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.     

Bis(phosphine)-Pd(II) and -Pt(II) complexes containing chiral tetrazole-thiolato rings: Synthesis, structures, and reactivity toward some electrophiles

Bis(azido)bis(phosphine)-Pd(II) and -Pt(II) complexes, [M(N₃)₂L₂] {L = PMe₃, PEt₃, PMe₂Ph, dppe = 1,2-bis(diphenylphosphino)ethane}, underwent 1,3-dipolar cycloaddition with organic chiral isothiocyanates (R^∗-NCS: R^∗ = (S)-(+)-1-phenylethyl, (R)-(−)-1-phenylethyl, (±)-1-phenylethyl, (S)-(+)-1-indanyl) to give the corresponding tetrazole-thiolato Pd(II) and Pt(II) complexes, trans-[M{S[CN₄(R^∗)]}₂L₂] or [M{S[CN₄(R^∗)]}₂(dppe)]. Spectroscopic (IR and NMR) and X-ray structural analyses of the products showed that the absolute configuration of the starting organic isothiocyanates is retained throughout the reaction. Further treatments of the isolated tetrazole-thiolato complexes with electrophiles such as HCl or benzoyl chloride produced heterocyclic compounds containing a tetrazole thione or a tetrazolyl sulfide group. In addition, organic tetrazole thiones, [S = {CN₄H(R^∗)}] containing a chiral moiety, were prepared from NaN₃ and R^∗-NCS in the presence of water.     

Adriamycin Complexes of Pd(II) and Pt(II)

Perturbations of the ¹H NMR spectrum of the free base of Adriamycin in DMF solution were found when MCl₂(DMF)₂ (M = Pd or Pt) was added to the Adriamycin solutions. These perturbations were greatest for the 3' proton on the sugar ring and the effect decreased as the distance from this site increased. No changes were observed in the NMR spectrum of the rest of the molecule nor was there any color change when the metal solutions were added. This is interpreted as evidence that Adriamycin binds to these metals at the 3 ' amino group in DMF solution and that there is no reaction at the chromophore. The complexes were found to be in the fast exchange regime on the NMR time scale. As well, some products were isolated from reactions of Adriamycin with MCl₂(DMF)₂ in 20% MeOH/CH₂Cl₂ and MCl₂ in DMF solution. They were characterized by their elemental analyses, as well as by ¹H NMR and infrared spectroscopies.     

Crystal structures of Pt(II) and Pd(II) complexes with the free radical 4-aminoTEMPO

Pt(II) and Pd(II) compounds containing the free radical 4-aminoTEMPO (4amTEMPO) were synthesized and characterised by X-ray diffraction methods. The disubstituted complexes cis- and trans-Pt(4amTEMPO)₂I₂ were studied. The trans isomer was prepared from the isomerisation of the cis analogue. The two Pd(II) compounds trans-Pd(4amTEMPO)₂X₂ (X = Cl and I) were also characterised by crystallographic methods. A mixed-ligand complex cis-Pt(DMSO)(4amTEMPO)Cl₂ was synthesized from the isomerisation of the trans isomer in hot water. Its crystal structure was also determined. In all the complexes, the 4amTEMPO ligand is bonded to the metal through the -NH₂ group, since the nitroxide O atom is not a good donor atom for the soft Pt(II) and Pd(II) metals. The conformation of the 4-aminoTEMPO ligand was compared to those of the few reported structures in the literature.     

Copper(II) complexes as superoxide dismutase mimics: Synthesis, characterization, crystal structure and bioactivity of copper(II) complexes

Two new copper(II) complexes of the type [Cu(L)X₂), where L = (E)-N-phenyl-2-[phenyl (pyridine-2-yl)methylene]hydrazinecarboxamide X = Cl/Br have been synthesized and characterized by elemental analyses, FAB (fast atomic bombardment) magnetic measurements, electronic absorption, conductivity measurements cyclic voltammetry (CV) and Electron paramagnetic resonance (epr) spectroscopy. The structures of these complexes determined by single crystal X-ray crystallography show a distorted square based pyramidal (DSBP) geometry around copper(II) metal center. The distorted CuN₂OX (X = Cl/Br) basal plane in them is comprised of two nitrogen and one oxygen atoms of the meridionally coordinated ligand and a chloride or bromide ion and axial position is occupied by other halide ion. The epr spectra of these complexes in frozen solutions of DMSO showed a signal at g ca. 2. The trend in g-value (g_|| > g_⊥ > 2.00) suggest that the unpaired electron on copper(II) has d_x²-y² character. Biological activities in terms of superoxide dismutase (SOD) and antimicrobial properties of copper(II) complexes have also been measured. The superoxide dismutase activity reveals that these two complexes catalyze the fast disproportionation of superoxide in DMSO solution.     

