Persistent Radical Effect in Action: Kinetic Studies of Copper-Catalyzed Atom Transfer Radical Addition in the Presence of Free-Radical Diazo Initiators as Reducing Agents

Kinetic features of the atom transfer radical addition (ATRA) of CCl4 to 1-octene, styrene, and methyl acrylate catalyzed by [Cu-II(TPMA)CI][CI] (TPMA = tris(2-pyridylmethyl)amine) in the presence of free-radical diazo initiator (AIBN) as a reducing agent were investigated, For 1-octene, the catalyst concentration was found to affect the alkene conversion and the yield of monoadduct for [1-octene](0)/[Cu-II](0) ratios above 10000:1. A more pronounced effect of the catalyst loading was observed in the case of methyl acrylate and styrene, due to the formation of AIBN-initiated oligomeric/polymeric side products. For all three alkenes, the optimum reaction conditions were achieved using 5 mol % AIBN relative to alkene. It was also found that excess alkyl halide (CCl4) was not necessary in ATRA reactions that utilize AIBN as a reducing agent. Kinetic studies of the ATRA process revealed that the rate of alkene consumption was dependent on the concentration and rate of decomposition of the radical initiator, but independent of the concentration of the copper catalyst. However, selectivity of the desired monoadduct ultimately depended on the nature of the catalyst.