Magnesium Complexes Containing η1- and η3-Pyrrolyl or Ketiminato Ligands: Synthesis, Structural Investigation and ϵ-Caprolactone Ring-Opening Polymerisation

A series of dimeric magnesium derivatives containing substituted pyrrolyl or ketiminato ligands was synthesised and the application of these derivatives for the ring opening polymerisation of ϵ-caprolactone has been carried out. Reactions of [Mg{N(SiMe3)2}]2 (1) with one equiv. of 2-dimethylaminomethyl pyrrole and 2-diethylaminomethyl pyrrole in toluene generates [Mg{C4H3N(2-CH2NMe2)}{N(SiMe3)2}]2 (2) and [Mg{C4H3N(2-CH2NEt2)}{N(SiMe3)2}]2 (3), respectively, in high yield. Similarly, the reaction of 1 with one equiv. of 2-tert-butylaminomethyl pyrrole in toluene at room temperature affords [Mg{C4H3N(2-CH2NHtBu)}{N(SiMe3)2}]2 (4). Furthermore, reactions of 1 with one equiv. of HOCMeCHCMeN(C6H3-2,6-iPr2) or HOCMeCHCMeN(C6H4-2-OMe) in toluene yielded the dimeric magnesium complexes, [Mg{OCMeCHCMeN(C6H3-2,6-iPr2)}{N(SiMe3)2}]2 (5) and [Mg{OCMeCHCMeN(C6H4-2-OMe)}{N(SiMe3)2}]2 (6), respectively, in satisfactory yields by means of deamination. All the complexes were characterised by NMR spectroscopy and X-ray diffraction analysis in the solid state. They show moderate reactivity towards the ring opening polymerisation of ϵ-caprolactone in dichloromethane or tetrahydrofuran.