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Highly Selective and Immortal Magnesium Calixarene Complexes for the Ring‐Opening Polymerization of rac ‐Lactide
Author(s) -
Walton Mark J.,
Lancaster Simon J.,
Redshaw Carl
Publication year - 2014
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201402041
Subject(s) - calixarene , chemistry , ring opening polymerization , stereoselectivity , lactide , polymerization , bimetallic strip , selectivity , tacticity , solvent , deoxygenation , medicinal chemistry , toluene , stereochemistry , ring (chemistry) , polymer chemistry , catalysis , polymer , organic chemistry , molecule
The lithiation of 1,3‐dipropoxy‐ p‐tert ‐butylcalix[4]arene (LH 2 ) followed by reaction with n BuMgBr in THF resulted in the formation of the hetero‐bimetallic complex [Li(THF)Mg( n Bu)L] ( 1 ). By contrast, the treatment of tripropoxy‐ p‐tert ‐butylcalix[4]arene (L′H) with n Bu 2 Mg afforded a mononuclear complex [L′Mg( n Bu)] ( 2 ). 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 1 . Both 1 and 2 were active for the ring‐opening polymerisation of rac‐ lactide. Compound 2 displayed not only exceptional activity (100 equivalents, 3 min, 92 % conversion, BnOH, room temperature) but also high selectivity (probability to form an r dyad, P r =0.85) and exhibited an immortal character in THF. Surprisingly, compound 2 also showed isotactic bias ( P r =0.30–0.36) and an immortal character if toluene was employed as the solvent; 2 D J ‐resolved 1 H NMR spectroscopy was employed for the assignment of the stereoselectivity.