Conformational change induced by hydration: trans‐dichloro­bis­[(1R,2R,3R,5S)‐(–)‐isopinocampheylamine]palladium(II) and trans‐dichloro­bis[(1S,2S,3S,5R)‐(+)‐isopinocampheylamine]palladium(II) hemihydrate

The title compounds, trans‐dichloro­bis[(1R,2R,3R,5S)‐(−)‐2,6,6‐trimethyl­bicyclo­[3.1.1]heptan‐3‐amine]palladium(II), [PdCl₂(C₁₀H₁₉N)₂], and trans‐dichloro­bis[(1S,2S,3S,5R)‐(+)‐2,6,6‐trimethyl­bicyclo­[3.1.1]heptan‐3‐amine]palladium(II) hemihydrate, [PdCl₂(C₁₀H₁₉N)₂]·0.5H₂O, present different arrangements of the amine ligands coordinated to Pd^II, viz. antiperiplanar in the former case and (−)anticlinal in the latter. The hemihydrate is an inclusion compound, with a Pd coordination complex and disordered water mol­ecules residing on crystallographic twofold axes. The crystal structure for the hemihydrate includes a short Pd⋯Pd separation of 3.4133 (13) Å.     

New Palladium(II) Complexes with a Tridentate PNO Ligand

The synthesis of neutral and cationic palladium complexes containing the tridentate monoanionic ligand [2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O]^? is described. Deprotonation of the Schiff base formed by condensation of 2-(diphenylphosphino)benzaldehyde with 2-aminophenol in the presence of the appropriate palladium precursor ([Pd(AcO)₂] or [PdCl₂(PhCN)₂]) form the corresponding neutral complexes [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(AcO)] (1) or [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(Cl)] (2) in good yield. The first reacts smoothly with thiols and activated phenols to give complexes of general formula [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(X)] (X = OC₆F₅ (3), SEt (4), S^tBu (5), SC₆H₅ (6), SC₆H₄-4Me (7), SC₆H₄-4NO₂ (8)). When the chloro complex is treated with silver perchlorate and tertiary phosphines (L) the cationic derivatives [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(L)][ClO₄] (L = PPh₃ (9), PMePh₂ (10), PMe₂Ph (11), PEt₃ (12)) were obtained. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, ¹H, ¹⁹F and ³¹P NMR).     

Synthesis and characterization of N-heterocyclic carbene palladium complex and its application on direct arylation of benzoxazoles and benzothiazoles with aryl bromides

A mixed-halogen bis(1-(4-tert-butylbenzyl)-3-(2, 4, 6-trimethylbenzyl)-1H-benzo[d]imidazol-2-ylidene) palladium(II) complex, trans-[Pd(Cl_0.7Br_0.3)₂(C₂₈H₃₂N₂)₂], has been synthesized and characterized by elemental analysis, ¹H-NMR, ¹³C-NMR, and IR spectroscopy, and single crystal X-ray diffraction. The palladium in the mononuclear complex is four-coordinate in a square-planar configuration with two carbenes of two benzo[d]imidazole rings and two halides. The two halides are disordered between Br and Cl, with the Cl: Br ratio approximately 0.7 : 0.3. The angles C1–Pd1–Br1, 88.63(11)° and C1ⁱ–Pd1–Br1ⁱ, 91.37(11)° (i: 1?x, 1?y, 1?z) in the coordination sphere are very close to the ideal value of 90°. The Pd–X distance is slightly longer than other carbene derivative Pd–Cl single bond distances and slightly shorter than Pd–Br single bond distances. These results agree with the Cl/Br disorder at the halogen position. The palladium–carbene complex was tested as a catalyst in the direct arylation reaction of benzoxazoles and benzothiazoles with aryl bromides.     

REACTION BETWEEN [PdCl4]2- AND 5,5-DIMETHYL-2-THIOXOIMIDAZOLIDIN-4-ONE

Abstract

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H2L) and [PdCl₄]^2- has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H₂L is completely monodeprotonated (HL^?); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)₂ and [Pd₂(HL)₂(μ-H₂O)(μ-OH)]⁺. Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H₂L)_nCl₂ (n = 2–4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H₂L)(HL)Cl and Pd(HL)Cl have been obtained with HL^? N,S-coordinated to the metal.     

