Hydrazone-Linked Donor-Acceptor Covalent Organic Polymer as a Heterogeneous Photocatalyst for C-S Bond Formation.

In the realm of solar energy utilization, there is a growing focus on designing and implementing effective photocatalytic systems, for the conversion of solar energy into valuable chemical fuels. The potential of Covalent Organic Polymers (COPs) as photocatalysts for visible-light-driven organic transformation has been widely investigated, positioning them as promising candidates in this field. In the design of COPs, introducing a donor-acceptor arrangement facilitates the transfer of electrons from the donor to the acceptor, creating a charge transfer complex and leading to enhanced conductivity and improved charge separation. Here we present a novel hydrazone-linked covalent organic polymer ETBC-PyHz containing TPE donor and pyridine acceptor. Utilizing this, an efficient method has been developed for an oxidative cross-coupling reaction involving C-S bond formation. This process involves arylhydrazines and arenethiols, and results in the production of unsymmetrical diaryl sulfides via the formation of aryl and thioarene radicals. This conversion holds significant importance because the byproducts produced during the process are nitrogen and water, making it environmentally benign.

Towards Sustainable Materials: A Review of Acylhydrazone Chemistry for Reversible Polymers.

Transitioning towards a circular economy, extensive research has focused on dynamic covalent bonds (DCBs) to pave the way for more sustainable materials. These bonds enable debonding and rebonding on demand, as well as facilitating end-of-life recycling. Acylhydrazone/hydrazone chemistry offers a material with high stability under neutral and basic conditions making it a promising candidate for materials research, though the material is susceptible to acid degradation. However, this degradation under acidic conditions can be exploited, making it widely applicable in self-healing and biomedical fields, with potential for reprocessing and recycling. This review highlights studies exploring the reversibility of acylhydrazone/hydrazone bonds in various polymers, altering their properties, and utilizing them in applications such as self-healing, reprocessing, and recycling. The review also focuses on how the mechanical properties are affected by the presence of dynamic linkages, and methods to improve the mechanical performance.

Synthesis, SARS-CoV-2 main protease inhibition, molecular docking and in silico ADME studies of furanochromene-quinoline hydrazone derivatives.

Seven furanochromene-quinoline derivatives containing a hydrazone linker were synthesized by condensing a furanochromene hydrazide with quinoline 2-, 3-, 4-, 5-, 6-, and 8-carbaldehydes, including 8-hydroxyquinoline-2-carbaldehye. Structure-activity correlations were investigated to determine the influence of the location of the hydrazone linker on the quinoline unit on SARS-CoV-2 Mpro enzyme inhibition. The 3-, 5-, 6- and 8-substituted derivatives showed moderate inhibition of SARS-CoV-2 Mpro with IC50 values ranging from 16 to 44 µM. Additionally, all of the derivatives showed strong interaction with the SARS-CoV-2 Mpro substrate binding pocket, with docking energy scores ranging from -8.0 to -8.5 kcal/mol. These values are comparable to that of N3 peptide (-8.1 kcal/mol) and more favorable than GC-373 (-7.6 kcal/mol) and ML-188 (-7.5 kcal/mol), all of which are known SARS-CoV-2 Mpro inhibitors. Furthermore, in silico absorption, distribution, metabolism, and excretion (ADME) profiles indicate that the derivatives have good drug-likeness properties. Overall, this study highlights the potential of the furanochromene-quinoline hydrazone scaffold as a SARS-CoV-2 Mpro inhibitor.

Recent Development on Copper-Sensor and its Biological Applications: A Review.

Metal ion recognition is one of the most prospective research topics in the field of chemical sensors due to its wide range of clinical, biological and environmental applications. In this context, hydrazones are well known compounds that exhibit metal sensing and several biological properties due to the presence of N=CH- bond. Some of the biological properties includes anti-cancer, anti-tumor, anti-oxidant, anti-microbial activities. Hydrazones are also used as a ligand to detect metal ion as well as to generate metal complexes that exhibit medicinal properties. Thus, in recent years, many attempts were made to develop novel ligands with enhanced metal sensing and medicinal properties. In this review, some of the recent development on the hydrazones and their copper complexes are covered from the last few years from 2015-2023. These includes significance of copper ions, synthesis, biological properties, mechanism and metal sensing properties of some of the copper complexes were discussed.

