Trinuclear Pd Research Articles

Linkage Isomers of Triangular Pd Metallacycles and Catalysis in Aqueous Suzuki Coupling Reaction.

The water-soluble trinuclear Pd metallacycles [Pd(tmeda)(4-Spy)]3(X)3 (tmeda = tetramethylethylenediamine, X = OTf, 2; NO3, 3) were synthesized from the ambidentate ligand 4-pyridylthiolate (Spy-) and [Pd(tmeda)X2] in 80 and 70% yield, respectively. Two possible linkage isomers are found in solution (slow interconversion found in the NMR) and in the solid state. Density functional calculations showed that the energy of the isomer with a D3-symmetric arrangement of the SPy ligand and all Pd atoms having N∧NPdSN coordination is only 7 kcal/mol lower. When reacting [Pd(tmeda)(NO3)2] with 4,4'-biphenyldithiolate (S2bph2-), the tetranuclear [{Pd(tmeda)}4(μ-S2bph)2](NO3)4 (1) was formed. A new type of undecanuclear Pd cluster was separated as a minor product from an acetone solution of 2 in air. The new complexes represent the first examples of water-soluble Pd metallacycles constructed from a pyridine-thiolate ligand. They show catalytic activity with turnover numbers ranging from 9 to 420 in aqueous Suzuki cross-coupling reactions using phenyl boronic acid and a number of aryl halides. An optimized system gave a TON of 6,900,000 and a TOF of 492,857 h-1. The catalyst could be reused eight times, and the activity has been attributed to the formation of PdNPs.

A triradical-containing trinuclear Pd(II) complex: spin-polarized electronic transmission, analog resistive switching and neuromorphic advancements.

Neuromorphic computation has emerged as a potential alternative to subvert the von Neumann bottleneck issue in conventional computing. In this context, the development of resistive switching-based memristor devices mimicking various synaptic functionalities has engendered paramount attention. Here, we report a triradical-containing trinuclear Pd(II) cluster with a cyclohexane-like framework constituted by the Pd-Se coordination motif displaying facile memristor property with neuromorphic functionality as a thin-film device. The metal-ligand complex (complex 1) possessed an St = 1/2 ground state by experiencing a spin-frustrated-type magnetic coupling phenomenon amongst the three ligand-based organic radicals (SR = 1/2), coordinated to the Pd(II) ions. Three reversible one-electron reduction waves countered with a one-electron and one two-electron reversible oxidation waves were noticed in the cyclic voltammogram of the complex, confirming electrons accepting and releasing capacity of the complex at low potentials, i.e., within +0.2 V to -1.1 V. Employing the radical-containing complex 1 as the active thin-film sandwiched between two orthogonal electrodes, resistive switching based memristor property with biological synaptic actions were successfully emulated. Intriguingly, the artificial neural network (ANN) simulated efficient pattern recognition demonstrated using the recorded potentiation and depression curves from the device, which is a step ahead for the hardware realization of neuromorphic computing. The performance of the ANN on MNIST data with reduced image resolution has further been evaluated. Density functional theory (DFT)-based theoretical calculation predicted that the spin-polarized electronic transmission substantiated the memristive property in the neutral complex 1.

Effect of the nuclearity on the catalytic performance of a series of Pd(II) complexes in the Suzuki-Miyaura reaction

Development of well-defined multivalent systems with densely packed multiple functional groups located within a single molecular structure provides an excellent opportunity to generate catalysts of enhanced activity. A series of mono-, di- and trinuclear Pd(II) complexes based on polyketonate ligands allied with 2,2′-bipyridine has been designed, synthesized and fully characterized in both solution and solid state. The mono-, di- and tritopic β-diketonate molecules serve as scaffolds for Pd(II) active sites which, in the two latter cases, are forced into close proximity. Application of the complexes as catalysts in Suzuki-Miyaura cross-coupling as a model reaction has revealed significant differences in reaction yields and a trend in reactivity reflecting their nuclearity.

