C-H bond Activation/Arylation over Arene-Ruthenium(II)-picolinate Complexes: Synthesis, Structure and Catalytic Activity

A series of water soluble arene-ruthenium(II) complexes [(η⁶-arene)RuCl(κ²-L)]ⁿ⁺ (n = 0, 1) ([Ru]-1 – [Ru]-12) containing pyridine based N,O or N,N ligands (L1-L6) were synthesized and employed for the catalytic C-H bond activation/ arylation of 2-phenylpyridine with aryl halides in water. Efficient C-H bond activation/ arylation of a wide range of substituted 2-phenylpyridines and aryl halides were achieved to afford corresponding mono and biarylated products. Exploring the reactivity of the synthesized complexes, our investigation with ruthenium catalysts inferred that pyridine based N,O donor ligands afforded enhanced catalytic activity compared to those obtained with the iminopyridine (N,N donor) ligands. Further, mass spectrometric investigations, during the catalytic and controlled reaction conditions, evidenced the presence of the crucial cycloruthenated species {(η⁶-p-cymene)Ru(κ²-CN-phenylpyridine)}⁺ (m/z [M⁺] 390.0), along with a ligand coordinated species, {(η⁶-p-cymene)Ru(L1)(κ²-CN-phenylpyridine)}⁺ (m/z [M⁺]+Na 539.0), suggesting the important role such intermediate species in C-H bond activation reactions. Moreover, molecular structures for few of the representative complexes were also authenticated by single crystal X-ray diffraction studies.