The clinical utility of platinum-based chemotherapeutics is limited by severe toxicity and acquired resistance, motivating the development of alternative metallo drugs. Here, we report a series of rhenium complexes, Re[HL1-4]3, synthesized via reduction of Re(VII) precursors followed by coordination with aromatic thiohydrazide ligands. The lead complex, Re[HL2]3, adopts an unusual trigonal-prismatic geometry and a favorable redox profile, correlating with enhanced cytotoxic potency. It demonstrates selective antiproliferative activity against cancer cells with minimal toxicity toward nonmalignant cells in both 2D and 3D culture systems. Mechanistic studies reveal DNA binding, induction of DNA damage, and reactive oxygen species (ROS) generation, triggering apoptosis via PARP and caspase 3 cleavage. Pharmacokinetic analysis indicates moderate stability and plasma retention, supporting sustained therapeutic levels while limiting accumulation-related toxicity. In a syngeneic 4T1 murine breast cancer model, Re[HL2]3 significantly inhibited tumor growth without observable systemic toxicity, supporting its further preclinical evaluation.

Iron–ascorbate (Fe–Asc) is a clinically approved drug for iron-deficiency anemia (IDA), yet its formation and redox behavior under varying conditions remain poorly understood. Herein, we report the first comprehensive examination of Fe–Asc formation and redox reactivity in Tris buffer as a function of stoichiometry, pH, and oxygen availability. Oxidation of Fe(II) in air-saturated buffer accelerates with pH, yielding multiple species, primarily di- and tri-nuclear clusters. Notably, FeSO₄ with AscH produces a distinct purple complex (λmax = 510 nm), whose assembly depends critically on O₂, 1:3 stoichiometry of Fe: AscH, and buffer pH 7.5, whereas no such species forms anaerobically. ESI-MS suggests trinuclear clusters, whose stability and redox dynamics are monitored by time-resolved absorbance. The purple color disappears with dithionite or H₂O₂, but dithionite-treated samples regain color upon air exposure, demonstrating redox reversibility. Electrochemically, FeSO₄ shows cathodic (-0.32 V) and anodic (-0.06 V) peaks vs. Ag/AgCl, but the cathodic current decreases markedly in presence of AscH, reflecting Fe–Asc interactions. EPR spectra of FeSO₄ and FeSO₄/AscH are similar, with g = 9.43, 4.37 (high-spin Fe(III), S = 5/2) and g = 1.92 (S = ½, [Fe(III)–Fe(II)] coupling). These results suggest the formation of mixed valence trinuclear clusters with a dynamic ligand environment. The interaction between Fe and AscH with a specific stoichiometric ratio (Fe: AscH; 1:3), in Tris-buffer at pH7.5 under aerobic conditions, forms a purple complex, suggested as a mixed valence cluster, whereas anaerobic or dithionite-treated purple solutions yield a colorless solution that can reversibly interconvert with the purple form.

The synthesis and characterization of two new square planer Ni(II)-azido complexes [Ni(N3)(L)]-1 of 1-N3 and 2-N3 using electronically varied N/S/O donor tridentate ligands (where H2LOMe: (E)-2-(((2-mercaptophenyl)imino)methyl)-6-methoxyphenol), H2Lt Bu: (E)-2,4-di-tert-butyl-6-(((2-mercaptophenyl)imino)methyl)phenol) were reported. Azido moiety in Ni-azido complexes was found as more dipolar than free azide ion. Six number of [3+2] cycloaddition coupling product of 1-N3/2-N3 and three different alkynes were isolated and well characterized as [Ni(triazolate)(L)]-1 (1/ t Bu-T) complexes. In triazolate complexes originated from terminal alkyne, the triazolate ligand was coordinated via the N1-T atom whose (1-T2) crystal structure was presented. The triazolato products of symmetrical and unsymmetrical nonterminal alkynes were isolated as N2-T mode of binding. The conversion of N1-T/N3-T to N2-T as well as the stability in a particular mode of binding was proposed as thermal control of their equilibrium based on the variable temperature 19F NMR studies on 1-T3/2-T3. The detail kinetic studies resulted that the reaction with methyl propiolate follows zero-order rate law, whereas other two alkynes showed first-order rate. Mostly, the electron-poor ethyl-4,4,4-trifluorobut-2-ynoate always react faster than dimethyl but-2-ynedioate, and Ni(II)-azido complex with Lt Bu ligated always react with a particular alkyne in a faster rate than the same of LOMe.

