Synthesis and characterization of zinc ketoiminate and zinc alkoxide-/phenoxide-ketoiminate complexes

Dimeric methylzinc ketoiminate complexes bis{4-[(2,6-diisopropylphenyl) imido]pentan-1-one}methylzinc, [{L1}ZnMe]2, and bis{1-phenyl-3[(2,6-diisopropylphenyl)imido]butan-1-one}methylzinc, [{L 2}ZnMe]2 have been synthesized and completely characterized along with the homoleptic zinc complex bis{1-phenyl-3[(2,6- diisopropylphenyl)imido]butan-1-one}zinc, [{L2}2Zn] by means of single-crystal X-ray structure analysis and NMR spectroscopy. The related dimeric zinc phenoxide-ketoiminate complexes [{L3}Zn] 2·(dmso)2, [{L4}Zn]2· (dmso)2, [{L5}Zn]2·(dmso)2, [{L6}Zn]2·(dmso)2 and [{L 4}Zn]2·(hmpa)2 (dmso = dimethyl sulfoxide; hmpa = hexamethylphosphoramide) have also been synthesized along with the tetrameric zinc alkoxide-ketoiminate complex [{L7}Zn] 4. In preliminary studies the complexes described in this report were assessed for their activity in the ring-opening polymerization of rac-lactide, either in the solution state (in the presence of benzyl alcohol initiator), or under industrially preferred melt conditions (130 °C no solvent). It could be shown that these compounds are able to act as initiators for lactide polymerization, with molecular weights (Mn) of up to 102050 g/mol.