorpo- ration of NBE in PE-co-poly(NBE). These complexes were also active in the copolymerization of ethylene with CPE, however, incorporation of CPE was less effective than that of NBE. [2, 11] We recently reported on [Me 2 Si(h 5 -Me 4 C 5 )(6-{2-(diethylboryl)- phenyl}pyrid-2-ylamido)TiCl 2 ], [12] [Me 2 Si(DbppN) 2 ZrCl 2 ·thf] (thf = Zr IV complexes of the type [Me 2 Si{(NR)(6-{2-(diethylboryl)phe- nyl}pyridyl-2-yl-N)}ZrCl 2 ·thf] (R = tBu (4), adamantyl (7a); thf = tetrahydrofuran), [Me 2 Si{(NAd)(6-{2-(diphenylboryl)phenyl}pyrid- yl-2-yl-N)}ZrCl 2 ] (Ad = adamantyl (7b)), the nonbridged half-tita- nocene complexes of the type [(N-{6-(2-diethylborylphenyl)pyr- id-2-yl}-NR)Cp’TiCl 2 ] (R = Me, Cp’ = C 5 H 5 (12), Cp’ = C 5 Me 5 (13)), and the titanium(IV)-based metallocene-type complex [bis{N- (6-{2-(diethylboryl)phenyl}pyrid-2-yl)NMe}TiCl 2 ](14) have been synthesized. The structures of complexes 7b, 12, and 13 were determined by single-crystal X-ray diffraction analysis. In solu- tion, complex 4 slowly rearranges to [Me 2 Si{(N-tBu)(6-{2-(dieth- ylboryl)phenyl}pyridyl-2-yl-N)} 2 Zr] (4a), the structure of which was unambiguously confirmed by single-crystal X-ray crystal- lography. Similarly, reaction of HfCl 4 with Me 2 Si({RNLi}{6-[2-(di- ethylboryl)phenyl]pyridyl-2-ylNLi}) yielded the corresponding Hf IV complexes [Me 2 Si{(NR)(6-{2-(diethylboryl)phenyl}pyridyl-2- ylN)} 2 Hf] (R = tBu (8) and Ad (9)). Upon activation of these com- plexes with methylalumoxane (MAO), complexes 4, 7a, 7b, and 12–14 showed activities up to 750 kg of polyethylene (PE)/mol cat. bar h in the homopolymerization of ethylene (E), producing mainly linear PE (high-density PE, HDPE) with mo- lecular weights in the range of 1 800 000 < M n < 410 6 g mol 1 . In the copolymerization of E with cyclopentene (CPE), the poly- merization activities of complexes 4, 7a, and 7b can be en- hanced by a factor of 140 up to 7500 kg PE/mol cat. bar h, which produced PE-co-poly(CPE) containing 3.5 mol % of CPE. This dramatic increase in polymerization activity for E in the pres- ence of CPE can be attributed to an involvement of CPE in the polymerization process rather than to solvent polarity. [a] Dr. G. V. Narayana, G. Xu, Dr. D. Wang, Prof. Dr. M. R. Buchmeiser Institut für Polymerchemie Lehrstuhl für Makromolekulare Stoffe und Faserchemie Universität Stuttgart Pfaffenwaldring 55, 70569 Stuttgart (Germany) Fax: (+ 49) 711-685-64050 E-mail : michael.buchmeiser@ipoc.uni-stuttgart.de [b] Dr. W. Frey Institut für Organische Chemie Universität Stuttgart Pfaffenwaldring 55, 70569 Stuttgart (Germany) [c] Prof. Dr. M. R. Buchmeiser Institut für Textilchemie und Chemiefasern (ITCF) Kçrschtalstrasse 26, 73770 Denkendorf (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201300378.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPlusChem 2014, 79, 151 – 162 151 CHEMPLUSCHEM FULL PAPERS