Tetranuclear Palladium Research Articles

Synthesis of tetranuclear cyclopalladated complex using thiosemicarbazone derivative ligand: Spectral, biological and molecular docking studies

New tetranuclear Palladium(II) complex, (Pd-(OMe)-TSC)4, has been successfully synthesized from the reaction of potassium tetrachloridopalladate (II) salt (K2[PdCl4]) with methoxy‑functionalized thiosemicarbazone ligand, OMe-TSC, and characterized using various spectroscopic techniques such as FT-IR, UV–Vis, 1H NMR, 13C NMR, 1H-1H COSY, 13C-APT, 1H-13C HMQC, elemental analyses and high-resolution mass spectroscopy. The in-vitro anticancer activity was investigated by using MTT test in breast cancer cells (MCF-7 cell line). Anticancer activity of the complex was higher than ligand and the results inferred that the complex showed comparable activitiy with cis-platin. Furthermore, fluorescence and UV–Vis spectroscopies had been used to investigate the binding interaction of the synthesized samples with Bovine Serum Albumin (BSA). Three different drugs namely, Warfarin, Ibuprofen, and Digoxin, were employed to study the competitive bindings to different sites on BSA. The obtained results demonstrated that the binding sites were mainly located within site I and II of BSA for the (Pd-(OMe)-TSC)4 complex and (OMe)-TSC ligand, respectively. In addition, the suggested structures of ligand and complex have been optimized by semi-emprical method and the aforementioned results of BSA interaction were supported by molecular docking and molecular dynamics calculations. Also, The free binding energies of -4.16 kcal/mol and -5.80 kcal/mol were calculated for the interaction of the ligand and complex with SARS-CoV-2, respectively, which indicated the interaction is a spontaneous process and is a evidence for antiviral potential of (Pd-(OMe)-TSC)4 complex.

Stereoelectronic Profiling of Neutral and Monoanionic Biimidazoles and Mixed Diimines.

14 mono-, di-, and tetranuclear palladium complexes were prepared to study the coordination chemistry of symmetrical and unsymmetrical azole-derived diimines and their anions. The diverse range of complexes obtained highlights the structural and electronic diversities imposed by these ligands. Using the monopalladium species, the electronic properties of selected bidentate ligands were determined, ranked, and compared by 13C NMR spectroscopy, extending the scope of the HEP2 (Huynh electronic parameter 2) scale, which can detect even subtle differences. Moreover, the %Vbur (percentage volume buried) values as an estimate for the steric bulk of some ligands were determined using the solid-state molecular structures of their complexes, and a preliminary stereoelectronic map was established.

Synthesis of a homoleptic tris(silylene)-palladium(0) complex and a silylyne-bridged tetranuclear palladium cluster.

We report the reactions of an iminophosphonamido-silylene (1) with different palladium complexes. The reaction of 1 with [Pd(PPh3)4] furnished a homoleptic tris(silylene)-palladium(0) complex. In contrast, treatment of 1 with [PdMe2(tmeda)] led to the unprecedented formation of a non-planar μ3-silylyne-bridged tetranuclear palladium cluster that contains palladium atoms in different oxidation states.

Synthesis of tetranuclear complex of Pd(II) with thiosemicarbazone ligands derived from 2‐quinolone and its catalytic evaluation in Suzuki–Miyaura‐type coupling reactions and alkoxylation of chloroquinolines

AbstractA tetranuclear palladium(II) complex [(Pd(H‐6MOQtsc‐Ph))4] was obtained from the reaction between 6‐methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde‐4(N)‐phenylthiosemicarbazone [H2‐6MOQtsc‐Ph] and K2[PdCl4]. The ligand and the Pd(II) complex were characterized by Fourier transform infrared spectroscopy (FT‐IR), UV–visible and 1H NMR spectroscopy. X‐ray diffraction studies confirmed the tetrameric nature of the complex with the coordination of ligand through quinolone carbonyl, azomethine nitrogen and thiolate sulfur atoms, and the fourth site is occupied by 2‐quinolone nitrogen atom of the adjacent ligand. The synthesized complex was tested as catalyst in Suzuki–Miyaura coupling reaction between various chloroquinoline derivatives with phenylboronic acid. The reactions afforded unexpected C‐alkoxylated (CO coupling) products instead of more expected C‐arylated (CC coupling) products in the respective alcoholic mediums. However, the reactions with traditional aryl halides probed with very good yield of the corresponding CC coupling products.