New palladium complexes with phosphino‐ and phosphinitopyridine ligands

Three new palladium complexes containing a difunctional P,N‐chelate, namely tris­(chloro­{[1‐methyl‐1‐(6‐methyl‐2‐pyridyl)ethoxy]diphenylphospine‐κ²N,P}methyl­palladium(II)chloro­form solvate, 3[Pd(CH₃)Cl(C₂₁H₂₂NOP)]·CHCl₃, (III), dichloro­[2‐(2,6‐dimethyl­phen­yl)‐6‐(diphenyl­phosphinometh­yl)­pyridine‐κ²N,P]palladium(II), [PdCl₂(C₂₆H₂₄NP)], (IV), and chloro­[2‐(2,6‐dimethyl­phen­yl)‐6‐(diphenyl­phos­phino­meth­yl)pyridine‐κ²N,P]methyl­palladium(II), [Pd(CH₃)Cl(C₂₆H₂₄NP)], (V), are reported. Geometric data and the conformations of the ligands around the metal centers, as well as slight distortions of the Pd coordination environments from idealized square‐planar geometry, are discussed and compared with the situations in related compounds. Non‐conventional hydrogen‐bond inter­actions (C—H⋯Cl) have been found in all three complexes. Compound (III) is the first six‐membered chloro–meth­yl–phosphinite P,N‐type Pd^II complex to be structurally characterized.     

Anion effect on the coordination behavior of N,O-hybrid pyrazole ligand towards Pd(II): synthesis,characterization, and supramolecular properties

Four new Pd(II) coordination complexes using 2-(3-methyl-5-phenyl-1H-pyrazol-1-yl)ethanol (L) with different counter-anions have been prepared to examine their effect on the coordination mode of the ligand as well as on the self-assembly of the supramolecular structure. Reaction of trans-[PdCl₂(L)₂] (R) with AgCF₃SO₃ gives the ionic complex [Pd(L)₂](CF₃SO₃)₂ (1). When AgNO₃ is used, [Pd(NO₃)(L)₂](NO₃) (2) and [Pd(L)₂](NO₃)₂ (3) are obtained in the ratio 70?:?30, respectively, where the nitrate ion is present in- and/or outside the coordination sphere. Reaction of R with Ag₂SO₄ in the presence of (NH₄)₂C₂O₄ yields [Pd(C₂O₄)(L)₂] (4). These new complexes have been characterized by elemental analyzes, conductivity measurements, mass spectrometry, IR, ¹H and ¹³C{¹H} NMR spectroscopies, and X-ray diffraction, whenever possible. The denticity varies from N-monodentate to NO-bidentate, depending on the conditions, showing the versatility of L. Finally, the results of X-ray diffraction analyzes of 1 reveal that CF₃SO₃^? plays a fundamental role in self-assembly, generating a 2-D supramolecular layer with different inter- and intra-molecular interactions. The easy preparation and the high efficiency of this ligand make it a promising alternative to improve established systems.     

trans‐[1,3‐Bis(2,4‐di­methyl­phenyl)­imidazolidin‐2‐yl­idene]­di­chloro­(tri­phenyl­phosphine‐κP)­palladium(II)

The title complex, [PdCl₂(C₁₉H₂₂N₂)(C₁₈H₁₅P)], shows slightly distorted square‐planar coordination of the palladium(II) metal center. The Pd—C bond distance between the N‐heterocyclic ligand and the metal atom is 2.008 (3) Å. The dihedral angle between the two di­methyl­phenyl ring planes is 33.17 (13)°.     

Formation of polynuclear palladium complexes with the benzimidazole-2-thiolate anion

The reactions of palladium(II) salts with 2-mercaptobenzimidazole (HL) and its 5,6-difluorinated derivative (HL^F) were investigated. In the presence of hydrochloric acid, PdCl₂ and K₂PdCl₄ react with HL and HL^F in the ethanol—water and acetonitrile—water systems to form the mono-nuclear dicationic complexes [Pd(HL)₄]Cl₂ (1) and [Pd(L^F)₄]Cl₂ (2). In the absence of HCl, the reactions afford the tetranuclear complex Pd₄[(L)₂(μ₃-S,N-(L))₂(μS,N-(L))₄] (3). The reaction of triethylamine with an ethanolic solution of 3 leads to degradation of 3 and the formation of the lantern-type dinuclear complex Pd₂[(μ₂-(L)₄] (4), in which the palladium atoms are in the nonequivalent coordination environment, PdN₄ and PdS₄. The reaction of K₂PdCl₄ with HL or HL^F in the THF—water or acetonitrile—water systems (for the reaction with HL^F) in the presence of Et₃N produces the lantern-type dinuclear complexes Pd₂[(μS,N′-(L³))₄] and Pd₂[(μ-S,N′-(L^F))₄] (5), in which the metal atoms are in the equivalent coordination environment (cis-PdN₂S₂). Dedicated to Academician G. A. Tolstikov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–52, January, 2008.     

Syntheses and Crystal Structures of Three Palladium（Ⅱ） Complexes with Isonitrosobenzoylacetoneimine Ligand

Three palladium (II) complexes with the isonitrosobenzoylacetoneimine (HIBI) ligand, Pd (p‐CH₃C₆H₄IBI)₂ (1), Pd (C₆H₅IBI)₂ (2) and Pd₂Cl₂ (C₆H₅CH₂IBI)₂ · CHCl₃ (3), were prepared and characterized by IR, Raman and X‐ray diffraction studies. The geometries around the palladium atoms in the complexes 1 and 2 are distorted trans‐PdN₄ square planes, and the Schiff base ligands RIBI^? are coordinated through their oximo‐nitrogen atoms and imino‐nitrogen atoms. The week Pd…H? C agostic interactions [Pd…H = 0.2764 nm] complete the hexacoordinate environment around palladium in the complex 1. The octahedral deformation of the classical square planar environment of the Pd atom is due to the week Pd…O (1b) interactions [Pd? O (1b) = 0.3157 (9) nm] in the complex 2. The complex 3 is a first example of binuclear complex with isonitrosoketoimine ligands, in which one of oximo groups is coordinated through oximo‐nitrogen and oximo‐oxygen atoms.     

Binuclear Pd(II) complexes with chiral ethylenediaminodioxime (H2L) and bis-α-thiooxime (H2L1), the derivative of monoterpenoid(+)-3-carene. Crystal structures of [Pd2(H2L)Cl4] and [Pd2(H2L1)Cl4] · 3CDCl3

Diamagnetic Pd(II) complexes with the chiral ethylenediaminodioxime (H 2 L) and bis-α-thiooxime (H₂L¹), the derivatives of monoterpenoid (+)-3-carene, of the composition Pd₂(H₂L)Cl₄(I), Pd₂(H₂L¹)Cl₄ (II), and the solvate Pd₂(H₂L¹)Cl₄·3DCl₃ (III) were synthesized. The crystal structures of complex I and solvate III were determined from X-ray diffraction data. The structures consist of acentric binuclear molecules with the coordination cores PdN₂Cl₂ (in I) and PdNSCl₂ (in III) in the form of the distorted squares. In complex I, each Pd atom coordinates two N atoms of the tetradentate bridge-cyclic ligand H₂L and two Cl atoms; in compound III, one N and one S atom of the tetradentate bridge-cyclic ligand H₂L¹, and 2 Cl atoms. The CDCl₃ molecules in compound III lie in the cavities formed by the molecules of complex II. In both structures, the PdCl₂ fragments are in the trans-positions. The ¹H NMR spectra indicate that the structures of complexes I, II in solutions are similar to the structures of compounds I, III in the solid state. Original Russian Text ? T.E. Kokina, L.I. Myachina, L.A. Glinskaya, A.V. Tkachev, R.F. Klevtsova, L.A. Sheludyakova, S.N. Bizyaev, A.M. Agafontsev, N.B. Gorshkov, S.V. Larionov, 2008, published in Koordinatsionnaya Khimiya, 2008, Vol. 34, No. 2, pp. 120–132.     

Palladium(II) complexes with R2edda-derived ligands

Four palladium(II) complexes with R₂edda ligands, dichlorido(O,O′-dialkylethylenediamine-N,N′-diacetate)palladium(II) monohydrates, [PdCl₂(R₂edda)]?H₂O, R = Me, Et, n-Pr, i-Bu, and the new ligand precursor i-Bu₂edda?2HCl?H₂O, O,O′-diisobutylethylenediamine-N,N′-diacetate dihydrochloride monohydrate, were synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopy, and elemental analysis. DFT calculations were performed for the palladium(II) complexes and a high possibility for isomer formation due to stereogenic N ligand atoms was confirmed. Moreover, DFT simulations revealed energetic profile of isomer formation. Computational outcomes are in agreement with spectroscopic instrumental findings, both strongly indicating a non-stereoselective reaction between selected esters and K₂[PdCl₄], forming isomers.     

Amidophosphine‐stabilized palladium complexes catalyse Suzuki–Miyaura cross‐couplings in aqueous media

We report a simple and efficient procedure for Suzuki–Miyaura reactions in aqueous media catalysed by amidophosphine‐stabilized palladium complexes trans‐{L³PPh₂}₂PdCl₂ ( 3 ), trans‐{L³PPhtBu}₂PdCl₂ ( 4 ), [Pd(η³‐C₃H₅)(L³PPh₂)Cl] ( 5 ) and {Pd[2‐(Me₂NCH₂)C₆H₄](L³PPh₂)Cl} ( 6 ). The acidity of the NH proton in complexes 3 , 4 , 5 , 6 plays an important role in their catalytic activity. In addition, the palladium complexes cis‐{L¹PPh₂}PdCl₂ ( 1 ) and trans‐{L²PPh₂}₂PdCl₂ ( 2 ) stabilized by phosphines containing Y,C,Y‐chelating ligands L^1,2 have also been found to be useful catalysts for Suzuki–Miyaura reactions in aqueous media. The method can be effectively applied to both activated and deactivated aryl bromides yielding high or moderate conversions. The catalytic activity of couplings performed in pure water increases when utilizing a Pd complex with more acidic NH protons. A decrease of palladium concentration from 1.0 to 0.5 mol% does not lead to a substantial loss of conversion. In addition, Pd complex 1 can be efficiently recovered using two‐phase system extraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization of mono- and dinuclear aryl palladium(II) complexes: oxidative additions of 1,4-dihalogenated benzene or 4,4′-dibromobiphenyl to Pd(PR3)4

Mononuclear palladium(II) complexes 1–12, (C₆H₄X-4)PdX?(PR₃)₂ (X?=?I, Br, or Cl; X??=?I or Br; R?=?Ph, Cy, Et, or Me), were synthesized by oxidative addition of 1,4-dihalogenated benzene to Pd(PR₃)₄; dinuclear palladium(II) complexes 13–15, (Me₃P)₂XPd(C₆H₄-1,4)PdX?(PMe₃)₂ (X, X??=?I or Br), could be obtained only using trimethylphosphine. Another method to prepare 13–15 is via re-oxidative addition of the corresponding mononuclear palladium(II) complexes and Pd(PMe₃)₄. Using 4,4′-dibromobiphenyl as the starting material, the mononuclear palladium(II) complexes [C₆H₄(C₆H₄Br-4)-4]PdBr(PPh₃)₂ (16) and [C₆H₄(C₆H₄Br-4)-4]PdBr(PCy₃)₂ (17) with bulky phosphines could be synthesized at relative low temperature, while dinuclear 18, (Cy₃P)₂BrPd(C₆H₄C₆H₄-4,4?)PdBr(PCy₃)₂, was prepared by bis-oxidative addition at higher temperature. The re-oxidative addition of 16 and Pd(PMe₃)₄ gave dinuclear 19, (Me₃P)₂BrPd(C₆H₄C₆H₄-4,4?)PdBr(PMe₃)₂, accompanying phosphine exchange. X-ray diffraction analysis revealed that formation of dinuclear palladium(II) complexes depends on the reaction temperature, phosphine ligands, and bridging groups.     

Synthesis,characterization and structures of solvent-mediated Na(I)–Pd(II) heterometallic complexes containing [Pd(barb)4]2− units (barb = 5,5-diethylbarbiturate)

Reaction of Na₂[PdCl₄] with the sodium salt of 5,5-diethylbarbituric acid (barbH) led to the formation of two complexes, [PdNa₂(μ-barb)₄(DMSO)₂]·2H₂O·DMSO (1), and {[PdNa₂(μ-barb)₄(H₂O)]·3H₂O}_n (2). The complexes were characterized by elemental analysis, FT-IR, NMR, and X-ray crystallography. Complex 1 was crystallized from H₂O/DMSO (1?:?1, v?:?v) and 2 was crystallized in H₂O. Both complexes contain square planar [Pd(barb)₄]^2? moieties, in which Pd(II) is coordinated by four barb ligands via the negatively charged nitrogens. In addition to the coordination of a DMSO ligand, two Na(I) ions in 1 are bridged by carbonyl O of four barb ligands in the [Pd(barb)₄]^2? unit, while the Pd(II) and Na(I) ions in 2 are bridged by the barb ligands in a tetradentate bridging fashion leading to a 2-D polymeric network. The bridging of metal centers in both complexes result in a significantly short Na?Pd distance of ca. 2.95 Å. Contrary to 2, the coordination of DMSO to Na(I) in 1 avoids the extension of the polymeric structure.     

