Formation and Decomposition of the Methylplatinum(IV) Complex in the Mechanically Activated K2PtCl4 Powder–MeI Vapor System

Mechanical treatment of the K₂PtCl₄ solid salt in a vibrating mill results in Pt–Cl bond heterolysis to form coordinatively unsaturated Pt(II) complexes. At room temperature, the freshly treated K₂PtCl₄ salt absorbs methyl bromide and evolves methyl chloride to the gas phase. The reaction mechanism involves the following sequence of steps: the oxidative addition of methyl iodide to Pt(II) with the intermediate formation of Pt(IV) methyl complexes and the decomposition of the latter due to intramolecular reductive elimination with methyl chloride formation. The first step of the reaction of MeI with the preactivated surface of the K₂PtCl₄ salt is assisted by active sites, which are regenerated in each act of the chemical transformation of MeI into MeCl involving in the chain substitution of halogen in methyl iodide. The coordinatively unsaturated surface platinum complexes can act as such active sites. Due to their effective positive charge, they can provide electrophilic assistance to nucleophilic substitution. Chain termination is probably due to the coordination of the complex with a coordination vacancy and an interstitial chloride ion to the inactive K₂PtCl₄ complex.     

Synthesis and structure of mixed-metal thiolate complex Cp′Cr(CO)2(μ-SBu)Pt(PPh3)2: Side-on-coordination of Cr–S double bond with platinum

The reaction of [Cp′Cr(CO)₂(μ-SBu)]₂ (1) (Cp′ = MeC₅H₄) with (PPh₃)₂Pt(PhCCPh) gives Cp′Cr(CO)₂(μ-SBu)Pt(PPh₃)₂ (2) which could be regarded as a product of the substitution of acetylene ligand at platinum by a monomeric chromium–thiolate fragment. According to the X-ray diffraction analysis 2 contains single Cr–Pt (2.7538(15)) and Pt–S (2.294(2) Å) bonds while Cr–S bond (2.274(3) Å) is shortened in comparison with ordinary Cr–S bonds (2.4107(4)–2.4311(4) Å) in 1. The bonding between Cr–S fragment and platinum atom is similar to the olefine coordination in their platinum complexes.     

Oxidation of Methanol on Pt,Pt–Ru,and Pt–Ru–Mo Electrocatalysts Dispersed in Polyaniline: An in situ Infrared Reflectance Spectroscopy Study

The electrochemical oxidation of methanol was investigated on a Pt–Ru–Mo catalyst with an in situ infrared reflectance spectroscopy. The electrocatalysts were prepared by an electrochemical deposition and dispersed in a conducting three-dimensional matrix of polyaniline (PAni). We observed that CO₂ is produced from methanol oxidation at 350 mV vs. RHE on PAni/Pt–Ru–Mo, which is 100 mV less negative than on PAni/Pt–Ru and 200 mV less than on PAni/Pt. The results suggest that Pt–Ru–Mo is less sensitive to CO_ADS poisoning than Pt–Ru and much more sensitive than Pt. Large differences are observed concerning the average wavenumber of _ADS between Pt–Ru–Mo, Pt–Ru, and Pt.     

Catalytically Promoted NOx Sorption by ZrO2-Based Oxides

Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO₂/Al₂O₃ for NO _x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO₂ was compared using the samples with and without Pt. The catalytic oxidation of NO to NO₂ and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO₂–Al₂O₃ prepared from H₂PtCl₆ in order to provide more active NO _x sorption sites. Of M–ZrO₂–Al₂O₃ samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO₂ demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO _x sorptive capacities of the Pt–ZrO₂/Al₂O₃ sorbents were expected to be deteriorated in dilute SO₂ as far as observed from FT-IR spectra.     