Structural isomerism involving an ambidentate ligand: the synthesis and characterization of diselenocyanato [bis(diphenylphosphino)methane] palladium(II) and cyano(selenocyanato) [diphenyl(diphenylphosphinomethyl)phosphine selenide] palladium(II)

The reaction, at 25 °C in methanol, between [Pd(SeCN)₄]²⁻ and bis(diphenylphosphino)methane (dpm) has been found to produce cyano(selenocyanato) [diphenyl(diphenylphosphinomethyl) phosphine selenide]palladium(II), [Pd(dpmSe)(CN)(SeCN)], wherein the cyanide group is trans to an Se atom which has been inserted into one PdP bond, and the selenocyanate group is trans to the unchanged diphenylphosphino group. The structure has been confirmed by the results of a single crystal X-ray diffraction study. The structural isomer, [Pd(dpm)- (SeCN)₂], of the foregoing complex has also been prepared by the reaction of Pd(C₂H₃O₂)₂ with dpm, followed by reaction with KSeCN. Heating the [Pd(dpm)(SeCN)₂] isomer converts it into [Pd- (dpmSe)(CN)(SeCN)]. A mechanism is proposed for the isomerization which involves an intramolecular selenium atom insertion.     

The crystallochemistry of tetracyanocomplexes. The crystal and molecular structures of tris(1,2-diaminoethane)zinc(II) tetracyanoniccolate(II) monohydrate and tris(1,2-diaminoethane)zinc(II) tetracyanoniccolate(II)

C₁₀H₂₆N₁₀ONiZn, tris(1,2-diaminoethane) zinc(II) tetrakis(cyano)niccolate(II) monohydrate (I), orthorhombic, Pbca, a = 1.1680(4), b = 1.5844(3), c = 1.9981(6) nm, Z = 8 d(meas) = 1.54, d(calc) = 1.53 g cm^?3. C₁₀H₂₄N₁₀NiZn, tris(1,2-diaminoethane) zinc(II) terakis(cyano)niccolate(II), (II), monoclinic, P2₁/n, a = 0.7957(2), b = 1.5170(5), c = 1.4932(4) nm, β = 96.41(2)°, Z = 4, d(meas) = 1.49, d(calc) = 1.51 g cm^?3. Both the structures (I) and (II) have been solved by the heavy atom method and refined by full-matrix least-squares to R(I) = 0.086 for 1890 independent reflections and R(II) = 0.058 for 1689 independent reflections, respectively. In the case of (II) the superlattice structure problem was solved. The crystal structure of (I) consists of [Zn(en)₃]²⁺ cations, [Ni(CN)₄]^2? anions and water molecules. Two of the cyano groups in trans positions are bonded to water molecules by hydrogen bonds, the distances CN?O being 0.289 and 0.291 nm, respectively. The crystal structure of (II) is constituted by [Zn(en)₃]²⁺ cations and [Ni(CN)₄]^2? anions.     

Palladium(II) complexes of imidazolin-2-ylidene N-heterocyclic carbene ligands with redox-active dimethoxyphenyl or (hydro)quinonyl substituents

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H₃L³Br reveals Br⁻?H-O bridged chiral chains of alternating [H₃L³]⁺ cations and Br⁻ counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr₂(L²)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr₃ afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2-4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)₂Br₂]-centred processes.     

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.     

