Controlled hydrolysis of [Ti(O-2,4,6-Br3C6H2)2(O-iPr)2]2: Synthesis, structural characterization and studies on bulk polymerization of cyclic esters and lactide

摘要

Controlled hydrolysis of [Ti(O-2,4,6-Br3C6H2)2(O-iPr)2]2 with water results in the formation of the Ti-oxo cluster Ti8O24C66H58Br_(24) (1). This compound has a very interesting cage structure. The crystal structure consists of centrosymmetric neutral octamers containing two planar Ti4 layers, interlinked by four linear oxo-bridges. The four independent Ti atoms have three different coordination environments. The four unique Ti centers are rigidly coplanar, giving a unique configuration. The bridging oxygen atoms linking the two inversion-center related Ti atoms give a novel assemblage reminiscent of an inverse "cake-plate". Compound 1 is an active initiator for the polymerization of cyclic ester monomers and lactide resulting in polymers with moderate number average molecular weights (Mn) and close to narrow molecular weight distribution (MWD).