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Use of titanocalix[4]arenes in the ring opening polymerization of cyclic esters

Sun, Ziyue; Zhao, Yanxia; Santoro, Orlando; Elsegood, Mark Robert James; Bedwell, Elizabeth; Zahra, Khadisha; Walton, Alex; Redshaw, Carl

Authors

Ziyue Sun

Yanxia Zhao

Mark Robert James Elsegood

Elizabeth Bedwell

Khadisha Zahra

Alex Walton

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Professor Carl Redshaw C.Redshaw@hull.ac.uk
Professor of Inorganic Materials Chemistry and REF Lead for Chemistry



Abstract

The known dichloride complexes [TiCl2L(O)2(OR)2] (type I: R = Me (1), n-Pr (2) and n-pentyl (3); L(OH)2(OR)2 = 1,3-dialkyloxy-p-tert-butylcalix[4]arene), together with the new complexes {[TiL(O)3(OR)]2(mu-Cl)2}∙6MeCN (R = n-decyl (4∙6MeCN), and [Ti(NCMe)Cl(L(O)3(OR)]∙MeCN (type II: R = Me, 5∙MeCN) are reported. Attempts to prepare type II for R = n-Pr and n-pentyl using [TiCl4] resulted in the complexes {[TiL(O)3(On-propyl)]2(mu-Cl)(mu-OH)} 6∙7MeCN and {[TiL(O)3(On-pentyl)]2(mu-Cl)(mu-OH)}∙7.5MeCN (7∙7.5MeCN), respectively; [TiCl4(THF)2] resulted in a co-crystallized THF ring-opened product [Ti(NCMe)(μ3-O)L(O)4TiCl(O(CH2)4Cl)]2 - 2[TiCl(NCMe)(L(O)3(On-Pr))]∙11MeCN (8∙11MeCN). Type I and II complexes have been screened for their ability to act as catalysts in the ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), delta-valerolactone (delta-VL), omega-pentadecalactone (omega-PDL) and rac-lactide (r-LA), both with and without benzyl alcohol present and either under N2 or in air. The copolymerization of epsilon-CL with delta-VL and with r-LA has also been investigated. For the ROP of epsilon-CL, all were highly active (>99% conversion) at 130 oC over 24 h both under N2 and in air, whilst over 1h, for the type I complexes the trend was 3>2>1 but all were poor (≤12% conversion). By contrast, 5 over 1h at 130 oC was highly active (85% conversion). At 80oC, the activity trend followed the order 5 ≈ 4 > 3 > 2 > 1. For delta-VL, at 80 oC the activity trend 5 ≈ 4 > 1 > 2 > 3 was observed. ROP of the larger omega-PDL was only possible using 5 at 130 oC over 24 h with moderate activity (48 % conversion). For r-LA, only low molecular weight products were obtained, whilst for the co-polymerization of epsilon-CL with delta-VL using 5, high activity was observed at 80 oC affording a polymer of molecular weight > 23,000 and with equal incorporation of each monomer. In the case of epsilon-CL/r-LA co-polymerization using 5 either under N2 or air, the polymerization was more sluggish and only 65% conversion of CL was observed and the resultant co-polymer had 65:35 incorporation. Complex 5 could also be supported on silica, however this system was not as active as its homogeneous counterpart.Finally, the activity of these complexes is compared to that of three benchmark species.

Journal Article Type Article
Journal Catalysis Science & Technology
Print ISSN 2044-4753
Electronic ISSN 2044-4761
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
APA6 Citation Sun, Z., Zhao, Y., Santoro, O., Elsegood, M. R. J., Bedwell, E., Zahra, K., …Redshaw, C. (in press). Use of titanocalix[4]arenes in the ring opening polymerization of cyclic esters. Catalysis science & technology, https://doi.org/10.1039/c9cy02571e
DOI https://doi.org/10.1039/c9cy02571e
Keywords Catalysis
Additional Information : This document is Similarity Check deposited; : Supplementary Information; : Single-blind; : Received 20 December 2019; Accepted 25 January 2020; Accepted Manuscript published 27 January 2020