The reaction of (BDI)MgiPr [BDI = HC(C(Me)=N-2,6-iPr2C6H3)2] with 2',4',6'-trimethylacetophenone in toluene affords the enolate complex [(BDI)Mg(mu-OC(=CH2)-2,4,6-Me3C6H2)]2 which is found to be an excellent initiator for the living, syndioselective (sigma r > 0.95) polymerisation of methyl methacrylate.