Ligand‐Tuned C–H Bond Activation/Arylation of 2‐Arylpyridines over Pyridine‐Based <italic>N</italic>,<italic>O/N</italic>,<italic>N</italic> Ligated Ruthenium–Arene Complexes.

Water‐soluble ruthenium(II)–arene complexes [(η6‐arene)Ru(κ2‐L)]<italic>n</italic>+ (<italic>n</italic> = 0, 1) (<bold>[Ru]‐1</bold>–<bold>[Ru]‐10</bold>) containing pyridine‐based bischelating <italic>N</italic>,<italic>O/N</italic>,<italic>N</italic> donor ligands (<bold>L1</bold>–<bold>L5</bold>) are synthesized and employed for the catalytic C–H bond activation/arylation of a wide range of 2‐phenylpyridines and aryl halides in water, affording the corresponding mono‐ and biarylated products. Exploring the reactivity of the synthesized complexes, our investigations, including time‐dependent 1H NMR spectroscopic studies with ruthenium–arene catalysts, demonstrate a remarkable structure–activity relationship for the ligand‐tuned C–H activation/arylation of 2‐phenylpyridine, where the complexes with bischelating <italic>N</italic>,<italic>O</italic> donor‐based ligands (acteylpyridine and picolinate) outperform those with <italic>N</italic>,<italic>N</italic> donor ligands (iminopyridine). Moreover, among the <italic>N</italic>,<italic>O</italic> donor ligands, a distinct effect of the nature of the coordinating oxygen donor on the catalytic activity is also observed, where ruthenium–arene complexes having <italic>N</italic>,<italic>O</italic> donor ligands (acetylpyridine) with neutral oxygen‐donor atoms exhibit enhanced catalytic activity over those with anionic oxygen‐donor atoms (picolinate). The observed trend in the catalytic activity is attributed to the ligand‐promoted facile deprotonation and coordination–decoordination interconversion behavior. In addition, molecular structures for a few of the representative complexes (<bold>[Ru]‐2</bold>, <bold>[Ru]‐4</bold>, and <bold>[Ru]‐5</bold>) are authenticated by single‐crystal X‐ray diffraction studies. [ABSTRACT FROM AUTHOR]