Abstract
Building on our previous studies, which have demonstrated that homochiral propagating species-(R*,R*)-[Me(2)Ga(µ-OCH(Me)CO(2)R)](2)-were crucial for the heteroselectivity of [Me(2)Ga(µ-OCH(Me)CO(2)Me)](2) in the ring-opening polymerization (ROP) of racemic lactide (rac-LA), we have investigated the effect of alkyl groups on the structure and catalytic properties of dialkylgallium alkoxides in the ROP of rac-LA. Therefore, we have isolated and characterized the rac-[R(2)Ga(µ-OCH(Me)CO(2)Me](2) (R = Et (1), (i)Pr (2) and rac-[R(2)Ga(µ-OCH(Me)C(5)H(4)N](2) (R = Et (3), (i)Pr (4)) complexes, to demonstrate the effect of alkyl groups on the chiral recognition induced the formation of the respective homochiaral species-(R*,R*)-[R(2)Ga(µ-OCH(Me)CO(2)Me)](2) and (R*,R*)-[R(2)Ga(µ-OCH(Me)C(5)H(4)N](2). Moreover, we have investigated the structure of (S,S)-[R(2)Ga(µ-OCH(Me)CO(2)Me](2) (R = Et ((S,S)-1, R = (i)Pr ((S,S)-2,) and their catalytic activity in the ROP of rac-LA. With an increase in the bulkiness of alkyl substituents on gallium the following can be observed: (a) the tendency for the formation of homochiral complexes decreased, (b) the symmetry of homochiral (S,S)-[R(2)Ga(µ-OCH(Me)CO(2)Me](2) (M = Me, Et (S,S)-1), (i)Pr (S,S)-2) changed, and both have resulted in (c) lower or no heteroselectivtity across these complexes in the ROP of rac-LA. Importantly, the results have confirmed the crucial role of the chiral-induced formation of homochiral asymmetric dimers on the heteroselectivity of dialkylgallium alkoxides in the ROP of rac-LA.