New Bisguanidine-Copper Complexes and their Application in ATRP

The ligands TMG(2)e [bis(N,N,N',N'-tetramethylguanidino)ethane] and DMEG(2)e [N-1,N-2-bis(1,3-dimethylimidazolin-2-ylidene)ethane-1,2-diamine] were used in the complexation of copper cations to give the new complexes [Cu(TMG(2)e)(2)][Cu2I4], [Cu(TMG(2)e)Cl-2] and [Cu(DMEG(2)e)(2)]-[CuCl2]. Single-crystal structure determination shows that the complexes [Cu(TMG(2)e)Cl-2] and [Cu(DMEG(2)e)(2)][CuCl2] both crystallise in the monoclinic space group C2/c, the complex [Cu(TMG(2)e)(2)][Cu2I4] in the orthorhombic space group Pbca. The copper atoms in all complex cations reside in a coordination environment between tetrahedral and square-planar geometry. The application of copper complexes with TMG(2)e and DMEG(2)e as ligands in atom transfer radical polymerisation (ATRP) was investigated with styrene as monomer. The polymerisation process with both ligand systems shows even at low temperature unexpected high conversions and molecular weight distributions that are evidence of a well controlled ATRP. These first results in the application of guanidine ligands in ATRP show that these ligands have high potential, but that further process optimisations and ligand tuning are necessary to develop highly active catalysts for ATRP.