Controlled ring‐opening polymerization of trimethylene carbonate and access to PTMC‐PLA block copolymers mediated by well‐defined N‐heterocyclic carbene zinc alkoxides. (20th May 2014)

• Record Type: Journal Article
• Authors: Fliedel, Christophe; Mameri, Samir; Dagorne, Samuel; Avilés, Teresa
• Is Part Of: Applied organometallic chemistry. Volume 28:Number 7(2014:Jul.)
• Page Start: 504
• Page End: 511
• Publication Date: 2014-05-20
• Subjects: Organometallic chemistry -- Periodicals; Organometallic compounds -- Periodicals; 547.05
• DOI: 10.1002/aoc.3154
• Languages: English
• ISSNs: 0268-2605

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Four novel Zinc–NHC alkyl/alkoxide/chloride complexes (<bold>4</bold>, <bold>5</bold>, <bold>9</bold> and <bold>9′</bold>) were readily prepared and fully characterized, including X‐ray diffraction crystallography for <bold>5</bold> and <bold>9′</bold>. The reaction of <italic>N</italic>‐methyl‐<italic>N</italic>′‐butyl imidazolium chloride (<bold>3.HCl</bold>) with ZnEt<sub>2</sub> (2 equiv.) afforded the corresponding [(<italic>C</italic><sub>NHC</sub>)ZnCl(Et)] complex (<bold>4</bold>) via a protonolysis reaction, as deduced from NMR data. The <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">alcoholysis</named-content> of <bold>4</bold> with BnOH led to quantitative formation of the dinuclear Zn(II) alkoxide species [(<italic>C</italic><sub>NHC</sub>)ZnCl(OBn)]<sub>2</sub> (<bold>5</bold>), as confirmed by X‐ray diffraction analysis. The NMR data are in agreement with species <bold>5</bold> retaining its dimeric structure in solution at room temperature. The protonolysis reaction of <italic>N</italic>‐(2, 6‐diisopropylphenyl)‐<italic>N</italic>′‐ethyl methyl ether imidazolium chloride (<bold>8.HCl</bold>) with ZnEt<sub>2</sub> (2 equiv.) yielded the [(<italic>C</italic><sub>NHC</sub>)ZnCl(Et)] species <bold>9</bold>. The latter was found to be reactive with CH<sub>2</sub>Cl<sub>2</sub> in solution and to cleanly convert to the corresponding Zn(II) dichloride [(<italic>C</italic><sub>NHC</sub>)ZnCl<sub>2</sub>]<sub>2</sub> (<bold>9′</bold>), whose molecular structure was also elucidated using X‐ray diffractometry. Unlike Zn(II)–NHC alkoxide species <bold>1</bold> and <bold>2</bold>, which contain a NHC flanked with an additional <italic>N</italic>‐functional group (i.e. thioether and ether, respectively), the Zn(II) alkoxide species <bold>5</bold> incorporates a monodentate NHC ligand. The Zn(II) complexes <bold>1</bold>, <bold>2</bold> and <bold>5</bold> were tested in the ring‐opening <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">polymerization</named-content> (ROP) of trimethylene carbonate (TMC). All three species are effective initiators for the controlled ROP of trimethylene carbonate, resulting in the production of narrow disperse PTMC material. Initiator <bold>1</bold> (incorporating a thioether moiety) was found to perform best in the ROP of TMC. Notably, the latter also readily undergoes the sequential ROP of TMC and <italic>rac</italic>‐LA in the presence of a chain‐transfer agent, leading to well‐defined and high‐molecular‐weight PTMC/PLA <named-content content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">block copolymers</named-content>. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>