Synthesis, characterization, and structural studies of mercury(II) complexes of new bidentate phosphorus ylide

The reaction of Ph₂PCH₂CH₂PPh₂ (dppe) with BrCH₂C(O)C₆H₄NO₂ (1:1.05 molar ratio) in acetone produces a mixture of the new monophosphonium salt [Ph₂PCH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br (1) and the diphosphonium salt [NO₂C₆H₄C(O)CH₂PPh₂CH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br₂ (2). Compound 2 was insoluble in acetone and thus easily separated from the solution of 1. Further, by reacting both the mono- and diphosphonium salts with the appropriate bases the bidentate phosphorus ylides, [Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (3) and [NO₂C₆H₄C(O)CHPPh₂CH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (4) were obtained. The reaction of ligand 3 with mercury(II) halides in dry methanol leads to the formation of the P,P-coordinated monomeric complexes {HgX₂(Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂)₂} [X = Cl (5), Br (6), I (7)]. The structure of complex 7 being unequivocally determined by single crystal X-ray diffraction techniques. Characterization of these species was also performed by elemental analysis, IR spectroscopy and ¹H, ³¹P, and ¹³C NMR techniques. These analyses being consistent with a 2:1 stoichiometry ylide/Hg(II) for compounds 5 through 7. Results obtained from theoretical studies are also consistent with a product in which two ylides are coordinated to the Hg(II) center through their phosphine groups, being this product the most stable among all the possible products.     

Coordination of (aminoalkyloxymethyl)dimethylphosphine oxides with palladium(II). Crystal structure of trans-bis[2-(dimethylphosphinoylmethoxy-1,1-dimethylethylamine)]palladium(II) dichloride

The synthesis, structure and spectroscopic properties of novel palladium(II) chloro complexes with a series of (aminoalkyloxymethyl)dimethylphosphine oxides (AOPO) are reported. The complexes with general formula PdCl₂(N,N′-AOPO₂) were obtained by the reaction of PdCl₂(CH₃CN)₂ with the ligands in dry ethanol. The crystal structure of the trans-bis[2-(dimethylphosphinoylmethoxy-1,1-dimethylethylamine)]palladium(II) dichloride has been determined from single-crystal X-ray diffraction data. The compound crystallizes in monoclinic crystal system with P2₁/n space group. The square-planar coordination sphere of palladium consists of two N atoms from two aminoalkyldimethylphosphine ligands and two Cl atoms in trans-arrangement. The AOPO ligand has monodentate coordination through the NH₂ group. The Pd-N and Pd-Cl distances are 2.0610(14) and 2.3225(4) Å, respectively. The preparation of complexes with a composition PdCl₂(AOPO)₂ in chloroform solution are also reported.     

Cyclopalladation of N-phenylbenzamides: Synthesis and structure of bimetallic palladium(II)-complexes

Three bimetallic palladium(II) complexes were generated by cyclopalladation of N-methyl-N-phenylbenzamide derivatives, substrates known to undergo oxidative intramolecular cross-coupling via palladium catalysis. These isolable Pd-complexes were characterized by X-ray crystallography. Stoichiometric and catalytic experiments with [(3-methoxy-N-methyl-N-phenylbenzamide)Pd(μ-TFA)]₂ were investigated, and this palladium complex was found to be an effective precatalyst for oxidative cross-coupling.     

Preliminary study on the cleavage of fusion protein GST-CMIV with palladium(II) complex

A novel method for post-treatment of gene-engineered proteins is reported. A coden of Cys-His unit is introduced into the N-terminal of cecropin CMIV by using PCR. The gene is expressed in E. coli fused with GST. After purification, the fusion protein is cleaved by [Pd(en)(H2O)2]2+ at the His-Arg bond and the cecropin CMIV with antibacterial activity is obtained. The preliminary results held some promise of success for application of the palladium(II) complex as cleavage agent for the production of peptide drugs from gene-engineering fusion proteins.     

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)).     

Complexes of vitamin B6. XVII. Crystal structure and molecular orbital calculations of the dichloro-bis-pyridoxol palladium(II) complex

The structure of dichloro-bis-pyridoxol palladium(II) complex [PdCl₂(C₈H₁₁O₃N)₂] has been determined from three dimensional X-ray data collection. The complex crystallizes in the monoclinic space group P2₁/c with Z=2 and cell dimensions a=5.265(3), b=17.250(6), c=10.253(6) Å, β= 95.40(2)°. The structure was refined to a final R factor of 0.060 for 1813 reflections with F ⩾ 3σ(F). The palladium atom lies in a symmetry center of inversion in a square plane coordinated to two chlorine atoms and two pyridine nitrogen atoms. Charge distributions and bond order matrix calculated from ARCANA-MO are given.     

