Insights into the structures adopted by titanocalix[6 and 8]arenes and their use in the ring opening polymerization of cyclic esters

Santoro, Orlando; Elsegood, Mark Robert James; Bedwell, Elizabeth; Pryce, Jake; Redshaw, Carl

Abstract

Interaction of p-tert-butylcalix[6]areneH6, L1H6, with [TiCl4] afforded the complex [Ti2Cl3(MeCN)2(OH2)(L1H)][Ti2Cl3(MeCN)3(L1H)]∙4.5MeCN (1∙4.5MeCN), in which two pseudo octahedral titanium centres are bound to one calix[6]arene. A similar reaction but employing THF resulted in the THF ring-opened product [Ti4Cl2(μ3-O)2(NCMe)2(L)2(O(CH2)4Cl)2]∙4MeCN (2∙4MeCN), where LH4 = p-tert-butylcalix[4]areneH4. Interaction of L1H6 with TiF4 (3 equiv.) led, after work-up, to the complex [(TiF)2(μ -F)L1H]2∙6.5MeCN (3∙6.5MeCN). Treatment of p-tert-butylcalix[8]areneH8, L2H8, with [TiCl4] led to the isolation of the complex [(TiCl)2(TiClNCMe)2(μ3-O)2(L2)]∙1.5MeCN (4∙1.5MeCN). From a similar reaction, a co-crystallized complex [Ti4O2Cl4(MeCN)2(L2)][Ti3Cl6(MeCN)5(OH2)(L2H2)]·H2O∙11MeCN (5·H2O 11MeCN) was isolated. Extension of the L2H8 chemistry to [TiBr4] afforded, depending on the stoichiometry, the complexes [(TiBr)2(TiBrNCMe)2(μ3-O)2(L2)]∙6MeCN (6∙6MeCN) or [Ti(NCMe)2Br]2[Ti(O)Br2(NCMe)](L2)]∙7.5MeCN (7∙7.5MeCN), whilst use of [TiF4] afforded complexes containing Ca2+ and Na+, thought to originate from drying agents, namely [Ti8CaF20(OH2)Na2(MeCN)4(L2)2]∙14MeCN (8∙14MeCN), [Na(MeCN)2][Ti8CaF20NaO16(L2)2]∙7MeCN (9∙7MeCN) or [Na]6[Ti8F20Na(MeCN)2(L2)][Ti8F20Na(MeCN)0.5(L2)]∙15.5(C2H3N) (10∙15.5MeCN). In the case of TiI4, the ladder [(TiI)2(TiINCMe)2(μ3-O)2(L2)]∙7.25CH2Cl2 (11∙7.25CH2Cl2) was isolated. These complexes have been screened for their potential to act as catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA), both in air and N2. For ε-CL and δ-VL, moderate activity at 130 oC over 24 h was observed for 1, 9 and 11; for r-LA, only 1 exhibited reasonable activity. In the case of the co-polymerization of ε-CL with δ-VL, the complexes 1 and 11 afforded reasonable conversions and low molecular weight polymers, whilst 4, 6, and 9 were less effective. None of the complexes proved to be active in the co-polymerization of ε-CL and r-LA under the conditions employed herein.

Citation

Santoro, O., Elsegood, M. R. J., Bedwell, E., Pryce, J., & Redshaw, C. (2020). Insights into the structures adopted by titanocalix[6 and 8]arenes and their use in the ring opening polymerization of cyclic esters. Dalton Transactions : an international journal of inorganic chemistry, 49(34), 11978-11996. https://doi.org/10.1039/d0dt02130j

• Journal Article Type: Article
• Acceptance Date: Aug 7, 2020
• Online Publication Date: Aug 10, 2020
• Publication Date: Sep 14, 2020
• Deposit Date: Aug 10, 2020
• Publicly Available Date: Aug 10, 2020
• Journal: Dalton Transactions
• Print ISSN: 1477-9226
• Electronic ISSN: 1477-9234
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 49
• Issue: 34
• Pages: 11978-11996
• DOI: https://doi.org/10.1039/d0dt02130j
• Keywords: Inorganic Chemistry
• Public URL: https://hull-repository.worktribe.com/output/3556805
• Publisher URL: https://pubs.rsc.org/en/content/articlelanding/2020/DT/D0DT02130J#!divAbstract