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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. [ABSTRACT FROM AUTHOR]

Efficient and selective catalytic reduction of aqueous nitrate to ammonia was achieved over Ni nanoparticles immobilized on Fe3O4@n-SiO2@h-SiO2-NH2. [a magnetic hierarchical mesoporous amine-functionalized (M-HMAF) silica] by using hydrazine hydrate as a reducing agent. The high hierarchical mesoporous structure (surface area of 416 m² g-1 and pore size of 3.7 nm) and Fe3O4 core (ca. 7 nm) of the M-HMAF silica support resulted in a high dispersion of Ni nanoparticles over the support and easy recovery of the catalyst, respectively. Interestingly, the Ni/M-HMAF silica catalyst exhibited an excellent catalytic turnover (275 mmol gmetal-1h-1) compared with most of the existing catalysts for the conversion of nitrate ions at room temperature. The mechanistic study using UV/Vis spectroscopy revealed that the catalytic conversion of nitrate ions to ammonia proceeded through in situ generated nitrite ions. Subsequently, the ammonia produced from nitrate ions was isolated and analyzed by ¹H and 15N NMR spectroscopy, whereas the N2 gas released as a byproduct of hydrazine was characterized by GC-MS. [ABSTRACT FROM AUTHOR]

Water-soluble arene-ruthenium complexes coordinated with readily available aniline-based ligands were successfully employed as highly active catalysts in the C−H bond activation and arylation of 2-phenylpyridine with aryl halides in water. A variety of (hetero)aryl halides were also used for the ortho-C−H bond arylation of 2-phenylpyridine to afford the corresponding ortho- monoarylated products as major products in moderate to good yields. Our investigations, including time-scaled NMR spectroscopy and mass spectrometry studies, evidenced that the coordinating aniline-based ligands, having varying electronic and steric properties, had a significant influence on the catalytic activity of the resulting arene-ruthenium-aniline-based complexes. Moreover, mass spectrometry identification of the cycloruthenated species, {(η6-arene)Ru(κ2- C, N-phenylpyridine)}+, and several ligand-coordinated cycloruthenated species, such as [(η6-arene)Ru(4-methylaniline)(κ2- C, N-phenylpyridine)]+, found during the reaction of 2-phenylpyridine with the arene-ruthenium-aniline complexes further authenticated the crucial roles of these species in the observed highly active and tuned catalyst. At last, the structures of a few of the active catalysts were also confirmed by single-crystal X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

A simple methodology was explored to access highly robust bimetallic Co–Zn based zeolitic imidazolate frameworks at room temperature. By tuning the content of Co and Zn precursors, CoZn-ZIF-8 frameworks with varying Co : Zn (25–90% of Co2+ as confirmed by ICP-AES results) were synthesized. Electron micrographs and powder X-ray diffraction (PXRD) patterns confirmed the formation of bimetallic CoZn-ZIF-8 frameworks of 150–300 nm size, where Zn atoms were partially replaced by Co atoms. The as-synthesized CoZn-ZIF-8 frameworks displayed a tuned pore size, pore volume and surface area, with the highest surface area (enhanced by ∼40% compared to Zn-ZIF-8) and pore volume (enhanced by ∼33% compared to Zn-ZIF-8) for Co75Zn25-ZIF-8. The as-synthesized CoZn-ZIF-8 frameworks also displayed enhanced CO2 and H2 uptakes at 298 K and 77 K, respectively, at 1 bar. Noteworthy enhancement of ∼30% in the CO2 and ∼23% in the H2 uptake was displayed by Co75Zn25-ZIF-8 frameworks as compared to Zn-ZIF-8 under analogous conditions. [ABSTRACT FROM AUTHOR]