Cationic (tripyrrinato)palladium(II) complexes

The formation of cationic palladium(II)complexes [TrpyPd^II]⁺X⁻ by salt metathesis of the respective trifluoroacetates with different salts of weakly coordinating anions X⁻ was investigated. With non-hydrolizable counterions, cationic mono- and dinuclear complexes are observed depending on the nature of the anion X⁻ and the solvent. The mononuclear cations, which are only formed with X = BAr^F, most probably carry a weakly bound molecule of dichloromethane at the fourth coordination site of Pd^II. When treated with diazoalkanes, only these are sufficiently reactive to form carbene complexes. Four- and five coordinate Lewis base adducts [TrpyPd^IIL]⁺ with L = CH₃NC, tBuNH₂, PMe₃, PEt₃ and PiPr₃ and [TrpyPd^IIL₂]⁺ with L = PMe₃ were prepared from the mononuclear cations [TrpyPd^II]⁺BAr^F−. From structural studies it becomes apparent, that the formation of stable five coordinate Pd^II species is restricted to medium size ligands and depends on the delicate balance between the steric influence of L and the strain, which is induced on the TrpyPd^II unit.     

Squarate complexes of diamine palladium(II) and platinum(II)

Reactions of cis-diaminediaqua palladium and platinum dinitrates and of trans-diaminediaqua platinum dinitrate give complexes of the type Pd(tmeda)(OH)(C₄O₄)Pd(tmeda)(C₄O₄H) (tmeda = tetramethylethylenediamine) (1), (en)M(C₄O₄)₂M(en) (en = ethylenediamine (M = Pd, Pt) and trans-[Pt- (NH₃)₂C₄O₄]_n, respectively. The structures of these compounds are discussed on the basis of their spectroscopic data.     

Synthesis, characterization and structural studies of new palladium(II) complexes including non-symmetric phosphorus ylides

The reaction of the non-symmetric phosphorus ylides, Ph₂P(CH₂)_nPPh₂C(H)C(O)PhR [Y₁-Y₄: n = 1, R = Cl, Br, NO₂, OCH₃ and Y₅-Y₈: n = 2, R = Cl, Br, NO, OCH₃] with dichloro(1,5-cyclooctadiene)palladium(II) in dichloromethane under mild conditions afford the monomeric P-C chelated complexes, [(Y)PdCl₂] (Y = Y₁-Y₈). These complexes were fully characterized by elemental analysis and spectroscopic techniques such as IR, ¹H, ³¹P, and ¹³C NMR. In addition, the identity of complexes [(Y₅)PdCl₂] (1b) and [(Y₈)PdCl₂] (4b) was unequivocally determined by single crystal X-diffraction techniques, both structures consisting of six-membered rings formed by coordination of the ligands through the phosphine group and the ylidic carbon atom to the metal center. The coordination geometry around the Pd atoms in both these complexes be defined as slightly distorted square planar. Furthermore, their electrochemical behavior was also investigated by cyclic voltammeters, thus the cyclic voltammetry of complex [(Y₁)PdCl₂], in dichloromethane solution with Pt electrode, shows that the redox reaction of the pair Pd(II)/Pd(0) is irreversible with the cathodic peak potential at −1.08 V versus Ag wire.     

Synthesis, spectroscopy, structure and photophysical properties of dinaphthylmethylarsine complexes of palladium(II) and platinum(II)

Dinaphthylmethylarsine complexes of palladium(II) and platinum(II) with the formulae [MX₂L₂] (M = Pd, Pt; L = di(1-naphthyl)methylarsine = Nap₂AsMe and X = Cl, Br, I), [M₂Cl₂(μ-Cl)₂L₂], [PdCl(S₂CNEt₂)L], [Pd₂Cl₂(μ-OAc)₂L₂] and [MCl₂(PR₃)L] (PR₃ = PEt₃, PPr₃, PBu₃, PMePh₂) have been prepared. These complexes have been characterized by elemental analyses, IR, Raman, NMR (¹H, ¹³C, ³¹P) and UV-vis spectroscopy. The stereochemistry of the complexes has been deduced from the spectroscopic data. The crystal structures of trans-[PdCl₂(PEt₃)(Nap₂AsMe)] and of [Pd(S₂CNEt₂)₂], a follow-up product, were determined. The UV-vis spectra of [MX₂L₂] complexes show a red shift on going from X = Cl to X = I. The complexes [PdX₂L₂] and [PtX₂L₂] are strongly luminescent in fluid solution and in the solid at ambient temperature.     

