Synthesis and characterization of Pd(II) and Pt(II) complexes with triazolopyrimidine derivatives: The crystal structure of [Pd2L2Cl4] where L = 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine

The Pd(II) and Pt(II) complexes with triazolopyrimidine C-nucleosides L¹ (5,7-dimethyl-3-(2′,3′,5′-tri-O-benzoyl-β-d-ribofuranosyl-s-triazolo)[4,3-a]pyrimidine), L² (5,7-dimethyl-3-β-d-ribofuranosyl-s-triazolo[4,3-a]pyrimidine) and L³ (5,7-dimethyl[1,5-a]-s-triazolopyrimidine), [Pd(en)(L¹)](NO₃)₂, [Pd(bpy)(L¹)](NO₃)₂, cis-Pd(L³)₂Cl₂, [Pd₂(L³)₂Cl₄] · H₂O, cis-Pd(L²)₂Cl₂ and [Pt₃(L¹)₂Cl₆] were synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of the [Pd₂(L³)₂Cl₄] · H₂O complex was established by X-ray crystallography. The two L³ ligands are found in a head to tail orientation, with a Pd?Pd distance of 3.1254(17) Å. L¹ coordinates to Pd(II) through N8 and N1 forming polymeric structures. L² coordinates to Pd(II) through N8 in acidic solutions (0.1 M HCl) forming complexes of cis-geometry. The Pd(II) coordination to L² does not affect the sugar conformation probably due to the high stability of the C-C glycoside bond.     

Synthesis and reactivity of binuclear halo-bridge palladium(II) isocyanide complexes

An equimolecular mixture of [Pd(RNC)₂Cl₂] (R = Ph, p-Me C₆H₄) and [Pd(MeCN)₂Cl₂] reacts in boiling, 1,2-dichloroethane to give the binuclear complexes [Pd(RNC)Cl₂]₂.These compounds undergo a variety of bridge-splitting reactions with neutral or anionic ligands yielding complexes of the type cis and trans [Pd(RNC)LX₂] or [Pd(RNC)X₃]⁻ (L = PPh₃, pyridine, C₆H₁₁NC; X = CL, Br).By reaction of [Pd(PhNC)Cl₃]⁻ with MeOH the anionic carbene complex [Pd{C(NHPh)OMe}Cl₃]⁻ is obtained.[Pd(PhNC)Cl₂]₂ reacts with p-toluidine (excess) or o-aminopyridine to give the corresponding mononuclear carbene derivatives.In the case of the mixed derivative [Pd(p-MeC₆H₄NC)(C₆H₁₁NC)Cl₂], only the more activated p-tolylisocyanide was found to react with p-toluidine.The complexes have been characterized by elemental analysis, conductivity measurements, i.r. and ¹H n.m.r. spectra where possible.     

Synthesis and crystal structures of cobalt(II), cadmium(II), and zinc(II) complexes of 4-nitro phenylcyanamide: enhancing the biological properties through bound to human serum albumin

Metal complexes of the type [Co(phen)₂(4-NO₂pcyd)₂].CH₃OH, 1, [Zn(phen)₂(4-NO₂pcyd)₂].CH₃OH, 2, [Cd(phen)₂(4-NO₂pcyd)₂], and 3, (phen?=?1,10-phenanthroline, 4-NO₂pcyd?=?4-nitro phenylcyanamide) have been studied. The synthesis, characterization, and the biological activities of complexes 1-3 have been investigated. The geometries of complexes 1-3 were confirmed by single-crystal X-ray crystallography. The interactions of complexes 1-3 with human serum albumin (HSA) were studied using fluorescence and circular dichroism spectroscopy. The thermodynamic studies have showed the reaction for the binding of complexes 1-3 with HSA is hydrophobic (ΔH_0???0 and ΔS₀ > 0). The in vitro cytotoxic potential of complexes 1-3 and their complexes with HSA were examined. The complexes 1-3 with HSA enhance about 3-fold cytotoxicity in cancer cells lines.     

