The reaction of N,N'-dibenzyl-2-amino-4-imino-pent-2-ene, nacnac(Bn)H, with 1 or 2 equiv. of MgnBu₂ afforded the homoleptic complex nacnac(Bn)₂Mg. The reaction of nacnac(Bn)H with Mg(N(SiMe₃)₂)₂ yielded nacnac(Bn)MgN(SiMe₃)₂, which reacted with tert-butanol to form nacnac(Bn)MgOtBu. The latter complex crystallizes as an alkoxide bridge dimer and is active in the ring-opening polymerisation of rac-lactide. Polymerisations at room temperature afforded atactic polylactide, while polymerisations at -17 and -26 °C afforded polylactide with a small isotactic bias (P(m) = 0.52, and 0.55, respectively).
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The Effect of Alkyl Substituents on the Formation and Structure of Homochiral (*,*)-[RGa(-OCH(Me)COR')] Species-Towards the Factors Controlling the Stereoselectivity of Dialkylgallium Alkoxides in the Ring-Opening Polymerization of -Lactide.
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Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland.
Building on our previous studies, which have demonstrated that homochiral propagating species-(*,*)-[MeGa(-OCH(Me)COR)]-were crucial for the heteroselectivity of [MeGa(-OCH(Me)COMe)] in the ring-opening polymerization (ROP) of racemic lactide (-LA), we have investigated the effect of alkyl groups on the structure and catalytic properties of dialkylgallium alkoxides in the ROP of -LA. Therefore, we have isolated and characterized the -[RGa(-OCH(Me)COMe] (R = Et (), Pr () and -[RGa(-OCH(Me)CHN] (R = Et (), Pr ()) complexes, to demonstrate the effect of alkyl groups on the chiral recognition induced the formation of the respective homochiaral species-(*,*)-[RGa(-OCH(Me)COMe)] and (*,*)-[RGa(-OCH(Me)CHN]. Moreover, we have investigated the structure of (,)-[RGa(-OCH(Me)COMe] (R = Et ((,)-, R = Pr ((,)-,) and their catalytic activity in the ROP of -LA.
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