Palladium Coordination Research Articles

Preparation, X-ray structure, spectral analysis, DFT calculation and thermal study on palladium(II) coordination compound with Schiff base derived from S-allyldithiocarbazate

A new palladium(II) complex of PdLCl (HL: S-allyl-3-(2-pyridyl-methylene)dithiocarbazate) has been synthesized and characterized by elemental analysis, IR, EI-MS, UV–Vis, 1H NMR, 13C NMR, TGA and SCXRD analysis. IR spectra reveled that the ligand was coordinated to the palladium ion in a tridentate thiolic form manner with NNS donor sites. The molar conductance data revealed that the complex was non-electrolytes. The complex shows square planar geometries around palladium. The dithiocarbazate coordinates as a uninegatively tridentate NNS ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. DFT and TD-DFT calculations on the complex were also carried out by the B3LYP/6-311++G(d,p) level of theory. The results were used to molecular orbital diagram, HOMO–LUMO, NBO, spin-allowed singlet-singlet electronic transitions studies (TD-DFT).

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe3O4 magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Photoreaction of adsorbed diiodomethane: halide effects of a series of neutral palladium(ii) coordination cages.

A series of Pd6L4-type neutral coordination cages, [Pd6X12L4] (X(-) = Cl(-) and Br(-)), are constructed via self-assembly of (COD)PdCl2 and K2PdBr4 with C3-symmetric N,N',N''-tris(2-pyridinylmethyl)-1,3,5-benzenetricarboxamide (L), respectively. The iodide analogue [Pd6I12L4] is smoothly synthesized from [Pd6Br12L4] in the presence of CH2I2 under mild conditions. The replacement of bromide to iodide in the nanocage system represents a landmark achievement in synthetic-methodology development. The CH2I2 molecules are adsorbed in the order [Pd6I12L4] > [Pd6Br12L4] > [Pd6Cl12L4] and in the "like-attracts-like" pattern, presumably owing to the van der Waals force. Irradiation of [Pd6I12L4]·3.5CH2I2 with 1-methylcyclohexene in chloroform at 350 nm preferentially affords the cyclopropanation product.

Tripyrrindione as a Redox‐Active Ligand: Palladium(II) Coordination in Three Redox States

The tripyrrin-1,14-dione scaffold of urinary pigment uroerythrin coordinates divalent palladium as a planar tridentate ligand. Spectroscopic, structural and computational investigations reveal that the tripyrrindione ligand binds as a dianionic radical, and the resulting complex is stable at room temperature. One-electron oxidation and reduction reactions do not alter the planar coordination sphere of palladium(II) and lead to the isolation of two additional complexes presenting different redox states of the ligand framework. Unaffected by stability problems common to tripyrrolic fragments, the tripyrrindione ligand offers a robust platform for ligand-based redox chemistry.

Tripyrrindione as a Redox‐Active Ligand: Palladium(II) Coordination in Three Redox States

AbstractThe tripyrrin‐1,14‐dione scaffold of urinary pigment uroerythrin coordinates divalent palladium as a planar tridentate ligand. Spectroscopic, structural and computational investigations reveal that the tripyrrindione ligand binds as a dianionic radical, and the resulting complex is stable at room temperature. One‐electron oxidation and reduction reactions do not alter the planar coordination sphere of palladium(II) and lead to the isolation of two additional complexes presenting different redox states of the ligand framework. Unaffected by stability problems common to tripyrrolic fragments, the tripyrrindione ligand offers a robust platform for ligand‐based redox chemistry.

Pb2PdO2(OH)2 and Pb2PdO(OH)4(H2O): Synthesis and Crystal Growth at Ambient Conditions

AbstractNew Pb2PdO2(OH)2 and Pb2PdO(OH)4(H2O) were synthesized at ambient conditions from respective KOH alkaline and metal nitrate aqueous feed stocks in high purity and as coarse crystals. The constitutions of the two lead palladates were determined by combined powder neutron and single‐crystal X‐ray diffraction studies. Both crystal structures exhibit a distinct pseudo symmetry, and settling the true lattice symmetry [Pb2PdO2(OH)2: a = 5.9512(3) Å, b = 5.9479(3) Å, c = 7.9480(2) Å, α = 90.256(4)°, β = 90.392(4)°, γ = 119.694(1)°; Pb2PdO(OH)4(H2O): a = 10.706(2) Å, b = 10.32(1) Å, c = 5.7813(3) Å, α = β = γ = 90°] required to employ high resolution synchrotron powder diffraction data. The combined use of neutron and X‐ray diffraction measurement has enabled solving the crystal structure of Pb2PdO2(OH)2 including hydrogen positions. For Pb2PdO(OH)4(H2O) only a high symmetry, heavy atoms (Pb, Pd, O) average structure was determined, since the background in the neutron data was strongly enhanced due to the high amount of incoherently scattering hydrogen atoms and considerable disorder present. The crystal structures feature unprecedent connectivities, however, as expected square‐planar coordination of palladium(II) and typical crooked surroundings of lead(II) with the 6s2 lone pair acting as a virtual ligand.

