ONO Pincer Type Research Articles

Suzuki Miyaura cross-coupling of 2-chloropyrazine with arylboronic acids catalyzed by novel palladium(II) ONO pincer complexes

The four novel ONO pincer type hydrazone ligands (H2L1, H2L2, H2L3 and H2L4) and their corresponding palladium(II) complexes of the type [Pd(L)(PPh3)] were synthesized and characterized by using FT-IR, UV–visible, 1H, and 13C NMR and spectroscopic techniques. And single-crystal XRD data revealed that all these complexes were adopted a distorted-square planar structure. These Pd (II) complexes were employed as catalysts for the Suzuki-Miyaura cross-coupling reactions of 2-chloropyrazine with various arylboronic acids and found superior activity under the optimized conditions in H2O/toluene media. The catalytic reaction progressed well with a low catalyst loading (0.01%) under an open-flask condition. The catalyst has demonstrated excellent recyclability.

ONO‐Pincer‐Type Coumarin‐Based Copper(II) Metalates: Effect on Alzheimer's Disease Pathologies in Caenorhabditis elegans

AbstractFour copper(II) complexes 1–4 of 3‐acetylchromene‐2‐one and substituted 3‐acetylchromene‐2‐one derived Schiff bases were synthesized and structurally characterized using analytical and spectral techniques. The molecular structure of complex 1 has been confirmed by single crystal X‐ray diffraction studies, which revealed that ligand 3‐acetylchromene‐2‐one‐4 N‐semicarbazone is coordinated to the metal as ONO pincer type ligand. Two nitrate molecules are coordinated to the copper ion through oxygen atoms, of which one nitrate molecule was found to coordinate via two oxygen atoms, thereby achieving six‐coordination. Preliminary biological studies like DNA and protein binding analyses indicated the binding of the ligands and complexes to CT‐DNA (Calf Thymus DNA) and BSA (Bovine Serum Albumin). We investigated the effects of complexes 1–4 against amyloid‐β (Aβ) toxicity using transgenic Caenorhabditis elegans strains expressing muscle‐ and neuronal‐specific human Aβ1‐42. The results showed that the complexes 2–4 remarkably reduced the Aβ‐induced paralysis phenotype, Aβ plaque deposition, and other Alzheimer's disease‐associated functional deficits in C. elegans by their potent antioxidant and anti‐aggregative properties. Complexes 2–4 delayed Alzheimer's disease pathologies, providing a basis for further investigating these effects on higher models.

Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

Benzoylhydrazone Schiff base–ligated three new ONO pincer–type palladium(II) complexes, [(PdL1(PPh3)] (1), [(PdL2(PPh3)] (2), and [(PdL3(PPh3)] (3), were synthesized by the reaction of the respective ligand, N‐(2‐hydroxybenzylidene)benzohydrazide (HL1), N‐(2‐hydroxy‐3‐methoxybenzylidene)benzohydrazide (HL2), or N‐(5‐bromo‐2‐hydroxybenzylidene) benzohydrazide (HL3), with Pd(OAc)2 and PPh3 in methanol and isolated as air‐stable reddish‐orange crystalline solids in high yields (78%–83%). All three complexes were fully characterized by elemental analysis, Fourier‐transform infrared spectroscopy, UV–Visible, 1H nuclear magnetic resonance (NMR), 13C{1H} NMR, and 31P{1H} NMR spectroscopic studies. The molecular structure of all three complexes was established unambiguously by single‐crystal X‐ray diffraction studies which revealed a distorted square planar geometry of all three complexes. The ONO pincer–type ligands occupied three coordination sites at the palladium, while the fourth site is occupied by the monodentate triphenylphosphine ligand. The catalytic potential of all three complexes was explored in the carbonylative Suzuki coupling of aryl bromides and iodides with arylboronic acids to yield biaryl ketones, using CHCl3 as the source of carbonyl. The reported protocol is convenient and safe as it obviates the use of carbon monoxide (CO) balloons or pressured CO reactors which are otherwise needed for the carbonylation reactions. The methodology has been successfully applied to the synthesis of two antineoplastic drugs, namely, phenstatin and naphthylphenstatin, in good yields (81% and 85%, respectively). Under the optimized reaction conditions, complex 2 exhibited the best catalytic activity in the carbonylative Suzuki couplings. The reported catalysts have wide reaction scope with good functional group tolerance. All catalysts could be retrieved from the reaction after completion and recycled up to three times with insignificant loss in the catalytic activity.

