Structural diversity of polynuclear Mg x O y cores in magnesium phenoxide complexes

Abstract

The binuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,2κO-(1,2-dimethoxyethane-1κ2O,O')bis(μ-phenylmethanolato-1:2κ2O: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-tBu2-4-MeC6H4 and Bn is benzyl). The trinuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,3κO-tetrakis(μ-2-methylphenolato)-1:2κ4O:O;2:3κ4O: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(nBu)(THF)2] and 2-methylphenol. An unusual tetranuclear complex, bis(μ3-2-aminoethanolato-κ4O:O:O,N)tetrakis(μ2-2-aminoethanolato-κ3O: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 ℇ-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 MgxOy core types for ArO-Mg complexes is also presented.