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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

Authors

Tian Xing

Kai Chen

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



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

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