Oxalic Amidines – Protonation Studies and Activity in Lactide Polymerisation


  • Dedicated to Professor Ernst Anders on the occasion of his 70th birthday


The oxalic amidine N,N′-dimethyl-N,N′-diphenyl-1,2-bis[4-tolylimino]ethane-1,2-diamine was used to synthesise a chloridozinc complex and two monoprotonated species either with chloride or triflate counterions. The compounds have been structurally characterised by X-ray crystallography. Proton affinities have been determined by quantum chemical calculations to investigate why only the iminium protonated species is selectively formed upon mild protonation. To better understand the coordination properties of the ligand, different possible coordination modes of the ligand to zinc chloride have been investigated by DFT calculations. The chloridozinc complex was applied as a catalyst in the melt polymerisation of rac-lactide and exhibited high activity combined with excellent agreement between the obtained and calculated molecular weights.