A Comprehensive Study of Copper Guanidine Quinoline Complexes: Predicting the Activity of Catalysts in ATRP with DFT

Abstract

Copper complexes of the hybrid guanidine ligands 1,3-dimethyl-N-(quinolin-8-yl)-imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)-guanidine (TMGqu) have been studied comprehensively with regard to their structural and electrochemical properties and their activity in atom transfer radical polymerization (ATRP). A simple analysis of the molecular structures of the complexes gives no indication about their activity in ATRP; however, with the help of DFT and NBO analysis the influence of particular coordinating donors on the electrochemical properties could be fully elucidated. With an adequate DFT methodology and newly applied theoretical isodesmic reactions it was possible to predict the relative position of the redox potentials of copper complexes containing DMEGqu and TMGqu ligands. In addition, predictions could be made as to whether the complexes of DMEGqu or TMGqu are more active in ATRP. Four new Cu(I) complexes were tested in standard ATRP reactions and kinetically investigated both in bulk and in solution. It could be proven that complexes featuring DMEGqu possess a lower redox potential and are more active in ATRP, although the tetramethylguanidine moiety represents the stronger donor.

Oxygen Activation by Copper Complexes with an Aromatic Bis(guanidine) Ligand

“…It is determined by the dihedral angles between the plane of three nitrogen atoms (N amine –N gua –N amine ) and the three carbon atoms (C amine –C gua –C amine ) of the guanidine unit. The twist angles of the guanidine moieties, which are closer to the aliphatic unit, are close to 34°, which has been found earlier for guanidines with TMG units , , , . In the guanidine moiety, which is closer to the aromatic unit, the guanidine twist is smaller.…”

“…Not only dinuclear copper complexes but also tri‐ and tetranuclear copper complexes were synthesised with aromatic guanidine ligands and were redox‐active as well , . Hybrid (guanidine)copper complexes displayed a good activity in atom transfer radical polymerisation (ATRP) underlined by DFT calculations . Moreover, it has been shown that aromatic bis(guanidine)copper complexes show a well‐controlled ATRP activity in the polymerisation of styrene .…”

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

“…Due to the different coordination strength, the bond lengths for Zn-N gua (1.986(3), 2.013(4), 2.065(5) Å) are shorter than for Zn-N amine (2.053(3), 2.065(4), 2.041(5) Å). This trend can be seen in recent studies [69,78] • , in good agreement with the value expected for an ideal tetrahedral geometry of 90 • . All complexes are tetrahedrally distorted coordinated, which can be shown by the structural parameter τ 4 .…”

“…Due to the different coordination strength, the bond lengths for Zn-Ngua (1.986(3), 2.013(4), 2.065(5) Å) are shorter than for Zn-Namine (2.053(3), 2.065(4), 2.041(5) Å). This trend can be seen in recent studies [69,78]. The angle of ZnN2 is around 100° and the angle between the coordination planes {∡ (ZnX2, ZnN2)} is 80.3°-83.4°, in good agreement with the value expected for an ideal tetrahedral geometry of 90°.…”

“…The optimized structures obtained were used to calculate the charge transfer energies (by second-order perturbation theory) and the NBO charges [86][87][88]. Normally, these two sets of computed values allow an estimation of the relative donor strength [78]. The influence of the electronic effects can be reflected well by the NBO charges, but these do not represent absolute charges.…”