Syntheses and Structures of Closely Related Copper(I) Complexes of Tridentate (2-Pyridylmethyl)imine and (2-Pyridylmethyl)amine Ligands and Their Use in Mediating Atom Transfer Radical Polymerizations

A series of five copper(I) bromide complexes of tridentate (N,N,L) pyridine–imine and pyridine–amine ligands with a third amine, ether, or thioether neutral donor was synthesized and utilized in the atom transfer radical polymerization of styrene. The ligand design illustrated a systematic approach to the development of copper complexes for use in ATRP. Variations in the nature of the ligand impacted the solid state structures of the complexes. A mononuclear [CuBr(L)] complex was observed for L = pyridine–amine–amine, whereas complexes of L = pyridine–imine–amine and −thioether formed dinuclear [CuBr(L)]2 structures with a central 10-membered ring. A doubly-bromide-bridged dimer was revealed for the [CuBr(L)] complex of L = pyridine–imine–ether and a polymeric species for [CuBr(L)], where L = pyridine–imine–amine and the imine–amine spacer was extended from two to three carbon atoms. In the application of these complexes to the ATRP of styrene, the redox potentials of the complexes were found to be one indicator of ATRP efficiency. Of the series presented, two complexes in particular provided fast polymerization rates and good to excellent molecular weight control. In both of these complexes, the ligand contained all nitrogen-based donor moieties.