Hydrazone-containing organotin(IV) complexes: synthesis, characterization, antimicrobial, antioxidant activity and molecular-docking studies.

The diorganotin(IV) complexes (5-20) were synthesized in the present research from 4-fluorophenoxyacetic hydrazide and salicylaldehyde derivatives-based hydrazone ligands (1-4) to get an effective biological agent to combat microbial and oxidant deformities. Numerous spectral techniques such as (1H, 13C, 119Sn) NMR, UV-Vis, IR, and mass spectrometry were executed to illuminate the composition of complexes. These techniques ascertained tridentate chelation of hydrazone ligands with tin metal through enolic, phenolic oxygens and imine nitrogen, revealing pentacoordinated geometry of the complexes. The single crystal XRD of complex (5) confirmed distorted trigonal bipyramidal geometry. The TGA studies showed thermal stability up to 180 °C of the complexes, whereas the low conductance observed pointed to the non-electrolytic nature of the compounds. Furthermore, serial dilution assay was implemented to uncover the microbial inhibition efficacy (against six strains) of the compounds using ciprofloxacin and fluconazole. Among the synthesized compounds, (1, 8) exhibited comparable MIC value to standard. The compound (8) was reported as four times more potent than the fluconazole against C. albicans. Using DPPH assay, the antioxidant efficiency was examined which advocates enhanced efficacy of complexes than the ligands. The potency of complex (8) against C. albicans makes it a point of interest for molecular docking investigation, so, complex (8) and its ligand (1) were studied against protein of C. albicans (5TZ1), revealing the more efficacy of complex (binding energy-11.6 kcal/mol) than ligand. Further, the compounds were analysed for ADME prediction which concluded the efficacy of compounds as orally efficient pharmaceuticals.

Organotin(IV) complexes of tridentate (ONO) hydrazone ligands: synthesis, spectral characterization, antituberculosis, antimicrobial, anti-inflammatory, molecular docking and cytotoxicity studies.

Infectious diseases have a significant impact in the historical trajectory of humanity, exerting profound influence on societies, driving advancements in medical science, and significantly impacting individuals on a worldwide scale. Consequently, this research endeavours to identify potent agents combatting tuberculosis, inflammation, and microbial deformities. The investigation focuses on hydrazones (1,2) endowed eight organotin(IV) complexes, where hydrazones were derived from 2-acetyl-1H-indene-1,3(2H)-dione and 2-phenoxypropanehydrazide/2-(2,4-dichlorophenoxy)propanehydrazide. All compounds underwent thorough characterization utilizing a variety of spectral and analytical techniques including, multinuclear NMR, FT-IR, HRMS, UV-Vis, SEM-EDAX, TGA, XRD, molar conductance measurements, establishing the pentacoordinated environment around tin(IV) ion with tridentate (ONO) mode of chelation of hydrazones. Powder XRD revealed the ligand's crystalline and complexes' semi-crystalline nature, while thermal analysis indicated two-step decomposition leaving tin oxide residue. In vitro evaluations utilize microplate alamar blue assay for assessing anti-tuberculosis activity, serial dilution technique for antimicrobial efficacy, and bovine serum albumin method for evaluating anti-inflammatory properties. The complexes exhibited higher biological activities than their respective ligands and the activity of the complexes follow the order: Ph2SnL1-2 > Bu2SnL1-2 > Et2SnL1-2 > Me2SnL1-2. Among them, phenyl complex (10) [Ph2SnL2] displays superior efficacy against TB dysfunction (MIC: 0.0180 ± 0.009 µmol/mL) and also demonstrates exceptional potency in combating inflammation (IC50: 7.27 ± 0.04 µM), and microbial (MIC: 0.0045 µmol/mL) infections, comparable to standard drugs. Additionally, cytotoxicity testing against vero cell line revealed decreased toxicity at lower concentrations, and attenuated by chelation. Phenyl complex (10) [Ph2SnL2] shows promising cytotoxicity at 3.12 µg/mL (19.29 ± 0.09%). Further, The diphenyltin(IV) complex (10), identified as the most effective against TB, shows stronger binding to key 3PTY protein residues (- 42.2 kJ/mol) compared to ligand (2) (- 33.4 kJ/mol), correlating with its superior anti-tuberculosis potency in biological assays. This comprehensive approach aims to actively contribute to ongoing initiatives addressing infectious diseases, thereby advancing global health and overall well-being.

