The reversible amination of tin(II)-ligated imines:: Latent initiators for the polymerization of rac-lactide

The 1:1 reactions of nine potentially tridentate salicylaldimines with tin(II) diamides, Sn(NR2)(2) (R = Me, Et, Pr-i, SiMe3) have been investigated. With Sn((NPr2)-Pr-i)(2) and Sn(NTMS2)(2), the anticipated products of amine elimination, iminophenoxy tin(II) mono(amide)s, are formed. However, for R = Me and R = Et, nucleophilic attack of the amide at the imino carbon occurs to generate tin(II) complexes of tetradentate, dianionic aminoamidophenoxide ligands. The transfer of the amide is shown to be reversible, with both alcoholysis and the initiation of rac-lactide polymerization apparently mediated by the terminal amide tautomer.