Salan Group 13 complexes – structural study and lactide polymerisation

Herein the preparation and characterisation of a series of group 13 salan complexes, with a bipyrrolidine or N,N’-ethylenediamine backbone are disclosed. For the bipyrrolidine derived-salan ligand 1H2, the Al(III) and Ga(III) complexes are pseudo trigonal bipyramidal in the solid-state, whereas the In(III) complexes are best described as square based pyramidal structures. However, for the ethylenediamine derived-salan ligand 2H2, all complexes are effectively square based pyramidal in their structure. The complexes’ solution behaviour is also investigated by NMR spectroscopic methods and it is observed that the solid-state structure is maintained in solution. The complexes have all been trialled for the ring opening polymerisation of rac-lactide. With In(1)Cl controlled polymerisation and narrow molecular weight distributions (1.01 – 1.08) are observed with heterotactic polylactide being prepared. Under the conditions tested the Ga(III) and Al(III) complexes were shown to be inactive.