Direct Arylation of 1,10-Phenanthroline Using an Organomagnesium Reagent

Substituted derivatives of 1,10-phenanthroline are important ligands in inorganic chemistry. Such ligands are often synthesized by nucleophilic addition of aryl- or alkyllithium reagents to the carbon positions adjacent to the phenanthroline nitrogens. The typical reaction sequence (organolithium addition, protonolysis, oxidation, and rearomatization) has been widely used and seldom improved. We sought to replace lithium-based reagents with safer reagents based on magnesium (i.e., Grignards). The effective use of an arylmagnesium reagent in the production of a phenanthroline ligand derivative is now disclosed. Additionally, our newly reported method avoids the use of a heterogeneous oxidant (MnO₂) which the traditional method employed in excess. Instead, oxidation due to air exposure is used to achieve the final aromatization step. This new reaction scheme produces 2,9-di-(p-methoxyphenyl)-1,10-phenanthroline in a process with a 10.2% average yield.