Palladium Complexes with Phenoxy- and Amidate-Functionalized N-Heterocyclic Carbene Ligands Based on 3-Phenylimidazo[1,5-a]pyridine: Synthesis and Catalytic Application in Mizoroki–Heck Coupling Reactions with Ortho-Substituted Aryl Chlorides

Mononuclear and tetranuclear palladium complexes with functionalized “abnormal” N-heterocyclic carbene (aNHC) ligands based on 3-phenylimidazo[1,5-a]pyridine were synthesized. All of the new comple...

Cover Feature: Silylene‐Bridged Tetranuclear Palladium Cluster as a Catalyst for Hydrogenation of Alkenes and Alkynes (ChemCatChem 1/2021)

Cover Feature: Silylene‐Bridged Tetranuclear Palladium Cluster as a Catalyst for Hydrogenation of Alkenes and Alkynes (ChemCatChem 1/2021)

Silylene‐Bridged Tetranuclear Palladium Cluster as a Catalyst for Hydrogenation of Alkenes and Alkynes

AbstractA planar tetranuclear palladium cluster was obtained from the reaction of a cyclotetrasilane with [Pd(CNtBu)2]3. Single‐crystal X‐ray diffraction analysis and DFT calculations revealed that the tetranuclear framework of the cluster was supported effectively by the bridging organosilylene ligand. Although [Pd(CNtBu)2]3 as well as mononuclear palladium bis(silyl) complex, cis‐Pd(SiMePh2)2(CNtBu)2, do not act as the effective catalyst, the planar tetranuclear palladium cluster acts as an efficient catalyst for the hydrogenation of alkenes and alkynes including sterically hindered tri‐ and tetra‐substituted alkenes.

Supramolecular Pd(II) complex of DPPF and dithiolate: An efficient catalyst for amino and phenoxycarbonylation using Co2(CO)8 as sustainable C1 source

Highly active, efficient and robust “dppf ligated tetranuclear palladium dithiolate complex” was synthesized and applied as a catalyst for chemical fixation of carbon monoxide for the synthesis value added chemicals such as tertiary amide and aromatic esters. The synthesized catalyst was characterized using different analytical techniques such as elemental analysis, 1H and 31P NMR spectroscopy. The use of Co2(CO)8 as a cheap, less toxic and low melting solid surrogate are additional advantages over the current protocol. The catalyst showed superior activity towards the Amino (10−3 mol % catalyst) and Phenoxycarbonylation (10-2 mol % catalyst) and high TON (104 to 103) and TOF (103 to 102 h-1). The Betol and Lintrin (active drug molecules) were synthesized under an optimized reaction condition. The scalability of the current protocol has been demonstrated up-to the gram level.

Tetranuclear Palladium Complexes of Abnormal N‐Heterocyclic Carbene Ligands and their Catalytic Activities in Mizoroki‐Heck Coupling Reaction of Electron‐Rich Aryl Chlorides

AbstractBased on the ligand scaffold of an imidazolyl/benziimidazolyl moiety and a N‐CH2C(=O)NHPh substituent, two series of ligand precursors with ortho hydroxy groups incorporated on the N‐phenyl rings were prepared. The structural fine tuning of the ligand scaffold allowed the synthesis of tetranuclear palladium complexes with abnormal N‐heterocyclic carbene (aNHC) ligands. For precursors with C2‐methyl blocking groups, pyridine‐assisted C−H bond activation led to the formation of mononuclear tridentate palladium aNHC complexes or tetranuclear complexes with tridentate CNO donors. Representative mononuclear and tetranuclearpalladium aNHC complexes were structurally characterized by X‐ray diffraction studies, revealing very short Pd−C bond distances. The tetranuclear palladium aNHC complexes were very effective in catalyzing Mizoroki‐Heck coupling reaction, and were capable of employing a range of aryl chlorides including deactivated substrates with low palladium loading of 0.2 mol%.magnified image

The chelate-to-bridging shift of phosphane dipalladacycles: convenient synthesis of double A-frame tetranuclear complexes.