Complexation associated rearrangement of iminobiphosphines to diphosphinoamines

The reaction of the iminobiphosphines RNPPh₂-PPh₂, where R = C₆H₄(p-CN), C₆H₄(m-CN), C₆H₄(o-C₆H₅), C₆F₅ or C₆H₄(o-CF₃), with one molecular equivalent of M(cod)Cl₂ (M = Pd or Pt) results in a rearrangement of the NPP unit to the more commonly encountered P-N-P unit, forming mono-chelating complexes of general formula M{RN(PPh₂)₂}Cl₂. The related reaction of the same range of iminobiphosphines with Pt(cod)Cl₂ (but not Pd(cod)Cl₂) in 2:1 ratio affords complexes of general formula [Pt{RN(PPh₂)₂}₂]2Cl. All 15 complexes are isolated in moderate to high yield and they have been fully characterised by spectroscopic methods. Six complexes, viz. [M{C₆H₄(p-CN)N(PPh₂)₂}Cl₂], [M{C₆H₄(m-CN)N(PPh₂)₂}Cl₂] and [M{C₆H₄(o-C₆H₅)N(PPh₂)₂}Cl₂] (M = Pd and Pt), have been characterised in the solid state by single crystal X-ray diffraction analysis.     

The C-N coupling reaction of pendant naphthyl group of palladium(II) complexes of 1-alkyl-2-(naphthyl-β-azo)imidazoles. Structural characterization, spectral and redox properties, and correlation with DFT computed data

The reaction of Pd(β-NaiR)Cl₂ (2) [β-NaiR (1) = 1-alkyl-2-(naphthyl-β-azo)imidazoles] with ArNH₂ in MeCN has yielded a C-N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-β-azo}imidazole-N,N′,N′′]palladium(II), Pd(β-NaiR-N-Ar)Cl (3-5) and coupling takes place at ortho-C-H position of pendant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure determination of the representative complexes, Pd(β-NaiEt)Cl₂ (2b) and Pd(β-NaiEt-N-C₆H₄-Cl-p)Cl (5b). The electronic spectra of the products, 3-5, exhibit characteristic transition within 600-900 nm those are absent in Pd(β-NaiR)Cl₂ (2). Cyclic voltammogram shows one oxidative response and two ligand reductions. The products are emissive. The excited state decays via radiative and non-radiative biexponential routes. The electronic structure, spectra and redox properties are explained by DFT computation.     

Synthesis and structural characterization of Pd(II) complexes containing 2,6-bis[(dimethylamino)methyl]-4-methylphenolate ligand

Treatment of 2,6-bis[(dimethylamino)methyl]-4-methylphenol (1) with [Pd(PhCN)₂Cl₂] in a 1:1 molar ratio gives the mononuclear Pd(II) complex [PdCl₂(OC₆H₂(CH₂NMe₂)-2-Me-4-(CH₂NHMe₂)-6)] (2) containing one ligand with an ammonium hydrogen atom, which forms a bifurcated hydrogen bonding to the phenoxy oxygen and the chlorine atoms, as shown by the single crystal X-ray diffraction study. The reaction between the lithium salt of 1 and [Pd(COD)Cl₂] gives the mononuclear Pd(II) complex [Pd(OC₆H₂(CH₂NMe₂)₂-2,6-Me-4)₂] (3). The X-ray structure of 3 showed the presence of two ligands coordinated to one palladium metal center in a trans fashion with two dangling dimethylamine groups. The yield of the complex 3 was improved by carrying out the reaction between [Pd(OAc)₂] and 1 in acetone. The solid state structures of the complexes 2 and 3 were confirmed by ¹H, ¹³C, HETCOR NMR, IR and elemental analysis methods. The ¹H NMR spectra of 2 and 3 showed two different chemical shifts corresponding to the coordinated and uncoordinated amine groups of the ligand. No decoalescence of signals for the chelate ring puckering process was observed in variable-temperature NMR spectra.     

