Structural diversity of polynuclear MgxOy cores in magnesium phenoxide complexes

The binuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,2κO-(1,2-dimethoxyethane-1κ² O,O′)bis(μ-phenylmethanolato-1:2κ² O:O)(tetrahydrofuran-2κO)dimagnesium(II), [Mg₂(C₇H₇O)₂(C₁₅H₂₃O)₂(C₄H₈O)(C₄H₁₀O₂)] or [(BHT)(DME)Mg(μ-OBn)₂Mg(THF)(BHT)], (I), was obtained from the complex [(BHT)Mg(μ-OBn)(THF)]₂ by substitution of one tetrahydrofuran (THF) molecule with 1,2-dimethoxyethane (DME) in toluene (BHT is O-2,6- ^t Bu₂-4-MeC₆H₄ and Bn is benzyl). The trinuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,3κO-tetrakis(μ-2-methylphenolato)-1:2κ⁴ O:O;2:3κ⁴ O:O-bis(tetrahydrofuran)-1κO,3κO-trimagnesium(II), [Mg₃(C₇H₇O)₄(C₁₅H₂₃O)₂(C₄H₈O)₂] or [(BHT)₂(μ-O-2-MeC₆H₄)₄(THF)₂Mg₃], (II), was formed from a mixture of Bu₂Mg, [(BHT)Mg( ⁿ Bu)(THF)₂] and 2-methylphenol. An unusual tetranuclear complex, bis(μ₃-2-aminoethanolato-κ⁴ O:O:O,N)tetrakis(μ₂-2-aminoethanolato-κ³ O:O,N)bis(2,6-di-tert-butyl-4-methylphenolato-κO)tetramagnesium(II), [Mg₄(C₂H₆NO)₆(C₁₅H₂₃O)₂] or Mg₄(BHT)₂(OCH₂CH₂NH₂)₆, (III), resulted from the reaction between (BHT)₂Mg(THF)₂ and 2-aminoethanol. A polymerization test demonstrated the ability of (III) to catalyse the ring-opening polymerization of ∊-caprolactone without activation by alcohol. In all three complexes (I)–(III), the BHT ligand demonstrates the terminal κO-coordination mode. Complexes (I), (II) and (III) have binuclear rhomboid Mg₂O₂, trinuclear chain-like Mg₃O₄ and bicubic Mg₄O₆ cores, respectively. A survey of the literature on known polynuclear Mg _x O _y core types for ArO–Mg complexes is also presented.