Sometimes unusual redox chemistry and modulation of enzyme activity Cu-proteins can be encountered by the presence of a trace amount of Cu-Tris interaction (Tris-(hydroxymethyl) aminomethane) during vitro studies. Herein, we addressed a redox chemistry of Cu-II-Tris with variable stoichiometric ratios in the presence of ascorbic acid (H(2)A) and O-2. The redox chemistry of Bs3 (Cu : Tris; 1 : 3) with H(2)A/O-2 was passed through several intermediates with progress on time yielding initially yellow precipitate, (Yp3), then green solution, (Gs3) and finally cyan solution (Cs3). The UV-Vis spectra of Bs3, Gs3 and Cs3 displayed peaks at 640, 690 and 710 nm respectively suggesting Cu-II. The redox potential of Cu-II/Cu-I in Bs3, Gs3 and Cs3 were -0.18 V, -0.15 V and -0.19 V (vs. Ag/AgCl) respectively. The EPR spectrum of Bs3 showed an axial signal with g(parallel to),(perpendicular to)=2.483/2.105 & A(parallel to)=160x10(-4) cm(-1) whereas Gs3 and Cs3 showed rhombic signal with g(1,2,3)=2.302/2.063/2.018 & A(parallel to)=177x10(-4) cm(-1) and g(1,2,3)=2.274/2.064/2.016 & A(parallel to)=164x10(-4) cm(-1) respectively suggesting a distorted tetragonal geometry. ESI-MS data indicated the probable composition of Bs2-Bs5, Gs3 and Cs3 in solution. Integration of all spectroscopies data demonstrated the probable composition and redox mechanism.

In mitochondria, the detoxification of molar excess H2S as polysulfide proceeded via an oxidation process promoted by Cu/Zn containing superoxide dismutase (SOD1) enzyme, which has been very recently reported as the alternative enzyme for cytosolic H2S oxidation. Herein, we present Ni(II) complexes bearing the terminal SH group as a synthetic functional analogue for the sulfide oxidase function of SOD1. Synthesis, crystal structure and complete spectroscopic characterization of two sets of complexes, [NiLOMe/tBu(PPh3)] (2OMe/tBu) and tetraethyl salt of [NiLOMe/tBu(SH)]-1 (3OMe/tBu), were described (LOMe = (E)-2-methoxy-6-(((2-sulfidophenyl)imino)methyl)phenolate and LtBu = (E)-2,4-di-tert-butyl-6-(((2-sulfidophenyl)imino)methyl)phenolate). Under anaerobic conditions, 3OMe/tBu responded to a catalytic sulfur atom transfer (SAT) reaction with PPh3 to produce SPPh3. The SAT reaction was analyzed using detailed studies of 1H and 31P NMR spectra. Finally, the SAT reactivity pattern was compared with the same in the native enzyme of SOD1.

The novel tetra-triazolium salt 1, featuring a tetrasubstituted central adamantane backbone, is introduced for the synthesis of tetranuclear PdII MIC complexes by quadruple C5–H deprotonation and subsequent addition of the corresponding PdII precursors. The three newly prepared palladium(II) complexes appeared to be stable and have been characterized using standard spectroscopic and HRMS techniques. The molecular structure of the tetranuclear PdII complex bearing a 4-methoxypyridine ligand has been established by using single-crystal XRD. All three newly prepared tetranuclear PdII complexes appeared as active precatalysts for the Sonogashira coupling reaction, which occurred in a homogeneous fashion; however, only the palladium(II) complex bearing a combination of MIC and phosphine ligands was found to be active for the intermolecular α-arylation of 1-methyl-2-oxindole, as the complexes bearing a pyridine or a 4-methoxypyridine ligand decomposed to Pd0 NPs and appeared to be inactive in the α-arylation reaction. The ancillary-ligand-dependent (Py vs PPh3) interplay between homogeneous and heterogeneous catalyses has also been correlated with the catalytic outcomes in α-arylation of 1-methyl-2-oxindole. The electrochemical responses of these complexes have been measured, and the effect of ancillary ligands in both electrochemistry and catalysis has also been examined.

