Abstract

Alkane elimination reactions of β-enaminoketonate ligands OCMeCHCMeN(2,6-Me₂C₆H₃) (1), OCMeCHCMeN(2,6,- ⁱ Pr₂C₆H₃) (2), OCMeCHCMeN(4-^tBu-C₆H₃) (3) with ZnEt₂ afforded bis-chelate and bimetallic zinc com-plexes [(OCMeCHCMeNAr)₂Zn]; Ar = 2,6-Me₂C₆H₃ (4), 2,6- ⁱ Pr₂C₆H₃ (5) and 4- ^t Bu-C₆H₃ (6) in 85–94% yield; and [{OCMeCHCMeN(2,6- ⁱ Pr₂C₆H₃)}ZnEt]₂ (8), [{OCMeCHCMeN(2,6-Me₂-C₆H₃)}ZnEt]₂ (7) and [{OCMeCHCMeN(4- ^t Bu-C₆H₃)}ZnEt]₂ (9) in 50–90% yield. 7–9 are mixed with 4–6, respectively, DFT computations of ¹H chemical shifts allowed the unambiguous assignment of the species in solution. X-ray single crystal analyses of 4, 6, 7–9 showed that 4 and 6 are bis-chelate complexes in which the coordination geometry about zinc is distorted tetrahedral and overall C₂ symmetry. 7–9 are bimetallic complexes in which the coordination geometry about zinc is distorted tetrahedral but with overall S₂ symmetry. The optimized geometry of DFT models 4a and 4b (CH₂Cl₂ as solvent) indicated that the distortion of the geometry in 4 is due in part to the CH₂Cl₂ present in the unit cell. ROP of rac-LA catalyzed by complexes 4–9 and 8-O ⁱ Pr was carried out in toluene solutions. All complexes were active but the best results were obtained with 7–9 and 8-O ⁱ Pr.

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Zinc β-enaminoketonate complexes: synthesis,characterization and ROP of rac -lactide