N-(2-Pyridyl)acetamide complexes of palladium(II), cobalt(II), nickel(II), and copper(II)

N-(2-Pyridyl)acetamide (aapH) complexes of palladium(II), cobalt(II), nickel(II), and copper(II) have been studied by means of magnetic susceptibilities, and infrared, electronic, and PMR spectra. In the octahedral complexes M(aapH)₂X₂(M = Co, Ni, Cu; X = Cl, Br, NCS, NO₃), bidentate aapH is chelated through the pyridine-N and amid-O atomes, whereas in the square-planar Pd(aapH)₂X₂ (X = Cl, Br) unidentate aapH is coordinated through the pyridine-N atom alone. Under alkaline conditions aapH is deprotonated in the presence of palladium(II) to form Pd(aap)₂·4H₂O, aap being an anionic bidentate ligand and chelating through the pyridine-N and amide-O atoms.     

Synthesis, structures and spectroscopic properties of palladium(II) complexes with tridentate piperidyl-containing pincer ligands

A new series of square planar palladium(II) complexes with pincer ligands, pip₂NCN⁻ (pip₂NCNH = 1,3-bis(piperidylmethyl)benzene) and pip₂NNN (2,6-bis(piperidylmethyl)pyridine), has been prepared: Pd(pip₂NCN)X (X = Cl, Br, I), [Pd(pip₂NCN)(L)](BF₄) (L = pyridine, 4-phenylpyridine), and [Pd(pip₂NNN)Cl]Cl. The X-ray crystal structures of Pd(pip₂NCN)Br, [Pd(pip₂NCN)(L)]BF₄, and [Pd(pip₂NNN)Cl]Cl confirm the tridentate coordination geometries of the pincer ligands. For the pip₂NCN⁻ complexes, each piperidyl ring adopts a chair conformation with the metal center at an equatorial position on the N(piperidyl) atom. However, one of the piperidyl groups of Pd(pip₂NNN)Cl⁺ adopts a previously unobserved coordination geometry, effectively placing the metal center at an axial position on the N(piperidyl) atom. ¹H NMR and UV-Vis absorption measurements provide additional insight into the electronic structures of these complexes. The ¹H NMR spectra of Pd(pip₂NCN)X (X = Cl, Br, I) are consistent with deshielding of the pip₂NCN⁻ ligand resonances along the Cl < Br < I series, in opposition to the relative halogen electronegativities. It is suggested that this trend is consistent with decreasing filled/filled repulsions between the dπ orbitals of the metal center and the lone pair orbitals of the halide ligands along this series. Electronic absorption spectra support the notion that ligand-to-metal charge-transfer states are stabilized in these palladium(II) complexes relative to their platinum(II) analogues.     

Stabilities,solubility, and kinetics and mechanism for formation and hydrolysis of some palladium(II)and platinum(II) iodo complexes in aqueous solution

Complex formation between Pd(II), Pt(II) and iodide has been studied at 25 °C for an aqueous 1.00 M perchloric acid medium. Measurements of the solubility of PdI₂(s) in aqueous mercury(II) perchlorate and of AgI(s) and PdI₂(s) in aqueous solutions of Pd²⁺(aq) and Ag⁺(aq) gave the solubility product of PdI₂(s) as K_s^o=(7±3) × 10⁻³² M³, which is much smaller than previous literature values.The stability constants β₁=[MI(H₂O)₃⁺]/([M(H₂O)₄²⁺][I⁻]) for the two systems were obtained as the ratio between rate constants for the forward and reverse reactions of (i).

The following values of k₁ (s⁻¹ M⁻¹), k₋₁ (s⁻¹) and β₁ (M⁻¹) were obtained at 25 °C: (1.14±0.11) × 10⁶, (0.92±0.18), (12±4) × 10⁵ for MPd, and (7.7±0.4), (8.0±0.7) × 10⁻⁵, (9.6±1.3) × 10⁴ for MPt. Combination with previous literature data gives the following values of log(β₁ (M⁻¹)) to log(β₄ (M⁻⁴)): 6.08, ∼22, 25.8 and 28.3 for MPd, and 4.98, ∼25, ∼28, and ∼30 for MPt. The present results show that the large overall stability constants β₄ observed for the M²⁺I⁻ systems are most likely due to a very large stability of the second complex MI₂(H₂O)₂, which is probably a cis-isomer. A distinct plateau in the formation curve for mean ligand number 2 is obtained both for MPd and Pt. The other iodo complexes are not especially stable compared to those of chloride and bromide.ΔH^≠ (kJ mol⁻¹) and ΔS^≠ (JK⁻¹ mol⁻¹) for the forward reaction of (i), MPd, are (17.3±1.7) and (−71±5), and for the reverse reaction of (i) MPd, (45±3) and (−95±6), respectively. The kinetics are compatible with associative activation (I_a). The contribution from bond-breaking in the formation of the transition state seems to be less important for Pd than for Pt.     

