Structural Aspects of Copper‐Mediated Atom Transfer Radical Polymerization with a Novel Tetradentate Bisguanidine Ligand

This contribution reports the synthesis of the novel tetradentate bisguanidine ligand 2',2'-[ethane-1, 2-diylbis(methylazanediyl)]bis(ethane-2, 1-diyl)bis(1, 1, 3, 3-tetramethylguanidine) (L1, TMG2dmtrien), which combines two weak amine and two strong guanidine donor functions. Two new copper(II) complexes were isolated and structurally characterized as complexes [Cu(TMG2dmtrien)][Br]2 center dot 3MeCN (C1[Br]2 center dot 3MeCN) and [Cu(TMG2dmtrien)][Cl]2 center dot 3MeCN (C2[Cl]2 center dot 3MeCN). The cations C1 and C2 [Cu(TMG2dmtrien)]2+ show a square-planar coordination environment and are chiral with both enantiomers being observed in the unit cell. We investigated the application of L1 in copper-mediated styrene ATRP. L1 shows with CuBr and PEBr as initiator a high polymerization activity according to the polymerization rate. First order kinetics confirm the living character of the polymerization. However, the deviation of molecular weights from theoretical molecular weights and the broad molecular weight distributions hint for a low controlled ATRP. The ATRP with further copper(I) salts {CuCl, [Cu(MeCN)4]BF4 and [Cu(MeCN)4]PF6} and PECl and PEBr as initiators were investigated as well. Herein the use of [Cu(MeCN)4]PF6 with PECl led to promising results.