Synthesis and Application of New Guanidine Copper Complexes in Atom Transfer Radical Polymerisation

The synthesis and copper coordination of the ligands TMGd(i)pae (L1) and DMEGd(i)pae (L2) is reported. The solid-state structures of obtained copper complexes [Cu(TMGd(i)pae)Cl] (C1), [Cu(TMGd(i)pae)Br] (C2), [Cu(TMGd(i)pae)I] (C3), [Cu(DMEGd(i)pae)Cl] (C4), [Cu(DMEGd(i)pae)Br] (C5) and [Cu(DMEGd(i)pae)I] (C6) show a trigonal distorted [2+1] coordination of the copper atom and indicate interesting binding properties of aliphatic guanidine hybrid ligands. DFT analysis and calculation of the intramolecular charge transfer by NBO studies allow for a deeper insight into the binding competition between guanidine, amine and halide donor at copper(I). Tetramethylguanidine units act as stronger donors than dimethylethyleneguanidine units. Both ligands in combination with CuCl and CuBr were screened with regard to their activity in atom transfer radical polymerisation of styrene in bulk and in MeCN solution. The polymerisation occurs very fast and has good control. Kinetic studies on the best-behaving system (2TMGd(i)pae/CuBr) evidence that controlled radical polymerisation occurs until a conversion of 70% and a polymerisation time of 100 min, after this a deviation towards higher molecular weights can be observed.