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[sbnd]O, two μ2[sbnd]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.