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Issue 27, 2015
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Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands

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Abstract

A series of alkyl organoaluminium complexes based on bulky heteroscorpionate ligands were designed as catalysts for the ring-opening polymerisation of cyclic esters. Thus, the treatment of AlX3 (X = Me, Et) with bulky acetamide or thioacetamide heteroscorpionate ligands nbptamH (1) [nbptamH = N-naphthyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide], fbpamH (2) [fbpamH = N-fluorenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide], ptbptamH (3) [ptbptamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ntbptamH (4) [ntbptamH = N-naphthyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ptbpamH (5) [ptbpamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] and (S)-mtbpamH (6) [(S)-mtbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] for 1 hour at 0 °C afforded the dialkyl aluminium complexes [AlX22-nbptam}] (X = Me 7, Et 8), [AlX22-fbpam}] (X = Me 9, Et 10), [AlX22-ptbptam}] (X = Me 11, Et 12), [AlX22-ntbptam}] (X = Me 13, Et 14), [AlX22-ptbpam}] (X = Me 15, Et 16) and [AlX22-(S)-mtbpam}] (X = Me 17, Et 18). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structure of 14 was also established. The alkyl-containing aluminium complexes 7–18 can act as efficient single-component initiators for the ring-opening polymerisation of ε-caprolactone and rac-lactide. The polymerisations are living, as evidenced by the narrow polydispersities of the isolated polymers and the linear nature of the number average molecular weight versus conversion plot. Finally, a comparative study of ring-opening polymerisation for new bulky heteroscorpionate aluminium initiators and the less congested aluminium analogues is reported.

Graphical abstract: Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands

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Supplementary files

Article information


Submitted
12 Nov 2014
Accepted
12 Dec 2014
First published
12 Dec 2014

Dalton Trans., 2015,44, 12388-12400
Article type
Paper
Author version available

Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands

J. A. Castro-Osma, C. Alonso-Moreno, A. Lara-Sánchez, A. Otero, J. Fernández-Baeza, L. F. Sánchez-Barba and A. M. Rodríguez, Dalton Trans., 2015, 44, 12388
DOI: 10.1039/C4DT03475A

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