One-milliliter wet-digestion for inductively coupled plasma mass spectrometry (ICP-MS): determination of platinum-DNA adducts in cells treated with platinum(II) complexes

Platinum (Pt)–DNA adducts formed by the anti-tumor agent cisplatin are recognized by the DNA mismatch repair (MMR) system. To investigate the involvement of MMR proteins including hMLH1 in the removal of these adducts, we developed a mL-scale wet-digestion method for inductively coupled plasma mass spectrometry (ICP-MS). The detection limit was 0.01 ng mL^–1 Pt, which corresponded to 2 pg Pt/g DNA when 10 g of DNA was used. The mean relative errors were 5.4% or better for a dynamic range of 0.01–10 ng mL^–1 Pt. DNA (~500 g) had no matrix effect. To improve the accuracy, DNA preparations were treated with ribonuclease and the apparent reduction in the concentration of Pt was corrected using cellular DNA levels, which were determined with Hoechst 33258. No significant differences were observed, in terms of the formation of Pt–DNA adducts or their removal over 6 h, between hMLH1-deficient HCT116 cells, a human colorectal cancer cell line, and hMLH1-complemented HCT116+ch3 cells (n=5; P>0.05), indicating that the hMLH1-dependent DNA repair systems contribute to neither the formation nor the removal of the adducts at detectable levels. In addition, approximately 19% of the adducts were removed within 6 h in both cell lines. A time course analysis (~24 h) suggested that the removal of cisplatin-generated Pt–DNA adducts follows first-order kinetics (t_1/2=32 h). The amount of Pt–DNA adduct formed by oxaliplatin in 1 h was 56% (ratio of means) of that generated by an equimolar concentration of cisplatin in HCT116. The proposed procedure could be useful for determining Pt–DNA adducts formed by Pt(II) complexes.     

Cyclohexane dehydrogenation over Pt-Dy/Al2O3 catalysts

The conversion of cyclohexane dehydrogenation over Pt–Dy/Al₂O₃ has been studied with a pulsed microcatalytic reactor. Two interesting experiments utilizing CS₂ and thiophene poisoning Pt/Al₂O₃ and Pt–Dy/Al₂O₃ for cyclohexane dehydrogenation are shown and the reaction mechanism is described. The kinetic parameters of cyclohexane dehydrogenation have been calculated. Correlation of the catalytic behavior with the properties of active sites is also discussed.     

The PtX n Coordination Polyhedra (X = S,Se, Te) in Crystal Structures

Using the Voronoi–Dirichlet partition procedure and the method of intersecting spheres, it is demonstrated that in the crystal structures of chalcogen-containing compounds, Pt(IV) atoms form only PtX₆ octahedra (X = S, Se, Te), whereas in the case of Pt(III) and Pt(II), square coordination by X atoms is typical. The Pt(II) atoms can also form PtX₅ square pyramids (X = S, Se), PtS₆ octahedra, and PtTe₃Pt₃ quasi-octahedra in which a platinum atom is located in the trans-position to each coordinated tellurium atom. It was found that Pt(II) atoms in the PtX₄ squares (X = S, Se), unlike square-coordinated Pt(III) atoms, can form one or two Pt–M bonds (M is a d metal) and 1 to 4 secondary Pt–Q bonds, where Q is an s metal or hydrogen. The main features of platinum stereochemistry depending on the metal valence state and coordination number (CN) and on the nature of the chalcogen atom were quantitatively characterized in terms of the Voronoi–Dirichlet polyhedra.     

2,6-Di-tert-butylphenols and phenoxyl radicals with metal—metal bonds

-Aryl trans-bistriphenylphosphine complexes based on 2,6-di-tert-butylphenol containing Pt—SnCl₃, Pt—GeCl₃ groups were synthesized. Oxidation of these compounds gives the corresponding phenoxyl radicals, which were studied by ESR spectroscopy. The transformation of the diamagnetic complexes to the paramagnetic state is accompanied by cleavage of the Pt—Sn, Pt—Ge bonds and by elimination of SnCl₂, GeCl₂.     

Activation of Homolytic SiZn and SiHg Bond Cleavage,Mediated by a Pt0 Complex,via Novel PtZn and PtHg Compounds

The thermally stable [(tBuMe₂Si)₂M] (M=Zn, Hg) generate R₃Si^. radicals in the presence of [(dmpe)Pt(PEt₃)₂] at 60–80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn ( 2 a and 2 b ), M=Hg ( 3 a and 3 b )) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt? MSiR₃ bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn ( 5 ), Hg ( 6 )) whose structures were determined by EPR spectroscopy and DFT calculations.     

