Structural comparison of CuII complexes in atom transfer radical polymerization

Abstract

The molecular structures of [Cu^II(dNbpy)₂Br]⁺[Cu^IBr₂]⁻, Cu^II(pmdeta)Br₂, Cu^II(tNtpy)Br₂, [Cu^II(hmteta)Br]⁺[Br]⁻ and [Cu^II(cyclam)Br]⁺[Br]⁻ [dNbpy = 4,4′-di(5-nonyl)-2,2′-bipyridine, pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tNtpy = 4,4′,4″-tris(5-nonyl)-2,2′:6′,2″-terpyridine, hmteta = 1,1,4,7,10,10-hexamethyltriethylenetetramine, Me₄cyclam = 1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecane] isolated from atom transfer radical polymerizations (ATRP) were determined. The Cu^II complexes showed either a trigonal bipyramidal structure as in the case of the dNbpy ligand, or a distorted square pyramidal coordination in the case of triamines and tetramines. Depending on the type of amine ligand, the complexes were either neutral (triamines) or ionic (bpy and tetramines). The counterions in the case of the ionic complexes were either bromide (Me₄cyclam and hmteta) or the linear [Cu^IBr₂]⁻ anion (dNbpy). No direct correlation was found between the Cu^II–Br bond length and the deactivation rate constant in ATRP, which suggests that other parameters such as the entropy for the structural reorganization between the Cu^I and Cu^II complexes might play an important role in determining the overall activity of the catalyst in ATRP.