| Abstract
| - The syntheses, structures, and lactide polymerization initiation are reported for a series of novel [{N,N‘-1,3-bis(P,P‘-di-isopropyloxophosphinic)-2,2-dimethylpropylenediamido}(amido)yttrium] complexes and contrasted with [{N,N‘-1,3-bis(P,P‘-di-isopropylthiophosphinic)-2,2-dimethylamido}{bis(trimethylsilyl)amido}yttrium].
- The syntheses, structures, and lactide polymerization initiation are reported for a series of novel [{N,N‘-1,3-bis(P,P‘-di-isopropyloxophosphinic)-2,2-dimethylpropylenediamido}(amido)yttrium] complexes andcontrasted with [{N,N‘-1,3-bis(P,P‘-di-isopropylthiophosphinic)-2,2-dimethylamido}{bis(trimethylsilyl)amido}yttrium]. The syntheses of the novel [{N,N‘-1,3-bis(P,P‘-di-isopropyloxo/thiophosphinic)-2,2-dimethylpropylenediamido}(amido)yttrium] complexes were achieved in excellent yields by reaction ofthe N,N‘-1,3-bis(P,P‘-di-isopropyloxo/thiophosphinic)-2,2-dimethylpropylenediamine ligands with [Y(NR2)3·xTHF] (R = SiMe3, SiMe2H, i-Pr, x = 0, 2). The new complexes were characterized by NMR and IR spectroscopies, elemental analyses, and for R = SiMe2H X-ray crystallography. The solution and solid-statestructures were compared using 2D NMR techniques and in particular using pulsed gradient spin echospectroscopy (PGSE) to derive the solution hydrodynamic radius and compare it to that calculated fromthe X-ray crystal structure: the [{N,N‘-bis(P,P‘-di-isopropyloxophosphinic)-2,2-dimethylpropylenediamido}(amido)yttrium] complexes were all dimeric in both the solid state and solution. They showed unusualstructures where each ligand has one oxophosphinic group bonded to a single yttrium center and oneoxophosphinic group bonded to two yttrium centers. The new complexes were tested as lactidepolymerization initiators; they all showed very high activities. The degree of polymerization controlexerted by the novel initiators was related to the size of the initiating amide group and the structure ofthe complex.
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