The synthesis, characterization, and catalytic application of six aluminum alkyl complexes supported by various imino-phosphanamidinate chalcogenide ligands are described. Six different unsymmetrical imino-phosphanamidinate chalcogenide ligands [NHIRP(Ph)(E)NH-Dipp] [R = 2,6-diisopropylphenyl (Dipp), E = S (2a-H), Se (2b-H); R = mesityl (Mes), E = S (3a-H), Se (3b-H); R = tert-butyl (tBu), E = S (4a-H), Se (4b-H)] were prepared by the oxidation of respective imino-phosphanamide ligands (1a, 1b and 1c) with elemental chalcogen atoms (S and Se). The aluminum complexes with imino-phosphanamidinate chalcogenide ligands with the general formulae [κ2NN-{NHIRP(Ph)(E)N-Dipp}AlMe2] [R = Dipp, E = S (5a), Se (5b); R = Mes, E = S (6a), Se (6b)] or [κ2NE-{NHIRP(Ph)(E)N-Dipp}AlMe2] [R = tBu, E = S (7a), Se (7b)] were synthesized in good yields from the reaction of the suitable protic ligands (2a,b-H-4a,b-H) and trimethylaluminum in a 1 : 1 molar ratio in toluene at room temperature. All the protic ligands and aluminum complexes were well characterized by multi-nuclear NMR spectroscopy, and the solid-state structures of 2a,b-H-4a,b-H, 5a,b-6a,b and 7b are established by single crystal X-ray diffraction analysis. The aluminum complexes 5a,b-7a,b were tested as catalysts for the hydroboration of nitriles, alkynes, and alkenes under mild conditions. The catalytic hydroboration reactions of nitriles, alkynes, and alkenes were accomplished with complex 5b at a mild temperature under solvent-free conditions to afford a high yield of the corresponding N,N-diborylamines, vinylboranes and alkyl boronate esters, respectively.

Competitive required electron donating effect either from aryl group or metal–imine moiety could facilities the 1,5-proton transfer in the unusual amine–imine inter-conversion of conjugated amine–ene–imine ligands.

Electronically varied Zn complexes as a common catalytic platform to activate CO 2 and CS 2 under mild and solvent-free conditions, which selectively yielded cyclic carbonates or cyclic thiocarbonates.

Bimetallic palladium(II) complexes containing classical NHC donor ligands are becoming increasingly popular owing to their various catalytic applications. However, examples of the aforementioned complexes with mixed NHC/PPh3 ligands are still rare. Bimetallic palladium(II) complexes possessing these mixed ligands are described starting from a C2‐symmetric bis‐imidazolium salt containing 4,4′‐substituted central biphenyl ring. All the palladium(II) complexes have been tested as precatalysts in α‐arylation of oxindole and Suzuki–Miyaura coupling reactions. The complex composed of mixed NHC/PPh3 donor ligands shows superior catalytic activity compared with the corresponding PEPPSI type complexes when applied in α‐arylation of oxindole. The dinuclear complexes display better activity compared with the mononuclear complexes. The preliminary electrochemical measurements show the facile oxidation of PdII in the presence of combined NHC/PPh3 ligands compared with a combination of NHC/Py ligands.

The catecholase activities were routinely modeled using transition metal complexes as catalyst and in some case basic pH were used as a reaction condition. In this article, the catalytic aerobic oxidation of proxy substrate 3,5-di-tert-butylcatechol (DTBC) in methanol using triethylamine/diethylamine as catalyst was demonstrated as a functional mimic of catecholase activity. The kinetic manifestation of DTBC oxidation was explained as enzymatic substrate inhibition pattern in Michaelis-Menten kinetic model. The mechanistic insight of the aerobic oxidation of DTBC was further validated using various spectroscopic techniques and DFT methods.

Herein, we report two newly synthesized salen-type ligands, 2,3-bis((3,5-di-tert-butyl-2-hydroxybenzyl)thio)maleonitrile (H2L1) and 2,3-bis((3,5-di-tert-butyl-2- hydroxybenzyl)amino)malenonitrile (H4L2), bearing different coordination sites (sulfur vs amine) at maleonitrile tethered moiety to investigate metal mediated non-innocence chemistry of these ligands. Upon metallation, ligand H2L1 did not yield simple metal-ligand complex, rather ligand was split into two organic fragments, dithiolene moiety (mnt)(2-) and phenol moiety via C-S bond cleavage wherein (mnt)(2-) formed a stable metal complex [M(mnt)(2])(2-). The C-S bond cleavage was interpreted in terms of strong p(pi)...d(pi) interaction between metal and dithiolene moiety in H2L1 ligand that invoked the intramolecular rearrangement facilitating C-S bond cleavage. Interestingly, the phenol moiety further transformed to either unprecedented 2,4-di-tert-butyl-6-methylenecyclohexa-2,4-dien-one (i.e. spiro compound; 5) or 2,4-di-tert-butyl-6-(hydroxymethyl)phenol (6) depending on the temperature of reaction and type of metal ion used which was further predicted using DFT calculation. On the other hand, combined experimental and DFT studies explained that upon metallation, ligand H4L2 yielded non-cleavage [M(H2L2)] (3 for M-Cu(II) and 4 for M-Ni(II) ) complex, which slowly oxidized at -NH-CH2-(amine) region to N-CH (imine) in H2L2 ligand under aerobic environment via C-H bond activation, yielding [Cu-II(L-3)] (1) (or [Ni-II(L-3)] (2) complex (H2L3 = oxidatively dehydrogenated prod- uct of H4L2 ligand.

Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, [Et4N]2[(mnt)Cu-SH] (2, mnt = maleonitrile dithiolene = S2C2(CN)2) and [Et4N]3[(mnt)Cu-(μ-SH)-Cu(mnt)] (3), have been synthesized. Coordination sites and O2 activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O2 activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O2 (ambient O2 from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

A tetranuclear Ni-complex of [(NiL)4] (1) (where H 2 L = (E)-2-(((2-mercaptophenyl)imino)methyl)-6-methoxyphenol) was synthesized and fully characterized. The solvent dependent behaviour of 1 showed the existence of monomeric species which was well explained using several spectroscopic evidences. Compound [NiL(PPh3)] (2) and [LNi(dppe)NiL] (3) were synthesized by the reaction of 1 with respective phosphine in acetone (dppe = (Ph2PCH2CH2PPh2). All Ni-complexes were characterized by x-ray structure analysis and other spectroscopy like NMR, ESI+ etc. The electrochemical responses for all Ni-complexes were explained. The reactivity of 2 and 3 with H2O2 and tBuOOH were explored in homogenous solution which identified that coordinated phosphine group at Ni(II) centre was oxidized and the reaction was preceded via oxygen atom transfer (OAT) reaction. The mechanism of OAT reaction of 2 with H2O2 was proposed based on the detection of the intermediates using several possible spectroscopic tools and density functional theory (DFT) calculation approaches which demonstrated the highly exothermic nature of overall reaction (ΔG sol = -85.3 Kcal) and the reaction pathway involved the oxidative addition of H 2 O 2 at Ni(II) center to form an intermediate Ni(IV) (OH)2 complex (INT1) followed by the reductive elimination of O=PPh3 occurred.

We herein report two salicyaldehyde-quinoxaline (HQS and HQSN) conjugates and a benzaldehyde-quinoxaline (QBN) conjugate to fabricate selective chemosensors for F- and Hg2+ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, -NEt2 , in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F- , whereas HQSN and QBN are selective for Hg2+ . In order to gain insights into the mechanism of sensing, geometry optimizations have been carried out on QS(-1) , QS(-1) ⋅⋅⋅HF, QSN(-1) and QSN(-1) ⋅⋅⋅HF and the experimental data are validated in terms of free energy and pKa values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.

Two configurationally isomeric ligands, namely, 2-((E)-benzylideneamino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (HL1) and 2-(benzylamino)-3-((E)-(pyridin-2-ylmethylene)amino)maleonitrile (HL2), were synthesized and fully characterized, which are malenonitrile-tethered, N atom donors tridentate ligands. Structurally, they differ in the interchangeable position of amine and imine group only. Under the same reaction condition, Ni(II) invoked the transformation of (L1)- to (L2)- via simultaneous oxidation of amine to imine and the reduction of imine to amine. Two sequential 1,5-proton transfer pathways were anticipated for this type of unusual amine-imine oxidation/reduction process under acidic medium. In contrast, Co(II) was silent to such amine-imine interconversion reactions under both HL1 and HL2 ligand environment. The variation in electronic requirement might differentiate between both ligands such that HL2 influenced the arial oxidation of Co(II) to Co(III) but HL1 could not. The redox chemistry of Co(II)/Co(III) complexes with either HL1 or HL2 was explained using cyclic voltammetry and UV-vis spectroscopy.

In this work, we have strategically incorporated a quinoxaline derivative and a diaminomaleonitrile moiety to construct a chemosensor, 2-amino-3-[(quinoxalin-2-ylmethylene)-amino]-but-2-enedinitrile (H2qm). The notable feature of this strategy is to generate a highly conjugated Schiff base platform with interesting binding properties. Remarkably, H2qm exhibited a visual sensing ability towards Cu2+ in 100% aqueous medium. The effectiveness of the chemosensor has been demonstrated by utilizing it to determine the Cu2+ concentration in real samples. Interestingly, the reaction between H2qm and Cu(ClO4)2·6H2O in DMSO yielded a quinoxaline-2-carboxylic acid based compound and single crystal X-ray diffraction analysis unveiled the resulting structure as [(qa)2Cu(H2O)2] (Hqa = quinoxaline-2-carboxylic acid).