Synthesis, characterization, X-ray crystallography analysis, and catalytic activity of bis(2-pyridylmethyl)amine copper complexes containing coupled pendent olefinic arms in atom transfer radical addition (ATRA) reactions

The synthesis, characterization, and catalytic activity of bis(2-pyridylmethyl)amine (BPMA) copper complexes incorporating olefinic pendent arms are reported. Four copper(I) and four copper(II) complexes were synthesized employing four different counterions [chloride (Cl^-), perchlorate (ClO₄^-), trifluoromethanesulfonate (CF₃SO₃^-), and tetraphenylborate (BPh₄^-)]. The counterions used ranged from coordinating (Cl^-) to non-coordinating (BPh₄^-), producing different coordination modes in respective complexes. Solid state results obtained for the copper(I) complex incorporating the non-coordinating (BPh₄^-) counterion displayed an associative bond between the metal center and the C=C group in the olefinic arm of a neighboring complex. This interaction led to augmentation of the C=C bond due to back-bonding from the metal center. Five solid state structures were obtained for the copper(II) complexes with two also displaying intermolecular associative bonding between olefinic pendent arms and the metal center. X-ray crystallography studies showed that the olefinic arm motifs incorporated were hemilabile. Solution studies indicated that the copper complexes had some inherent reducing power and could be potential candidates for use as catalysts in atom transfer radical processes. However, only moderate conversions and yields were obtained in atom transfer radical addition (ATRA) reaction studies performed utilizing the copper complexes due to the presence of a competing reaction.