Ni(II), Pd(II), and Pt(II) complexes of two new ditertiary phosphines, 1-diphenylphosphino-2-bis(m- or p-fluorophenyl) phosphinoethane

New complexes of the type cis-[MX₂(PP′)] (M= Ni, Pd and Pt; X=Cl, Br, I or NCS and PP′=(m- FC₆H₄)₂PCH₂CH₂PPh₂ or (p-FC₆H₄)₂PCH₂CH₂PPh₂) have been synthesized and characterized on the basis of ³¹P{¹H}NMR¹H NMR, IR and UV spectroscopy, elemental analysis and magnetic susceptibility measurements. All these complexes are found to be low spin, diamagnetic and square planar. ³¹P{¹H} spectra of these complexes exhibit extraordinarily large downfield coordination chemical shifts, J(³¹P³¹P′) and J(¹⁹⁵pt³¹P) couplings are discussed. Ring contribution (ΔR) values for palladium and platinum complexes are calculated from ³¹P NMR data.     

Cadmium(II) complex formation with glutathione

Complex formation between heavy metal ions and glutathione (GSH) is considered as the initial step in many detoxification processes in living organisms. In this study the structure and coordination between the cadmium(II) ion and GSH were investigated in aqueous solutions (pH 7.5 and 11.0) and in the solid state, using a combination of spectroscopic techniques. The similarity of the Cd K-edge and L₃-edge X-ray absorption spectra of the solid compound [Cd(GS)(GSH)]ClO₄·3H₂O, precipitating at pH 3.0, with the previously studied cysteine compound {Cd(HCys)₂·H₂O}₂·H₃O⁺·ClO₄ ^? corresponds to Cd(S–GS)₃O (dominating) and Cd(S–GS)₄ four-coordination within oligomeric complexes with mean bond distances of 2.51 ± 0.02 Å for Cd–S and 2.24 ± 0.04 Å for Cd–O. For cadmium(II) solutions (C _Cd(II) ~ 0.05 M) at pH 7.5 with moderate excess of GSH (C _GSH/C _Cd(II) = 3.0–5.0), a mix of Cd(S–GS)₃O (dominating) and Cd(S–GS)₄ species is consistent with the broad ¹¹³Cd NMR resonances in the range 632–658 ppm. In alkaline solutions (pH 11.0 and C _GSH/C _Cd(II) = 2.0 or 3.0), two distinct peaks at 322 and 674 ppm are obtained. The first peak indicates six-coordinated mononuclear and dinuclear complexes with CdS₂N₂(N/O)₂ and CdSN₃O₂ coordination in fast exchange, whereas the second corresponds to Cd(S–GS)₄ sites. At high ligand excess the tetrathiolate complex, Cd(S–GS)₄, characterized by a sharp δ(¹¹³Cd) NMR signal at 677 ppm, predominates. The average Cd–S distance, obtained from the X-ray absorption spectra, varied within a narrow range, 2.49–2.53 Å, for all solutions (pH 7.5 and 11.0) regardless of the coordination geometry.     

Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

Synthesis of palladium(II) 3d-metal(II) paddlewheel acetate-bridged heterodimetallic complexes: Unexpected catalysis by water molecules

A study of the reaction kinetics between the trinuclear palladium(II) acetate Pd₃(μ-OOCMe)₆ (1) and the mononuclear 3d-metal (Ni^II, Co^II, Cu^II) acetates in acetic acid under water-specified conditions revealed a fairly complicated reaction mechanism triggered by the primary hydrolytic cleavage of an acetate bridge in molecule 1. The isolated reaction products, as established by X-ray diffraction study, are 1D polymeric complexes {Pd(μ-OOCMe)₄M(OH₂)(HOOCMe)₂}_n (M = Ni^II, Co^II, Cu^II, Mn^II, Zn^II) built of the Pd^II-based paddlewheel units [Pd(μ-OOCMe)₄M] and linked trough the H-bonded H₂O and MeCOOH molecules.     