New monocationic methylpalladium(II) compounds with several bidentate nitrogen-donor ligands: synthesis, characterisation and reactivity with CO

Two series of methylpalladium(II) compounds with mono and bidentate nitrogen-donor ligands, namely [Pd(N-N)₂(CH₃)][X] (N-N=phen (1a), dm-phen (1b) (dm-phen=4,7-dimethyl-1,10-phenanthroline), tm-phen 1c (tm-phen=3,4,7,8-tetramethyl-1,10-phenanthroline); X=OTf, PF₆ ⁻) and [Pd(N-N)(L)(CH₃)][OTf] (N-N=phen and L=py (1ad) (py=pyridine), N-N=phen and L=2-Ph-py (1ae) (2-Ph-py=2-phenyl-pyridine), N-N=phen and L=BzQ (1af) (BzQ=7,8-benzoquinoline), N-N=tm-phen and L=BzQ (1cf)), have been synthesised and fully characterised both in solid state and in solution. The crystal structures of [Pd(phen)₂(CH₃)][PF₆] and [Pd(phen)(2-Ph-py)(CH₃)][OTf] show a square planar coordination geometry for palladium with the monodentate ligand (one phen molecule plays this role in 1a) bound to the metal with its plane almost perpendicular to the coordination plane. In both structures the PdN bond length trans to the methyl is remarkably affected by its trans influence. The behaviour in solution is characterised for the first series of compounds by a dynamic process which makes the two N-N ligands equivalent, as corroborated by the ¹⁵N NMR analysis: only one averaged signal is shown for all of the four nitrogen atoms. No fluxional process is present for the compounds of the second series, and three main crosspeaks are shown in the ¹⁵N-¹H HMQC spectra. In particular, the signal of the ¹⁵N trans to the methyl group has a typical chemical shift, which differs from those of two ¹⁵N trans to each other. Both series of complexes are reacted with carbon monoxide and the reaction products are studied by ¹H NMR spectroscopy and, when possible, by isolating the acyl derivatives. The products of this reaction are affected by the nature of the second molecule of N-ligand.     

Palladium(II) complexes of 1,10-phenanthroline: Synthesis and X-ray crystal structure determination

Two palladium(II) complexes, [Pd(phen)(NCCH₃)₂][O₃SCF₃]₂ (1) and [Pd(phen)(μ-OH)]₂[O₃SCF₃]₂ · 2H₂O (2) (where phen = 1,10-phenanthroline), have been crystallized following the reaction of Pd(phen)Cl₂ with silver triflate, Ag(O₃SCF₃), in acetonitrile and water, respectively. The structures of both complexes are based on a Pd(phen)²⁺ metal core, with two acetonitrile molecules binding in a monodentate fashion in complex 1 and two hydroxo bridges holding together two cores to form a dimer in complex 2. Additionally, both complexes present a hydrogen bonded 3-D network involving the triflate anions in 1, and water and triflate anions in 2. Both complexes have been characterized by infrared and ¹H NMR spectroscopy and their crystal structures determined by X-ray crystallography.     

Synthesis of new palladium(II) complexes containing tetradentate-nitrogen donor ligands: Combined structural studies by NMR spectroscopy and X-ray crystallography

Treatment of the tetradentate (NN′N′N) N-alkylaminopyrazole ligands 3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diazaoctane (ddad) and 1,4-bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]piperazine (bedp) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in acetonitrile produces [Pd₂Cl₄(L)] and [PdCl₂(L)] (L = ddad and bedp). Treatment of the corresponding complex [PdCl₂(L)] (L = ddad, bedp) in the presence of AgBF₄ in CH₂Cl₂/methanol (2:1) or NaBF₄ in acetonitrile gives [Pd(L)](BF₄)₂. The Pd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and ¹H and ¹³C{¹H} NMR spectroscopies when possible. The X-ray structure of the complex [Pd(ddad)]Cl₂ · 3H₂O has been determined. The Pd(II) is coordinated to the ddad ligand by two nitrogen atoms of pyrazolyl groups and two nitrogen atoms of the amine groups, in a slightly distorted square-planar geometry.     

