Enhancing the stereoselectivity of MeGaOR(NHC) species in the ring-opening polymerization of -lactide, with the help of the chelation effect.

Using dialkylgallium alkoxides with N-hetrocyclic carbenes (MeGaOR(NHC)) for the ring-opening polymerization of -lactide, we have demonstrated the effect of the chelate interaction between the growing PLA chain and gallium on the stereoselectivity of dialkylgallium alkoxide propagating species - MeGa(OPLA)(NHC). In order to do so, we have conducted the structure-activity studies of both MeGa(OCHCHOMe)(NHC) (NHC = SIMes (1) and IMes (2)) and MeGa(OCH(Me)COMe)(NHC) (NHC = SIMes (3) and IMes (4)), the latter mimicking active species in the ROP of lactide with growing PLA chain. Based on VT NMR and FTIR spectroscopy, the effect of toluene, CHCl and THF on the structure of 3 and 4 have been demonstrated, especially with regard to the interaction of methyl lactate ligand with gallium.