Preparation and protonation of 2-pyrimidyl- and 2-pyrazylpalladium(II) complexes

The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh₃)₄] yields a mixture of trans-[PdCl(C₄H₃N₂-C²)(PPh₃)₂] (I) and [PdCl(μ-C₄H₃N₂-C²,N¹)(PPh₃ (II) (C₄H₃N₂ = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H₂O₂. The reaction of II with HCl gives the N-monoprotonated derivatives cis-[PdCl₂(C₄H₄N₂-C²)(PPh₃)] (III), from which the cationic complexes trans-[PdCl(C₄H₄N₂-C²)(L) (L = PPh₃, IV; PMe₂Ph, V; PEt₃, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature ¹H NMR spectra of trans-[PdCl(C₄H₄N₂-C²)(PMe₂Ph)₂]ClO₄ show that the heterocyclic moiety undergoes restricted rotation around the PdC² bond and that the 2-pyrazyl group is protonated predominantly at the N¹ atom. These results and the ¹³C NMR data for the PEt₃ derivatives are interpreted on the basis of a significant d_π → π^★ back-bonding contribution to the palladium—carbon bond of the protonated ligands.     

The Syntheses and crystal structures of trans-dichlorobis (10-thiabenzo-15-crown-5)-palladium(Ⅱ)and trans-dichlorobis-(10-selenabenzo-15-crown-5)palladium(Ⅱ)

The preparation and X-ray crystal structures of the adducts of 10-thiabenzo-15-crown-5 and 10-selenabenzo-15-crown-5 with PdCl2 are reported. [PdCl2(C14H20O4S)2] (1): or-thorhombic, space group Pbca with cell dimensions of a=17.285(5), 6=8.354(3), c=21.689(4) A, K=3131.9 A3, Z=4;R=0.0330 for 2301 reflections with I > 3o(I), [PdCl2(C14H2oO4Se)2] (2): monoclinic, space group P21/n with cell dimensions of a=18.928(4), b=8.912(3), c=9.813(2) A, β=96.90(2)0, V=1643.4 A3, Z=2; R=0.0289 for 2617 reflections with I> 3σ(I), Both complexes are monomeric, square-planar palladiurn(Ⅱ) compounds with the Pd(Ⅱ) ion situating on a crystal-lographic inversion centre, and the crown ligands all adopt the axial coordination with the Pd-S bond of 2.3233(7) A and the Pd-Se bond of 2.4357(3) A. Their complexing characteristics are discussed in brief.     

Synthesis of a new class of unsymmetrical PCP′ pincer ligands and their palladium (II) complexes: X-ray structure determination of PdCl{C6H3-2-CH2PPh2-6-CH2PBu2}

The unsymmetrical PCP′ pincer ligands {C₆H₄-1-CH₂PPh₂-3-CH₂PBu^t₂} and {C₆H₄-1-CH₂PPh₂-3-CH₂PPrⁱ₂} and the corresponding palladium complexes: PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PBu^t₂} and PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PPrⁱ₂} have been synthesized in good yields. The molecular structure of PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PBu^t₂} was determined through a single crystal X-ray diffraction study. The palladium center was found to be located into a slightly distorted square planar environment in which the {C₆H₄-1-CH₂PPh₂-3-CH₂PBu^t₂} ligand is coordinated as a tridentate, PCP pincer type chelate. The complex, PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PPrⁱ₂} catalyzes the Heck coupling of iodobenzene with styrene.     

