Titanium complexes bearing oxa- and azacalix[4, 6]arenes: structural studies and use in the ring opening homo-/co-polymerization of cyclic esters.

Xing, Tian; Prior, Timothy J.; Chen, Kai; Redshaw, Carl

Abstract

Reaction of excess [Ti(OiPr)4] with p-tert-butyltetrahomodioxacalix[6]areneH6 (L1H6) afforded, after work-up (MeCN), the complex [Ti2(OiPr)2(MeCN)L1]∙3.5MeCN (1∙3.5MeCN), whilst the oxo complex [Ti4(3-O)2(H2O)(L1)2]∙MeCN (2∙MeCN) was isolated via a fortuitous synthesis involving the use of two equivalents of [Ti(OiPr)4]. Reactions of p-methyl-dimethyldiazacalix[6]areneH6 (L2H6) with [TiF4] (four equivalents), [TiCl4(THF)2] (two equivalents) or [TiBr4] (>four equivalents) resulted in the titanium-based azacalix[n]arene complexes [Ti4F14L2H2(H)2]∙2.5MeCN (3∙2.5MeCN), [Ti2X4(H2O)2OL2H2(H)2] (X = Cl (4∙5MeCN), Br (5∙4.5MeCN) and [Ti4Br12L2(H)2(MeCN)6]∙7MeCN (6∙7MeCN), respectively. Reaction of four equivalents of [TiF4] with L3H4 (L3H4 = p-methyl-dimethyldiazacalix[4]areneH4) afforded the product [Ti2F2(μ-F)3L3(H)2(SiF5)]∙2MeCN (7∙2MeCN). These complexes have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA). Generally, the titanium complexes bearing oxacalixarene exhibited better activities than the azacalixarene-based pre-catalysts. For ε-CL, δ-VL and r-LA, moderate activity at 130 °C over 24 h was observed for 1-6. In the case of the co-polymerization of ε-CL with r-LA, 1-6 afforded reasonable conversions and high molecular weight polymers; 7 exhibited lower catalytic performance due to low solubility. None of the complexes proved to be active in the polymerization of ω-pentadecalactone (ω-PDL) under the conditions employed herein.

Citation

Xing, T., Prior, T. J., Chen, K., & Redshaw, C. (2021). Titanium complexes bearing oxa- and azacalix[4, 6]arenes: structural studies and use in the ring opening homo-/co-polymerization of cyclic esters. Dalton Transactions : an international journal of inorganic chemistry, 50(12), 4396-4407. https://doi.org/10.1039/d1dt00189b

• Journal Article Type: Article
• Acceptance Date: Mar 4, 2021
• Online Publication Date: Mar 5, 2021
• Publication Date: Mar 5, 2021
• Deposit Date: Mar 6, 2021
• Publicly Available Date: Mar 8, 2021
• Journal: Dalton Transactions
• Print ISSN: 1477-9226
• Electronic ISSN: 1477-9234
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 50
• Issue: 12
• Pages: 4396-4407
• DOI: https://doi.org/10.1039/d1dt00189b
• Keywords: Inorganic Chemistry
• Public URL: https://hull-repository.worktribe.com/output/3737748