Aminopiperidine based complexes for lactide polymerisation

Herein we report the synthesis and characterisation of a series of salalen and salan ligands derived from 2-(aminomethyl)piperidine. Depending on the choice of starting salicylaldehyde, a bicyclic salan type ligand ( 1-3 H 2 ) or imino salalen type ligand ( 4-6 H, 7-9 H 2 ) were prepared. The ligand...

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Published in:Dalton transactions : an international journal of inorganic chemistry 2016-01, Vol.45 (12), p.5374-5387
Main Authors: McKeown, P, Davidson, M. G, Lowe, J. P, Mahon, M. F, Thomas, L. H, Woodman, T. J, Jones, M. D
Format: Article
Language:English
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Summary:Herein we report the synthesis and characterisation of a series of salalen and salan ligands derived from 2-(aminomethyl)piperidine. Depending on the choice of starting salicylaldehyde, a bicyclic salan type ligand ( 1-3 H 2 ) or imino salalen type ligand ( 4-6 H, 7-9 H 2 ) were prepared. The ligands were successfully complexed to group 4 metals and aluminium; with hafnium and zirconium octahedral complexes, M( 1-3 ) 2 , were realised; whilst with aluminium tetrahedral and trigonal bipyramidal complexes, Al( 1-9 )Me x ( x = 1,2), were isolated. The complexes have been characterised in solution via 1 H and 13 C{ 1 H} NMR spectroscopy and in the solid state by X-ray crystallography. The group 4 complexes were observed to have a fac - fac arrangement of ligands and there were two isomers present when 3 H 2 was ligated. The imino aluminium complexes Al( 7-9 )Me were isolated as a mixture of diastereoisomers. The resultant complexes were trialed in the ring opening polymerisation of rac -lactide with both heterotactic and isotactic PLA being demonstrated. Tacticity was found to be dependent on the nature of the ligand and metal used; the M( 1-3 ) 2 complexes were generally found to have a heterotactic preference ( P r = 0.67-0.76) and the aluminium polymerisation outcome was dictated more by the steric influence of the ligand, particularly for Al( 4 / 6 )Me 2 /Al( 7 / 9 )Me. A series of new ligands based on a 2-(aminomethyl)piperidine motif have been prepared. An interesting diversity in structure is observed, all complexes have been trialled for the polymerisation of rac -lactide.
ISSN:1477-9226
1477-9234
DOI:10.1039/c5dt04695e