Mechanistic understanding of methane combustion over H-SSZ-13 zeolite encapsulated palladium nanocluster catalysts

Catalytic methane (CH4) combustion to CO2 and H2O is of great practical significance and an important prototype catalytic reaction. Extensive experimental studies have suggested that zeolite supported palladium (Pd) catalysts are very active for catalytic CH4 oxidation, while the structure-performance relationship is still not clear. Herein, using H-SSZ-13 zeolite encapsulated Pd nanoclusters as a demonstration case, reaction mechanisms and kinetics of complete CH4 combustion were systematically investigated using first-principles density functional theory (DFT) calculations combined with atomistic thermodynamic analysis and the energetic span model (ESM). Four H-SSZ-13 zeolite encapsulated PdⅡxOmHn model catalysts, i.e., PdⅡ/H-SSZ-13, PdⅡO/H-SSZ-13, PdⅡ2O/H-SSZ-13, and PdⅡ3O3H/H-SSZ-13 were studied. The encapsulated [PdⅡ2O]2+ and [PdⅡ3O3H]+ nanoclusters were identified as the most stable binuclear and trinuclear Pd structures under experimental oxidative conditions. DFT calculations indicated that the most kinetically relevant step in the complete CH4 oxidation reaction over four Pd model catalysts is different. The first, third, third, and fourth C–H bond cleavage were identified as the most kinetically relevant steps over PdⅡ/H-SSZ-13, PdⅡO/H-SSZ-13, PdⅡ2O/H-SSZ-13, and PdⅡ3O3H/H-SSZ-13, respectively. Using the energetic span model, the relative turnover frequencies of CH4 oxidation over four PdⅡxOmHn/H-SSZ-13 model catalysts were calculated. Consistent with recent experimental observation, the encapsulated PdⅡ3O3H/H-SSZ-13 nanocluster was found to be the most active catalyst for complete CH4 oxidation. On the basis of DFT results and the ESM model analysis, it is noted that the reaction rate of complete CH4 oxidation over the PdⅡxOmHn/H-SSZ-13 catalysts is not completely dependent on one “highest” activation barrier, i.e., the barrier for the most kinetically relevant step. Neither one specific transition state nor one reaction step carried all the kinetics information that determines the catalytic performance of the PdⅡxOmHn/H-SSZ-13 catalysts. The present work sheds light on the structure-performance relationship for CH4 combustion over the zeolite supported noble metal catalysts.

Star-shaped Pd(II) and Pt(II) complexes containing C3-symmetric conjugated thiophenes: Synthesis, characterization, and chemical reactions with organic unsaturated molecules

Triple oxidative addition reactions of [M0(styrene)(PMe3)2] (M = Pd/Pt) with C3-symmetric star-shaped molecules containing 1-, 3-, and 5-thiophene-substituted benzene, in 1:0.3 ratio, afforded new Pd(II) and Pt(II) trinuclear complexes in suitable yields. Analogous trinuclear complexes were formed by similar reactions of thiophenyl halide derivatives containing triazine or triphenylamine cores. Alternatively, a trinuclear Pd(II) complex was obtained by oxidative addition of a Pd(0) complex (synthesized from allyl(cyclopentadienyl) palladium(II), [(η5-C5H5)Pd(η3-C3H5)] with PEt3. Sonogashira-type coupling between trinuclear Pt(II) halides (containing C3-symmetric conjugated thiophenes) and alkynes, in the presence of cuprous halide and diethylamine, afforded alkynyl-containing trinuclear Pt(II) complexes with extended π-conjugation. Insertion reactions of organic isocyanides (CN-R) with trinuclear Pd(II) complexes yielded trinuclear Pd(II) imidoyl complexes by insertion of CN-R into Pd-carbon (thiophene) bonds. Reactions of trinuclear Pt(II) halides with Ag(OCOCF3) and NaN3 formed pseudohalogen-containing Pt(II) complexes.

Polyanionic Imido-P(V) Ligands: From Transition Metal Complexes to Coordination Driven Self-Assemblies.

