Herein we report the synthesis and characterisation of a series of Zr(IV) 2,2'-bipyrrolidine-salan derived complexes and their exploitation for the ring opening polymerisation of rac-lactide to afford highly isotactically enriched polymers.

In this paper nine various salalen ligands have been prepared and characterised. The steric and electronic effects of both the salen and salan fragments have been varied in a systematic fashion to ascertain how this affects the selectivity for the ROP of rac-lactide. These were complexed to AlMe3 to generate pseudo trigonal bypyramidal metal centred complexes. Upon addition of benzyl alcohol the active initiator can be easily prepared. The complexes were screened for the ROP of rac-lactide in solution and melt conditions. PLA with narrow molecular weight distributions (PDIs range from 1.07-1.67) could be isolated with moderate degrees of tacticity. Significantly it was found that chloro groups on the imine fragment increased the degree of heterotactic enchainment in the polymer. The kinetics for one series of salalen-Al complexes was also investigated.

In this paper a series of eight Ti(IV) piperazine based complexes have been prepared and fully characterised in the solid-state by X-ray crystallography and in solution via NMR spectroscopy. In the solid-state either Ti(2)(L)(O(i)Pr)(6) or Ti(2)(L)(2)(O(i)Pr)(4) were observed depending upon the nature of the starting ligand. For complexes with less sterically demanding ligands (1H(2) and 2H(2)) an equilibrium was observed: 2 Ti(2)(L)(O(i)Pr)(6) ⇔ Ti(2)(L)(2)(O(i)Pr)(4) + 2 Ti(O(i)Pr)(4). The thermodynamic properties (ΔG, ΔH and ΔS) have been investigated via variable temperature NMR spectroscopy. With more sterically demanding ligands (3-8H(2)) the Ti(2)(L)(O(i)Pr)(6) form was the most prevalent in the solid-state and in solution. These complexes have been tested for the production of polylactide under melt and solution conditions with high conversions being obtained.

In this paper we describe the preparation and characterisation, by single‐crystal X‐ray diffraction, of twelve ZrIV/HfIV complexes based on piperazine or homopiperazine salan ligands. With the piperazine ligands, a mixture of species was observed and various solid‐state structures were isolated. However, with homopiperazine salan ligands, 1:1 ligand‐to‐metal complexes were observed both in solution and in the solid state. Interestingly, for the homopiperazine complexes the isopropoxide ligands are trans to one another in the solid state, most likely because of the rigid nature of the homopiperazine backbone. All homopiperazine HfIV and ZrIV complexes were tested for the ring‐opening polymerisation (ROP) of rac‐lactide. The complexes are active and produce polylactide with narrow polydispersity indices. The kinetics and living characteristics of the polymerisation have also been investigated.

In this paper we report the synthesis and full characterisation of a range of Ti(IV)-catecholato systems complexed to piperazine or homopiperazine salan ligands. The steric/electronic environment of the catecholate moiety has been varied and the effect this has on cytotoxicity discussed. It was observed that the 7-membered homopiperazine complexes are more stable to hydrolysis than their piperazine cousins in biological media. In general the homopiperazine complexes show higher cytotoxicity than the piperazine complexes, with the most cytotoxic complex exhibiting IC50 (μM) values of 3 ± 0.5 μM (HT-29) and 4 ± 1 μM (OVCAR).