Assessment of Mononuclear/Dinuclear copper acylhydrazone complexes for lung cancer treatment.

Non-platinum metal-based complexes have good potential for cancer treatment. Here, we designed and synthesized five hydrazone copper(II) complexes, [Cu2(HL)2Cl2] 1A, [Cu2(HL)2(NO3)H2O]·NO3 2A, [Cu2(HL)2Br2] 3A, [Cu(L)pyridine] 1B and [Cu(HL)(pyridine)Br] 3B, and evaluated their anti-lung cancer activities. MTT experiments revealed that these copper(II) complexes exhibit higher anticancer activity than cisplatin. Mechanism studies revealed that complex 3A induced G1 phase cell cycle arrest, and induced cell apoptosis via reactive oxygen species (ROS)-mediated mitochondrial dysfunction. Scratch wound healing assay was also performed, revealing that complex 3A have good anti-cell migration activity. Hemolysis assays showed good blood biocompatibility of complex 3A. Furthermore, complex 3A can significantly inhibit the proliferation of A549 3D tumor spheroid. An in vivo anticancer study showed that complex 3A could delays the growth of A549 tumor xenografts with lower systemic toxicity. These results highlight the great possibility of developing highly active copper complexes as anti-lung cancer agents.

Synthesis biological evaluation and molecular docking of isatin hybrids as anti-cancer and anti-microbial agents.

Isatin, known as 1H-indole-2,3-dione, was originally recognised as a synthetic molecule until its discovery in the fruits of the cannonball tree, Couroupita guianensis. It is naturally occurring in plants of the genus Isatis and serves as a metabolic derivative of adrenaline in humans. Isatin possesses significant pharmacological importance, and its synthetic versatility has prompted extensive interest in its derivative compounds due to their diverse biological and pharmacological properties. These derivatives represent a valuable class of heterocyclic compounds with potential applications as precursors for synthesizing numerous valuable drugs. In the pursuit of advancing our research on isatin hybrids, we investigate the utilisation of readily available hydrazonoindolin-2-one and isatin as starting materials for the synthesis of a wide range of analogues. Characterisation of the synthesized compounds was carried out through various analytical techniques. Furthermore, the obtained compounds were subjected to extensive testing to evaluate their anticancer and antimicrobial activities. Specifically, their efficacy against key proteins, namely Staphylococcus aureus protein (PDB ID: 1JIJ), Escherichia coli protein (PDB ID: 1T9U), Pseudomonas aeruginosa protein (PDB ID: 2UV0), and Acinetobacter baumannii protein (PDB ID: 4HKG), was examined through molecular docking calculations. Several molecules, such as 3, 4, 6, 16, and 19, displayed remarkable activity against the renal cancer cell line UO-31. Additionally, the results of antimicrobial activity testing revealed that compound 16 exhibited significant cytotoxicity against Candida albicans and Cryptococcus neoformans. Subsequently, ADME/T calculations were performed to gain insights into the potential effects and reactions of these molecules within human metabolism. This comprehensive study provides valuable insights into the potential pharmacological applications of isatin derivatives and underscores their significance in drug development.

Chemical modification of bradykinin-polymer conjugates for optimum delivery of nanomedicines to tumors.

We recently prepared pH-responsive HPMA copolymer conjugates of bradykinin (P-BK), which release BK in response to the acidic tumor microenvironment, and found that administration of P-BK increased the tumor accumulation and therapeutic efficacy of nanomedicine. Because the release of BK from P-BK determines its onset of action, P-BKs with different release rates were prepared, and their properties were evaluated. The release kinetics were significantly altered by substitution proximal to hydrazone bond, release constant of methyl-substituted P-BK (P-MeBK) was approximately 4- and 80-fold higher than that of cyclopropyl-substituted P-BK (P-CPBK) and phenyl-substituted P-BK (P-PhBK). None of the P-BKs were active, but the release of BK restored their BK-like activity. Pre-administration of the P-BKs increased the tumor accumulation of nanomedicine in C26 tumor-bearing mice by 2- and 1.4-fold for P-MeBK and P-PhBK at 3 and 6 h. Altogether, this study provides insights into the design of pH-responsive nanodrugs with the desired release properties to target acidic lesions such as cancer and inflammation.

P(III)-Mediated Formal Reductive N-H Bond Insertion Reaction of Hydrazones to α-Keto Esters.