The chemistry of the imido-anions of the main group elements has been studied for more than three decades. The imido (NR)- group is isoelectronic to the oxo (=O) group and can coordinate with metal ions through its lone pairs of electrons. The polyimido-P(V) anions are well explored as they resemble the phosphorus oxo moieties such as H3 PO4 , H2 PO4 - , HPO4 2- and PO4 3- species. These imido anions are typically generated using strong main group organometallic reagents such as n BuLi, Et2 Zn, Me3 Al and n Bu2 Mg, etc. As a result, their coordination chemistry has been restricted to reactions in anhydrous aprotic solvents for a few main group metal ions. This account presents our findings on using certain soft transition metal such Ag(I) and Pd (II) for isolating these imido-P(V) anions as their corresponding self-assembled clusters and cages. Using the various salts of Ag(I) ions in reaction with 2-pyridyl (2 Py) functionalized phosphonium salts and phosphoric triamides, we obtained the mono- and dianionic form of these imido ligands {[P(N2 Py)2 (NH2 Py)2 ]- , [P(N2 Py)2 (NH2 Py)]- , [PO(N2 Py)(NH2 Py)2 ]2- } and derived interesting examples of tri, penta, hepta and octanuclear Ag(I) clusters. Interestingly, by using the salts of Pd (II) ions, the elusive imido-phosphate trianions of the type [(RN)3 PO]3- (R=t Bu, c Hex, i Pr) were generated in a facile one pot reaction as their corresponding tri- and hexanuclear clusters of the type {Pd3 [(NR)3 PO](OAc)3 }n (n=1 or 2). These trianions acts as a cis-coordinated hexadentate ligand for a trinuclear Pd (II) cluster and serve as the polyhedral building units for constructing hitherto unknown family of neutral cages in tetrahedral {Pd3 [(Ni Pr)3 PO]4 (L)6 } and cubic {Pd3 [(Ni Pr)3 PO]8 (L)12 } structures in the presence of suitable linker ligands (L2- ). These cages show interesting host-guest chemistry and post-assembly reactions. Remarkably, by employing chiral tris(imido)phosphate trianions, enantiopure chiral cages of the type [(Pd3 X*)4 (L)6 ], ([X*]3- =RRR- or SSS-[PO(N(*CH(CH3 )Ph)3 ]3- ), were synthesized and used for the chiral-recognition and enantio-separation of small racemic guest molecules. Some of these chiral cages were also shown to exhibit polyradical framework structures. In future, these and other similar types of cages are envisioned as potential molecular vessels for performing the reactions in their confined environment. The enantiomeric cages can be probed for asymmetric catalysis and the separation of a range of small chiral molecules.

Rational Synthesis and Electronic Structure of Functionalized Trinuclear Pd Metal Sheet Sandwich Complexes

In this article we present the rational synthesis and full characterization of molecular Pd3 clusters sandwiched by imidazolium- and pyridinium-functionalized cycloheptatrienide ligands, of general formula [Pd3Br3(C7H6R)2]+. From functionalized η3-cycloheptatrienide Pd complexes as starting materials, PdBr2(η3-C7H6R), a number of synthetic routes were tested and a generally applicable strategy was developed on the basis of the formation of dimeric “preclusters”, [{PdBr(η3-C7H6R)}2(μ-Br)]+, which exhibit a Pd–Pd interaction. Spectroscopic and electrochemical results indicate a noninteger, common oxidation state of Pd in the trinuclear clusters, and crystallographic analysis reveals distinct differences in the binding properties of the Pd atoms in the solid state, suggesting that in certain environments there are even two discernible oxidation states, which is supported by computational analysis of the charge distribution.

Structurally different mono-, bi- and trinuclear Pd(ii) complexes and their DNA/protein interaction, DNA cleavage, and anti-oxidant, anti-microbial and cytotoxic studies

A series of new structurally different Pd(ii) complexes was obtained by the reactions between K2[PdCl4], 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazone [H2L1–H2L4] and bis(diphenylphosphino)ethane [dppe].

Catalytic Role of Multinuclear Palladium-Oxygen Intermediates in Aerobic Oxidation Followed by Hydrogen Peroxide Disproportionation.