Binding studies of a novel antitumor palladium(II) complex to calf thymus DNA

The interaction of new 1, 10-phenanthrolineoctyldithiocarbamatopalladium (II) nitrate with DNA from calf thymus was investigated at 300 and 310 K in a Tris-HCl buffer of pH 7.0 medium containing 20 mM sodium chloride. This water soluble, square planar Pd(II) complex has been synthesized and spectroscopic (electronic, infrared, and nuclear magnetic resonance) and elemental analysis of the complex are discussed. This complex shows greater growth inhibitory activity against human tumor cell line K562 than cisplatin. Results of UV-visible studies show that the complex exhibits cooperative binding with DNA and denatures the DNA at an extremely low concentration (～11.98 μM). Fluorescence studies reveal that the mode of binding of this complex with DNA seems to be intercalation. The results of sephadex G-25 column show that the binding of metal complex with DNA is so strong that it does not readily break. Several binding and thermodynamic parameters are also described. They may shed light on the mechanisms of interaction of this agent with DNA, which should be quite different from that of cisplatin.     

A general approach to the synthesis of neutral and cationic binuclear trithiocarbonato-bridged complexes of palladium(II) or of palladium(II)—platinum(II)

Addition (1:2) of Tl₂CS₃ to solutions of perchloratocomplexes of palladium(II) Pd(OClO₃)(C₆F₅)(PR₃) leads to neutral binuclear derivatives of the type (PR₃)(C₆F₅)Pd(μ-S₂CS)Pd(C₆F₅)(PR₃)₂, whilst the reaction of perchloratocomplexes of palladium(II) or platinum(II) with the neutral Pd(η²-CS₃)(PR₃)₂ affords cationic complexes of the type [L₂Pd(μ-S₂CS)M(C₆F₅)L₂]ClO₄ (M = Pd or Pt). Spectral data (IR and ³¹P, NMR) permit the inequivocal structural characterization of both the neutral and the cationic complexes.     

Interaction of palladium (II) with DNA

The nature of interaction of palladium (II) with calf thymus DNA was studied using viscometry, ultraviolet, visible and infrared spectrophotometry and optical rotatory disperison and circular dichroism measurements. The results indicate that Pd(II) interacts with both the phosphate and bases of DNA. The ORD/CD data indicate that the binding of Pd(II) to DNA brings about considerable conformational changes in DNA.     

Synthesis and crystal structures of trans-dichlorobis{tri(2-methylphenyl)stibine}palladium(II) and trans-dibromobis{tri(2-methylphenyl)stibine}palladium(II)

Tri(2-methylphenyl)stibine reacts with [PdX₂(cod)] or PdX₂ (X = Cl or Br) to give the trans-[PdX₂{Sb(2-Me- C₆H₄)₃}₂]. The single crystal X-ray structures of trans-[PdX₂{Sb(2-Me-C₆H₄)₃}₂] (X = Cl or Br) revealed that the palladium atom is a square planar environment with mutually trans-Sb(2-methylphenyl)₃ ligands. Iodine analogous of complex can also be prepared from trans metallation reaction with sodium iodine.     

Crystal structure and exchange pathways of the complex l-(trypthophyl-glycinato)copper(II)

The crystal structure and the EPR characterization of the compound Cu [C₁₃H₁₃N₃O₃] is reported. It crystallizes in the P2₁2₁2₁ space group, with a=8.2829(5), b=9.347(2), c=16.499(2) Å and Z=4. The copper ion is in a distorted square planar coordination, bonded to two nitrogen and one oxygen atoms from one dipeptide and to an oxygen atom from a symmetry-related molecule. Thus, neighbor copper atoms at 5.14 Å are connected by equatorial syn–anti carboxylate bridges giving rise to a chain structure along the b-axis. The chains are connected via hydrogen bonds and cation–π interactions, the latter being provided by the ‘sandwich’ structure involving each copper atom and two tryptophan residues from neighbor molecules. The EPR spectra of polycrystalline sample imply an essentially d_x2−y2 ground state orbital for the Cu(II) ions. The g-values reflect a slightly distorted axial symmetry around the Cu(II) ions as expected from the structural results. No hyperfine interaction is observed, which is indicative of the presence of exchange interactions between the copper atoms as suggested by the X-ray results as well.     

Molecular dynamics of N,N′-di-p-fluorophenyltriazenido complex of platinum (II)

The triazenide complex of Pt(II) trans-(o-Tol)Pt(PEt₃)₂N₃Ar₂(1) (Ar = p-FC₆H₄) was synthesized by reaction of (o-Tol)Pt(PEt₃)₂BF₄ with Ar₂N₃Na. The ¹H, ¹⁹F and ³¹P NMR spectra of this complex in toluene-d₈ were studied at different temperatures. Two kinds of dynamic processes were observed. The first one is the intramolecular N,N′ migration of the (o-Tol)Pt(PEt₃)₂ group, detected by ¹⁹F NMR. The second process, revealed by ¹H, ¹⁹P NMR, is the rotation around the partially double N(2)–N(3) bond. Thermodynamic parameters for these processes were calculated from dynamic NMR spectra.     

