The synthesis and characterisation of a magnesium amine bis(phenolate) complex as a potential initiator for the ring-opening polymerisation of cyclic esters

The synthesis, solid-state and solution structure of a magnesium amine bis(phenolate) complex [Mg{(O-2,4-^tBu₂C₆H₂-6-CH₂N(Me)CH₂}₂(C₆H₅CH₃)_1.5]₂ 4-Mg is reported. The complex was prepared by combining MgBu₂ with an equimolar amount of the parent bis(aminophenol) at ambient temperature in toluene. In the solid-state, the complex exists as a dimer. Each Mg centre is five-coordinate – bonding to one μ₁—O, two μ₂—O and two N moieties. NMR spectroscopy indicates that the solid-state structure is maintained in solution. Complex 4-Mg was investigated as a catalyst for ring opening polymerisation (ROP) of ε-caprolactone and L-lactide at both ambient and elevated temperatures, but was shown to be inactive, presumably as a direct result of the high steric bulk of the amine bis(phenolate) ligand.