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.