Structural diversity of polynuclear MgO cores in magnesium phenoxide complexes.

The binuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,2κO-(1,2-dimethoxyethane-1κO,O')bis(μ-phenylmethanolato-1:2κO:O)(tetrahydrofuran-2κO)dimagnesium(II), [Mg(CHO)(CHO)(CHO)(CHO)] or [(BHT)(DME)Mg(μ-OBn)Mg(THF)(BHT)], (I), was obtained from the complex [(BHT)Mg(μ-OBn)(THF)] by substitution of one tetrahydrofuran (THF) molecule with 1,2-dimethoxyethane (DME) in toluene (BHT is O-2,6-Bu-4-MeCH and Bn is benzyl). The trinuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,3κO-tetrakis(μ-2-methylphenolato)-1:2κO:O;2:3κO:O-bis(tetrahydrofuran)-1κO,3κO-trimagnesium(II), [Mg(CHO)(CHO)(CHO)] or [(BHT)(μ-O-2-MeCH)(THF)Mg], (II), was formed from a mixture of BuMg, [(BHT)Mg(Bu)(THF)] and 2-methylphenol. An unusual tetranuclear complex, bis(μ-2-aminoethanolato-κO:O:O,N)tetrakis(μ-2-aminoethanolato-κO:O,N)bis(2,6-di-tert-butyl-4-methylphenolato-κO)tetramagnesium(II), [Mg(CHNO)(CHO)] or Mg(BHT)(OCHCHNH), (III), resulted from the reaction between (BHT)Mg(THF) 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 MgO, trinuclear chain-like MgO and bicubic MgO cores, respectively. A survey of the literature on known polynuclear MgO core types for ArO-Mg complexes is also presented.