Substitution effect on new Co(II) addition compounds with salicylaldehydes and the nitrogenous bases phen or neoc: Crystal and molecular structures of [Co(5-NO2-salicylaldehyde)2(phen)], [Co(5-CH3-salicylaldehyde)2(neoc)] and [Co(5-Cl-salicylaldehyde)2(neoc)]

The cobalt(II) addition compounds [Co(X-salo)₂(Y)], where X-salo is the anion of substituted salicylaldehydes (X = 3-OCH₃, 5-CH₃, 5-Cl, 5-NO₂ and Y = the neutral 1,10 phenanthroline or neocuproine), were synthesized and characterized by physicochemical and spectral (IR, UV-Vis) data. Theoretical calculations (DFT, ZINDO, TD DFT) with gaussian 03 for the prediction of the electronic spectrum for the compounds, gave good correlation with the experimental one in the solid state and in solution. The cyclic voltammetry study in CH₃CN gave all the expected waves for the redox processes of the metal Co(II) and the ligands phen or neoc and salicylaldehydes. The X-ray diffraction study of three compounds [Co(5-NO₂-salo)₂(phen)], [Co(5-CH₃-salo)₂(neoc)] and [Co(5-Cl-salo)₂(neoc)] verified their analogous proposed octahedral arrangement of the ligands around the cobalt(II) atom.     

1,10-Phenanthroline-dithiolate mixed ligand transition metal complexes. Synthesis, characterization and EPR spectroscopy

A series of new N₂S₂ mixed ligand transition metal complexes, where N₂ is phenanthroline and S₂ is 1,2-dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal that the 1,2-dithiolate ligands are coordinated via the sulfur atoms forming a N₂S₂ coordination sphere. The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper complex calculated from the experimental data is compared to the results of EHT and DFT calculations. Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate [(phen)₂CuCl]·C₂H₅OH·H₂O, was formed by a reduction process and characterized by X-ray diffraction. In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant π-π interactions.     

Crystal structure and chemical oxidation of the palladium(II) cyclam complex within the cavity of cucurbit[8]uril

Inclusion compound of a macrocyclic cavitand cucurbit[8]uril (C₄₈H₄₈N₃₂O₁₆, CB[8]) with a square-planar palladium(II) complex of a polyamine ligand cyclam, {[Pd(cyclam)]@CB[8]}Cl₂·16?H₂O (1), was synthesized and characterized by X-ray crystallography, elemental analysis, IR, and electrospray ionization (ESI) mass spectrometry. The complex [Pd(cyclam)]²⁺ undergoes chemical oxidation within the CB[8] cavity leading to the formation of the palladium(IV) inclusion compound {trans-[Pd(cyclam)Cl₂]@CB[8]}Cl₂·14H₂O (2). The Pd(II) and Pd(IV) complexes are completely encapsulated within the CB[8] cavity. The cyclam ring in 1 and 2 adopts the most stable configuration (trans-III (S,S,R,R)).     

Alkylimido complexes of titanium(IV)

TiCl₄ reacts with t-butylamine in benzene to give [Ti(NCMe₃)Cl₂(NH₂CMe₃)₂]_x and t-butylamine hydrochloride. The IR spectrum indicates both c/s and trans metal dichlorides (300; and 308, 208 cm⁻¹). In the ¹³C NMR spectrum the t-butylimido quaternary carbon resonance occurs at 72.1 ppm. A dimeric structure incorporating symmetric t-butylimido bridges is proposed. TiCl₄ in benzene react under reflux with two equivalents of Me₃SiNHCMe₃ to give [Ti(NCMe₃)Cl₂(NH₂CMe₃)]_x and with iso-propylamine and ethylamine to give complexes of the form [Ti(NR)Cl₂(NH₂R)₂]_x. Broad bands below 800 cm⁻¹ in the IR spectra suggest polymeric MNM bridges. For [Ti(NCHMe₂)Cl₂(NH₂CHMe₂)]_x the iso-propylimido CH resonance in the ¹³C NMR spectrum occurs at 67 ppm. [Ti(NCMe₃)Cl₂(NH₂CMe₃)₂]₂ reacts with L=bipy or tmed to give [Ti(NCMe₃)Cl₂(L)]₂, and TiCl₄ reacts with two equivalents of Me₃SiNHCMe₃ in benzene and then tmed to give [Ti(NCMe₃)Cl₂(tmed)]₂. The ¹³C NMR spectrum shows the t-butylimido quaternary carbon resonance at 73.5 ppm and the tmed resonances are chemically equivalent. A dimeric μ-NCMe₃ bridging structure is proposed for the complex.     

