Nickel(II) complexes containing thiosemicarbazone ligands [Ni(L)₂] (1-3) (L = 9,10-phenanthrenequinonethiosemicarbazone (HL₁), 9,10-phenanthrenequinone-N-methylthio semicarbazone (HL₂) and 9, 10-phenanthrenequinone-N-phenylthiosemicarbazone (HL₃)) have been synthesized and characterized by elemental analysis and spectroscopic (IR, UV-Vis, ¹H, ¹³C-NMR and ESI mass) methods. The molecular structures of complexes 1 and 2 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate ONS fashion. The catalytic activity of complexes towards some C–C coupling reactions (viz., Kumada-Corriu, Suzuki-Miyaura and Sonogashira) has been examined. The complexes behave as efficient catalysts in the Kumada-Corriu and Sonogashira coupling reactions rather than Suzuki-Miyaura coupling.

The present contribution describes the synthesis and characterization of a family of robust ruthenium complexes, supported by a tridentate pincer ligand of the type bis-phenolate-𝑁-heterocyclic carbene [^𝑡Bu(OCO)²⁻] (NHC). Ruthenium(II) complexes (1-3) bearing bis-phenolate-𝑁-heterocyclic carbene ligand were synthesized in good yields by the reaction of imidazolinium proligand (HL) with metal precursors [RuHCl(CO)(EPh₃)₂(B)] (E = P or As; B = PPh₃, AsPh₃ or Py) by transmetalation from the corresponding silver carbene complex. All the Ru(II)-NHC complexes have been characterized by elemental analyses, spectroscopic methods as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The tridentate nature of the ^𝑡Bu(OCO)²⁻ ligand as well as some level of steric protection provided by the ^𝑡Bu groups may rationalize the excellent stability of the Ru-C_carbene bond in the present systems. Moreover, for the explorations of catalytic potential of the synthesized compounds, all the three [Ru-NHC] complexes (1-3) were tested as catalysts for amidation of alcohols with amines. Notably, the complex 1 was found to be very efficient and versatile catalyst towards amidation of a wide range of alcohols with amines.

A series of four imidazolium salts was synthesized by the reaction of 2-bromopyridine with 1- substituted imidazoles. These imidazolium salts (1a–d) were successfully employed as ligand precursors for the syntheses of new ruthenium(II) complexes bearing neutral bidentate ligands of N-heterocyclic carbene and pyridine donor moiety. The NHC-ruthenium(II) complexes (3a–d) were synthesized by reacting the appropriately substituted pyridine-functionalized N-heterocyclic carbenes with Ag₂O forming the NHC–silver bromide in situ followed by transmetalation with [RuHCl(CO)(PPh₃)₃]. The new complexes were characterized by elemental analyses and spectroscopy (IR, UV-Vis, ¹H, ¹³C, ³¹P-NMR) as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The complexes were shown to be efficient catalysts for the one-pot conversion of various aldehydes to their corresponding primary amides with good to excellent isolated yields using NH₂OH.HCl and NaHCO₃. The effects of solvent, base, temperature, time and catalyst loading were also investigated. A broad range of amides were successfully synthesized with excellent isolated yields using the above optimized protocol. Notably, the complex 3a was found to be a very efficient and versatile catalyst towards amidation of a wide range of aldehydes.

A simple Schiff base probe PADP ((1,2-phenylenebis(azanylylidene)) bis(methanylylidene)) bis(3-(diethylamino)phenol) was synthesized from 4-(diethylamino)salicylaldehyde and o-phenylenediamine and has been characterized using analytical and spectral methods. The emission spectrum of PADP Schiff base shows notable enhancement in the emission intensity at 500 nm in the presence of Al³⁺ in MeOH-H₂O (1:9 v/v). On the other hand, other relevant metal ions did not influence considerably the emission spectrum of PADP. The detection limit and binding constant (Kb) of PADP towards Al³⁺ were found to be 0.104 lM and 3.0 9 10⁶ M^-1 from the fluorescence titration experiments. The 1:1 binding stoichiometry was further determined by Job’s plot and ESI-MS spectroscopy. The MTT assay shows no or negligible toxicnature of probe and thus it was utilized in vitro cell imaging studies of Al³⁺ ions. The results show that the probe PADP could be useful to detect Al³⁺ in an aqueous medium