Highly Selective and Immortal Magnesium Calixarene Complexes for the Ring‐Opening Polymerization of rac‐Lactide. Issue 7 (21st May 2014)

• Record Type: Journal Article
• Authors: Walton, Mark J.; Lancaster, Simon J.; Redshaw, Carl
• Is Part Of: ChemCatChem. Volume 6:Issue 7(2014:Jul.)
• Page Start: 1892
• Page End: 1898
• Publication Date: 2014-05-21
• Subjects: Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201402041
• Languages: English
• ISSNs: 1867-3880

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The lithiation of 1, 3‐dipropoxy‐<italic>p‐tert</italic>‐butylcalix[4]arene (LH₂) followed by reaction with <italic>n</italic>BuMgBr in THF resulted in the formation of the hetero‐bimetallic complex [Li(THF)Mg(<italic>n</italic>Bu)L] (<bold>1</bold>). By contrast, the treatment of tripropoxy‐<italic>p‐tert</italic>‐butylcalix[4]arene (L′H) with <italic>n</italic>Bu₂Mg afforded a mononuclear complex [L′Mg(<italic>n</italic>Bu)] (<bold>2</bold>). Single‐crystal XRD studies revealed that in both structures the calix[4]arene adopts a cone conformation, and a Li cation resides in the cavity for <bold>1</bold>. Both <bold>1</bold> and <bold>2</bold> were active for the ring‐opening polymerisation of <italic>rac‐</italic>lactide. Compound <bold>2</bold> displayed not only exceptional activity (100 equivalents, 3 min, 92 % conversion, BnOH, room temperature) but also high selectivity (probability to form an <italic>r</italic> dyad, <italic>P</italic>_r=0.85) and exhibited an immortal character in THF. Surprisingly, compound <bold>2</bold> also showed isotactic bias (<italic>P</italic>_r=0.30–0.36) and an immortal character if toluene was employed as the solvent; 2 D <italic>J</italic>‐resolved ¹H NMR spectroscopy was employed for the assignment of the stereoselectivity.</p> </abstract>