A diazo-, metal-, and base-free multi-substituted hydrazone synthesis via a formal reductive N-H bond insertion reactions of hydrazones to α-keto esters has been developed. The protocol features a broad substrate scope and good functional group tolerance, providing N-H bond insertion products in moderate to excellent yields. Moreover, P(III)-mediated N-H functionalization of pharmaceutical containing hydrazone moiety was also successfully achieved.

New Sulfonate Ester-Linked Fluorinated Hydrazone Derivatives as Multitarget Carbonic Anhydrase and Cholinesterase Inhibitors: Design, Synthesis, Biological Evaluation, Molecular Docking and ADME Analysis.

In this study, some new hydrazone derivatives (2a-g) was designed, synthesized for first time, and evaluated as multitarget inhibitors of AChE, BChE, hCA I and hCA II. The chemical structures of new hybrids were confirmed by elemental analysis and some spectroscopic techniques. All tested compounds showed low nanomolar inhibition with IC50 values of in the range of 30.4-264.0 nM against hCA I, 23.2-251.6 nM against hCA II, 12.1-114.3 nM against AChE, and 76.4-134.0 nM against BChE. These compounds inhibited hCA I and AChE more than acetazolamide (AZA) and neostigmine. Among them, compounds 2c and 2e, which have a linear structure, were determined to be the most active inhibitor candidates against these selected enzymes. Molecular docking studies were carried out on the compounds (2a--g), revealing their binding interactions with the active site of AChE, BChE, hCA I and hCA II thus supporting the experimental findings. Additionally, in silico absorption, distribution, metabolism, and excretion (ADME) prediction studies of the obtained compounds (2a--g) with in silico approaches were carried out to determine their solubility, whether they have the potential to cross the blood-brain barrier (BBB), values such as GI absorption and drug likeness principles.

Synthesis, Antimicrobial - Cytotoxic Evaluation, and Molecular Docking Studies of Quinolin-2-one Hydrazones Containing Nitrophenyl or Isonicotinoyl/Nicotinoyl Moiety.

By applying the hybrid molecular strategy, in this study, we reported the synthesis of fifteen quinolin-2-one hydrazones containing nitrophenyl or nicotinonyl/isonicotinoyl moiety, followed by in vitro and in silico evaluations of their potential antimicrobial and anticancer activities. In vitro antimicrobial evaluation of the target compounds on seven pathogenic strains, applying the broth microdilution method, revealed that compound 4a demonstrated the most potential antifungal activity against C. albicans (MIC 512 µg mL-1) and C. krusei (MIC 128 µg mL-1). In vitro cytotoxic evaluation of the target compounds on three human cancer cell lines, employing the MTT method, suggested that compound 5c exhibited the most potential cytotoxicities against HepG2 (IC50 10.19 µM), A549 (IC50 20.43 µM), and MDA-MB-231 (IC50 16.82 µM) cells. Additionally, molecular docking studies were performed to investigate the binding characteristics of compounds 4a and 5c with fungal lanosterol 14α-demethylase and human topoisomerase I-II, respectively, thereby contributing to the elucidation of their in vitro antifungal and cytotoxic properties. Furthermore, compounds 4a and 5c, via SwissADME prediction, could exhibit favorable physicochemical and pharmacokinetic properties. In conclusion, this study provides valuable insights into the potential of quinolin-2-one hydrazones as promising candidates for the development of novel antimicrobial and anticancer agents in the future.

Designing and Synthesis of Novel Fexofenadine-Derived Hydrazone-Schiff Bases as Potential Urease Inhibitors: In-Vitro, Molecular Docking and DFT Investigations.

Thirteen novel hydrazone-Schiff bases (3-15) of fexofenadine were succesfully synthesized, structurally deduced and finally assessed their capability to inhibit urease enzyme (in vitro). In the series, six compounds 12 (IC50=10.19±0.16 µM), 11 (IC50=15.05±1.11 µM), 10 (IC50=17.01±1.23 µM), 9 (IC50=17.22±0.81 µM), 13 (IC50=19.31±0.18 µM), and 14 (IC50=19.62±0.21 µM) displayed strong inhibitory action better than the standard thiourea (IC50=21.14±0.24 µM), while the remaining compounds displayed significant to less inhibition. LUMO and HOMO showed the transferring of charges from molecules to biological transfer and MEP map showed the chemically reactive zone appropriate for drug action are calculated using DFT. AIM charges, non-bonding orbitals, and ELF are also computed. The urease protein binding analysis benefited from the docking studies.