Selective recovery of palladium using an innovative functional polymer containing phosphine oxide

A new polymeric sorbent powder (MP-102) containing phosphine oxide groups was developed for the selective recovery of palladium by sorption from acidic effluents containing base metals such as nickel and copper. Experiments show an interesting affinity of MP-102 to palladium species with sorption capacity up to 1mmolg−1 at pH 2, fast kinetics and up to 96% selectivity for Pd in presence of Cu and Ni at pH 1. It was found that 99% of the sorbed palladium can be stripped by elution with an acidified solution of thiourea. The influence of various operating parameters (pH, chloride concentrations and temperature) on Pd sorption equilibria was studied in presence of copper and nickel in order to investigate their influence on the sorption selectivity of the palladium species and to investigate the metal binding mechanisms. Experiments, supported by DFT calculations, suggest a coordination of Pd and Ni by the phosphine oxide groups, preferably in a bidentate mode (chelation), whereas Cu appears to bind to both amine and phosphine oxide groups. The sorption selectivity for palladium is likely due to the energy gain upon palladium coordination to MP-102 which is at least 40kJmol−1 higher than upon copper and nickel coordination.

Redox-active phosphines: synthesis and crystal structures of palladium(ii) complexes of a metallaphosphine in two different oxidation states

The redox-active metallaphosphine [Fe(dppe)(η(5)-C5Me5)(C≡C-PPh2)] reacts with [Pd(1,5-cod)Cl2] to give mono- and bis-phosphine coordinated palladium centres as a function of stoichiometry, and these complexes provide a stable redox-active platform which allows reversible one-electron {Fe(II)→Fe(III)(+)} oxidations within the palladium coordination sphere.

The Synthesis and Structure of Palladium 2,4-dimethyl-8-hydroselenoquinolinate

The internal complex palladium 2,4-dimethyl-8- hydroselenoquinolinate Pd[C9H4(CH3)2NSe]2 (I) has been synthesized in the course of study of the complexing activity of 8- hydroselenoquinoline and investigation of the nature of chemical bond metal-selenium in the five-membered metal-containing ring. X-ray diffraction data for I: Monoclinic, space group P21/n, a = 9.0092(4), b = 16.3290(7), c = 14.1073(6) A,  = 106.710(2)o, V = 1987.7(2) A3, Z = 4, R1=0.0477, wR2=0.1182 for 4499 reflections (diffractometer Bruker-Nonius KappaCCD, MoK). The crystal structure of the complex I is formed by neutral asymmetric molecules Pd[C9H4(CH3)2NSe]2 in which the central atom palladium is connected bidentically (Se,N) with two 2,4- dimethyl-8-hydroselenoquinoline ligands. The structure of palladium coordination polyhedron is cis-square (2Se+2N) somewhat tetrahedrally distorted. Dihedral angle between the SePdN / SePdN coordination planes is 20.15(1)o. The Pd–Se and Pd–N bonds are covalent. The transition of trans- (complex Pd(C9H6NSe)2 (II) to cis-coordination (complex I) causes the weakening of the Pd–N bonds (compare 2.162(5) and 2.159(5) A (I) , 2.065(3) A (II) ).

Coordination of cobalt(III), nickel(II), copper(II), palladium(II) and platinum(II) with N-ethyl-N′-(4′-methylthiazol-2′-yl)thiourea (HL)

Coordination complexes of formula [ML2], [CoL3], [Pd(HL)Cl2], [CuLCl(H2O)] and [CuL2(H2O)2] {L=anion of N-ethyl-N′-(4′-methylthiazol-2′-yl)thiourea; M=PtII, PdII or NiII} were prepared and characterized by elemental analyses, magnetic susceptibilities, and by IR, NMR, electronic and mass spectral measurements.

Interaction of palladium(II) coordination compounds with calf thymus DNA and their antibacterial activity

Abstract The palladium(II) complexes of the formulations [Pd(clpbpy)Cl 2 ], [Pd(clcpbpy)Cl 2 ], [Pd(brcpbpy)Cl 2 ], [Pd(clmpbpy)Cl 2 ] {clpbpy═4-(4-chlorophenyl)-6-phenyl-2,2′-bipyridine (L 1 ), clcpbpy═4,6-bis(4-chlorophenyl)-2,2′-bipyridine (L 2 ), brcpbpy═4-(4-bromophenyl)-6-(4-chlorophenyl)-2,2′-bipyridine (L 3 ) and clmpbpy═6-(4-chlorophenyl)-4- p -tolyl-2,2′-bipyridine (L 4 )} have been synthesized and characterized using elemental analysis, electronic spectra, IR and mass spectra. The study on the interaction of the palladium complexes with calf thymus DNA (CT DNA) has been performed using absorption titration, viscosity measurements and thermal denaturation techniques. The study suggests the intercalative mode of DNA binding. Gel electrophoresis assay demonstrates the ability of the complexes to cleave the pUC19 DNA. The antibacterial activity of complexes has been screened against two Gram (+ ve) and three Gram (− ve) microorganisms.

