Kinetics of Fe-Mediated ATRP with Triarylphosphines

Phosphines have been successfully used as additives for Fe-based ATRP. To understand their role in detail, the kinetics of Fe-based ATRP in the presence of tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP) and of triphenylphosphine (TPP) was studied via online vis/near-IR and 31P NMR spectroscopy. No significant effect on the ATRP equilibrium constant, KATRP, was observed upon the addition of up to 1.5 equiv of phosphine relative to Fe. The strongly Lewis basic TTMPP may coordinate to FeII species, but primarily it acts as a reducing agent for [FeIIIBr4]− in ATRP above 100 °C, thus transforming TTMPP to TTMPP-Br+. TPP is a weaker Lewis base and consequently a less effective reducing agent.