Synthesis and X-ray crystal structures of three new nickel(II) complexes of benzoylhydrazones: Catalytic applications in the synthesis of 2-arylbenzoxazoles

Three new complexes of nickel(II), having general formula [Ni(L1)(PPh3)] (1), [Ni(L1)(4-picoline)] (2), and [Ni(L2)(4-picoline)] (3) were synthesized by the reaction of Ni(OAc)2·4H2O with corresponding benzolyhydrazine-derived Schiff base ligands i.e. [4-(diethylamino)-2-hydroxybenzylidene]-benzohydrazonic acid (H2L1) or [2-(hydroxynaphthalen-1-yl)methylene]-benzohydrazonic acid (H2L2) and PPh3/4-picoline as co-ligand in 1:1:1 ratio in methanol. All the three complexes were air-stable, isolated as reddish brown solids and characterized by Elemental analysis, FT-IR, 1H, 13C{1H}, 31P{1H} NMR spectroscopy and mass spectrometry. The structures of all three complexes were determined by single crystal X-ray diffraction studies which revealed the distorted square planar geometry of the complexes. In these complexes, three coordination sites were occupied by ONO pincer type Schiff base ligand and the fourth site was blocked by phosphorus (P) or nitrogen (N) atom of the co-ligand. The catalytic potential of all three complexes was explored in the synthesis of a series of 2-arylbenzoxazoles from aldehydes and 2-aminophenol, using low catalyst loading (0.5 mol%). Complex 1 was found to be the best catalyst among three complexes, for the synthesis of a series of 2-aryl benzoxazoles. The ease of synthesis, air-stability and robustness of the catalyst, and good TONs are some of the key characteristics of the described catalytic system.

ONO pincer type ligand complexes of Al(III) as efficient catalyst for chemical fixation of CO2 to epoxides at atmospheric pressure

Carbon dioxide, the main cause of environmental pollution, its utilization to produce valuable products is of utmost interest. A series ONO pincer hydrazone based most active mono-nuclear Al(III) complexes were successfully synthesized and characterized with the help of NMR, IR, mass spectrometry and only complex 2a was confirmed by single-crystal analysis. The synthesized Al(III) complexes were then employed as capable catalysts for the solvent-free chemical fixation of CO2 with epoxides at atmospheric pressure and could be reused five times without loss of any catalytic activity. In addition, the catalytic mechanism was investigated by analyzing intermediates via 1H NMR, 13C NMR, and mass MALDI-TOF. The excellent catalytic performance could be due to simultaneous attack and the opening of the epoxide by metal centers to form an alkoxide ion which activates the CO2 the same time.

Chemical fixation of carbon dioxide catalyzed via cobalt (III) ONO pincer ligated complexes

Chemical insertion of carbon dioxide into epoxides under ambient conditions has become one of the most important methods for the construction of cyclic organic carbonates. Various active salen, salophen, and phenolate ligand based complexes have been reported for the synthesis of cyclic organic carbonates. Here we demonstrate a series of ONO pincer type cobalt (III) complexes as efficient catalysts for the cycloaddition of carbon dioxide to epoxides in neat conditions at atmospheric pressure with and without co-catalyst. A turnover number of up to 200,000 under atmospheric pressure is achieved. Moreover, the in situ generated complex shows high activity and the catalyst can be reused for at least 11 cycles without any decline in catalytic performance.

Studies on heterocyclic anchored Cu(II) complexes with ONO pincer type donor ligand as an efficient biomimetic and anticorrosion agent

Four complexes of the composition [Cu(ASBINH) (H2O)],(1), [Cu(ASBINH)imdz],(2), [Cu(ASBINH)py],(3) and [Cu(ASBINH)2],(4) have been synthesized. These complexes are novel due to the presence of newly synthesized ONO tridentate pincer type ligand, anchored with imidazole/pyridine as a co-ligand. The structure of ligand ASBINH and complexes 1–4 has been discussed in the light of molar conductance, magnetic susceptibility, electronic spectra, FT-IR, 1H-NMR, 13C-NMR, ESI-MS, TGA and EPR analysis. The structure of compounds has been satisfactorily modelled by density functional theory calculations. The FT-IR data have suggested the presence of diazo and azomethine group in the ligand and the ligand is coordinated with metal through azomethine-N and phenolic-O. 1H-NMR and 13C-NMR of ligand exhibit correlation coefficient of 0.964 and 0.990 respectively. EPR spectrum of complex 1 at RT and LNT suggests a distorted square-planar geometry around Cu(II). Solvent effects on the keto-enol equilibria of ligand ASBINH were observed using electronic spectra. The ligand was in keto-enol tautomeric equilibrium in polar and non-polar solvents. The μeff values for the complexes fall at ∼1.72 BM which rules out the possibility of any M-M interaction in the structural unit of the complexes. The synthesized complexes display efficiency in the disproportionation reactions of hydrogen peroxide. Moreover, imidazole anchored complex 2 shows excellent catalytic activities for the disproportionation of H2O2. The kinetics of the catalase-like activity was investigated and data was applied to Lineweaver Burk plot, which reveals Michaelis Menten behaviour of complexes. The corrosion inhibition performance of ligand and complexes on mild steel in 1 M HCl solution was studied by weight loss measurement method.

