| Summary: | The direct reaction of the highly sterically demanding acetamidinate-based NNN′-scorpionate protioligand Hphbp<sup>t</sup>amd [Hphbp<sup>t</sup>amd = <i>N</i>,<i>N</i>′-di-p-tolylbis(3,5-di-tertbutylpyrazole-1-yl)acetamidine] with one equiv. of ZnMe<sub>2</sub> proceeds in high yield to the mononuclear alkyl zinc complex [ZnMe(<i>κ</i><sup>3</sup>-phbp<sup>t</sup>amd)] (<b>1</b>). Alternatively, the treatment of the corresponding lithium precursor [Li(phbp<sup>t</sup>amd)(THF)] with ZnCl<sub>2</sub> yielded the halide complex [ZnCl(<i>κ</i><sup>3</sup>-phbptamd)] (<b>2</b>). The X-ray crystal structure of <b>1</b> confirmed unambiguously a mononuclear entity in these complexes, with the zinc centre arranged with a pseudotetrahedral environment and the scorpionate ligand in a <i>κ</i><sup>3</sup>-coordination mode. Interestingly, the inexpensive, low-toxic and easily prepared complexes <b>1</b> and <b>2</b> resulted in highly efficient catalysts for the ring-opening polymerisation of lactides, a sustainable bio-resourced process industrially demanded. Thus, complex <b>1</b> behaved as a single-component robust initiator for the living and immortal ROP of <i>rac</i>-lactide under very mild conditions after a few hours, reaching a TOF value up to 5520 h<sup>−1</sup> under bulk conditions. Preliminary kinetic studies revealed apparent zero-order dependence on monomer concentration in the absence of a cocatalyst. The PLA materials produced exhibited narrow dispersity values, good agreement between the experimental <i>M</i><sub>n</sub> values and monomer/benzyl alcohol ratios, as well as enhanced levels of heteroselectivity, reaching <i>P</i><sub>s</sub> values up to 0.74.
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