The Curious Case of a Phenylated Guanidinoquinoline Ligand: Synthesis, Complexes and ATRP Properties of DMEG6phqu

Abstract

In previous studies, copper halide complexes of the guanidinoquinoline (GUAqu) ligands 1,3‐dimethyl‐N‐(quinolin‐8‐yl)‐imidazolidin‐2‐imine (DMEGqu) and 1,1,3,3‐tetramethyl‐2‐(quinolin‐8‐yl)‐guanidine (TMGqu) were successfully implemented in atom transfer radical polymerization (ATRP) and could be further enhanced by introduction of alkyl substituents at C6 position of the quinoline backbone. Herein, the ligand DMEG6phqu is presented. The quinoline backbone of this ligand is equipped with a phenyl substituent at C6 position. This study deals with the influence of the phenyl substituent on solubility and molecular structural properties of DMEG6phqu CuI and CuII bromide complexes. In contrast to previously reported systems, the CuIBr complex of DMEG6phqu crystallizes as a trigonal coordinated monochelate complex. However, NMR and UV/Vis spectroscopic experiments indicate that DMEG6phqu forms a bischelate species in solution. The influence of the substituent on the complex redox potential and ATRP equilibrium constant KATRP is discussed. In contrast to expectations, it turned out that copper halide complexes of DMEG6phqu are completely insoluble in the apolar monomer styrene. However, ATRP kinetics were performed in solution and the results are compared to previous studies.