Palladacycles of the type [Pd2(Ph2PCH2PPh2-P,P)2(C,N:C,N)] (C,N:C,N = bis(N-2,3,4-trimethoxybenzylidene)-4,4'-sulfonyldianiline or -4,4'-oxydianiline) can undergo a spontaneous slow chelate-to-bridging diphosphane coordination shift in solution. Following this strategy a tailor-made synthetic procedure was devised that culminates in isolation of double A-frame tetranuclear palladium complexes.

Synthesis, characterization and single crystal structures of chiral Schiff base and its tetranuclear palladium complex with Pd[sbnd]O[sbnd]Pd bridging and Pd[sbnd]Pd bonds

A new chiral Schiff base ligand 2-{N-[(2S)-(1-hydroxy-3-phenylpropan-2-yl]ethanimidoyl} phenol ((S)H2L) was obtained by acid catalyzed condensation of (2S)-(−)-2-amino-3-phenyl-1-propanol with 2′-hydroxyacetophenone. The palladium complex was prepared by treating a solution of (S)H2L in acetone with a solution of Na2PdCl4 in water in 1:1 M ratio. The new ligand and its complex were characterized by FT-IR, 1H, 13C{1H} NMR spectroscopy, polarimetry and elemental analysis and their molecular structures were determined by single crystal X-ray diffraction. Both the compounds crystallizes in monoclinic system in the space group P21. There exists an intra [OH⋯N (1.62(5) Å)] and intermolecular [OH⋯O (1.53(5) Å) and CH⋯O (2.59 Å)] hydrogen bonding and secondary interactions in the crystal of (S)H2L. The structure of the palladium complex was found very interesting wherein the ligand coordinated to metal center as tridentate dianionic (O−, N, O−) fashion, (S)-L, resulting in a tetranuclear palladium cluster, [Pd4((S)-L)4]. In these supramolecular structures phenolate oxygen coordinated to Pd(II) ion as PdO terminal bonds [1.934(12) - 1.977(11) Å] and the alkoxide oxygen coordinated as PdOPd bridging bonds [1.993(11) - 2.012(12) Å]. The PdN bond lengths found were in the range of 1.949(13) to 1.919(12) Å. There exists two asymmetric tetranuclear complex molecules in its crystal lattice. There exists very strong metal-metal bond interaction, Pd(2)Pd(3) [3.0410(18) Å] and Pd(6)Pd(7) [3.0517(19) Å] respectively in the two asymmetric units.

Synthesis of Tetranuclear Palladium(II) Complexes and Their Catalytic Activity for Cross-Coupling Reactions.

We have developed a short and simple synthesis of tetranuclear palladium(II) complexes that have been structurally confirmed by X-ray analysis. These complexes were formed in about 30 % overall yield by spontaneous metalation of dimethylaminoarene derivatives and exhibit a high stability. We have studied the utility of the tetranuclear palladium(II) complexes as precatalysts for Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g., for the Suzuki-Miyaura reaction: TON up to 538000 and TOF up to 23400 h-1 at room temperature).

Di‐ and Tetranuclear Palladium(II) Complexes Containing C,N‐Bidentate Furoylhydrazone for Suzuki–Miyaura Reactions

Furoylhydrazones of general formula 4‐R–C6H4–CH=NNH–CO–2‐C4H3O [R = H (HL1) and OCH3 (HL2)] have been conveniently prepared from furan‐2‐carbohydrazide. The reaction of HL1 with Li2[PdCl4] and CH3COONa provided the di‐µ‐chloro‐bridged cyclopalladated complex [Pd(C6H4–CH=N–NH–CO–2‐C4H3O)(µ‐Cl)]2 (1) through aryl C–H bond activation, whereas the unusual tetranuclear cluster [Pd(4‐CH3O–C6H4–CH=N–NH–CO–2‐C4H3O)(µ‐Cl)]4 (2) was obtained from the reaction with ligand HL2. The crystal structures of 1 and 2 show a slightly distorted square‐planar coordination geometry around the palladium ion to which the furoylhydrazone is attached in a bidentate fashion. The two palladium(II) complexes were able to catalyze the Suzuki–Miyaura coupling reactions of phenylboronic acid with aryl halides to afford the desired biaryl derivatives in excellent yields (up to 99.2 %).

Selective B(4)-H Activation of an o-Carboranylthioamide Based on a Palladium Precursor.

Palladium(II)-induced selective B(4)-H activation of an o-carboranylthioamide has been developed. A tetranuclear palladium(II) complex has been obtained in high yield with excellent regioselectivity. DFT calculations have confirmed that the B(4)-borometalate is lower in energy than the corresponding B(3)-borometalate. The product proved to be a good precursor for target mononuclear or trinuclear B(4)-H activated complexes.

