Binuclear Palladium Research Articles

Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with different substituents

A series of ethylene bridged di-NHC dipalladium complexes (1–5) with different substituents on N of imidazolydene were prepared. The influence of the different substituents on the structure and catalytic reactivity of the complexes were studied. The molecular structures of 3 and 4 were determined by X-ray diffraction studies. The structures of complexes consist of two perpendicular pseudo-square-planar subunits in a cis configuration. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki–Heck reaction. The complexes with aryl substituent have better activity than that with alkyl substituent, meanwhile, the different substituents on phenyl group have a little effect on both regioselectivity and the yield of the product as well.

Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with different alkane bridge

Abstract A series of di-NHC dipalladium complexes Pd2LPy2Cl4 (L = LC3, LC5, LC6 and LC10) with alkyl bridges of different chain lengths were prepared. The molecular structures of Pd2LC3Py2Cl4 (1) and Pd2LC6Py2Cl4 (3) were determined by X-ray diffraction studies. The influence of the different bridges on the structure and reactivity of the complexes was studied. The structure of complex 3 consists of two pseudo-square-planar subunits in a trans configuration, however complex 1 shows an X configuration due to π–π stacking of both imidazole rings and pyridine rings. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki–Heck reaction of styrene with aryl bromides. The length of the bridged ligands had some effect on the yield and regioselectivity of the products.

Novel binuclear palladium(II) complexes of 2-oxoquinoline-3-carbaldehyde Schiff bases: Synthesis, structure and catalytic applications

A series of novel binuclear Pd(II) complexes of the type [(PPh3)2ClPd(L)PdCl] [where L=dianionic bridged ligands derived from 2-oxo-1,2-dihydroquinoline-3-carbaldehyde or its derivatives with o-aminophenol/o-aminothiophenol] have been reported. The new complexes have been characterized by elemental analysis, FT-IR, UV–Vis and NMR (1H and 31P) spectroscopic techniques. The coordination mode of the ligands and the geometry of the complexes were confirmed by single crystal X-ray crystallography of one of the complexes. The catalytic efficiency of one of the binuclear Pd(II) complexes was tested for N-arylation of imidazole.

Binuclear Palladium Complexes Supported by Bridged Pincer Ligands

A series of binucleating ligands each containing two tridentate pincer sites based on a central, monoanionic aryl (C) donor flanked by neutral phosphinito (P) and imino (N) donors, [(PCN)-(CH2)n-(PCN)] (1), or a central, monoanionic amido (N) flanked by neutral phosphine (P) and imino donors (N), [(PNN)-(CH2)n-(PNN)] (4), are presented. The metalating sites were linked through the condensation of two equivalents of m-hydroxybenzaldehyde or the purposively built asymmetric diarylamine [(H)N(2-C(O)H-4-Me-C6H3)(2-P(iPr)2-4-Me-C6H3)] (3) with primary α,ω-diamines (1,2-diaminoethane, n = 2; 1,4-diaminobutane, n = 4), which simultaneously constructed the imino arms and bridged the pincer cores. Ligands 1 and 4 were then used in the synthesis of neutral, square-planar palladium(II) complexes 5 and 6, [(PCN-Cn)Pd2X2, (PNN-Cn)Pd2X2; n = 2, 4; X = Cl, OAc, OTf]. The difference in the trans influence of the central donor was demonstrated through X-ray crystal structures of 5b-Cl, (PCN-C4)Pd2Cl2, and 6b-Cl, (PNN-C4)Pd2Cl2. The (PNN-Cn)Pd2X2 complexes (6) proved to be redox-active, presumably via oxidation of the ligand, and cyclic voltammetry illustrated the extent to which electronic communication between the two pincer sites is mediated by the length of the bridge between them. (PCN-Cn)Pd2OTf2 (5-OTf) and (PNN-Cn)Pd2OTf2 (6-OTf) complexes reacted with hydride donors such as Et3SiH or β-hydride-containing alkoxides such as NaOiPr to generate bridging-hydride monocations [(PCN)Pd-H-Pd(PCN)-Cn][OTf] (5-H, n = 2, 4) and [(PNN)Pd-H-Pd(PNN)-C2][OTf] (6a-H), where the supported Pd–Pd separation was also found to be affected by the bridge length. In the case of the (CH2)4-bridged (PNN-C4)PdOTf (6b-OTf), a bridging-hydride monocation was not observed. Instead, the formation of [(PN(H)N)Pd-Pd(PNN)-C4][OTf] (6b-H), protonated at the amido N of the ligand with a direct Pd(I)–Pd(I) bond, was recorded.

