Copper(I/II) and cobalt(II) coordination chemistry of relevance to controlled radical polymerization processes

The reaction of various alkyl halides (1-bromoethylbenzene, BEB; 1-chloroethylbenzene, CEB; methyl iodide; 1-bromoethylacetate, BEA; and ethyl-2-bromopropionate, EBP) with CuBr/L (L = bipy, Me6TREN) has been investigated in the presence of [Co(acac)2] or [Co(acac)2]/py, with the goal of generating radicals by halogen atom transfer to CuI for subsequence trapping by CoII and generation of an alkylcobalt(III) product. No evidence for the formation of the target product has been obtained. The various reactions, carried out under different conditions, have led to the crystallization of the following compounds: {[Cu(bipy)2Br]+}2{[Cu2Br4]2−} (1); [Cu(Me6TREN)Br]Br; [Cu(Me6TREN)Br0.37Cl0.63]Br (2); trans-[Co(acac)2(THF)2] (3); [Co(Me6TREN)Br]Br (4); [Cu(Me7TREN)I]{[Cu2I2(Br0.628I0.372)2]0.9[I]0.2} (5); [C6H8N]2[CoI4] (6); [Co(acac)3]; and [Co(acac)2(THF)2CoBr2] (7). The structures of 1–7 have been determined by single-crystal X-ray diffraction.

Graphical abstractThe reaction between CuBr/Ln (Ln = 2 bipy or Me6TREN) and a variety of alkyl halides in the presence of [Co(acac)2] leads to a variety of products originating from atom transfer and ligand redistribution reactions. The formation of a stable alkylcobalt(III) derivative was not observed.Figure optionsDownload full-size imageDownload as PowerPoint slide