The imidazo{[4,5-f][1,10]-phenanthrolin}l-2-ylidene and its palladium complexes: Synthesis, characterization, and application in C-C cross-coupling reactions

1,3-dibutyl-1H-imidazo[4,5-f][1,10]phenanthrolinium iodide, L5.2HI ligand and their mono-, di-, tri-, tetra-nuclear palladium(II) complexes (5.HPF6, 6–8) were synthesized and characterized by elemental analysis, FTIR, UV–visible and NMR spectroscopy. In addition, the complexes (5.HPF6, 6–8) were determined by mass spectrometry (MALDI). The ligand L5.2HI was determined by X-ray diffraction. The complexes (5.HPF6, 6–8) were tested in Suzuki-Miyaura and Mizoroki-Heck reactions at elevated temperatures. The activities of the catalysts were monitored by NMR and GC analysis. We found that the poly-nuclear complexes display better activities compared to the mono-nuclear derivatives, thus proposing that an increase in metal moieties which leads to an increase in activity in cross-coupling reaction.

Synthesis of Aryl-, Benzoyl-, and Iminobenzoyl-Palladium(II) Complexes Derived from N-Phenyl Formamide. Synthesis of a Homoleptic Ball-Shaped Tetranuclear Palladium Complex

The complex [Pd{C6H4NHCHO-2}I(tBubpy)] (A, tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine) reacts with CO or XyNC, affording the benzoyl or iminobenzoyl complexes [Pd{C(O)C6H4NHCHO-2}I(tBubpy)] (1) or [Pd{C(═NXy)C6H4NHCHO-2}I(tBubpy)] (2), respectively. Dehydroiodination of 2 with Tl(acac) (acacH = acetylacetone) produced the iminobenzoyl(amide) complex [Pd{C,N-C(═NXy)C6H4NCHO-2}(tBubpy)] (3) from which complex [Pd{C,N-C(═NXy)C6H4NCHO-2}(CNXy)2] (4) was obtained upon substitution of the tBubpy ligand with 2 equiv of XyNC. Heating complex 3 in mesitylene at 160 °C for 3 h caused tBubpy loss, and the generated coordination vacancies were occupied by the amido oxygen and the iminobenzoyl nitrogen atoms, both acting as bridging ligands to give the tetranuclear species [Pd4{N,O-{C,N-C(═NXy)C6H4NCHO-2}4] (5). Removal of the iodo ligand in A by reacting it with TlOTf (OTf = trifluoromethanesulfonate, triflate) caused coordination of the amido oxygen atom to give the cationic complex [Pd{C,O-C6H4NHCHO-2}(tBubpy)]OTf...

Polydentate chalcogen reagents for the facile preparation of Pd2 and Pd4 complexes

The silylated organochalcogen reagents 1,2-(Me3SiSCH2)2C6H4, and 1,2-(Me3SiSeCH2)2C6H4, were prepared from the corresponding organobromides and lithium trimethylsilanechalcogenolate Li[ESiMe3] (E = S, Se). They have been characterized by multinuclear NMR spectroscopy ((1)H, (13)C, (77)Se) and electrospray ionization mass spectrometry. and react under mild conditions with (1,3-bis(diphenylphosphino)propane)palladium(ii) chloride, [PdCl2(dppp)], to provide the dinuclear organochalcogenolate-bridged complexes [(dppp)2Pd2-μ-κ(2)S-{1,2-(SCH2)2C6H4}]X2, []X2 and [(dppp)2Pd2-μ-κ(2)Se-{1,2-(SeCH2)2C6H4}]X2, []X2 (X = Cl, Br) in good yield, respectively. Furthermore, the tetranuclear palladium complex [(dppp)4Pd4-μ-κ(4)S-{1,2,4,5-(SCH2)4C6H2}]X4, []X4 (X = Cl, Br) can be synthesized from the reaction of the tetrathiotetrasilane 1,2,4,5-(Me3SiSCH2)4C6H2, and [PdCl2(dppp)]. The structures of []X2, []X2 and []X4 were determined by single crystal X-ray diffraction methods. A variety of NMR experiments including two-dimensional homonuclear and heteronuclear correlated spectra were used to probe the solution behaviour of the dinuclear complexes in more detail. These complexes were further characterized by electrospray ionization (ESI) mass spectrometry, and for []X2 and []X2, UV-Vis absorption spectroscopy.