Structure of bis(2-acetylpyridine 3-hexamethyleneiminylthiosemicarbazonato) palladium II,a potential antitumor complex

The crystal structure of the potential antitumor complex bis(2-acetyppyridine 3-hexamethyleneiminylthiosemicarbazonato)palladium(II) has been solved. The palladium(II) atom is in a square planar environment surrounded by two cis nitrogen atoms and two cis sulfur atoms. The ligands are not equivalent, one being tridentate with (N,N,S) donation, the other being monodentate using only the sulfur atom to coordinate to the metal. The tridentate ligand shows a Z, E, Z configuration while the monodentate ligand shows an E, E, Z. Intermolecular hydrogen bonds stabilize the structure, while the crystal packing is determined by Pd-C, Pd-pi, C-H-pi and pi-pi interactions.     

Molecular modeling of the three-dimensional structure of Fe(II)-bleomycin: are the Co(II) and Fe(II) adducts isostructural?

The molecular modeling of Co(II)-bleomycin previously performed by us through NMR and molecular dynamics indicates that the most favorable structure for this complex is six-coordinate, with the secondary amine in beta-aminoalanine, the N5 and N1 nitrogens in the pyrimidine and imidazole rings, respectively, and the amide nitrogen in beta-hydroxyhistidine as equatorial ligands. The primary amine and either the carbamoyl group or a solvent molecule are proposed to occupy the axial sites. In this report, the results of the molecular modeling of Fe(II)-bleomycin are presented. The NMR data for the ferrous derivative of the drug have already been reported by us, and were used here to generate the necessary restraints for this modeling work. For Co(II)-bleomycin, two new models exhibiting N-carbamoyl ligation to the metal centers were also assayed and compared with the ones previously examined. The results of this investigation on Fe(II)- and Co(II)-bleomycin are most consistent with a six-coordinate structure with five endogenous N-donors and a solvent molecule or the carbamoyl group as the sixth ligand. Comparisons of the best Co(II)- and Fe(II)-bleomycin models with the NMR-generated structures for some relevant metallo-BLMs favor the model with only endogenous ligands and N-carbamoyl ligation as the structure probably held in solution by both Co(II)- and Fe(II)-bleomycin.     

Bis(O2S2 macrocycle) complexes of palladium(II)

Two isomeric dibenzo-O₂S₂ macrocycles L¹ and L² have been synthesised and their coordination chemistry towards palladium(II) has been investigated. Two-step approaches via reactions of 1:1-type complexes, [cis-Cl₂LPd] (1a: L = L¹, 1b: L = L²), with different O₂S₂ macrocycle systems (L¹ and L²) have led to the isolation of the following bis(O₂S₂ macrocycle) palladium(II) complexes in the solid state: [Pd(L¹)₂](ClO₄)₂ (2a) and a mixture of [Pd(L¹)₂](ClO₄)₂ (2a) + [Pd(L²)₂](ClO₄)₂ (2b).     

Bidentate palladium(II) chelation by the common aldoses

The [Pd^II{(R,R)-chxn}(OH)₂] reagent (chxn = 1,2-diaminocyclohexane) is introduced as a metal probe for the detection of the bidentate chelating sites of a glycose. Two moles of hydroxide per mole palladium support double deprotonation of potentially chelating diol functions at a glycose’s backbone. The individual chelating sites are detected using one- and two-dimensional NMR techniques. At equimolar amounts of palladium(II) and aldose, the metal-binding sites include mostly the hydroxy function at the anomeric carbon atom. Chelators are derived from both the pyranose and the furanose isomers. Most pyranose-based chelators form five-membered chelate rings by using their 1,2-diol function. Though 1,2-diolate bonding is also common to the furanoses, the formation of six-membered chelate rings by 1,3-bonding is more significant for them. Metal-excess conditions provoke mostly bis-bidentate 1,2;3,4-chelation but unusual isomers form also: thus d-xylose is dimetallated in its all-axial β-pyranose form, and erythrose’s dimetallation results in the formation of two isomers of a metal derivative of the open-chain hydrate. The spectroscopic results are supported by crystal-structure determinations on [Pd{(R,R)-chxn}(α-d-Xylp1,2H₋₂-κO^1,2)]·H₂O (Xyl = xylose), [Pd{(R,R)-chxn}(α-d-Ribp1,2H₋₂-κO^1,2)]·2.25H₂O (Rib = ribose), [Pd{(R,R)-chxn}(α-l-Thrf1,3H₋₂-κO^1,3)]·2H₂O (Thr = threose) and [Pd{(R,R)-chxn}(α-d-Eryf1,3H₋₂-κO^1,3)]·3H₂O (Ery = erythrose).