Hessen, Bart

Meppelder, Geert-Jan

Ringelberg, Stephanie N.

Teuben, Jan H.

English

Incorporation of heteroatom functionalities in the catalytic formation of polyolefin materials can be accomplished either by copolymerization of the olefin with an olefinic substrate that has a heteroatom-containing substituent, or by using a heteroatom-containing chain-transfer agent. In the first case the functionalities introduced are located in side-groups on the polyolefin backbone, in the second case the functionality will cap the polymer on one end of the chain. The latter strategy has been applied recently using chain-transfer agents with reactive X-H bonds (X = Si, B) in conjunction with group 3 and group 4 metal catalysts. We have sought to apply the capacity of lanthanide metallocenes to perform ethene polymerization as well as C-H activation to this chemistry, using heteroatom-containing hydrocarbons with activated C-H bonds as chain-transfer agents, and to compare this with analogous cationic group 4 metallocenes

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   University of GroningenSynthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metalcatalystsHessen, Bart; Ringelberg, Stephanie N.; Meppelder, Geert-Jan; Teuben, Jan H.Published in:Abstracts of Papers of the American Chemical SocietyIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2000Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Hessen, B., Ringelberg, S. N., Meppelder, G-J., & Teuben, J. H. (2000). Synthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metal catalysts. Abstracts of Papers of theAmerican Chemical Society, 219, U361-U361.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Synthesis of heteroatom end-functionalized polyethene withlanthanide and transition-metal catalystsBart Hessen, Stephanie N. Ringelberg,Geert-Jan Meppelder and Jan H. TeubenCenter for Catalytic Olefin Polymerization, Stratingh Institute, University ofGroningen, Nijenborgh 4, NL-9474 AG Groningen, NetherlandsIntroductionIncorporation of heteroatom functionalities in the catalytic formation ofpolyolefin materials can be accomplished either by copolymerization of theolefin with an olefinic substrate that has a heteroatom-containing substituent,or by using a heteroatom-containing chain-transfer agent. In the first case thefunctionalities introduced are located in side-groups on the polyolefinbackbone, in the second case the functionality will cap the polymer on oneend of the chain. The latter strategy has been applied recently using chain-transfer agents with reactive X-H bonds (X = Si,1 B2) in conjunction withgroup 3 and group 4 metal catalysts. We have sought to apply the capacity oflanthanide metallocenes to perform ethene polymerization as well as C-Hactivation3 to this chemistry, using heteroatom-containing hydrocarbons withactivated C-H bonds as chain-transfer agents,4 and to compare this withanalogous cationic group 4 metallocenes.Results and DiscussionThe compounds [Cp*2LnH]2 (Cp* = η5-C5Me5; Ln = Y, 1a; La, 1b) areknown to polymerize ethene readily to high molecular weight HDPE.3 Thesecompounds also readily activate the ortho-CH bonds of the heteroaromaticspyridine, furan and thiophene to give Cp*2Ln(2-C5H4N) (2a,5b) and[Cp*2Ln(2-C4H3X)]n (X = O, 3a,6b; X = S, 4a,4,6b4; n = 2). These systemsshould therefore in principle be suited to the type of polymerization/chaintransfer chemistry described above.Pyridine.  Our group observed previously that the Y-pyridyl 2a readilyinserts one molecule of ethene into the Y-C bond, but that subsequentinsertions are extremely slow (only a very slow formation of 2-ethylpyridinewas observed with ethene and excess pyridine).5 The La-derivative essentiallyshows the same chemistry. This is due to the strong intramolecularcoordination of the pyridyl nitrogen in the product of the first ethene insertion.Only in the presence of H2 were good conversions to 2-ethyl- and 2,6-diethylpyridine observed. Thus the reactivity of these systems is similar to thatof the cationic zirconocene system studied by Jordan et al.7 Dihydrogen isneeded to cleave the M-C bond of the stable chelate complex that results fromthe first ethene insertionFuran.  The oxygen in furan is less Lewis basic than the oxygen in THFor the nitrogen in pyridine. This is seen by the fact that coordination of furanto the Y-furyl 3a is readily reversible. This should facilitate multiple etheneinsertions into the metal carbon bond of 3. However, the use of this substrateas chain-transfer agent is prevented by another feature of its reactivity. It turnsout that the furyl C-H and C-O bonds are sufficiently reactive to let 3adecompose in solution even at ambient temperature to give furan and acompound with the stoichiometry [Cp*2Y]2(C4H2O). NMR spectrocopysuggests that cleavage of one of the furyl C-O bonds has occurred. An X-raystructure determination of the product is in progress.Thiophene.  