Zirconium complexes of bipyrrolidine derived salan ligands for the isoselective polymerisation of rac-lactide.

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.

Heteroleptic titanium(IV) catecholato/piperazine systems and their anti-cancer properties.

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).

Monomeric Ti(IV) homopiperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide.

BACKGROUND: The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics. Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation. Thus, in this paper we report the synthesis and characterisation of a series of monometallic homopiperazine Ti(IV) complexes where we have systematically varied the sterics of the phenol moieties. RESULTS: When the ortho substituent of the ligand is either a Me, tBu or amyl then the ß-cis isomer is isolated exclusively in the solid-state. Nevertheless, in solution multiple isomers are clearly observed from analysis of the NMR spectra. However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution. The complexes have been screened for the polymerisation of rac-lactide in solution and under the industrially preferred melt conditions. Narrow molecular weight material (PDI 1.07 - 1.23) is formed under melt conditions with controlled molecular weights. CONCLUSIONS: Six new Ti(IV) complexes are presented which are highly active for the polymerisation. In all cases atactic polymer is prepared with predictable molecular weight control. This shows the potential applicability of Ti(IV) to initiate the polymerisations.

Aluminium salalen complexes based on 1,2-diaminocyclohexane and their exploitation for the polymerisation of rac-lactide.

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.

Crystallographic characterisation of Ti(IV) piperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide.

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.