Preparation, characterizations and biological evaluations of new copper(II) complexes containing ONO pincer type ligands

A new heterocyclic Schiff bases, 6‐methyl/8methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde semicarbazones (H2‐6MOQsc‐H) (H2L1) and (H2‐8MOQsc‐H) (H2L2) and their corresponding copper(II) complexes [CuCl2(H2‐6MOQsc‐H)].3H2O (1), [CuCl2(H2‐8MOQsc‐H)].3H2O (2), [CuNO3(H2‐6MOQsc‐H)(H2O)].NO3 (3) and [CuNO3(H2‐8MOQsc‐H)(H2O)].NO3 (4) have been synthesized and characterized by various physicochemical techniques. The single crystal X‐ray diffraction and spectral data revealed that all of the complexes (1‐4), the ligands coordinated to the Cu(II) ion in a neutral manner via ONO donor atoms and all the complexes exhibited distorted squarepyramidal geometry. The consequence of electronegativity and ring size of nitrogen heterocyclic moiety of ONO donor type of copper(II) chelates on nucleic acid interaction and albumin binding was investigated by in vitro experiments. The interaction of compounds with calf‐thymus DNA (CT‐DNA) has been explored by absorption and emission titration, which exposed those ligands/complexes, could bind with CT‐DNA through electrostatic interaction. The results of gel electrophoresis proved the ability of complexes (1‐4) to cleave the pBR322 plasmid DNA. The interaction of serum albumin (BSA) was investigated by UV‐Vis, fluorescence, synchronous and three dimensional fluorescence spectra. In addition, radical scavenging activity, antifungal activity and cytotoxicity of the newly synthesized compounds were also evaluated. From the results of in vitro studies, it is seen that complex 3 has more potential as compared with other complexes and ligands.

Palladium complexes catalyzed regioselective arylation of 2-oxindole via in situ C(sp2)−OH activation mediated by PyBroP

Pd(II) complexes appended with ONO pincer type ligand were synthesized, structurally characterized and successfully applied as catalysts for regieoselective C−2 arylation of 2-oxindole via in situ C (sp2)−OH activation in aqueous-organic media under an open atmosphere at room-temperature. This catalyst was reused up to four cycles. Favourably, the present protocol doesn't require the addition of any external oxidant, additives or phase transfer agents.

ONO pincer type binuclear Pd(II) complex: Synthesis, crystal structure and catalytic utilization of the resulting organopalladium complex in catalytic copper-free Sonogashira coupling reaction

New binuclear palladium (II) complex featuring ONO pincer type hydrazone ligand was synthesized and characterized by spectroscopic and single-crystal XRD analysis. This complex showed excellent catalytic activity towards the copper-free Sonogashira cross coupling reaction. The main advantages over previous methodologies include low catalyst loading, less problematic reaction media (H2O–DMSO) and reusability in homogenous systems for optimal performance.

ChemInform Abstract: ONO Pincer Type Pd(II) Complexes: Synthesis, Crystal Structure and Catalytic Activity Towards C‐2 Arylation of Quinoline Scaffolds.

Four new palladium(II) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. These complexes showed excellent catalytic activity towards the Suzuki–Miyaura cross coupling reaction of 2-chloroquinoline derivatives with various aryl boronic acids. The main advantages over previous methodologies include low catalyst loading, less problematic reaction media (H2O–DMF (80 : 20%)) and a lower reaction temperature of 60 °C for optimal performance.

ONO pincer type Pd(ii) complexes: synthesis, crystal structure and catalytic activity towards C-2 arylation of quinoline scaffolds

Four new palladium(ii) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. Utility of these complexes to catalyze C–C bond formation in quinoline scaffolds were assessed.