New binuclear Pd(II) thioamide complexes for the Heck reaction of aryl bromides

The reaction of binucleating thioamide ligands (L 1–L 3) with [PdCl 2(PPh 3) 2] in 1:2 molar ratio in methanol medium afforded a series of binuclear palladium(II) complexes. The synthesized complexes were characterized by elemental analysis and 1H NMR. The molecular structure of one of the complexes was established by X-ray diffraction method. The binuclear palladium(II) thioamide complex has been shown to be an active catalyst for the Heck reaction of aryl bromides with alkenes.

Observation of Binuclear Palladium Clusters upon ESI-MS Monitoring of the Suzuki–Miyaura Cross-Coupling Catalyzed by a Dichloro-bis(aminophosphine) Complex of Palladium

Electrospray ionization mass spectrometry (ESI-MS) is used for monitoring the progress of the Suzuki–Miyaura cross-coupling reaction between bromobenzene and arylboronic acids using a palladium dichloro-bis(aminophosphine) complex as a precatalyst. The ESI-MS studies demonstrate that initiation of the catalytic reaction requires the presence of a base and that the selectivity for cross-coupling is favorable at elevated temperatures. Interestingly, after completion of the coupling reaction, the palladium is present as a dinuclear Pd0/PdII cluster, which still acts as an active catalyst when a new aliquot of reactants is added to the reaction mixture.

Synthesis of and ethylene oligomerization with binuclear palladium catalysts having sterically modulated bis-imine ligands with methylene spacer

Sterically modulated bis-imine ligands (L 1–L 3) were prepared by reacting 4,4′-methylene bis-(2,6-dialkyl aniline) and antipyrine-4-carboxaldehyde in a 1:2 stoichiometric ratio. The reactions of L 1–L 3 with dichloro(cycloocta-1.5-diene)palladium(II) [PdCl 2(cod)] yield the corresponding binuclear palladium complexes with the general formula Pd 2Cl 4L (L = L 1, L 2, and L 3). The binucleating ligands bind to the palladium ion via the lone pair on the imine nitrogen and amide oxygen atoms, resulting in a square-planar geometry around the metal center. All the palladium catalysts efficiently oligomerize ethylene to produce C 4–C 20 fractions at activities of up to 1308 kg-oligomer mol-Pd −1 bar −1 h −1 at 30 °C in combination with ethylaluminum sesquichloride. The formation of active sites by the change in geometry of the metal complexes could be traced using spectroscopic and electrochemical techniques.

Cyclodiphosphazane appended with thioether functionality: Synthesis, transition metal chemistry and catalytic application in Suzuki–Miyaura cross-coupling reactions

The coordination chemistry of thioether functionalized cyclodiphosphazane ligand, cis-{ t BuNP(OCH 2CH 2SCH 3)} 2 ( 1) is described. The reactions of 1 with [Pd (COD)Cl 2] in 1:1, 1:2 and 2:1 M ratios afforded cis-[PdCl 2{ t BuNP(OCH 2CH 2SCH 3)} 2] ( 2), cis-[{PdCl 2} 2{ t BuNP(OCH 2CH 2SCH 3)} 2] ( 3) and trans-[PdCl 2{( t BuNP(OCH 2CH 2SCH 3)) 2} 2] ( 4), respectively. Treatment of 1 with [Pd(PEt 3)Cl 2] 2 or [PdCl( η 3-C 3H 5)] 2 in appropriate molar ratios produce the mono- and binuclear complexes [PdCl 2(PEt 3{ t BuNP(OCH 2CH 2SCH 3)} 2] ( 5) and [{PdCl( η 3-C 3H 5)} 2{ t BuNP(OCH 2CH 2SCH 3)} 2] ( 6) in good yield. The reaction of 1 with [{Ru( p-cymene)Cl 2} 2] afforded the mononuclear cationic complex, [{( p-cymene)RuCl{ t BuNP(OCH 2CH 2SCH 3)} 2]Cl ( 7), whereas the reactions of [Rh(COD)Cl] 2, [Pt(COD)Cl 2] and [Au(SMe 2)Cl] with 1 yielded the corresponding P-coordinated neutral complexes, [RhCl(COD){ t BuNP(OCH 2CH 2SCH 3)} 2] ( 8) cis-[PtCl 2{ t BuNP(OCH 2CH 2SCH 3)} 2] ( 9), respectively. The binuclear palladium(II) complex 3 was found to be an effective catalyst for the Suzuki–Miyaura cross-coupling reactions.

Cyclopropenylidene carbene ligands in palladium catalysed coupling reactions: carbene ligand rotation and application to the Stille reaction

Reaction of [Pd(PPh(3))(4)] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl(2)(PPh(3))(C(3)(Ar)(2))] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)(2)] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl(2)(C(3)(Ar)(2))](2) (Ar = Ph 7, p-(OMe)C(6)H(4)8, p-(F)C(6)H(4)9). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl(2)(NCMe)(C(3)(Ar)(2))] (Ar = Ph 10, p-(OMe)C(6)H(4)11 and p-(F)C(6)H(4)) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7 or acetonitrile adducts 11 and 12 gave complexes of the type cis-[PdCl(2)(PR(3))(C(3)(Ar)(2))] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C(6)H(4), R = Ph 14, Ar = p-(F)C(6)H(4), R = Ph 15). Crystal structures of complexes 6·3.25CHCl(3), 10, 11·H(2)O and 12-15 are reported. DFT calculations of complexes 10-12 indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5-9 were tested for catalytic activity in C-C coupling (Mizoroki-Heck, Suzuki-Miyaura and, for the first time, Stille reactions) and C-N coupling (Buchwald-Hartwig amination) showing excellent conversion with moderate to high selectivity.

New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties

The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear Pd II-complex [(PPh 3)Pd( HL1)Cl]Cl·2CH 3CN ( 1). The complex [(PPh 3)Pd( HL1)I]Cl·1/2H 2O ( 2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh 3) 2ClPd( L1)Pd(PPh 3)Cl]Cl·1/3H 2O·CH 3OH ( 3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol. All the complexes have been characterized by a combination of FT-IR-, 31P NMR-spectroscopy, elemental analyses and mass spectrometry. The molecular structures of the complexes were determined by X-ray diffraction studies. The unit cell of 2 exhibits two crystallographically independent complexes, while the unit cell of 3 contains three crystallographically independent molecules. While the triazole moiety in 1 and 2 acts as a bidentate chelating ligand, the deprotonated triazole compound in 3 acts as a bridging agent between two metal centers. Single-crystal X-ray diffraction revealed that the packing mode of the heterocycle by the phenyl rings of the PPh 3 moiety is responsible for the interesting observed “sandwich” effect. The X-ray structure of the complex [Pd(py) 4]Cl 2·1/2H 2O ( 4) is also reported.

Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}2Pd2H]+: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Durch basenunterstützte Reduktion einer Palladium(II)-Vorstufe wurde der erste Palladium(I)-NHC-Komplex (NHC=N-heterocyclisches Carben) in hoher Ausbeute hergestellt und isoliert. Die Position des einzigartigen terminalen Hydridliganden (siehe Bild; PdI cyan, H weiß, N blau) wurde durch Neutronenbeugung am Einkristall bestimmt, und das fluktuierende Verhalten des Komplexes in Lösung wurde untersucht. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}2Pd2H]+: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Catalytic processes featuring N-heterocyclic carbene (NHC) ligands have been extensively studied following the isolation of free imidazol-2-ylidenes An important reaction class is the base-assisted palladium-mediated C–C/N coupling, such as the Sonogashira, Buchwald–Hartwig, and Mizoroki–Heck reactions

Binuclear palladium complexes bridged by dicarbene with different lengths and their application in Mizoroki–Heck reaction

A series of di-NHC ligands with alkyl bridges of different chain lengths ( n = 2–4) and their bi-palladium complexes ( 4, 5 and 6) have been prepared. The molecular structure of 4 and 6 were determined by X-ray diffraction studies. The structures of complex 4 consist of two pseudo-square-planar subunits in a trans configuration, however 6 consist of two subunits in a cis configuration with π–π stacking between two pyridines. The influence of the different bridges on the structure and reactivity of the complexes has been studied. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki–Heck reaction of styrene with bromobenzene. The complex with 2 and 4 carbon linker gave higher yield, while the one with 3 carbon linker gave better regioselectivity.

ChemInform Abstract: Chemistry of Palladium and Platinum with Selenium and Tellurium Ligands

Reactions of NaER (E = Se, Te; R = Ph, substituted Ph or 2-pyridyl) with a number of mono- and bi-nuclear palladium and platinum complexes have been investigated. Complexes of the type [M(Sepy)2], [M(ER)2(PR3)2], [M2Cl2(μ-ER)2(PR3)2] and [M2Cl2(μ-Cl)(μ-ER)(PR3)2] (M = Pd, Pt) were isolated. They were characterized by elemental analysis, NMR (1H, 13C, 31P, 77Se, 125Te, 195Pt) data and in a few cases by X-ray diffraction studies. The [M(Sepy)2(PPh3)2] dissociates into PPh3 and [M(Sepy)(η2-Sepy)(PPh3)] in solution. 2-Selenopyridine in its complexes acts in a monodentate (bonding through selenium) as well as in chelating (Se⌢N) or bridging fashion. The mononuclear complexes [M(ER)2(PR3)2] are useful precursors for stepwise synthesis of cationic bi- and tri-nuclear derivatives.

Synthesis and characterization of binuclear palladium(I) compounds and the influence of competing arenes

The binuclear palladium(I) compounds, [Pd 2(Ga 2Cl 7) 2(C 7H 8) 2] ( 1), [Pd 2(GaCl 4) 2(C 9H 12) 2]·C 9H 12 ( 2) and [Pd 2(Ga 2Cl 7) 2(C 6H 5Cl) 2] ( 3), have been prepared from palladium(II) chloride in gallium(III) chloride-arene reaction media. All isolated crystalline solids ( 1, 2 and 3) have been structurally characterized by single crystal X-ray diffraction and Raman spectroscopy. The results form quantum chemical calculations on the interaction energies of the arenes and the dipalladium unit of these compounds is also presented.

Highly preorganized pyrazolate-bridged palladium(ii) and nickel(ii) complexes in bimetallic norbornene polymerization

New derivatives of pyrazolate-based binucleating ligands HL with appended imine functions have been synthesized to provide a versatile set of ligand systems with different backbone substituents both at the pyrazole-C(4) and the imine-C (H, Me, Ph). These scaffolds have two adjacent coordination compartments akin to the alpha-diimine type. A series of binuclear palladium(II) complexes [LPd(2)Cl(3)] (1-4) and tetranuclear nickel(II) complexes [L(2)Ni(4)Br(6)(solvent)(4)] (5, 6) of the various ligands have been prepared and characterized, including X-ray structural analyses for two representative Pd and the two Ni complexes. Complexes 5 and 6 were found to contain an unusual central mu(4)-bromide. Mononuclear nickel(II) complexes [L(2)Ni] were detected as intermediates in the formation of the tetranuclear complexes and have been characterized by X-ray analyses in two cases (7, 8). The interconversion between 5' and 7 has been investigated by UV/Vis spectroscopy and ESI mass spectrometry, and magnetic coupling in the [L(2)Ni(4)Br(6)(solvent)(4)] complexes has been studied (SQUID). Trans-coupling via the central mu(4)-bromide is suggested to mediate significant antiferromagnetic interaction. The reactivity of such types of Pd and Ni complexes has been tested for the vinyl/addition polymerization of norbornene. In the presence of an excess of cocatalyst methylaluminoxane (MAO) the palladium complexes show high activity up to 5.9 x 10(6) g(PNB) mol(Pd)(-1) h(-1) at 20 degrees C, while activities of the nickel systems are much lower, but strongly solvent dependent. Detailed studies on the dependence of activity on polymerization conditions such as molar ratios of catalyst and cocatalyst, temperature, reaction time and solvent were carried out. All obtained polynorbornenes (PNB) were noncrystalline and insoluble, but have high glass transition temperatures (T(g)). Microstructures were analyzed by IR spectroscopy and solid state (CP/MAS) (13)C NMR, revealing distinct patterns for the PNB produced by Ni- or Pd-catalysts. Structure/activity correlations deduced for the complexes with different ligand systems suggest that activities and polymer microstructures depend rather on the metal type than on ligand intricacies.

Synthetic Access to a Novel Binaphthyl Ligand Bearing a Phosphine and a Triazole Donor Site

The combination of a diphenylphospinyl and a triazol-3-yl unit was realized for the first time at a 1,1'-binaphthyl backbone. This novel type of P,N-ligand is accessible as an enantiomerically pure compound in just a few steps. First experiments on the coordination chemistry with palladium(II) chloride have been carried out. A series of intermediates and a binuclear palladium(II) complex could be characterized by X-ray crystal structure analysis

Structure of a biologically active binuclear palladium complex in the compound bis(bis[(μ2-2-chloroethylammonium) (1,10-phenanthroline)-palladium(I)]) · octanitrates · dihydrates

The structure of a biologically active binuclear palladium complex, namely, [(1,10-phenanthroline) Pd(μ2-2-chloroethylammonium) 2 4+ · 4NO 3 − · H2O, has been determined using X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group of symmetry Cc, with the unit cell parameters a = 24.527(3) A, b = 13.097(1) A, c = 22.651(3) A, β = 104.23(1)°, V = 7052(2) A3, Z = 8, and ρ = 1.88 g/cm3. The final discrepancy factor is R1 = 0.0316 for 15581 symmetrically nonequivalent reflections with I ≥ 2σ(I), wR2 = 0.0513, and GooF = 1.047. The palladium atoms reside in the oxidation state of 1+, which is rarely encountered in organometallic compounds. The asymmetric part of the unit cell contains two chemically equivalent but crystallographically independent positively charged binuclear palladium complexes, eight NO 3 − anions, and two water molecules. The π-π stacking interaction between the nearest 1,10-phenanthroline rings of the neighboring layers takes place. Moreover, the interlayer and intralayer interactions occur through electrostatic interaction forces and a complex three-dimensional system of hydrogen bonds, which are formed by water molecules and N 3 + groups.

Structure of a biologically active binuclear palladium complex, bis(bis[(μ2-cysteine)(2,2′-dipyridyl)-palladium(II)]) · hexanitrates · novemhydrates

The structure of a biologically active binuclear palladium complex, namely, [(dipy)Pd(μ-cysH) (μ-cys)Pd(dipy)]3+ · 3NO3− · 4.5H2O (dipy = 2,2′-dipyridyl, C10H8N2; cys = cysteine, C3H7NO2S), has been determined from X-ray diffractometry data. The compound crystallizes in the triclinic system, symmetry space group P1, with the unit cell parameters a = 13.863(1) A, b = 13.819(1) A, c = 12.170(1) A, α = 122.13(1)°, β = 103.61(1)°, γ = 91.40(1)°, V = 1887.02 A3, Z = 2, and ρ = 1.82 g/cm3. The final discrepancy factor is R1 = 0.0495 for 12884 symmetrically nonequivalent reflections with F0 ≥ 4σ(F0), wR2 = 0.1071, and GooF = 0.978. The unit cell contains two chemically equivalent but crystallographically independent positively charged binuclear palladium complexes, six NO3− anions, and nine water molecules. The π-π stacking interaction between the nearest pyridyl rings of the neighboring layers takes place. Moreover, the interlayer and intralayer interactions occur through van der Waals interactions and a complex three-dimensional system of hydrogen bonds, which are formed by water molecules, NH3+ groups, and carboxyl groups.

Ligand Modifications for Tailoring the Binuclear Microenvironments in Schiff-Base Calixpyrrole Pacman Complexes

The synthesis and structures of two new octadentate, Schiff-base calixpyrrole macrocycles are presented in which modifications at the meso-substituents (L(1)) or the aryl spacer between the two pyrrole-imine donor compartments (L(2)) are introduced. The outcomes of these changes are highlighted in the structures of binuclear Pacman complexes of these macrocycles, [M(2)(L(1))] and [M(2)(L(2))]. Both palladium and cobalt complexes of the fluorenyl-meso-substituted macrocycle H(4)L(1) adopt rigid, but laterally twisted geometries with enclosed bimetallic microenvironments; a consequence of this spatial constraint is an exo-exo-bonding mode of pyridine in the dicobalt complex [Co(2)(py)(2)(L(1))]. In contrast, the use of an anthracenyl backbone between the two donor compartments (H(4)L(2)) generates a binuclear palladium complex in which the two PdN(4) environments are approximately cofacial and separated by 5.3 A, so generating a bimetallic complex that is structurally very similar to binuclear compounds of cofacial diporphyrins.