Activation of Homolytic Si?Zn and Si?Hg Bond Cleavage,Mediated by a Pt0 Complex,via Novel Pt?Zn and Pt?Hg Compounds

The thermally stable [(tBuMe₂Si)₂M] (M=Zn, Hg) generate R₃Si^. radicals in the presence of [(dmpe)Pt(PEt₃)₂] at 60–80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn ( 2 a and 2 b ), M=Hg ( 3 a and 3 b )) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt MSiR₃ bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn ( 5 ), Hg ( 6 )) whose structures were determined by EPR spectroscopy and DFT calculations.     

Theoretical studies upon the electronic structures and spectroscopic properties for a series of luminescent terpyridyl platinum(II) phenylacetylide complexes

A comprehensive calculations were carried out to get a deep insight into the ground- and excited-state electronic structures and the spectroscopic properties for a series of [Pt(4-X–trpy)CCC₆H₄R]⁺ complexes (trpy = 2,2′,6′,2″-terpyridine; X = H, R = NO₂ (1), Cl (2), C₆H₅ (3) and CH₃ (4); R = Cl, X = CH₃ (5) and C₆H₅ (6)). MP2 (second-order Møller–Plesset perturbation) and CIS (single-excitation configuration interaction) methods were employed to optimize the structures of 1–6 in the ground and excited states, respectively. The investigation showed that substituted phenylacetylide and trpy ligands only give rise to a small variation in geometrical structures but lead to a sizable difference in the electronic structures for 1–6 in the ground and excited states. The introduction of electron-rich groups into the phenylacetylide and/or terpyridyl ligands produces two different low-lying absorptions for 1 and 2–6, i.e., Pt(5d) → π^*(trpy) metal-to-ligand charge transfer (MLCT) mixed with π → π^*(CCPh) intraligand charge transfer (ILCT) for 1 and Pt(5d)/π(CCPh) → π^*(trpy) charge transfer (MLCT and LLCT) for 2–6. Remarkable electronic resonance on the whole Pt–CCPh–NO₂ moiety for 1 may be responsible for the difference. Solvatochromism calculation revealed that only LLCT/MLCT transitions showed the solvent dependence, consistent with the experimental observations.     

Stepwise isolation of low-valent,low-coordinate Sn and Pb mono- and dications in the coordination sphere of platinum

Synthetic access to low-coordinate Pb mono- and dications is in general impeded due to their poor solubility and highly electrophilic nature. However, the electrophilicity of these cations can be tamed by attaching them to electron-rich transition metals. Following this principle we have isolated low-valent Pb mono- ([(Cy₃P)₂Pt–PbCl]₂[AlCl₄]₂, 8a) and dications ([(Cy₃P)₂Pt(Pb)][AlCl₄]₂, 11) in the coordination sphere of platinum. The same approach then has been implemented for the isolation of analogous low-valent Sn mono- (7a) and dications (10). An energy decomposition analysis (EDA-NOCV) was performed to investigate the nature of Pt–Pb and Pb–Cl bonding in [(Cy₃P)₂Pt(PbCl₂)] (2), 8a and 11. The results show that the Pt–Pb bonds in 8a and 11 are electron-sharing in nature, whereas that of the precursor 2 is a dative bond. The breakdown of attractive interactions in 2, 8a and 11 reveals that the ionic interactions in the analyzed Pt–Pb and Pb–Cl bonds are always stronger than the covalent interactions, except for the Pb–Cl bond in 8a. The calculated D3 dispersion energies show that dispersion interactions play a key role in the thermodynamic stability of 2, 8a and 11.     

Formation of Platinum–Tin Bond by Tin(II)Chloride Insertion

The first ¹¹⁹Sn NMR evidence for the presence of direct platinum–tin bond in solution has been obtained for PtCl(SnCl₃)(bdpp) complex (bdpp = (2S,4S)-2,4-bis(diphenylphosphino)pentane). Various PtCl₂(L₂) complexes (L₂ = heterobidentate P–P, P–O, P–N, P–S chelating ligands) have been reacted with tin(II)chloride resulting in the formation of the corresponding PtCl(SnCl₃)(L₂) derivatives. Tin(II)chloride has been inserted into the Pt–Cl bond transto the harder donor atom of the L₂ ligand.     

