Atom transfer radical addition (ATRA) catalyzed by copper complexes with tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand in the presence of free-radical diazo initiator AIBN?

Dalton Transactions Pub Date: 2011-03-23 DOI: 10.1039/C1DT10189G

Abstract

In this article, we focus on the evaluation of tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand in copper catalyzed ATRA in the presence of free-radical diazo initiator AIBN (2,2′-azobis(2-methylpropionitrile)). The addition of carbon tetrachloride to 1-hexene, 1-octene and cis-cyclooctene proceeded efficiently to yield 89, 85 and 85% of monoadduct, respectively, using the catalyst to alkene ratio of 1?:?2500. For alkenes that readily undergo free radical polymerization, such as methyl acrylate, catalyst loadings as high as 0.4 mol-% were required. Furthermore, modest yields of the monoadduct were obtained with less active alkyl halides (chloroform and bromoform) using 250?:?1 and 500?:?1 ratios of alkene to copper(II). Interestingly, the addition of carbon tetrachloride to cis-cyclooctene produced only 1-chloro-4-(trichloromethyl)-cyclooctene, while carbon tetrabromide yielded 1,2 and 1,4-regioisomers in 75?:?25 ratio. The activity of [CuII(Me6TREN)X][X] (X = Br? and Cl?) complexes in ATRA in the presence of AIBN was additionally probed by adding excess free ligand, source of halide anions and triphenylphosphine. The results indicated that disproportionation is a likely cause for lower activity of Me6TREN as compared to TPMA (tris(2-pyridylmethyl)amine).

Graphical abstract: Atom transfer radical addition (ATRA) catalyzed by copper complexes with tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand in the presence of free-radical diazo initiator AIBN
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