Mechanistic insight into ruthenium catalysed: meta -sulfonation of 2-phenylpyridine

The catalytic meta-functionalization of arenes has emerged as an important synthetic methodology in the last decade. We report herein structural and mechanistic studies of the meta-sulfonation of phenylpyridine using ruthenium complexes. Furthermore, we disclose that the catalytically active species does not require the presence of a η⁶-arene ligand. Furthermore, the novel cycloruthenated phenylpyridine complex tosylated at the para position to the metal has been isolated and fully characterised. Protodemetallation studies suggest that a concerted C-H activation-demetallation process may be involved. Overall, this study provides fundamental insight into the meta-sulfonation phenylpyridine reaction pathway and uncovers new reaction intermediates that will guide the design of new catalytic systems for remote meta-functionalization.