Platinum(II) and platinum(IV) complexes of 2-amino-4, 6-dimethylpyrimidine

Summary Platinum(II) and platinum(IV) complexes of 2-amino-4, 6-dimethylpyrimidine, ADMPY, have been prepared. Solids of formula Pt(ADMPYH⁺)Cl₃, Pt(ADMPY)₂Cl₄ and Pt(ADMPY)₂Cl₄·2HCl have been isolated and characterized by elemental analyses in conjuction with i.r. and n.m.r. spectra. A paramagnetic tan to reddishbrown complex has been reproducibly prepared from the direct reaction of K₂PtCl₄ and ADMPY at pH 6.     

Insertion of ethyl diazoacetate into the platinum–carbon bond of Pt(diphosphine)(halide)(aryl) complexes. X-ray structure of the Pt{(2<Emphasis Type="BoldItalic">S</Emphasis>,4<Emphasis Type="BoldItalic">S</Emphasis>)-bdpp)}I(Ph) complex

Pt(diphosphine)X(aryl) complexes [diphosphine = 1,3-bis(diphenylphosphino)propane (dppp), 2,4-bis(diphenylphos phino)pentane (bdpp); aryl = phenyl, 2-thiophenyl; X = Cl, I] have been reacted with ethyl diazoacetate in chloroform. It has been revealed by in␣situ n.m.r. studies that the starting compounds insert the carbene, formed from ethyl diazoacetate, into the Pt–aryl group resulting in Pt(diphosphine)X{CH(aryl)COOC₂H₅}. Depending on the reaction conditions (reaction time, ratio of the reactants) and the ligands various side-reactions have been observed: (i) the formation of Pt(diphosphine)X₂ in chloroform, (ii) the insertion of the :CHCOOC₂H₅ fragment into the Pt–halide bond of the dihalogeno complexes Pt(diphosphine)X₂ resulting in the exclusive formation of Pt(diphosphine)X(CHXCOOC₂H₅). Diastereoselective insertion reactions have been observed in the presence of (S,S)-bdpp as diphosphine. The Pt{(S,S)-bdpp)}I(Ph) complex has been characterized by X-ray crystallography.     

Does increased chelation enhance the rate of ligand substitution at PtII (N,N,N) centres? A detailed kinetic & mechanistic study

The rate of substitution of the chloride and aqua moieties from the platinum(II)-amine complexes, viz. [Pt(dien)Cl]Cl(Pt1-Chloro) and [Pt(en)(NH₃)Cl]Cl (Pt2-Chloro) and their corresponding aqua analogues, viz. [Pt(dien)(OH₂)] (ClO₄)₂ (Pt1-Aqua) and [Pt(en)(NH₃)(OH₂)](ClO₄)₂ (Pt2-Aqua), by a series of neutral and anionic nucleophiles,viz. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU), iodide (I⁻) and thiocyanate (SCN⁻), was determined under pseudo first-order conditions as a function of concentration and temperature using UV/Visible spectrophotometry and standard stopped-flow techniques. The observed pseudo first-order rate constants for the substitution reactions obeyed the simple rate law k _obs = k ₂[Nucleophile]. Second-order kinetics and negative activation entropies, ca. −93 J K⁻¹ mol⁻¹ and −71 J K⁻¹ mol⁻¹, for the chloro and aqua complexes respectively, support an associative mode of activation. The rate of substitution of both the chloro and aqua moieties are observed to decrease with an increase in the steric bulk of the neutral nucleophiles, whilst rate of substitution by SCN⁻ was observed to be faster than that of I⁻, in correlation with the observed nucleophilicities of the two nucleophiles. A comparison of the second-order rate constants, k ₂, at 298 K, obtained for the substitution reactions of Pt1and Pt2 shows that an increase in chelation in moving from Pt2 to Pt1 results in a corresponding increase in the reactivity, by a factor of ca. 3, (28.31 ± 0.15 and 8.02 ± 0.13 m ⁻¹ s⁻¹ for Pt1 and Pt2 respectively, in the case of substitution of the aqua species by TU). Computational analysis of the chloro complexes, viz. Pt1-Chloro, Pt2-Chloro and [Pt(NH₃)₃Cl]Cl (Pt3) support this conclusion by demonstrating that the Pt–N bond trans to the leaving group is shortened and that the Pt–Cl bond is lengthened when chelation is increased from Pt3 to Pt1. Consequently, these results suggest that the increase in reactivity of Pt1 over Pt2, promoted by increased chelation, is as a result of ground state destabilization.     