The palladium(II) promoted hydrolysis of the methyl esters of glycyl-L-leucine,glycyl-L-alanine and L-alanylglycine

The palladium(II)-promoted hydrolysis of the methyl esters of glycyl-L-leucine, glycyl-L-alanine and L-alanylglycine have been studied at 25 °C and I=0.1 M in the pH range 4–5. At a 1:1 metal to ligand ratio the peptide esters act as tridentate ligands, donation occurring via the terminal amino group, the deprotonated amide nitrogen, and the carbonyl group of the ester. Due to the high Lewis acidity of Pd(II) rapid hydrolysis of the ester function by water and hydroxide ion occurs. Rate constants k_OH and k_H2O have been obtained for base hydrolysis and water hydrolysis of the coordinated peptide esters at 25 °C. The rate constants for base hydrolysis are 3.4 X 10⁶ M⁻¹ s⁻¹ (L-alaglyOMe), 6.4 X 10⁶ M⁻¹ s⁻¹ (gly-L-alaOMe) and 2.3 X 10⁷ M⁻¹ s⁻¹ (gly-L-leuOMe). Base hydrolysis of the coordinated peptide esters is at least 10⁶ times that of the free unprotonated ligand. Activation parameters have been obtained for both water and base hydrolysis of the Pd(II) complex of methyl L-alanylglycinate and possible mechanisms for the hydrolyses are considered.     

DNA-Binding and Photocleavage Properties of Ru(II) Polypyridyl Complexes with DNA and Their Toxicity Studies on Eukaryotic Microorganisms

Four Ru(II) polypyridyl complexes, [Ru(bpy)₂(7-NO₂-dppz)]²⁺, [Ru(bpy)₂(7-CH₃-dppz)]²⁺, [Ru(phen)₂(7-NO₂-dppz)]²⁺, and [Ru(phen)₂(7-CH₃-dppz)]²⁺ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), (7-Nitro-dppz = 7-Nitro dipyrido[3,2-a:2′-3′-c]phenazine, 7-CH₃-dppz = 7-Methyl dipyrido[3,2-a:2′-3′-c]phenazine), have been synthesized and characterized by IR, UV, elemental analysis, ¹H NMR, ¹³C-NMR, and mass spectroscopy. The DNA-binding properties of the four complexes were investigated by spectroscopic and viscosity measurements. The results suggest that all four complexes bind to DNA via an intercalative mode. Under irradiation at 365 nm, all four complexes were found to promote the photocleavage of plasmid pBR 322 DNA. Toxicological effects of the selected complexes were performed on industrially important yeasts (eukaryotic microorganisms).     

Synthesis, crystal structure and action on Escherichia coli by microcalorimetry of copper complexes with 1,10-phenanthroline and amino acid

Copper complexes: [Cu(phen)(L-Ser)(H₂O)Cl] (1), [Cu(phen)(Gly)(H₂O)]Cl·3H₂O (2), [Cu(phen)(L-Ala)(H₂O)]Cl·H₂O (3), [Cu(phen)(L-Phe)(H₂O)]Cl·2.5H₂O (4), Cu(phen)₂Cl₂·6H₂O (5) (phen = 1,10-phenanthroline) were synthesized and characterized. The structure of 1 was characterized by X-ray crystallography and showed in a triclinic system with space group P1, a = 6.8953(15) Å, b = 10.737(2) Å, c = 11.894(3) Å, α = 110.395(3)°, β = 94.183(4)° and γ = 100.540(3)°. The antibacterial activities on Escherichia coli (E. coli) of these five copper complexes and CuCl₂ (6) were investigated by microcalorimetry. By analyzing the obtained metabolic thermogenic data and curves, crucial parameters such as rate constant of bacterial growth (k), half inhibitory concentration (IC₅₀), and generation time (t_G) were determined. All these copper complexes could stimulate the growth of the E. coli at their lower concentration. At their higher concentration they all showed antibacterial action. The inhibition on E. coli was 5 > 1 ≈ 2 ≈ 3 ≈ 4 > 6. And the antibacterial mechanism was discussed preliminarily.     

