Synthesis and characterization of dimethylbismuth and -indium phenoxy-imine complexes as potential catalysts for the ring opening polymerization of cyclic esters

Abstract

Traditional plastics and polymers, that began to be mass produced in the 1940’s, are petrochemically derived and lack renewability, biodegradability and sustainability. Further, their use and production does not satisfy the principles of “Green Chemistry”. The consequences surrounding the use of plastics can be avoided through the development of biodegradable plastics, or bioplastics. The most extensively studied and industrially available bioplastic is poly(lactic acid), which can be synthesized through the ring opening polymerization (ROP) of cyclic esters. This reaction requires a catalyst, where metal alkoxide species have been found to been effective. However, there are issues of toxicity and high cost related to the species currently being used, which poses an opportunity for new catalyst development. A more environmentally friendly option is using bismuth and indium as metal centres in these catalysts as they are both relatively non-toxic, inexpensive and reactive. Therefore, this research focuses on the synthesis and characterization of novel dimethylbismuth and -indium phenoxy-imine complexes for the ROP of cyclic esters. It was determined that the three target phenoxy-imine supported bismuth complexes can be generated in situ, however, their hydrolytic instability disallows recrystallization of these complexes. Contrastingly, the three target phenoxy-imine indium complexes were all successfully synthesized and characterized by 1H NMR, 13C{1H} NMR, FT-IR and FT-Raman spectroscopy. Indium complexes 5 and 6 have been analyzed by X-ray crystallography.