Yttrium(III) complex as a highly active catalyst for lactide polymerization

The application of Yttrium(III) complex as a S-N-N-S donor ligand for lactide polymerization catalysis was analyzed. The complex was prepared in situ in a quantitative yield, as determined by NMR spectrometry, by the stirring of 1,3-bis(P,P-di-i-propyl thiophosphinic amine)-2,2-dimethylpropane and [Y{N(TMS)2}3] in THF until the ligand signal disappeared from the NMR spectrum. Initial polymerizations were conducted in toluene at 70 °C and at a catalyst concentration of 5mM and showed complete conversion in 10 s. and thus polymerization was rapid to monitor with the conventional aliquot technique. The catalyst used a softer S-N-N-S donor ligand, and the complex showed very fast polymerization rates. The end-group analysis indicated that polymerization proceeds via a coordination insertion mechanism, which leads to a polymer chain terminated with the bis(trimethylsilyl)amide group.