Understanding the structure-activity relationship and performance of highly active novel ATRP catalysts

Copper bromide complexes based on a series of substituted guanidine-quinolinyl and -pyridinyl ligands are reported. The ligand systems were chosen based on the large variation with regard to their flexibility in the backbone, different guanidine moieties and influence by electron density donating groups. Relationships between the molecular structures and spectroscopic and electronic properties are described. Beside the expected increase in activity by substituting the 4-position (NMe₂vs. H), we showed that a higher flexibility, such as TMG vs. DMEG moiety, leads to a better stabilsiation of the copper(II) complex. Due to the correlation of the potentials and K_ATRP values, the catalyst based on the ligand TMGm4NMe₂py is the most active copper complex for ATRP with a bidentate ligand system. The combination of the strong donating abilities of dimethylamine pyridinyl, the donor properties of the TMG substituent, and the improved flexibility due to the methylene bridging unit leads to high activity. With all NMe₂-substituted systems standard ATRP experiments were conducted and with more active NMe₂-substituted pyridinyl systems, ICAR ATRP experiments of styrene were conducted. Low dispersities and ideal molar masses have been achieved.