The sulfur in thiophene is again less Lewis basic than theheteroatoms in the other substrates. This is seen by the fact that the 2-thienylcompounds 4 are dimeric, but do not give observable thiophene adducts insolution. These compounds are now stable in solution up to 100°C. Thereactivity of the yttrium complex 4a is rather sluggish, but even with asubstituted olefin (1-butene) very slow catalytic formation of 2-sec-butylthiophene was observed. The more reactive La-derivative 4b now readilyforms low molecular weight end-functionalized polyethene H(CH2CH2)n(2-C4H3S) at 80°C even in neat thiophene.The nature of this material was evident from its NMR spectra, and the1H NMR spectrum in C2D2Cl4 solvent is shown in Figure 1a. The integral ratiobetween the α-CH2 protons and the methyl end-group show that each polymerchain has one methyl and one 2-thienyl end-group. In this spectrum two smalladditional resonances are observed at around δ 6.6 (s) and δ 2.8 (t) ppm.These are attributed to a small amount of 2,6-di(n-alkyl)thiophene that can beformed by metallation and subsequent alkylation of the reactive C-H bond onthe 5-position of the 2-alkylthiophene. Performing a similar reaction in neat 2-methylthiophene corroborated this. The 1H NMR spectrum of this polymer isshown in Figure 1b. The resonances of the furyl aromatic protons and the α-CH2 protons in this polymer correspond well to those of the small additionalresonances seen in Figure 1a.Figure 1.  1H NMR spectra (C2D2Cl4, 95°C) of (a, top) H(CH2CH2)n-2-C4H3Sand (b, bottom) H(CH2CH2)-2-(5-Me-C4H2S), prepared with catalyst 4b inneat thiophene and 2-methylthiophene respectively.The catalyst activity of 4b is modest, but its catalyst stability isexcellent. In neat thiophene at 80°C, 7.5 bar ethene pressure and a run time of2 h the productivity is 27 kg mol-1 h-1, giving a low polymer with an Mn of 950(by NMR). The activity and molecular weight can be increased by decreasingthe concentration of thiophene. In a 10:90 volume% thiophene-toluenemixture under otherwise identical conditions the productivity of 4b is 102 kgmol-1 h-1 of a polymer with an Mw of 3330 (Mw/Mn = 2.0, by GPC). Thissuggests there is noticeable inhibition of the reactivity by thiophene, probablyby reversible coordination to the metal center. This appears to be corroboratedby comparable experiments that are performed in neat thiophene and neat 2-methylthiophene. At 2.5 bar ethene pressure (80°C, 2 h run time) theproductivity in thiophene (5.0 kg mol-1 h-1) is half of that in 2-methylthiophene (10.4 kg mol-1 h-1), but the product Mn is similar (700 vs740). It is likely that the sterically more hindered 2-substituted thiophene is aless efficient inhibitor.Polymer Preprints 2000, 41(1), 397Zirconocene catalyst.  In order to compare the reactivity of theneutral lanthanum catalyst with a representative of the well-known cationicgroup 4 metallocene olefin polymerization catalysts, we have performed somesimilar experiments with the [Cp*2ZrMe][MeB(C6H5)3]8 catalyst. In neatthiophene at 80°C and 2.5 bar ethene pressure (2 h run time) this systemproduced polyethene with an Mw of 12600 (Mw/Mn = 2.4 by GPC) and aproductivity of 17 kg mol-1 h-1. 1H NMR spectroscopy of this product showedpredominantly olefinic end-groups, and only a small amount of thienyl end-capped chains. This suggests that with the zirconium catalyst used here, C-Hactivation cannot effectively compete with β-H transfer as chain transfermechanism.ConclusionsThe cleavage of activated C-H bonds of thiophenes can be used as chaintransfer mechanism in the catalytic polymerization of ethene by alanthanocene catalyst. This yields polyethene (of a relatively low molecularweight) that is selectively capped on one end with a thienyl functionality.Thus far, only thiophene and substituted derivatives have been successful aschain-transfer agents, as pyridine and furan were found to be either too Lewisbasic or too reactive, leading to catalyst deactivation. A first experiment usinga cationic zirconocene catalyst revealed that this too can produce polyethenein neat thiophene, but in this case thiophene C-H activation cannot competeeffectively with the usual route for chain transfer, β-H elimination.Acknowledgement.  This research has been financially supported by theCouncil for Chemical Sciences of the Netherlands Foundation for ScientificResearch (CW-NWO).References(1) (a) Fu, P.-F.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 10747. (b) Koo,K.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 4019.(2)  Xu, G; Chung, T. C. J. Am. Chem. Soc. 1999, 121, 6763.(3) (a) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51. (b)Jeske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann, H.;Marks, T. J. J. Am. Chem. Soc. 1985, 107, 8091.(4) Ringelberg, S. N.; Meetsma, A.; Hessen, B.; Teuben, J. H. J. Am. Chem.Soc. 1999, 121, 6082.(5) Deelman, B.-J.; Stevels, W. M.; Teuben, J. H.; Lakin, M. T.; Spek, A. L.Organometallics 1994, 13, 3881.(6) Deelman, B.-J.; Booij, M.; Meetsma, A.; Teuben, J. H.; Kooijman, H.;Spek, A. L. Organometallics 1995, 14, 2306.(7) Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1989, 111, 778.(8) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113, 3623.(9) Storey, R.F.; Chisholm, B.J.; Brister, L.B. Macromolecules 1995, 28,4055.Polymer Preprints 2000, 41(1), 398

Synthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metal catalysts

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Synthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metal catalysts

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