How Does Palladium Coordination Affect the Electrophilicities of Allyl Cations? Development of a Robust Kinetic Method for Following Reactions of [(η3-Diarylallyl)Pd(PPh3)2]+ with Nucleophiles

Kinetics of the reactions of [(η3-1,3-diarylallyl)Pd(PPh3)2]+ complexes with carbanions, enamines, amines, and triphenylphosphine have been investigated photometrically in dichloromethane, DMSO, and acetonitrile solutions at 20 °C. Amines were found to react both at palladium (substitution of PPh3) and at the allyl ligands, causing complex and poorly reproducible kinetics. Excellent reproducibility of the second-order rate constants for the attack at the allyl ligand was achieved when the reactions were studied in the presence of traces of PPh3 and fumaronitrile. The second-order rate constants (k2) for the attack of nucleophiles at the allyl ligands were found to follow the correlation log k2 = sN(N + E), where sN and N are solvent-dependent nucleophile-specific parameters and E is an electrophilicity parameter (J. Am. Chem. Soc.2001, 123, 9500–9512). While the electrophilicities of the free 1,3-bis(3,5-difluorophenyl)allyl (E = 6.11) and the 1,3-bis(4-dimethylaminophenyl)allyl cations (E = −7.50) differ by more than 13 orders of magnitude, the electrophilicities of the corresponding Pd(PPh3)2 complexes were found to be almost independent of the nature of the substituents (E ≈ −14), showing that Pd(PPh3)2 coordination reduces the electrophilic reactivities of allyl cations by 7–20 orders of magnitude.

From 21,23-Dioxaporphyrin to a 3-Pyranone Dioxacorrole Skeleton: The Achmatowicz Rearrangement in the Porphyrin Frame

Be independent: Under basic conditions a furan ring entrapped in an aromatic macrocycle readily recovered the properties characteristic for a free molecule and assimilated a water molecule forming the Achmatowicz rearrangement product with a 3-pyranone subunit built in. Coordination of palladium(II) created a complex stabilizing the second tautomer with two sp3 carbon atoms (oxygen red, water green, palladium purple, and the aryl group blue).

Linear Triphosphines as Ligands for Metal Complexes Immobilization in Ionic Liquids: Palladium-Catalyzed Methoxylation of Alkynes

Several novel palladium triphosphine complexes have been synthesized and tested as recyclable catalysts for the methoxylation of alkynes into acetals in ionic liquids. A complete conversion of phenylacetylene was achieved with only 0.2% of (Pd(Triphos)NCMe)((PF6)2) in a methanol/(BMIM)(BF4) mixture. We discovered that the addition of an ionic liquid to methanol allowed not only to increase the activity of the palladium catalyst but also to provide a recyclable catalyst which can be reused several times with a weaker drop of activity. To complete these catalytic studies, we describe the synthesis of the first poor -electron-donating/strong -electron-acceptor linear Triphosphine which, after palladium coordination, led to a better selectivity compared to its Triphos analogue. The performances of recovered ionic liquid re- action mixtures show for the first time that P-tridentate ligands efficiently immobilize palladium catalysts and lead to se- lective catalytic systems benign for environment.

Toward aceneporphyrinoids: synthesis and transformations of palladium(ii) meso-anthriporphyrin

meso-Anthriporphyrin is a carbaporphyrinoid with an anthracene ring embedded in the tripyrrolic framework. The coordination of palladium(II) results in a specific intramacrocyclic metal(II)-η(2)-CC interaction which facilitates the cleavage to palladium(II) acyclic oligopyrrole with the appended anthracene moiety.

A facile route for preparing a mesoporous palladium coordination polymer as a recyclable heterogeneous catalyst

To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica, polymers and nanoparticles. For the same purpose, we describe a general and facile method to immobilize palladium bis(phosphine) complexes on the basis of the technique widely used for metal-organic framework (MOF) synthesis, yielding a mesoporous coordination polymer palladium-CP1. Although palladium complexes are generally not stable enough to allow further manipulation, we succeeded in preparation of a palladium coordination polymer without by-product Pd clusters or nanoparticles. The fresh palladium-CP1 catalyst exhibits a yield close to 55% for tolane at room temperature and 24 h in Sonogashira coupling of iodobenzene and phenylacetylene, as compared with a yield of 89% for its homogeneous counterpart [Pd(PPh(3))(2)Cl(2)]. Furthermore, this catalyst is stable enough to be reused more than four times with no Pd and Zn leaching. Therefore this new immobilization method offers great promise for the produce of recyclable palladium heterogeneous catalysts with higher activity and higher thermal and chemical stability in the future.