Interaction of copper(II) complexes with bis(p-nitrophenyl)phosphate: Structural and spectral studies

When the complexes [Cu(L1)(H₂O)](ClO₄)₂1, where L1 = 4-methyl-1-(pyrid-2-ylmethyl)-1,4-diazacycloheptane, and [Cu(L2)Cl₂] 2, where L2 = 4-methyl-1-(quinol-2-ylmethyl)-1,4-diazacycloheptane are interacted with one/two equivalents of bis(p-nitrophenylphosphate, (p-NO₂Ph)₂PO₂, BNP), no hydrolysis of BNP is observed. From the solution the adducts of copper(II) complexes [Cu₂(L1)₂((p-NO₂Ph)₂PO₂)₂]-(ClO₄)₂3 and [Cu(L2)((p-NO₂Ph)₂PO₂)₂]·H₂O 4 have been isolated and structurally characterised. The X-ray crystal structure of 3 contains two Cu(L1) units bridged by two BNP molecules. The Cu···Cu distance (5.1 Å) reveals no Cu-Cu interaction. On the other hand, the complex 4 is mononuclear with Cu(II) coordinated to the 3N ligand as well as BNP molecules through phosphate oxygen. The trigonality index (τ, 0.37) observed for 4 is high suggesting the presence of significant trigonal distortion in the coordination geometry around copper(II). The complexes are further characterized by spectral and electrochemical studies.     

Studies on Antibacterial Mechanisms of Copper Complexes with 1,10-phenanthroline and Amino Acid on Escherichia coli

The antibacterial mechanisms of Cu(phen)₂Cl₂·6H₂O, [Cu(phen)(Gly)(H₂O)]Cl·3H₂O, [Cu(phen)(l-Ser)(H₂O)Cl] (1,10-phenanthroline (phen)) on Escherichia coli were investigated. In the inductively coupled plasma atomic emission spectroscopy experiments, it showed that lipophilic phen ligand can cause elevation of intracellular copper, but intracellular copper is not the decisive factor. The UV–vis and gel electrophoresis experiments reveal that the DNA binding and cleavage activity are decisive factors for the antibacterial action of these compounds. It is revealed by the cyclic voltammetry experiments that the redox potential was bound to the cleave activity.     

The rate of reduction of cis-, cis-, trans-[PtIV(NH2Pri)2Cl2(OH)2], CHIP,the anti-cancer drug by ascorbic acid

cis,cis,trans-[Pt^IV(NH₃)₂Cl₂(OH)₂] reacts reversibly with ascorbic acid to give dehydroascorbic acid and mainly cis-[Pt^II(NH₂Prⁱ)₂Cl₂]. The parameters for the forward reaction are: k_f = 0.584 M⁻ s⁻ at 37.0 °C, ΔH^≠_f = 108.6 −+ 6.4 kJ mol⁻¹ andΔS^≠_f = 101 −+ 22 J K⁻¹ mol⁻¹.     

Concentration-dependent palladium(II)-indole bond formation in complexes with a 2N-donor ligand containing an indole moiety: Synthesis, characterization, and reaction analysis

The Pd(II) complexes of a 2N-donor ligand containing a pendent indole, 3-(2-pyridylmethylamino)ethylindole (L), were synthesized and characterized. Reaction of the ligand with [PdCl₂(CH₃CN)₂] at room temperature gave [Pd(L)Cl₂] (1) as pale yellow crystals. The X-ray crystal structure analysis and ¹H NMR spectrum of 1 revealed that the complex has a 2N2Cl-donor set in a square-planar geometry and that the pendent indole ring has no characteristic intramolecular interaction with the Pd(II) ion and the coordinated pyridine moiety. Refluxing a solution of 1 in CH₂Cl₂/DMF for a few hours under basic conditions gave yellow crystals, which were shown to be an indole-C2 binding complex [Pd(L)Cl] (2) by X-ray analysis. Conversion of complex 1 to 2 in DMSO was observed upon dilution of the solution of complex 1. From solution equilibrium and kinetic studies the initial step of the conversion by dilution has been assigned to the replacement of a coordinated Cl⁻ ion with the DMSO molecule. The ligand replacement easily occurred at low concentrations of 1. The complex with a coordinated solvent molecule exhibited a high reactivity and formed a stable Pd-C bond with the indole ring located close to the Pd(II) center. We discussed the concentration dependent formation of the indole-C2 binding complex 2 and its detailed mechanism.