Novel phosphite palladium complexes and their application in C-P cross-coupling reactions

A mono- and a 1,3-bis-phosphite arene ligand based on 2,2′-biphenol have been synthesized in order to study the synthesis of the corresponding palladium(II) complexes starting from different Pd precursors. Novel bis-phosphite palladium complex 1 [PdCl₂(L)₂] (L = dibenzo[d,f][1,3,2]dioxaphosphepin, 6-phenoxy), C,P-chelate bonded monophosphite palladium complex 2 [Pd(κ₂-L)(μ-Cl)]₂, and PCP-pincer palladium complex 3 have been prepared from these ligands in promising to excellent yields (50-95%). Additionally, complexes 1 and 3 have been characterized by X-ray crystal structure determinations. The application of 2,6-bis-phosphite pincer palladium(II) complex 3 in C-P cross-coupling between diphenylphosphine-borane and a wide range of various aryl iodides under very mild conditions is reported. Kinetic investigations indicate that 3 merely acts as a pre-catalyst and that Pd nanoparticles are the actual catalytically active species.     

Tellurium-chlorine secondary interactions in palladium(II) complex of MeOC6H4TeCH2CH2NHCH(CH3)C6H4-2-OH resulting in self-assembled bimolecular aggregates with short palladium-palladium distances

A non-Schiff base (Te, N, O) ligand MeOC₆ H₄TeCH₂CH₂NHCH(CH₃)C₆H₄–2–OH (LH) having a chiral center and its palladium(II) complex [PdClL]·CH₂Cl₂ (1) have been synthesized. Both have characteristic ¹H and ¹³C NMR spectra. The single crystal structure of the complex 1 has been determined by X-ray diffraction methods. The monoclinic crystals of 1 (space group P2₁/n) have a=14.581(5) Å, b=13.160(5) Å and c=20.249(5) Å, β=99.398(5)°. The Te $\cdots A non-Schiff base (Te, N, O) ligand MeOC₆ H₄TeCH₂CH₂NHCH(CH₃)C₆H₄–2–OH (LH) having a chiral center and its palladium(II) complex [PdClL]·CH₂Cl₂ (1) have been synthesized. Both have characteristic ¹H and ¹³C NMR spectra. The single crystal structure of the complex 1 has been determined by X-ray diffraction methods. The monoclinic crystals of 1 (space group P2₁/n) have a=14.581(5) ?, b=13.160(5) ? and c=20.249(5) ?, β=99.398(5)°. The TeCl secondary interactions [3.303(2)–3.352(2) ?] between two nearly square planar palladium complex molecules results in a bimolecular aggregate having a PdPd distance 3.203(1) ?. The Pd–Te, Pd–N and Pd–O bond lengths are 2.5005(7)/2.4914(7), 2.060(4)/2.061(4) and 2.054(3)/2.044(3) ?, respectively.     

Quantum chemical calculations of stability constants: study of ligand effects on the relative stability of Pd(II)�Cpeptide complexes

Replacement of [Pd(H₂O)₄]²⁺ by cis-[Pd(en)(H₂O)₂]²⁺, [PdCl₄]^2?, and [Pd(NH₃)₄]²⁺ on the hydrolytic cleavage of the Ace-Ala-Lys-Tyr-Gly?CGly-Met-Ala-Ala-Arg-Ala peptide is theoretically investigated by using different quantum chemical methods both in the gas phase an in water solution. First, we carry out a series of validation calculations on small Pd(II) complexes by computing high-level ab initio [MP2 and CCSD(T)] and Density Functional Theory (B3LYP) electronic energies while solvent effects are taken into account by means of a Poisson-Boltzmann continuum model coupled with the B3LYP method. After having assessed the actual performance of the DFT calculations in predicting the stability constants for selected Pd(II)-complexes, we compute the relative free energies in solution of several Pd(II)?Cpeptide model complexes. By assuming that the reaction of the peptide with cis-[Pd(en)(H₂O)₂]²⁺, [Pd(Cl)₄]^2?, and [Pd(NH₃)₄]²⁺ would lead to the initial formation of the respective peptide-bound complexes, which in turn would evolve to afford a hydrolytically active complex [Pd(peptide)(H₂O)₂]²⁺ through the displacement of the en, Cl^?, and NH₃ ligands by water, our calculations of the relative stability of these complexes allow us to rationalize why [Pd(H₂O)₄]²⁺ and [Pd(NH₃)₄]²⁺ are more reactive than cis-[Pd(en)(H₂O)₂]²⁺ and [PdCl₄]^2? as experimentally found.