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Issue 19, 2009
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Bidentate salicylaldiminato tin(ii) complexes and their use as lactide polymerisation initiators

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Abstract

A study of the reactions of several salicylaldimines (ortho-iminophenols) with Sn(NMe2)2 reveals that the sterics and electronics of the N-substituent play a principal role in determining the product mixture. Thus mono(chelate) tin(II) amides have only been isolated with bulky N-anilido substituents, including [2,4-X2–6-{CH[double bond, length as m-dash]N-2,6-iPr2C6H3}-C6H2O]Sn(μ-NMe2)]2, X = Cl, 1; X = I, 2 and [2,4-Cl2–6-{CH[double bond, length as m-dash]N-2,4,6-tBu3C6H2}-C6H2O]Sn(NMe2), 3. With smaller N-aryl and N-alkyl substituted salicylaldimines, mixtures of mono- and bis- chelate complexes are formed, even if the phenoxide ring bears large tert-butyl substituents. Further, when the anilido group bears electron-withdrawing substituents, the imino carbon is activated towards nucleophilic attack (as demonstrated by the formation of [2,4-tBu2–6-{CH(NMe2)N-2,4,6-Br3C6H2}-C6H2O]Sn, 4); no such reactivity has been observed when the halo substituents are located on the phenolic ring. The abilities of complexes 1–4 to initiate the ring-opening polymerisation of rac-lactide have also been studied. Complexes 1, 2 and 4 possess comparitively similar activities, but propagation with 3 is at least one order of magnitude slower, an observation rationalised in terms of steric congestion.

Graphical abstract: Bidentate salicylaldiminato tin(ii) complexes and their use as lactide polymerisation initiators

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Supplementary files

Article information


Submitted
28 Jul 2008
Accepted
14 Nov 2008
First published
17 Mar 2009

Dalton Trans., 2009, 3710-3715
Article type
Paper

Bidentate salicylaldiminato tin(II) complexes and their use as lactide polymerisation initiators

N. Nimitsiriwat, V. C. Gibson, E. L. Marshall and M. R. J. Elsegood, Dalton Trans., 2009, 3710
DOI: 10.1039/B812877D

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