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

Abstract

The synthesis and copper coordination of the ligandsTMGdipae (L1) and DMEGdipae (L2) is reported. The solid‐state structures of obtained copper complexes [Cu(TMGdipae)Cl] (C1), [Cu(TMGdipae)Br] (C2), [Cu(TMGdipae)I] (C3), [Cu(DMEGdipae)Cl] (C4), [Cu(DMEGdipae)Br] (C5) and [Cu(DMEGdipae)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 (2TMGdipae/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.

Implications of Guanidine Substitution on Copper Complexes as Entatic‐State Models

“…The donor interplay between the guanidine and quinoline units as well as the large steric encumbrance of the guanidine units were crucial for the entatic coordination. The guanidine units provide σ and π contributions to the metal bonding, and copper guanidine complexes have been studied intensively in coordination chemistry, bioinorganic chemistry and for polymerisation applications …”

“…Following our strategy of generating Cu complexes with intermediate coordination environments, we continued with guanidine–quinoline ligands and varied the guanidine moiety from tetramethylguanidine (TMG) to dimethylethyleneguanidine (DMEG), which is a slightly weaker donor. [14b] Herein, we report the resulting series of bis(chelate) Cu I and Cu II complexes in which the cationic units again have very similar structures. By XAS studies, we obtained insights into the solution structures and the impact of the anion.…”

New Guanidine-Pyridine Copper Complexes and Their Application in ATRP

“…The donor properties can be tuned through the choice of guanidine substituents, amine and spacers. These ligands have already been intensely investigated in bioinorganic coordination chemistry [12][13][14][15][16][17][18], but also in the ATRP of styrene [19][20][21][22][23][24]. In all of these studies, it appeared that the polyfunctional guanidines support the oxidation state change from Cu(I) over Cu(II) to Cu(III) and stabilize the corresponding complexes excellently.…”

Guanidine Metal Complexes for Bioinorganic Chemistry and Polymerisation Catalysis

“…52) [190]. The molecular structure of the complex as well as DFT calculations revealed a stronger donation of the TMG unit in TMGd i pae than the respective DMEG unit.…”

“…For bidentate ligands, it should be noted that they are generally used in a 2:1 ratio towards copper for controlled Fig. 50 Left, the bidentate ethylene-bridged bis(imidazolin-2-imine) ligand (BLiPr) synthesised by Petrovic et al; right, the CuCl complex used in ATRP of styrene [43] [190] polymerisation reactions. However, in this particular case, polymerisations were also conducted successfully in a 1:1 ratio.…”