Aerobic oxidation of alcohols are catalyzed by the Pd-acetate compound [LPd(OAc)]2(OTf)2 (L = neocuproine = 2,9-dimethyl-1,10-phenanthroline) to form ketones and the release of hydrogen peroxide, but the latter rapidly undergoes disproportionation. We employ a series of kinetic and isotope labeling studies made largely possible by electrospray ionization mass spectrometry to determine the role of intermediates in causing this complex chemical transformation. The data suggested that multiple catalytic paths for H2O2 disproportionation occur, which involve formation and consumption of multinuclear Pd species. We find that the trinuclear compound [(LPd)3(μ(3)-O)2](2+), which we have identified in a previous study, is a product of dioxygen activation that is formed during aerobic oxidations of alcohols catalyzed by [LPd(OAc)]2(OTf)2. It is also a product of hydrogen peroxide activation during disproportionation reactions catalyzed by [LPd(OAc)]2(OTf)2. The results suggest that this trinuclear Pd compound is involved in one of the simultaneous mechanisms for the reduction of oxygen and/or the disproportionation of hydrogen peroxide during oxidation catalysis. Electrospray ionization mass spectrometry of hydrogen peroxide disproportionation reactions suggested the presence of other multinuclear Pd-O2 species in solution. Theoretical calculations of these compounds yield some insight into their structure and potential chemistry.

Di- and tri-nuclear-palladium complexes bearing piperidoimidazolin-2-ylidenes: synthesis, characterization, and catalytic applications

A series of di- and tri-nuclear Pd(II) complexes with piperidoimidazolin-2-ylidenes anchored to benzene ring via methylene spacers were synthesized. The obtained complexes were fully characterized by IR, 1H NMR, 13C NMR spectroscopy and elemental analysis. Molecular structures of two of the products have been determined by means of X-ray crystallography. Their catalytic performances in Suzuki-Miyaura and Mizoroki-Heck cross-coupling reactions were thoroughly investigated. The catalytic reactivity of new di- and tri-metallic complexes was compared with the monometallic systems. It is observed that the activities of the tri-nuclear Pd(NHC) complexes were higher than the corresponding mono- and di-nuclear complexes under the same conditions.

Design and synthesis of a novel trinuclear palladium(ii) complex containing an oxime chelate ligand: determining the interaction mechanism with the DNA groove and BSA site I by spectroscopic and molecular dynamics simulation approaches

The trinuclear Pd(II) complex containing an oxime ligand showed significant interaction with both CT-DNA and BSA.

Time-resolved IR spectroscopy of a trinuclear palladium complex in solution.

This paper presents a combined spectroscopic and theoretical analysis of a trinuclear [Pd3{Si(mt(Me))3}2] complex (mt(Me) = methimazole) which has been demonstrated to be a potential catalyst for coupling reactions. It is a highly symmetric model system (D3 in the electronic ground state) for the investigation of electronic states and the structure of polynuclear transition metal complexes. Different time-resolved IR spectroscopic methods covering the femtosecond up to the microsecond range as well as density functional computations are performed to unravel the structure and character of this complex in the electronically excited state. These are the first time-resolved IR studies on a trinuclear Pd complex. Based on the interplay between the computational results and those from the IR studies a (3)A state is identified as the lowest lying triplet state which has C2 symmetry.

Synthesis of trinuclear Pd–Ru–Pd porphyrin complexes with axially ligated Pd centers. Prominent metal-to-ligand charge transfer band in the visible region

Ru–porphyrin complexes with pyridylpyrazine as metal coordination sites were synthesized. Introduction of Pd-alkyl units to the binding site led to the formation of a novel Pd–Ru–Pd trinuclear complex. The metalation causes drastic changes in the electrochemical and photophysical properties. The trinuclear complex exhibited a prominent metal-to-axial ligand charge transfer band in the visible region due to small energy gap between the Ru-based HOMO and the axial ligand-based LUMO. These changes resulted in the drastic color change from orange to green.