Influence on reactivity of chloro ligand substitution in mononuclear cationic Pd(II) and Pt(II) triphos complexes: X-ray structure of the nitrate derivatives

The substitution of chloro ligand in [M(triphos)Cl]Cl complexes [M=Pd (1), Pt (2); triphos=Ph₂PC₂H₄P(Ph)C₂H₄PPh₂] by reaction with 1 equiv. of KX resulted in the formation of the ionic complexes [M(triphos)X]Cl [X=I, M=Pd (3), Pt (4); X=CN, M=Pd (5), Pt (6)]. Methanolic solutions of silver nitrate in excess displace the chloro ligand and counterion of 1 and 2, giving rise to the formation of the crystalline complexes [M(triphos)(ONO₂)](NO₃) [M=Pd (7), Pt (8)] suitable for X-ray diffraction studies. The complexes show a distorted square-planar environment around the metal, there being three coordination sites occupied by phosphorus atoms from the triphos and the fourth by the oxygen atom from a nitrate acting as monodentate ligand. A second NO₃ ⁻ is acting as counterion with D_3h symmetry. The use of a high excess of SnCl₂ in the presence of 1 equiv. of PPh₃ enabled the formation of complexes [M(triphos)(PPh₃)](SnCl₃)₂ [M=Pd (9), Pt (10)]. These complexes, in addition to [M(triphos)X]X [X=Br, M=Pd (1a), Pt (2a); X=I, M=Pd (1b), Pt (2b)], were synthesised and all Pt(II) complexes characterised by microanalysis. Mass spectrometry, IR spectroscopy, NMR spectroscopy and conductivity measurements were also used for characterisation. The structure and reactivity studies in solution were carried out by ³¹P{¹H} NMR. The trends in chemical shifts δ (P) and ¹J(¹⁹⁵Pt, ³¹P) coupling constants were used to establish a sequence in the X ligand exchange reactions. While [Pd(triphos)I]I (1b) undergoes a ring-opening reaction by titration with AuI, the analogous Pt(II) complex (2b) does not react. The formation of new five-coordinate Pd(II) and Pt(II) complexes was observed by titration of 5–8 with potassium cyanide.     

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.     

Hydrolysis of the amide bond in histidine- and methionine-containing dipeptides promoted by pyrazine and pyridazine palladium(II)-aqua dimers: Comparative study with platinum(II) analogues

Two dinuclear palladium(II) complexes, [{Pd(en)Cl}₂(μ-pz)](NO₃)₂ and [{Pd(en)Cl}₂(μ-pydz)](NO₃)₂, have been synthesized and characterized by elemental microanalysis and spectroscopic (¹H and ¹³C NMR, IR and UV–vis) techniques (en is ethylenediamine; pz is pyrazine and pydz is pyridazine). The square planar geometry of palladium(II) metal centers in these complexes has been predicted by DFT calculations. The chlorido complexes were converted into the corresponding aqua complexes, [{Pd(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pd(en)(H₂O)}₂(μ-pydz)]⁴⁺, and their reactions with N-acetylated l-histidylglycine (Ac–l–His–Gly) and l-methionylglycine (Ac–l–Met–Gly) were studied by ¹H NMR spectroscopy. The palladium(II)-aqua complexes and dipeptides were reacted in 1:1 M ratio, and all reactions performed in the pH range 2.0 < pH < 2.5 in D₂O solvent and at 37 °C. In the reactions of these complexes with Ac–l–His–Gly and Ac–l–Met–Gly dipeptides, the hydrolysis of the amide bonds involving the carboxylic group of both histidine and methionine amino acids occurs. The catalytic activities of the palladium(II)-aqua complexes were compared with those previously reported in the literature for the analogues platinum(II)-aqua complexes, [{Pt(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pt(en)(H₂O)}₂(μ-pydz)]⁴⁺.