Ligand-Tuned C–H Bond Activation/Arylation of 2-Arylpyridines over Pyridine-Based N,O/N,N Ligated Ruthenium–Arene Complexes

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) 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 N,O donor-based ligands (acteylpyridine and picolinate) outperform those with N,N donor ligands (iminopyridine). Moreover, among the N,O 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 N,O 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 ([Ru]-2, [Ru]-4, and [Ru]-5) are authenticated by single-crystal X-ray diffraction studies. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim