Synthesis, characterization and catalytic activity of three palladium(II) complexes containing Schiff base ligands

Three new Pd(II) complexes of Schiff base ligands, namely, [Pd₄(L¹)₄] (1), [Pd₂(L²)₂Cl₂] (2) and [Pd(L³)₂Cl₂] (3) [HL ¹ ?=?N-(benzylidene)-2-aminophenol; L ² ?=?N-(2,4-dichlorobenzylidene)-2,6-diethylbenzenamine, L ³ ?=?4-(2,4-dichlorobenzylide-neamino)phenol] have been synthesized using solvothermal methods and characterized by elemental analysis, spectroscopy and single crystal X-ray diffraction. The crystal structures of the free ligands were also determined. The ??-oxygen-bridged tetranuclear cyclometallated Pd(II) complex (1) contains four nearly planar units, in which Pd^II is four-coordinate. Complex 2 is a ??-chloro-bridged dinuclear cyclometallated Pd(II) complex, whereas complex 3 is mononuclear. The Heck reactions of bromobenzene with acrylic acid catalyzed by complexes 1?C3 have also been studied.     

ESI‐MS studies of palladium (II) complexes with 1‐(p‐toluenesulfonyl)cytosine/cytosinato ligands

The mononuclear complex Pd(1‐TosC‐N3)₂Cl₂ (2) containing 1‐(p‐toluenesulfonyl)cytosine (1) as a ligand, as well as dinuclear complexes Pd₂(1‐TosC^?‐N3,N4)₄ (3) and Pd₂(1‐TosC^?‐N3,N4)₂DMSO₂Cl₂ (4) containing the ligand anion (1‐TosC^?), was mass analyzed by electrospray ionization ion trap MS/MS and high resolution MS. Complexes 3 and 4 were obtained by recrystallization of 2 from DMF and DMSO, respectively. The behavior of complex 2 in different solutions was monitored by electrospray ionization mass spectrometry (ESI‐MS). Under the applied ESI‐MS conditions, complex 2 in methanol reorganized itself dominantly as new complex 3 and the solvent did not coordinate the formed species. In H₂O/DMSO, CH₃CN/DMSO and CH₃OH/DMSO solutions, complex 2 formed several new species with solvent molecules involved in their structure, e.g. complex 4 was formed as the major product. The newly formed species were also examined by LC‐MS‐DAD, confirming the solvent induced reorganization and the solution instability of complex 2. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation and structural characterization of novel polynuclear palladium selenolato complexes [Pd3Se(SePh)3(PPh3)3]Cl and [Pd6Cl2Se4(SePh)2(PPh3)6]

In addition to well-known dinuclear phenylselenolato palladium complexes, the reaction of [PdCl₂(PPh₃)₂] and NaSePh affords small amounts of novel trinuclear and hexanuclear complexes [Pd₃Se(SePh)₃(PPh₃)₃]Cl (1) and [Pd₆Cl₂Se₄(SePh)₂(PPh₃)₆] (2). Complex 1 is triclinic, P1?, a=13.6310(2), b=16.2596(2), c=16.9899(3) Å, α=83.1738(5), β=78.9882(5), γ=78.7635(5)°. Complex 2 is monoclinic, C2/c, a=25.7165(9), b=17.6426(8), c=27.9151(14) Å, β=110.513(2)°. There are no structural forerunners for 1, but the hexanuclear complex 2 is isostructural with [Pd₆Cl₂Te₄(TeR)₂(PPh₃)₆] (R=Ph, C₄H₃S) that have been observed as one of the products in the oxidative addition of R₂Te₂ to [Pd(PPh₃)₄]. Mononuclear palladium complexes may play a significant role as building blocks in the formation of the polynuclear complexes.     

η-Phosphole tricarbonylmanganates: a new type of chelating ligands for transition metals

3,4-Dimethylphosphacymantrene (1) reacts with tert-butyllithium to give the corresponding (η⁴-3,4-dimethyl-1-tert-butylphosphole)tricarbonylmanganate (2) which can act as a chelating ligand (L) toward a Pd₂Cl₂ dimeric core. The X-ray crystal structure of L₂Pd₂Cl₂ (3) shows a bite angle of 60.5°.     

Synthesis of binuclear complexes of PdCl2 with chiral α,α′-diamino-meta-xylene dioximes H2L1, H2L2, and H2L3, the derivatives of the terpenes (+)-3-carene, (R)-(+)-limonene, and (S)-(−)-α-pinene. Crystal structure of [Pd2(H2L1)Cl4]

Chiral α,α′-diamino-meta-xylene dioximes H₂L¹, H₂L², and H₂L³ were obtained from the naturally occurring terpenoids (+)-3-carene, (R)-(+)-limonene, and (S)-(?)-α-pinene, respectively. Reactions of these ligands with PdCl₂ gave the diamagnetic complexes Pd₂(H₂L¹)Cl₄ (I), Pd₂(H₂L²)Cl₄ (II), and Pd₂(H₂L³)Cl₄ (III). According to X-ray diffraction data, the crystal structure of complex I consists of acentric binuclear molecules [Pd₂(H₂L¹)Cl₄]. The coordination polyhedron PdN₂Cl₂ is a square distorted in a tetrahedral manner (trapezium) made up of two N atoms of the tetradentate bridging cyclic ligand H₂L¹ and two Cl atoms. The fragments PdCl₂ in the complex are cis to each other. According to the ¹H NMR spectra of complexes I–III in CDCl₃, the organic ligands are coordinated through the N atoms; in solution, the complexes exist in several forms.     

Study on the interaction of a palladium complex with DNA

The complex [Pd(bipy)Cl₂] (1) (bipy = 2,2′-bipyridyl) has been synthesized and characterized by NMR spectroscopy, elemental analysis and X-ray diffraction method. The first step hydrolysis reaction kinetics for the complex was studied by UV-absorption spectroscopy; the speed constant (k ₁) was found to be 3.0×10^?4 s^?1. The fluorescence spectra have been collected to investigate the interaction of complex (1) with fish sperm DNA (FS-DNA) and the results indicate that the complex (1) has an effective intercalation within DNA. The reaction of complex (1) with adenine in ethanol/water results in the compound [Pd₂(bipy)₂(ade)₂]Cl₂·3H₂O (2) (ade = adenine) whose crystal structure was determined by X-ray diffraction method. The structure is orthorhombic, Pmmn, a = 12.993(4) Å, b = 14.512(5) Å, c = 9.837(3) Å, V = 1854.8(11) ų, Z = 2 (C₃₀H₃₀Cl₂N₁₄O₃Pd₂), final R ₁ = 0.0675. The palladium complex is a binuclear cation, where two ade ligands bridge two Pd(II) centers, while each Pd(II) is also chelated by one bipy ligand.     

Synthesis and coordination properties of palladium(II) and platinum(II) complexes with phosphonated triphenylphosphine derivatives

Two triphenylphosphine derivatives, diethyl [4-(diphenylphosphanyl)benzyl]phosphonate (3a) and tetraethyl {[5-(diphenylphosphanyl)-1,3-phenylene]dimethylene}bis(phosphonate) (3b), and also the corresponding free acids 4a and 4b were prepared. These ligands were characterized by ¹H, ¹³C and ³¹P NMR spectroscopy and mass spectrometry. A full set of their Pd(II) and Pt(II) complexes of the general formula [MCl₂L₂] and one dinuclear complex trans-[Pd₂Cl₄(3a)₂] were synthesized and their isomerization behaviour in solution was studied. The complexes were characterized by ¹H, ¹³C, ³¹P and ¹⁹⁵Pt NMR spectroscopy, mass spectrometry and far-IR spectroscopy. The X-ray structures of all complexes with 3a or 3b have usual slightly distorted square-planar geometry on the metal ion. Salts of phosphonic acids 4a and 4b and their complexes are freely soluble in aqueous solution; therefore, they can be potentially useful in aqueous or biphasic catalysis.     

anti-Bis(μ-2-ammonio­ethane­thiol­ato-κ2S:S)­bis­[di­chloro­palladium(II)] dihydrate

Each of two square-planar Pd^II ions in the title compound, [Pd₂Cl₄(μ-Haet-S)₂]·2H₂O (Haet = 2-ammonio­ethane­thiol­ate, C₂H₇NS), which was obtained by rearrangement of [Pd₂{Pd(aet-N,S)₂}₄]⁴⁺ in acidic solution, is coordinated by two bridging S atoms from two Haet ligands and by two terminal Cl atoms, forming the dinuclear structure. Since the complex is situated on a center of symmetry, the two monodentate Haet arms are located on opposite sides of the central Pd₂S₂ square plane, i.e. the present complex is the anti isomer. The S—C—C—N torsion angle is 177.3 (6)° and some intermolecular hydrogen bonds are observed.     

Synthesis,characterization and X-ray crystal structure of an allyloxo functionalized nonsymmetric nickel coordination complex based on N2O2 chelating ferrocenyl ligand

The synthesis of the new air and thermally stable orange neutral dinuclear iron–nickel unsymmetrical Schiff base complex, [8-(2-oxo,5-allyloxo-phenyl)-4,7-diaza-3-methyl-1-ferrocenyl-1-one-octa-1,3,7-trienato]nickel(II) (2), was achieved via the Williamson coupling reaction between the 2-oxo,5-hydroxyphenyl precursor 1 and allyl chloride in the presence of base. Complex 2 was isolated in 68% yield and characterized by IR, UV–Vis, ¹H and ¹³C NMR spectroscopy, HRMS and authenticated by a single crystal X-ray diffraction analysis. The organometallic/inorganic hybrid complex 2 consists in a ferrocenyl fragment linked to a classical Werner-type complex made of an unsymmetrical quadridentate N₂O₂ Schiff base ligand with a pendant allyl ether functionality as a potential anchoring group. The Ni(II) center displays a square-planar geometry with the nitrogen and oxygen atoms occupying mutually trans positions. The structure of 2 · H₂O shows that the water crystallization molecule interacts through two distinct intermolecular hydrogen bonds with the two oxygen atoms of the tetradentate N₂O₂ acyclic chelating ligand, forming in the solid state, a distorted six-membered ring.     

Synthesis and characterization of cyclometallated palladium(II) and platinum(II) complexes with amide-thiolate ligands

The redox reaction of bis(2-benzamidophenyl) disulfide (H₂L-LH₂) with [Pd(PPh₃)₄] in a 1:1 ratio gave mononuclear and dinuclear palladium(II) complexes with 2-benzamidobenzenethiolate (H₂L⁻), [Pd(H₂L-S)₂(PPh₃)₂] (1) and [Pd₂(H₂L-S)₂ (μ-H₂L-S)₂(PPh₃)₂] (2). A similar reaction with [Pt(PPh₃)₄] produced only the corresponding mononuclear platinum(II) complex, [Pt(H₂L-S)₂(PPh₃)₂] (3). Treatment of these complexes with KOH led to the formation of cyclometallated palladium(II) and platinum(II) complexes, [Pd(L-C,N,S)(PPh₃)]⁻ ([4]⁻) and [Pt(L-C,N,S) (PPh₃)]⁻ ([5]⁻). The molecular structures of 2, 3 and [4]⁻ were determined by X-ray crystallography.     

Synthesis and characterization of palladium(II) and platinum(II) metal complexes with iminophosphine ligands: X-ray crystal structures of platinum(II) complexes and use of palladium(II) complexes as pre-catalysts in Heck and Suzuki cross-coupling reactions

The reactions of N-(2(diphenylphosphino) benzylidene) (phenyl) methanamine, Ph₂PPhNHCH₂-C₅H₄N, 1 and N-(2-(diphenylphosphino) (benzylidene) (thiophen-2-yl) methanamine, Ph₂PPhNHCH₂-C₄H₃S, 2 with MCl₂(cod) and MCl(cod)Me (M = Pd, Pt; cod = 1,5-cyclooctadiene) yield the new complexes [M(Ph₂PPhNHCH₂-C₅H₄N)Cl₂], M = Pd1a, Pt1b, [M(Ph₂PPhNHCH₂-C₅H₄N)ClMe], M = Pd1c, Pt 1d, [M(Ph₂PPhNHCH₂-C₄H₃S)Cl₂], M = Pd2a, Pt 2b, and [M(Ph₂PPhNHCH₂-C₄H₃S)ClMe], M = Pd2c, Pt 2d, respectively. The new compounds were isolated as analytically pure crystalline solids and characterized by ³¹P-, ¹H-NMR, IR spectroscopy, electro spray ionization-mass spectrometry (ESI-MS) and elemental analysis. The representative solid-state molecular structures of the platinum complexes 1b and 2b were determined using single crystal X-ray diffraction analysis and revealed that the complexes exhibit a slightly distorted square-planar geometry. Furthermore, the palladium complexes were tested as potential catalysts in the Heck and Suzuki cross-coupling reactions.     

Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal ions PdII,PtII, and RhIII

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L¹-L³ towards Platinum Group metal ions Pd^II, Pt^II, and Rh^III. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H₂O or MeOH/H₂O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and ¹H- and ¹³C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L¹)Cl]₂[Pd₂Cl₆], [Pt(L¹)Cl](BF₄), [Rh(L¹)Cl₂](PF₆), and [Rh(L³)Cl₂](BF₄)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the Pd^II/Pt^II, and Rh^III complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L₃ with PtCl₂ in MeCN/H₂O gave by serendipity the complex [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)](BF₄)₂·H₂O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d⁸-d⁸ Pt^II-Pt^II ground-state nature for this compound, rather than the alleged d⁹-d⁷ Pt^I-Pt^III mixed-valence character reported for related dinuclear Pt-complexes.     

Synthesis and structure of palladium(II) and copper(II) complexes with chiral bis-α-aminooximes containing (+)-3-carene or (+)-limonene fragments and 4,4′-methylenedianiline linker. Crystal structure of the complex [Cu(i-PrOH)Cl2(μ-H2L3)CuCl2·H2O]

Coordination compounds Pd₂(H₂L²)Cl⁴ (I), Cu₂(H₂L²)Cl₄ (II), Pd₂(H₂L³)Cl₄ (III), and Cu₂(H₂L³)Cl₄ (IV), where H₂L² and H₂L³ are chiral bis-α-aminooxime ligands consisting of (+)-3-carene or (+)-limonene fragments and 4,4′-methylenedianiline linker, were synthesized and examined by NMR, ESR, and IR spectroscopy. The structure of [Cu(i-PrOH)CL₂(μ-H₂L³)CuCL₂·H₂O] (V) was determined by X-ray analysis.     

Synthesis of binuclear complexes of PdCl2 with chiral ethylenediamine dioxime (H2L1), piperazine dioxime (H2L2), and propylenediamine dioxime (H2L3), the derivatives of the natural monoterpenoid (R)-(+)-limonene. The crystal structures of [Pd2(H2L1)Cl4] and [Pd2(H2L2)Cl4]

The diamagnetic complexes [Pd₂(H₂L¹)Cl₄] (I), [Pd₂(H₂L²)Cl₄] (II), and Pd₂(H₂L³)Cl₄(III) with chiral ligands derived from the natural monoterpenoid (R)-(+)-limonene are obtained (H₂ L¹ is ethylenediamine dioxime, H₂L² is piperazine dioxime, and H₂L³ is propylenediamine dioxime). According to X-ray diffraction data, the crystal structures of complexes I and II are composed of binuclear acentric molecules. The coordination polyhedra PdN₂Cl₂ are trapeziums (squares distorted in a tetrahedral manner) made up of two N atoms of the tetradentate bridging cyclic ligands H₂L¹ and H₂L² and two Cl atoms. The fragments PdCl₂ are trans in the complexes. The ¹³C and ¹H NMR spectra of complexes I and II in CDCl₃ also suggest their binuclear structures.     

Synthesis, structure and thermogravimetric analysis of Ni–Cd and Cu–Cd heterometallic complexes based on flexible carboxylate ligands

Two 3d–4d heterometallic coordination polymers, namely NiCd(mal)₂(H₂O)₄ (1) and [CuCd(bicH₂)(NO₃)Cl₂(H₂O)]?H₂O (2) [H₂mal = malonic acid, bicH₃ = N,N-bis(2-hydroxyethyl) glycine], have been synthesized under mild conditions and characterized by single-crystal X-ray diffraction, elemental analysis and IR spectrophotometry. Complex 1 is a Ni–Cd heterometallic polymer with 2D extended structure bridged by the mal^2? groups. Complex 2 displays an intriguing 3D Cu–Cd architecture and is the first 3d–4d heterometallic bicinate complex. The TG analyses of both complexes are reported.     

Construction of chlorido-bridged dinuclear copper(II) complexes with similar tridentate Schiff bases

Two new chlorido-bridged dinuclear copper(II) complexes [Cu₂Cl₂(L¹)₂] (1) and [Cu₂Cl₂(L²)₂] (2), where L¹ and L² are the deprotonated form of Schiff bases 2-[1-(2-morpholin-4-ylethylimino)ethyl]phenol (HL¹) and 2-[1-(2-piperidin-1-ylethylimino)ethyl]phenol respectively, are prepared and structurally characterized by elemental analysis, IR spectra, and single crystal X-ray crystallography. Complex 1 crystallizes in the monoclinic space group P2₁/c with unit cell dimensions a = 8.0816(2) Å, b = 19.1780(3) Å, c = 9.6757(3) Å, β = 106.465(2)°, V = 1438.13(6) ų, Z = 2, R ₁ = 0.0409, and wR ₂ = 0.1085. Complex 2 crystallizes in the monoclinic space group P2₁/c with unit cell dimensions a = 7.7640(10) Å, b = 19.930(3) Å, c = 9.628(2) Å, β = 103.890(3)°, V = 1446.2(4) ų, Z = 2, R ₁ = 0.0634, and wR ₂ = 0.1316. Each Cu atom in the complexes is coordinated by three donor atoms of the Schiff bases and by two bridging Cl atoms, forming square pyramidal geometry. The Cl anions are preferred bridging groups for the construction of dinuclear copper complexes with tridentate Schiff bases.     

A new tripod PPN bridging ligand and its copper,silver and palladium complexes: syntheses,characterizations and X-ray structures

A new tripod bridging ligand 2-{bis(diisopropylphosphino)methyl}-1-methylimidazole, MeImCH(Pi-Pr₂)₂ (PPN) was synthesized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-1-methylimidazole and chlorodiisopropylphosphine. The dicationic dinuclear complex [Cu₂(PPN)₂][ClO₄]₂ (1) was prepared by the reaction of the ligand with [Cu(MeCN)₄]ClO₄ in acetonitrile. The reaction of the ligand with AgNO₃ in propane-2-ol followed by addition of NH₄PF₆ led to the formation of a similar type complex [Ag₂(PPN)₂][PF₆]₂ (2). The X-ray diffraction studies of 1 and 2 revealed a μ₂-η¹:η² tripod-like bonding of the PPN ligand, with one P and one N atom chelating to one metal ion and the remaining one P atom binds to another metal ion, affording a face-to-face type molecule. An eight-membered M₂P₄C₂ and a 10-membered M₂P₂N₂C₄ ring are thus formed with this new functional diphosphine ligand. In both complexes the two metal ions are held in very close proximity [2.6707 Å for 1 and 2.859(3) Å for 2]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinuclear complexes the ligand also afforded a mononuclear palladium complex, [PdCl₂(PPN)] (3), when it was treated with an equimolar amount of [PdCl₂(PhCN)₂] in benzene. In 3 the ligand acts as a bidentate chelate through its two phosphorus atoms, leaving the imidazole donor dangling. On the other hand, a P,P-bridged dinuclear Pd(I) complex [Pd₂Cl₂(PPN)₂] (4) was achieved by reacting two moles of the ligand with one mole of [PdCl₂(PhCN)₂], followed by the addition of one mole of Pd(dba)₂ [dba=dibenzylideneacetone].     

Synthesis and electrochemical properties of calix[4]arene derivatives containing ferrocene units in the cone and 1,3-alternate conformation

Two novel calix[4]arene receptors containing ferrocene units in cone (L₁) and 1,3-alternate (L₂) conformations have been synthesized from 25,27-dihydroxy-26,28-bis[(3-aminopropyl)oxy]calix[4]arene 4 or 25,26,27,28-tetra[(3-aminopropyl)oxy]calix[4]arene 6 and ferrocenecarboxaldehyde via condensation, respectively. Their structures have been characterized by ¹H, ¹³C, APT, COSY NMR, FTIR, HSMR, and UV–vis spectral data. The electrochemical behavior of L₁ and L₂ has been investigated in the presence of F^?, Cl^?, Br^?, H₂PO₄^?, CH₃COO^? anions. Electrochemical studies show that these receptors electrochemically recognize CH₃COO^?, H₂PO₄^?, and Cl^?, anions. Using an UV–vis study, the selectivity to these anions in DMSO solution was confirmed.     

Synthesis,crystal structures and phosphodiesterase activities of alkoxide-bridged asymmetric dinuclear nickel(II) complexes

An asymmetric dinuclear ligand, N-4-methyl-homopiperazine-N′-[N-(2-pyridylmethyl)-N-2-(2-pyridylethyl)amine]-1,3-diaminopr-opan-2-ol (HL) and two dinuclear Ni(II) complexes [Ni₂L(DNBA)₂]ClO₄ (1) and [Ni₂L(BPP)₂]ClO₄·2H₂O (2) (3,5-dinitrobenzoic acid, bisphenyl phosphate) have been synthesized and characterized. Single crystal X-ray crystallographic analysis reveals that the coordination environments of the two Ni(II) atoms in complexes 1 and 2 are five and six coordinate, respectively. The phosphodiesterase activity of a di-Ni(II) complex Ni₂L formed in situ from a 2:1 mixture of Ni²⁺ and HL was investigated using bis(4-nitrophenyl) phosphate (BNPP) as the substrate. The pH dependence of the rate of BNPP cleavage in aqueous buffer indicates a bell-shaped profile with an optimum at about pH 8.4, which is parallel to the formation of the dinuclear species [Ni₂LOH]²⁺ according to UV–vis spectroscopy. At pH 8.4 and 25 °C, the k _cat (7.40 × 10^?5 s^?1) is ca.10⁶-fold higher than that of the uncatalyzed reaction. A possible mechanism for BNPP cleavage promoted by Ni₂L is proposed.     

Reactions of nitrosoarenes containing electron-withdrawing substituents with coordinated CO. Synthesis and structure of complexes Pd2(OAc)2(p-ClC6H4N[p-ClC6H3NO])2 and Pd2(OAc)2(o-ClC6H4N[o-ClC6H3NO])2

The reaction of tetranuclear Pd₄(μ-COOCH₃)₄(μ-CO)₄ cluster (1a) with p- and o-chloronitrosobenzenes was found to give dinuclear nitrosoamide complexes, Pd₂(OAc)₂(p-ClC₆H₄N[p-ClC₆H₃NO])₂ (4) and Pd₂(OAc)₂(o-ClC₆H₄N[o-ClC₆H₃NO])₂ (5), respectively. The formation of complexes 4 and 5 is accompanied by evolution of CO₂, resulting from oxidation of CO coordinated in cluster 1. Complexes 4 and 5 were characterized by elemental analysis and IR and ¹H NMR spectroscopy; their structures were studied by EXAFS. The reactions of dinuclear complex 4 with molecular hydrogen and CO were studied. The major products of reduction of 4 with hydrogen include metallic palladium, acetic acid, cyclohexanone, and molecular nitrogen. Treatment of complex 4 with CO under mild conditions (1 atm, 20 °C) affords p-chlorophenyl isocyanate.