A Kinetico-Mechanistic Study on Cu^II Deactivators Employed in Atom Transfer Radical Polymerization

Abstract

Copper complexes of tertiary amine ligands have emerged as the catalysts of choice in the extensively employed atom transfer radical polymerization (ATRP) protocol. The halide ligand substitution reactions of five-coordinate copper(II) complexes of tris[2-(dimethylamino)ethyl]amine (Metren), one of the most active ATRP catalysts, has been studied in a range of organic solvents using stopped-flow techniques. The kinetic and activation parameters indicate that substitution reactions on [Cu(Metren)X] (X = Cl and Br) and [Cu(Metren)(Solv)] (Solv = MeCN, DMF, DMSO, MeOH, EtOH) are dissociatively activated; this behavior is independent of the solvent used. Adjusting the effective concentration of the solvent by addition of an olefinic monomer to the solution does not affect the kinetics of the halide binding (k) but can alter the outer-sphere association equilibrium constant (K) between reactants prior to the formal ligand substitution. Halide (X/Y) exchange reactions (X = Br and Y = Cl) involving the complex [Cu(Metren)X] and Y reveal that the substitution is thermodynamically favored. The influence of solvent on the substitution reactions of [Cu(Metren)X] is complex; the more polar DMF confers a greater entropic driving force but larger enthalpic demands than MeCN. These substitution reactions are compared with those for copper(II) complexes bearing the tris[2-(diethylamino)ethyl]amine (Ettren) and tris[2-(pyridyl)methyl]amine (tpa) ligands, which have also been used as catalysts for ATRP. Changing the ligand has a significant impact on the kinetics of X/Y exchange. These correlations are discussed in relation to the ability of five-coordinate [CuLX] complexes to deactivate radicals in ATRP.

Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {CoIII/FeII}2 Square

“…[47] For experiments run at variable pressure with t 1/2 <10 s, a previously described pressurised stopped-flow mixing unit was used that was connected with fibre optics to a J&M TIDAS instrument. [72] Observed rate constants were derived from absorbance versus time traces at the wavelengths where a maximum increase and/or decrease of absorbance were observed. The calculation of the observed rate constants from the absorbance versus time monitoring of reactions, studied under first order concentration conditions, were carried out using the SPECFIT or ReactLab software packages; [40,41] the general kinetic technique is that previously described.…”

ATRP in Water: Kinetic Analysis of Active and Super-Active Catalysts for Enhanced Polymerization Control

“…To study these reactions, we used a set of electrochemical methods suitable for the determination of a wide range of k act values, including rate constants of extremely fast reactions with k act approaching the diffusion-controlled limit. Although some of these methods have already been used to analyze ATRP systems in organic solvents, ,− in the first part of the manuscript we provide a brief description of all electrochemical methods used to determine k act , with peculiar attention to application of such techniques to aqueous media. In the second part of the manuscript, the obtained k act values are discussed in terms of effect of initiator, effect of copper ligand, and role of the monomer in aqueous ATRP.…”

Kupfervermittelte radikalische Polymerisation mit reversibler Deaktivierung in wässrigen Medien

“…Electrochemical investigation of activation and deactivation rates in aqueous media for common catalyst systems by Fantin et al demonstrate that deactivation by dissociated complex is in fact highly efficient, but is hampered by the weak Cu-X bond. [11] It has been suggested that the free coordination site is then occupied by solvent [12] or by polar monomers. [11,13] Hydrolysis of the alkyl halide at the ω chain end can be a significant problem in aqueous media which results in a loss of end group fidelity as the hydroxyl terminated polymer is unable to participate in further chain growth.…”