Ligand‐tuned C‐H bond activation/arylation of 2‐arylpyridines over pyridine based N,O/N,N ligated ruthenium‐arene complexes

Chinky Binnani; Rohit Kumar Rai; Deepika Tyagi; Shaikh M. Mobin; Sanjay Kumar Singh

Index: 10.1002/ejic.201701446

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Abstract

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