Phenoxide and alkoxide complexes of Mg, Al and Zn, and their use for the ring-opening polymerization of ϵ-caprolactone with initiators of different natures

A new packing polymorph of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(tetrahydrofuran-κO)magnesium, [Mg(C₁₅H₂₃O)₂(C₄H₈O)₂] or Mg(BHT)₂(THF)₂, (BHT is the 2,6-di-tert-butyl-4-methylphenoxide anion and THF is tetrahydrofuran), (1), has the same space group (P2₁) as the previously reported modification [Nifant'ev et al. (2017d). Dalton Trans. 46, 12132–12146], but contains three crystallographically independent molecules instead of one. The structure of (1) exhibits rotational disorder of the tert-butyl groups and positional disorder of a THF ligand. The complex of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(μ₂-ethyl glycolato-κ² O,O′:κO)dimethyldialuminium, [Al₂(CH₃)₂(C₄H₇O₃)₂(C₁₅H₂₃O)₂] or [(BHT)AlMe(OCH₂COOEt)]₂, (2), is a dimer located on an inversion centre and has an Al₂O₂ rhomboid core. The 2-ethoxy-2-oxoethanolate ligand (OCH₂COOEt) displays a μ₂-κ² O,O′:κO semi-bridging coordination mode, forming a five-membered heteronuclear Al–O–C–C–O ring. The same ligand exhibits positional disorder of the terminal methyl group. The redetermined structure of the heptanuclear complex octakis(μ₃-benzyloxo-κO:κO:κO)hexaethylheptazinc, [Zn₇(C₂H₅)₆(C₇H₇O)₈] or [Zn₇(OCH₂Ph)₈Et₆], (3), possesses a bicubic Zn₇O₈ core located at an inversion centre and demonstrates positional disorder of one crystallographically independent phenyl group. Cambridge Structural Database surveys are given for complexes structurally analogous to (2) and (3). Complexes (2) and (3), as well as derivatives of (1), are of interest as catalysts for the ring-opening polymerization of ∊-caprolactone, and polymerization results are reported.