Ferrocene-amide-functionalized 1,8-naphthyridine (NP) based ligands {[(5,7-dimethyl-1,8-naphthyridin-2-yl)amino]carbonyl}ferrocene (L(1) H) and {[(3-phenyl-1,8-naphthyridin-2-yl)amino]carbonyl}ferrocene (L(2) H) have been synthesized. Room-temperature treatment of both the ligands with Rh2 (CH3 COO)4 produced [Rh2 (CH3 COO)3 (L(1) )] (1) and [Rh2 (CH3 COO)3 (L(2) )] (2) as neutral complexes in which the ligands were deprotonated and bound in a tridentate fashion. The steric effect of the ortho-methyl group in L(1) H and the inertness of the bridging carboxylate groups prevented the incorporation of the second ligand on the {Rh(II) -Rh(II) } unit. The use of the more labile Rh2 (CF3 COO)4 salt with L(1) H produced a cis bis-adduct [Rh2 (CF3 COO)4 (L(1) H)(2) ] (3), whereas L(2) H resulted in a trans bis-adduct [Rh2 (CF3 COO)3 (L(2) )(L(2) H)] (4). Ligand L(1) H exhibits chelate binding in 3 and L(2) H forms a bridge-chelate mode in 4. Hydrogen-bonding interactions between the amide hydrogen and carboxylate oxygen atoms play an important role in the formation of these complexes. In the absence of this hydrogen-bonding interaction, both ligands bind axially as evident from the X-ray structure of [Rh2 (CH3 COO)2 (CH3 CN)4 (L(2) H)2 ](BF4 )2 (6). However, the axial ligands reorganize at reflux into a bridge-chelate coordination mode and produce [Rh2 (CH3 COO)2 (CH3 CN)2 (L(1) H)](BF4 )2 (5) and [Rh2 (CH3 COO)2 (L(2) H)2 ](BF4 )2 (7). Judicious selection of the dirhodium(II) precursors, choice of ligand, and adaptation of the correct reaction conditions affords 7, which features hemilabile amide side arms that occupy sites trans to the Rh-Rh bond. Consequently, this compound exhibits higher catalytic activity for carbene insertion to the CH bond of substituted indoles by using appropriate diazo compounds, whereas other compounds are far less reactive. Thus, this work demonstrates the utility of steric crowding, hemilability, and hydrogen-bonding functionalities to govern the structure and catalytic efficacyof dirhodium(II,II) compounds.

Oxygenation of 1,5-cyclooctadiene (COD) is achieved on an iridium center using water as a reagent. A hydrogen-bonding interaction with an unbound nitrogen atom of the naphthyridine-based ligand architecture promotes nucleophilic attack of water to the metal-bound COD. Irida-oxetane and oxo-irida-allyl compounds are isolated, products which are normally accessed from reactions with H2O2 or O2. DFT studies support a ligand-assisted water activation mechanism.

The present study aims to understand the hydrochemistry vis-à-vis As-exposure from drinking groundwater in rural Bengal. The characteristic feature of the groundwaters are low Eh (range, −151 to −37 mV; mean, −68 mV) and nitrate (range, 0.01-1.7 mg/l; mean, 0.14 mg/l) followed by high alkalinity (range, 100-630 mg/l; mean, 301 mg/l), Fe (range, 0.99-38 mg/l; mean, 8.1 mg/l), phosphate (range, 0.01-15 mg/l; mean, 0.54 mg/l), hardness (range, 46-600 mg/l; mean, 245 mg/l) and sulphate (range, 0.19-88 mg/l; mean, 7.2 mg/l), indicating reducing nature of the aquifer. The land use pattern (sanitation, surface water bodies, sanitation coupled with surface water bodies and agricultural lands) demonstrates local enrichment factor for As/Fe in groundwater. Among these, sanitation is the most prevailing where groundwater is generally enriched with As (mean, 269 μg/l) and Fe (mean, 9.8 mg/l). Questionnaire survey highlights that ∼70% of the villagers in the study area do not have proper sanitation. This demonstrating the local unsewered sanitation (organic waste, anthropogenic in origin) could also cause As toxicity in rural Bengal. In the agricultural lands, higher mean values of alkalinity, phosphate, sulphate, hardness and electrical conductivity was observed, and could be linked with the excessive use of fertilizers for agricultural production. Bio-markers study indicates that the accumulation of As in hair and nail is related with the construction of exposure scenario with time dimension. The strength and weakness of the on-going West Bengal and Bangladesh drinking water supply scenario and achievability towards alternative options are also evaluated.

Heteroatom assisted C-H bond activation of 2-substituted naphthyridines with solvated Pd(I)2(CH3CN)6(BF4)2 provides bi- and trinuclear Pd(II) cyclometalated complexes, which provide valuable insight into potential intermediates in palladium catalyzed direct arylation reactions.

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