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Issue 7, 2010
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Reverse orders of reactivities in the polymerization of cyclic esters using N2O2 aluminium alkoxide complexes

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Abstract

Three aluminium alkoxide complexes containing N2O2 bis(phenoxy)-amine ligands were synthesized from reactions of the corresponding N2O2 ligands with Al(OiPr)3 in toluene. Different amine side chains of the ligands included pyridine (1), CH2NMe2 (2), and CH2NEt2 (3). The related chloro aluminium analog (4) was prepared from a reaction between AlCl3 and the potassium salt of the N2O2 ligand having CH2NMe2 side chain. X-Ray crystallography reveals that complexes 3 and 4 have a monomeric five-coordinate aluminium center. Complexes 1–3 catalyzed the polymerization of ε-caprolactone (ε-CL) at 70 °C in toluene with the relative reactivities of 1 < 2 < 3. In contrary, only complex 1 was active for the polymerization of lactide under the same polymerization conditions. 1H NMR spectroscopy shows that treatment of 2 with 1 equivalent of lactide afforded the ring-opened product L2Al-OCH(Me)C(O)OCH(Me)C(O)OiPr. Electronic effects are believed to be responsible for the observed trend in the ε-CL polymerization rates. On the other hand, steric hindrance at the amine side chain is the main contributor to the observed rates of lactide polymerization.

Graphical abstract: Reverse orders of reactivities in the polymerization of cyclic esters using N2O2 aluminium alkoxide complexes

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Publication details

The article was received on 17 Sep 2009, accepted on 18 Nov 2009 and first published on 23 Dec 2009


Article type: Paper
DOI: 10.1039/B919340E
Citation: Dalton Trans., 2010,39, 1865-1871
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    Reverse orders of reactivities in the polymerization of cyclic esters using N2O2 aluminium alkoxide complexes

    K. Phomphrai, P. Chumsaeng, P. Sangtrirutnugul, P. Kongsaeree and M. Pohmakotr, Dalton Trans., 2010, 39, 1865
    DOI: 10.1039/B919340E

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