Formation and Possible Reactions of Organometallic Intermediates with Active Copper(I) Catalysts in ATRP

The Cu^I complex obtained in situ from Cu^I and tris­((4-methoxy-3,5-dimethylpyridin-2-yl)­methyl)­amine (TPMA*) is currently the most reducing and the most active catalyst for atom transfer radical polymerizations (ATRP). The complex has a high affinity for alkyl halides (ATRP pathway) but also has sufficient affinity toward organic radicals to potentially participate in organometallic-mediated radical polymerization (OMRP). Thus, the radical polymerization of <i>n</i>-butyl acrylate initiated by AIBN (azobisisobutyronitrile) was significantly retarded, and the molecular weights decreased in the presence of the Cu^I/TPMA* complex. These results suggest the presence of a Cu-mediated termination processes, even after the amount of radicals generated from AIBN exceeded the initial amount of Cu^I/TPMA*. Nevertheless, in the presence of alkyl bromides, which act as ATRP initiators for acrylates, control was gained through metal-mediated halogen atom transfer, i.e., ATRP, not OMRP