Crystallographic characterisation of novel Zn(II) silsesquioxane complexes and their application as initiators for the production of polylactide

Herein, the solid state structures of the products from the reaction of the silsesquioxane triol (iso-C4H9)7Si7O12(OH)3 (1) with two equivalents of ZnMe2 in both THF and toluene are reported. In both cases tetrametallic Zn(II) complexes were isolated, with toluene [(iso-C4H9)7Si7O12]2Zn4Me2 (2) was prepared while performing the reaction in THF the analogous complex [(iso-C4H9)7Si7O12]2Zn4Me2(THF)2 (3) was formed. Both species have also been characterised via1H, 13C{1H} and 29Si{1H} NMR spectroscopy, which confirm the solid state structures are maintained in solution. Both 2 and 3 show modest activities for the polymerisation of rac-lactide and a heterogeneous catalyst has also been prepared.

Graphical abstractThe crystal structures of two novel Zn(II) silsesquioxane complexes are reported together with the free trisilanol. The complexes have a unique tetrametallic Zn(II) core, with almost perpendicular four membered Zn2O2 rings. The outer zinc atoms have a coordinated methyl group. These complexes and a heterogeneous catalyst have been trialled for the polymerisation of rac-lactide.Figure optionsDownload full-size imageDownload as PowerPoint slide