A comparative computational study of the homolytic and heterolytic bond dissociation energies involved in the activation step of ATRP and SET‐LRP of vinyl monomers

Abstract

A quantum‐chemical calculation of the homolytic and heterolytic bond dissociation energies of the model compounds of the monomer and dimer is reported. These model compounds include the dormant chloride, bromide, and iodide species for representative activated and nonactivated monomers containing electron‐withdrawing groups as well as for a nonactivated monomer containing an electron‐donor group. Two examples of sulfonyl and N‐halide initiators are also reported. The homolytic inner‐sphere electron‐transfer bond dissociation is known as atom transfer and is responsible for the activation step in ATRP. The heterolytic outer sphere single electron transfer bond dissociation is responsible for the activation step in single electron transfer mediated living radical polymerization (SET‐LRP). The results of this study demonstrated much lower bond dissociation energies for the outer sphere single electron transfer processes. These results explain the higher rate constant of activation, the higher apparent rate constant of propagation, and the lower polymerization temperature for both activated and nonactivated monomers containing electron‐withdrawing groups in SET‐LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1607–1618, 2007

A density functional theory computational study of the role of ligand on the stability of CuI and CuII species associated with ATRP and SET‐LRP

“…The energy of homolysis was calculated in a previous work 10. The energy of electron transfer was calculated via eq 10.…”

“…ET2, the acceptance of the free electron by the dormant propagating macroradical and the activation energy, the energy required to dissociate the radical anion heterolytically were calculated previously 10…”

“…A previous computational effort has suggested that the independence of rate and halide is attributable to the difference between bond dissociation energies (BDEs) of homolytic cleavage in ATRP and heterolytic cleavage in SET‐LRP. In ATRP‐type homolytic cleavage, the BDEs for the halides increase sharply from iodine to bromine to chlorine whereas in heterolytic cleavage of the radical anion in SET‐LRP all dissociations of the radical anion are exothermic and there is a much smaller difference in energy between halides 10…”

“…In this study, we aim to use similar computational methods10 to ascertain the effect of the N‐ligand on the stability of Cu I X, Cu II X, and Cu II species in an effort to understand how to promote disproportionation of Cu I X and allow for entrance into SET‐LRP mechanisms over ATRP mechanisms.…”

Aqueous SET-LRP catalyzed with “in situ” generated Cu(0) demonstrates surface mediated activation and bimolecular termination

“…10,46,57 The catalyst most frequently employed in SET-LRP is Cu(0) in the form of powder 2,4,12,58 including powder generated by the disproportionation of Cu(I)X in a large diversity of solvents, 12 wire, 12,64,69 activated wire [59][60][61][62] and tubes. 63,64 Almost all initiators employed in other metal catalyzed LRP such as alkyl halides, 65,66 sulfonyl halides, 33,48,65,[67][68][69] N-halides 2,70 can be used as such or modified to become soluble for SET-LRP in various media including H 2 O. Only very few systematic investigations on SET-LRP with Cu(0) generated by disproportionation of Cu(I)X "in situ" in water 26,37,38,42 and in mixtures of water with other solvents are available.…”