Successive coordination of palladium(II)-ions and terpyridine-ligands to a pyridyl-terminated self-assembled monolayer on gold

The deposition of palladium on a novel, reversibly protonatable, pyridyl-terminated self-assembled monolayer on gold substrates has been studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS spectroscopy) and time of flight-secondary ion mass spectrometry (ToF-SIMS). For this purpose, 12-(pyridin-4-yl)dodecane-1-thiol, consisting of a surface-active head group, an unfunctionalized hydrocarbon backbone and a terminal pyridyl group, has been synthesized and deposited on gold surfaces. Coordination of Pd(II) ions to the pyridyl group was examined. Furthermore, a reversible protonation/deprotonation cycle has been applied, and the relation between protonation and the amount of complexed palladium was studied. Investigation of the SAM by angle-resolved NEXAFS spectroscopy revealed the aliphatic backbone to be preferentially upright oriented with the aromatic head group being not preferentially oriented. The palladium layer was further coordinated with a CF3-labeled terpyridine ligand in order to prove the accessibility of the Pd(II) ions to further complexation and the platform useful for deposition of further layers toward a multi-layered system.

Tridentate N‐Donor Palladium(II) Complexes as Efficient Coordinating Quadruplex DNA Binders

Fifteen complexes of palladium, platinum, and copper, featuring five different N-donor tridentate (terpyridine-like) ligands, were prepared with the aim of testing their G-quadruplex-DNA binding properties. The fluorescence resonance energy transfer melting assay indicated a striking positive effect of palladium on G-quadruplex DNA stabilization compared with platinum and copper, as well as an influence of the structure of the organic ligand. Putative binding modes (noncoordinative π stacking and base coordination) of palladium and platinum complexes were investigated by ESI-MS and UV/Vis spectroscopy experiments, which all revealed a greater ability of palladium complexes to coordinate DNA bases. In contrast, platinum compounds tend to predominantly bind to quadruplex DNA in their aqua form by noncoordinative interactions. Remarkably, complexes of [Pd(ttpy)] and [Pd(tMebip)] (ttpy = tolylterpyridine, tMebip = 2,2'-(4-p-tolylpyridine-2,6-diyl)bis(1-methyl-1H-benzo[d]imidazole)) coordinate efficiently G-quadruplex structures at room temperature in less than 1 h, and are more efficient than their platinum counterparts for inhibiting the growth of cancer cells. Altogether, these results demonstrate that both the affinity for G-quadruplex DNA and the binding mode of metal complexes can be modulated by modifying either the metal or the organic ligand.

Conformational fluxionality in a palladium(II) complex of flexible click chelator 4-phenyl-1-(2-picolyl)-1,2,3-triazole: A dynamic NMR and DFT study

An experimental and theoretical DFT study was carried out on the solution behavior in [D 7]DMF for bis-chelate complex [Pd( L) 2](BF 4) 2·2CH 3CN ( L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd( L) 2] 2+, the central square–planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti- trans-[Pd( L) 2] 2+ and syn- trans-[Pd( L) 2] 2+ in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) 1H NMR spectroscopy in the temperature range of 223–353 K. The equilibrium lies on the side of the anti- trans-[Pd( L) 2] 2+ conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 ± 0.5 kcal mol −1 and 0.8 ± 1 cal mol −1 K −1, respectively. From the full-line-shape analysis of resonances in the VT 1H NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 ± 0.4 kcal mol −1 and 2.7 ± 1.6 cal mol −1 K −1, respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol −1. The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers.

In situ NMR studies of the mechanism of homogeneously and heterogeneously catalysed Heck reactions of aryl chlorides and bromides

This paper presents for the first time detailed NMR investigations of the changes of the palladium coordination sphere for dissolved Pd salts (Pd(OAc)2) and chosen solid, heterogeneous catalysts (Pd(II)/Al2O3, Pd(II)/NaY zeolite) under Heck reaction conditions for the interesting model substrates bromobenzene and chlorobenzene (and styrene as olefin) using catalytic amounts of Pd only. The information obtained from the mechanistic studies led us to new optimized simple “ligand free” catalyst systems and reaction conditions that allow the activation of chlorobenzene in an unexpected manner under relatively mild reaction conditions.