Biological and Computational Studies of Hydrazone based Transition Metal(II) Complexes.

In the chronicles of human history, infectious diseases played a pivotal role, influencing societies, steering advancements in medicine, and significantly impacting the well-being of people worldwide. Consequently, in the pursuit of identifying effective combating agents for infectious ailments, the Co(II), Ni(II), Cu(II), Zn(II) complexes of N'-(4-nitrobenzylidene)benzohydrazide were synthesized in the current investigation. Numerous spectral and physical analysis were conducted to characterize the compounds which revealed octahedral stereochemistry of complexes. The anti-tuberculosis, anti-inflammatory, antibacterial and antifungal investigations demonstrated that the compounds (1-5) have significant efficacy for these infectious ailments. The [Zn(L)2(H2O)2] complex (5) has comparable TB inhibition potency to streptomycin as shown by MIC value of 0.0196 ± 0.0003 µmol/mL. Additionally, the anti-inflammatory, antibacterial and antifungal studies also revealed the comparable inhibiting property of (5) to standard drugs with significant IC50 (07.49 ± 0.08 µM) and MIC (0.0098 µmol/mL) values. Furthermore, pharmacophore modeling with addition of molecular docking, DFT, MESP, ADMET were employed against (1-5) to give a new insight in biological evaluations. The pharmacophore modeling suggested that (5) has a distinctive pharmacophoric features including cationic sites, hydrogen-bond donors and acceptors which provide valuable insights into drug design for pharmacological applications. Moreover, another in silico investigations authenticate the bioactivity of (5).

Synthesis and Antifungal Activity of Coumarin Derivatives Containing Hydrazone Moiety.

Plant disease control mainly relies on pesticides. In this study, a series of coumarin derivatives containing hydrazone moiety were designed and synthesized. The synthesized compounds were characterized and used to evaluate the antifungal activity against four pathogens, Botrytis cinerea, Alternaria solani, Fusarium oxysporum, and Alternaria alternata. The results showed that the inhibition rate of some compounds at 100 µg/mL in 96 hours reached around 70 % against A. alternata, higher than that of the positive control. The corresponding EC50 values were found at around 30 µg/mL. Finally, the compound 3 b was screened out with the lowest EC50 value (19.49 µg/mL). The analysis of SEM and TEM confirmed that the compound 3 b can obviously damage the morphological structure of hyphae, resulting in the depletion of the cells by the destruction of morphological matrix and leakage of contents. RNA sequencing showed that compounds 3 b mainly affected the pentose phosphate pathway, which caused to destroy the layer of mitochondrial structure. Molecular docking showed that compounds 3 b fitted the binding pocket of yeast transketolase and interacted with lysine at the hydrazone structure. Our results suggested that the introduction of hydrazone was an effective strategy for the design of novel bioactive compounds.

Design, synthesis, molecular modeling, in vitro evaluation of novel piperidine-containing hydrazone derivatives as cholinesterase inhibitors.

In an effort to develop new and effective therapeutic agents for Alzheimer's disease, a series of hydrazone derivatives bearing piperidine rings have been designed and synthesized. The chemical structures of the compounds were characterized by various spectroscopic techniques. In vitro antioxidant and cholinesterase activities of the compounds were evaluated. Among the compounds, N12 exhibited the most antioxidant activity in all methods (CUPRAC, FRAP, DPPH, ABTS). In vitro acetylcholinesterase (AChE) activity results of the compounds showed good IC50 values between 14.124 ± 0.084 and 49.680 ± 0.110 µM were obtained (IC50 = 38.842 ± 0.053 µM for Donepezil). Among the compounds, N7 and N6 are much more effective derivatives than the standard compound donepezil with IC50 values of 14.124 ± 0.084 and 17.968 ± 0.072 µM, respectively. In vitro, butyrylcholinesterase (BChE) inhibition values of the compounds were between 13.505 ± 0.025 and 52.230 ± 0.027 µm. Among the compounds, N6 has the highest BChE inhibition with an IC50 value of 13.505 µm in the series. The cytotoxicity and AChE inhibitory activity of the compounds on SH-SY5Y cell lines were also evaluated. Kinetic studies were also performed to determine the behavior of the compounds as competitive or noncompetitive inhibitors. The binding modes of N6, which was determined to be highly effective according to in vitro analyses, with AChE and BChE were investigated using molecular docking studies, and the stability of the complexes was determined by molecular dynamics simulations. These findings indicated that AChE and BChE enzymes maintained their overall structural stability and compactness during interactions with compound N6.