New palladium(II) complexes containing 3-mercapto-1,2,4-triazole ligands: synthesis, characterization, crystal structure, and density functional theory calculations

Two new palladium(II) complexes of 4-amino-3-methyl-1,2,4-triazol-5-thione (H3L) have been synthesized and characterized. The reaction of H3L, palladium(II) chloride, and sodium acetate in a molar ratio 2:1:2 gave the homoleptic binuclear palladium(II) complex [Pd2(H2L)4]·2DMSO (1), while its treatment with palladium(II) chloride, sodium acetate, and triphenylphosphane in a molar ratio 4:4:7:4 gave the tetranuclear palladium(II) complex [Pd4(H2L)2(HL)(L)(PPh3)4]Cl·7MeOH·3H2O (2) with terminal phosphane ligands. All complexes have been characterized by a combination of IR, 1H and 31P NMR spectroscopy, ESI(+) mass spectrometry, and elemental analysis as well as X-ray diffraction studies. On the basis of determined molecular structures, each triazole moiety in the binuclear complex is singly deprotonated, whereas the centrosymmetric tetranuclear complex contains three different 3-mercapto-1,2,4-triazolate moieties, namely singly, twofold, and threefold deprotonated in its solid state. In the binuclear complex, the triazolate ligands act as N,S-bidentate bridging ones and coordinate with the metal centers in a trans-(2,2) fashion. In the tetranuclear complex, the four triazolate ligands act as bridging agents between four metal centers through their thiol sulfur atoms and their endocyclic nitrogen atoms in a head-to-head fashion. In addition, each deprotonated NH2 group of the ligand acts as bridging agent between two adjacent palladium metals. According to density functional theory calculations, the structural constraints imposed by the bridging deprotonated NH2 groups are responsible for the observed close Pd–Pd distance in this complex. No indication for metallophilic interactions was found.

Spectroscopic, thermal characterization and cytotoxic activity of bi-, tri- and tetra-nuclear Pd(II) and Pt(II) complexes with diSchiff base ligands

In this paper; new di-, tri-, and tetra-nuclear Pd(II) and Pt(II) complexes of N,N′-bis(3,4-dihydroxybenzylidene)ethan-1,2-diamine (EDH4), N,N′-bis(3,4-dihydroxy-benzylidene)-benzene-1,2-diamine (PDH4) and N,N′-bis-(3,4-dihydroxybenzylidene)-4,5-dimethyl-1,2-diamine (MPDH4) ligands were synthesized by two different methods. The first method involve the synthesis of the three ligands from condensation reaction of 3,4-dihydroxybenzaldehyde (L′H2) with ethylenediamine (en), o-phenylenediamine (o-PD), or 4,5-dimethyl-1,2-phenylendiamine (DMPD) in a mole ratio of 2:1 followed by the reaction of the resulting Schiff bases ligands with Pd(II) or Pt(II) ions in the presence of 2,2′-dipyridyl (L) to form the di- and tri-nuclear metal complexes. The second method involve the condensation of the Pd complex LPd(II)L′, (L=2,2′-dipyridyl, L′=4-formylbenzene-1,2-bis(olate)) with en, o-PD, or DMPD in a mole ratio of 2:1, respectively, followed by reaction with PdCl2 to form di-, tri-, and tetra-nuclear palladium(II) complexes, respectively. Structures of ligands and metal complexes are characterized by physical properties, FT-IR spectra and nuclear magnetic resonance. The geometries of metal complexes are suggested according to elemental analysis, electronic absorption spectra, thermal analysis, atomic absorption, magnetic susceptibility and molar conductance. Cytotoxic activity against lung large cell carcinoma (H460), prostate carcinoma (DU145), breast adenocarcinoma (MCF-7), amelanotic melanoma (M-14), colon adenocarcinoma (HT-29), and chronic myelogenous leukemia (K562) is also reported.

Reversible switching of the coordination modes of a pyridine-functionalized quinonoid zwitterion; its di- and tetranuclear palladium complexes.

The coordination chemistry of a new functional quinonoid zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)](+) moieties, from the NPy sites in 3, to the N,O donor sites of the quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2-5 and 7.