Synthesis and Structure of a Trinuclear Pd–Ag–Pd Carbene Acetato Complex

AbstractWe describe the synthesis and the solid‐state structure of a trinuclear Pd–Ag–Pd carbene acetato complex. The structure was determined by single‐crystal X‐ray experiments [P21/n (no. 14) a = 12.0241(4), b = 25.7201(10), c = 21.3564(8) Å, β = 93.841(2)°, V = 6589.9(4) Å3, Z = 4, R1 = 0.0319, wR2 = 0.0721]. The complex consists of two palladium biscarbene units connected to a silver atom by bridging acetate ions with Pd–Ag bond lengths of 2.89 Å, which are shorter than the sum of the van der Waals radii. Additionally the 13C NMR shifts of the carbene carbon atoms indicate that a palladium silver interaction is present. The repeat unit in the unit cell contains one complex and an infinite chain of two water molecules, one acetic acid and one acetate ion. We show that the hydrogen bond between the complex and a water molecule is the reason for the distorted arrangement.

Norspermidine and Novel Pd(II) and Pt(II) Polynuclear Complexes of Norspermidine as Potential Antineoplastic Agents Against Breast Cancer

BackgroundNew strategies are needed for breast cancer treatment and one initial step is to test new chemotherapeutic drugs in breast cancer cell lines, to choose candidates for further studies towards clinical use.Methodology and FindingsThe cytotoxic effects of a biogenic polyamine analogue – norspermidine – and its trinuclear Pd(II) and Pt(II) complexes – Pd3NSpd2 and Pt3NSpd2, respectively – were investigated in one immortalized normal-like and three breast cancer cell lines. The normal-like MCF-10A cells were least sensitive to the compounds, while growth inhibition and cell death was observed in the cancer cell lines. Norspermidine and its Pd(II) complex were generally shown to have stronger antiproliferative effects than the corresponding Pt(II) complex. Moreover, both norspermidine and the Pd(II) complex reduced the cellular activity of the growth-related enzyme, ornithine decarboxylase (ODC) to a lower level than the Pt(II) complex in most of the cell lines examined. Treatment with norspermidine or the Pd(II) complex reduced the number of colonies formed in a soft agar assay performed with the breast cancer cell lines, indicating that these compounds reduced the malignancy of the breast cancer cells. The effect of norspermidine or the Pd(II) complex on colony formation was much stronger than that observed for the Pt(II) complex. The results from a new mammalian genotoxicity screen together with those of a single cell gel electrophoresis assay indicated that none of the drugs were genotoxic at a 25 µM concentration.Main ConclusionsOverall, norspermidine and its Pd(II) complex were shown to have strong antiproliferative effects. In comparison, the effects obtained with the Pd(II) complex were much stronger than that of the Pt(II) complex. The results obtained in the present study demonstrate that the trinuclear Pd(II) complex of norspermidine (Pd3NSpd2) may be regarded as a potential new metal-based drug against breast cancer, coupling a significant efficiency to a low toxicity.

Room temperature C–H bond activation on a [PdI–PdI] platform

Heteroatom assisted C-H bond activation of 2-substituted naphthyridines with solvated Pd(I)2(CH3CN)6(BF4)2 provides bi- and trinuclear Pd(II) cyclometalated complexes, which provide valuable insight into potential intermediates in palladium catalyzed direct arylation reactions.

Synthesis and solution behaviour of stable mono-, di- and trinuclear Pd(II) complexes of 2,5-pyridinedihydroxamic acid: X-ray crystal structure of a novel Pd(II) hydroxamato complex

