Comparing Halogen Atom Abstraction Kinetics for Mn(I), Fe(I), Co(I), and Ni(I) Complexes by Combining Electroanalytical and Statistical Modeling

First-row transition metal complexes have garnered attention due to their ability to activate aliphatic halides for catalytic cross-coupling reactions. However, mechanistic investigation of these systems is challenging as a consequence of difficulties associated with preparing the relevant metal complexes and the resultant poor stability of such intermediates for subsequent analytical interrogation. In this context, we have developed a platform to rapidly measure kinetic data using electroanalytical methods, which facilitates a wide range of physical organic studies. As a result, we have investigated and compared the reaction of benzyllic halides with electrogenerated Mn-I(PyBox)Cl, Fe-I(Pyrox)OTf, Co-I(Pyrox)Br, Co-I(PyBox)Br, Ni-I(Phox)Br complexes. The experimental results support a unified inner-sphere halogen atom abstraction mechanism for these different complexes while also providing the ability to directly compare through multivariate linear regression analyses the subtle differences imparted by metal/ligand combinations. The information gleaned by this study has implications why certain metal complexes are matched to oxidative addition processes relevant in catalytic processes.

Automated summary

This study investigates the reaction mechanism of different metal complexes and compares the effects of metal/ligand combinations on the reaction. The results show that these complexes follow a unified inner-sphere halogen atom abstraction mechanism, but there are subtle differences imparted by metal/ligand combinations.