Paramagnetic complexes of nickel(I) stabilized by norbornadiene

Nickel(I) compounds whose concentration was 10^–4–10^–6 of the total concentration of nickel added to the system were identified by EPR in the reaction of 2,5-norbornadiene with nickel homoligand allyl complexes Niall₂ (all is C₃H₅, 1-CH₃C₃H₄, or 2-CH₃C₃H₄). The Ni(I) complexes were stable at room temperature under oxygen-free conditions. It was shown that the paramagnetic complexes were in equilibrium with diamagnetic forms. The temperature dependence of the concentration of the paramagnetic species was determined. The structure of the paramagnetic nickel(I) complexes and the possible routes of their formation are discussed on the basis of the obtained data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 490–493, July–August, 1990.     

Elektrochemische Untersuchungen des Systems Ozon/Sauerstoff an verschiedenen Elektrodensubstraten

The cathodic reduction of O₃ and O₂ in O₃/O₂ gas mixtures was studied at Pt–Pt/Au-alloy-, Au–Ir and Rh-electrodes in 1N-H₂SO₄.The steady state polarization curves exhibitTafel-regions withb-values from 110–160 mV (260–280 mV at Rh). A single electron transfer reaction is found to be the rate determining step. In a region of high cathodic polarization limiting currents are observed which are controlled by diffusion. Platinum is the only electrode material at the O₃-electrode which is stable against corrosion.In the presence of O₃ a decrease of the cathodic polarization of +300 to +400 mV for the O₂ reduction is observed on Pt.This activation of the O₂-electrode is only quasi-stationary because the reduction of the Pt–O layer, which is electrocatalytically effective, proceeds at a low rate for the potentials concerned.The triangular voltage sweep curves show that formation and reduction of oxygen layers and the electrochemical reactions of O₃ and O₂ respectively occur independently of each other.

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Mit 6 Abbildungen     

Synthesis and x-ray crystal structure of tetraethylammonium bis[1, 1-dicyanoethylene-2, 2-dithiolato]platinate(II)

Summary [(NEt₄)]₂[Pt(S₂C₄N₂)₂] has been prepared from K₂PtCl₄ and K₂S₂C₄N₂·H₂O with NEt₄Cl and characterized by single crystal x-ray structural analysis.The title compound crystallizes in the monoclinic space group P2₁/a witha=14.800(2),b=11.679(2),c=9.497(1) Å, =94.51(4)° andZ=2. In the complex anion Pt sits on a centre of symmetry and is coordinated by four S atoms of the ligand (S₂C₄N₂)^2– (i-mnt). The Pt–S distances are 2.315(3) and 2.316(3) Å. The intra-and interligand S–S distances are 2.807(4) and 3.682(4) Å, respectively, indicating the rectangular planar arrangement of the sulfurs about platinum. Within the isomaleonitriledithiolate there is still some suggestion of resonance indicated by the geometry of i-mnt.     

Outer-sphere electron-transfer reactions with the participation of platinum(IV) haloammines

The kinetics of some outer-sphere electron-transfer reactions with the participation of the complexes [Pt(NH₃)_nX_6–n]² (n=6–0, X=Cl^–, Br^–) and dipyridyl complexes of Os(II), Ru(II), Ir(III), and Cr(II) have been investigated by means of luminescence-quenching measurements and flash photolysis. Estimates of the values of the Pt(IV)/Pt(III) one-electron potential and the change in the free energy of activation of electron self-exchange processes of the type Pt(IV) Pt(III) have been obtained on the basis of an analysis of the dependence of the rate constant on the change in the free energy accompanying the electrontransfer process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 455–462, July–August, 1990.