Mono-, di- and trinuclear Pd(II) complexes of 2,5-pyridinedihydroxamic acid (2,5-pyha) are reported. The X-ray crystal structure of the mononuclear complex, [Pd(en)(2,5-pyha-1H)]Cl (en=ethylenediamine), was determined exhibiting an (Npy,N) binding mode of 2,5-pyha where (Npy,N) is through a pyridine N and deprotonated hydroxamate N. Such a coordination mode has never previously been observed for a Pd(II) hydroxamato complex. The first examples of di- and trinuclear Pd(II) complexes of a hydroxamic acid are described where one 2,5-pyha ligand acts as a bridge for two and three Pd(en) moieties, respectively. The stability of potential binding modes of 2,5-pyha for a proposed dinuclear complex were investigated by density functional theory at the RI-BP86/def2-TZVP level, in the Turbomole package. It was found that (Npy,N), (O,O′)2 gave the more stable complex where (Npy,N′) is through a pyridine N and deprotonated hydroximate N and (O,O′)2 is via the carbonyl oxygen atom and the deprotonated hydroxyl group of the hydroxamic acid at the 2-position on the pyridine ring. A trinuclear complex, [{Pd(en)}3(2,5-pyha-4H)](PF6)2 was isolated and fully characterised. Spectroscopic studies indicate that the coordination modes are (Npy,N), (O,O′)2 and (O,O′)5 where (Npy,N′) is through a pyridine N and deprotonated hydroximate N and (O,O′) is via doubly deprotonated hydroximate groups at positions 2 and 5 on the pyridine ring. Stability constants for the mono-, di- and trinuclear [Pd(en)]2+ complexes of 2,5-pyridinedihydroxamic acid are also reported. In solution at equimolar concentrations, 2,5-pyha effectively binds one equivalent of Pd(II) to give a mononuclear Pd(II) 2,5-pyha complex and under strongly acidic conditions. In addition formation of stable trinuclear Pd(II) 2,5-pyha complexes are favoured at an excess of Pd(II).

Binary palladium carboxylates with electron-donating and electron-withdrawing substituents in the carboxylate ligand: Synthesis and structural studies. The crystal structures of Pd3(μ-CH2ClCO2)6 · CH2Cl2, Pd3(μ-C6H11CO2)6, and Pd3(μ-CMe3CO2)6

Replacement of the acetate ligands in Pd3(μ-MeCO2)6 in benzene gave complexes of the general formula Pd3(μ-RCO2)6 (R = CF3, CCl3, CH2Cl, Me, cyclo-C6H11, and CMe3). The structures of the complexes were determined using IR spectroscopy, ESI mass spectrometry, and X-ray diffraction. It was found that the complexes contain a trinuclear Pd framework and that their spectroscopic and structural parameters depend on the donor-acceptor properties of the substituent in the carboxylate ligand.

A Trinuclear Pd−Diimine Catalyst for “Core-First” Synthesis of Three-Arm Star Polyethylenes via Ethylene “Living” Polymerization

A Trinuclear Pd−Diimine Catalyst for “Core-First” Synthesis of Three-Arm Star Polyethylenes via Ethylene “Living” Polymerization

Synthesis and Characterization of Linear Trinuclear Pd, Co, and Pd/Co Pyrazolate Complexes

AbstractA family of dinuclear and linear trinuclear Co/Pd pyrazolate compounds, namely, [Bu4N]2[Co2(μ‐4‐Cl‐3,5‐Me2‐pz)2Cl4] (1), [Bu4N]2[Co2(μ‐4‐Br‐3,5‐Me2‐pz)2Br4] (2), [Bu4N]2[Co2(4‐I‐3,5‐Me2‐pz)2Cl4] (3), [Et4N]2[Pd2Co(4‐Br‐3,5‐Me2‐pz)4Cl4] (4), [Et3NH]4[PdCo2(4‐Br‐3,5‐Me2‐pz)4Cl4][NO3]2 (5), [Et3NH]2[Pd Co2(3‐Me‐5‐Ph‐pz)4Cl4] (6), [Et3NH]2[Pd3(4‐Br‐3,5‐Me2‐pz)4Cl4] (7), and [Co3(3,5‐Me2‐pz)4(3,5‐Me2‐pzH)2(CH3CO2)2] (8) was synthesized. The single‐phase nature of the solids was established by single‐crystal X‐ray diffraction, thermal analysis, and spectroscopic techniques. Moreover, the magnetic behavior is studied and a magnetostructural comparison to the corresponding carboxylate analogues is made. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)