An Effective and Promising Strategy for Plant Protection: Synthesis of L-Carvone-Based Thiazolinone-Hydrazone/Nanochitosan Complexes with Antifungal Activity and Sustained Releasing Performance.

The development of novel natural product-derived nano-pesticide systems with loading capacity and sustained releasing performance of bioactive compounds is considered an effective and promising plant protection strategy. In this work, 25 L-carvone-based thiazolinone-hydrazone compounds 4a~4y were synthesized by the multi-step modification of L-carvone and structurally confirmed. Compound 4h was found to show favorable and broad-spectrum antifungal activity through the in vitro antifungal activity evaluation of compounds 4a~4y against eight phytopathogenic fungi. Thus, it could serve as a leading compound for new antifungal agents in agriculture. Moreover, the L-carvone-based nanochitosan carrier 7 bearing the 1,3,4-thiadiazole-amide group was rationally designed for the loading and sustained releasing applications of compound 4h, synthesized, and characterized. It was proven that carrier 7 had good thermal stability below 200 °C, dispersed well in the aqueous phase to form numerous nanoparticles with a size of~20 nm, and exhibited an unconsolidated and multi-aperture micro-structure. Finally, L-carvone-based thiazolinone-hydrazone/nanochitosan complexes were fabricated and investigated for their sustained releasing behaviors. Among them, complex 7/4h-2 with a well-distributed, compact, and columnar micro-structure displayed the highest encapsulation efficiency and desirable sustained releasing property for compound 4h and thus showed great potential as an antifungal nano-pesticide for further studies.

Shedding Light on Heavy Metal Contamination: Fluorescein-Based Chemosensor for Selective Detection of Hg2+ in Water.

This article discusses the design and analysis of a new chemical chemosensor for detecting mercury(II) ions. The chemosensor is a hydrazone made from 4-methylthiazole-5-carbaldehyde and fluorescein hydrazide. The structure of the chemosensor was confirmed using various methods, including nuclear magnetic resonance spectroscopy, infrared spectroscopy with Fourier transformation, mass spectroscopy, and quantum chemical calculations. The sensor's ability in the highly selective and sensitive discovery of Hg2+ ions in water was demonstrated. The detection limit for mercury(II) ions was determined to be 0.23 µM. The new chemosensor was also used to detect Hg2+ ions in real samples and living cells using fluorescence spectroscopy. Chemosensor 1 and its complex with Hg2+ demonstrate a significant tendency to enter and accumulate in cells even at very low concentrations.

Complexes of Gold(III) with Hydrazones Derived from Pyridoxal: Stability, Structure, and Nature of UV-Vis Spectra.

Pyridoxal and pyridoxal 5'-phosphate are aldehyde forms of B6 vitamin that can easily be transformed into each other in the living organism. The presence of a phosphate group, however, provides the related compounds (e.g., hydrazones) with better solubility in water. In addition, the phosphate group may sometimes act as a binding center for metal ions. In particular, a phosphate group can be a strong ligand for a gold(III) ion, which is of interest for researchers for the anti-tumor and antimicrobial potential of gold(III). This paper aims to answer whether the phosphate group is involved in the complex formation between gold(III) and hydrazones derived from pyridoxal 5'-phosphate. The answer is negative, since the comparison of the stability constants determined for the gold(III) complexes with pyridoxal- and pyridoxal 5'-phosphate-derived hydrazones showed a negligible difference. In addition, quantum chemical calculations confirmed that the preferential coordination of two series of phosphorylated and non-phosphorylated hydrazones to gold(III) ion is similar. The preferential protonation modes for the gold(III) complexes were also determined using experimental and calculated data.

Preparative and Catalytic Properties of MoVI Mononuclear and Metallosupramolecular Coordination Assemblies Bearing Hydrazonato Ligands.

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H2L1), nicotinic hydrazide (H2L2), 2-aminobenzhydrazide (H2L3), or 4-aminobenzhydrazide (H2L4)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO2(L1,2)]n (1 and 2) and [MoO2(L3,4)]2 (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO2(L1-4)(MeOH)] (1a-4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes.