Synthesis and reactivity of dichloroboryl complexes of platinum(II)

The reaction between [Pt(nbe)3] (nbe=norbornene), two equivalents of the phosphines PPh3, PMePh2 or PMe2Ph and 1 equivalent of BCl3 affords the platinum dichloroboryl species [PtCl(BCl2)(PPh3)2], [PtCl(BCl2)(PMePh2)2] and [PtCl(BCl2)(PMe2Ph)2]. All three complexes were characterised by X-ray crystallography and reveal that the boryl group lies trans to the chloride. With PMe3 as the phosphine, the complex [PtCl(BCl2)(PMe3)2] is isolated in high yield as a white crystalline powder although crystals suitable for X-ray crystallography were not obtained. Crystals were obtained of a product shown by X-ray crystallography to be the unusual dinuclear species [Pt2(BCl2)2(PMe3)4(micro-Cl)][BCl4] which reveals an arrangement in which two square planar platinum(II) centres are linked by a single bridging chloride which is trans to a BCl2 group on each platinum centre. The reaction of [PtCl(BCl2)(PMe3)2] with NEt3 or pyridine (py) affords the adducts [PtCl{BCl2(NEt3)}(PMe3)2] and [PtCl{BCl2(py)}(PMe3)2], respectively, both characterised spectroscopically. The reaction between [PtCl(BCl2)(PMe3)2] and either 4 equivalents of NHEt2 or piperidine (pipH) results in the mono-substituted boryl species [PtCl{BCl(NEt2)}(PMe3)2] and [PtCl{BCl(pip)}(PMe3)2], respectively, the former characterised by X-ray crystallography. Treatment of either [PtCl(BCl2)(PMe3)2] (in the presence of excess NEt3) or [PtCl{BCl(NEt2)}(PMe3)2] with catechol affords the B(cat) (cat=catecholate) derivative [PtCl{B(cat)}(PMe3)2] which is also formed in the reaction between [Pt(PMe3)4] and ClB(cat) and also from the slow decomposition of [Pt{B(cat)}2(PMe3)2] in dichloromethane over a period of months. The compound [Pt{B(cat)}2(PMe3)2] was prepared from the reaction between [Pt(PMe3)4] and B2(cat)2.     

杂环反铂(Ⅱ)抗癌药物水解反应机理的DFT研究

用DFT-B3LYP方法和IEF-PCM溶剂化模型研究了反铂抗癌药物trans-[PtCl2(piperidine)(Am)](Am=2-picoline(1),3-picoline(2),4-picoline(3)),trans-[PtCl2(piperidine)(piperazine)](4),trans-[PtCl2(pipera-zine)2](5)and trans-[PtCl2(iminoether)2](6)的水解过程.水解反应是药物与DNA靶分子作用的关键活化步骤.全优化和表征了一水解和二水解反应经由一般的SN2路径过程所有物种的势能面稳定点.结果发现反应过程遵循已经建立的平面正方形配合物的配体取代反应理论,即取代反应通常通过一个三角双锥过渡态结构的铂配体交换反应发生.得到的过渡态结构与以前的相关工作一致,所有反应都是吸热反应;所有体系的二水解能垒都高于一水解.与顺铂相比,这些配合物都有更快的水解反应速率;并与以前类似的反铂配合物的研究做了比较.研究结果提供了这些配合物水解反应过程的详细能量变化,对理解药物与DNA靶分子的作用机理和新型反铂抗癌药物的设计有帮助.     

Electrodeposition of platinum nanoparticles in a room-temperature ionic liquid

The electrochemistry of the [PtCl(6)](2-)-[PtCl(4)](2-)-Pt redox system on a glassy carbon (GC) electrode in a room-temperature ionic liquid (RTIL) [i.e., N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMEBF(4))] has been examined. The two-step four-electron reduction of [PtCl(6)](2-) to Pt, i.e., reduction of [PtCl(6)](2-) to [PtCl(4)](2-) and further reduction of [PtCl(4)](2-) to Pt, occurs separately in this RTIL in contrast to the one-step four-electron reduction of [PtCl(6)](2-) to Pt in aqueous media. The cathodic and anodic peaks corresponding to the [PtCl(6)](2-)/[PtCl(4)](2-) redox couple were observed at ca. -1.1 and 0.6 V vs a Pt wire quasi-reference electrode, respectively, while those observed at -2.8 and -0.5 V were found to correspond to the [PtCl(4)](2-)/Pt redox couple. The disproportionation reaction of the two-electron reduction product of [PtCl(6)](2-) (i.e., [PtCl(4)](2-)) to [PtCl(6)](2-) and Pt metal was also found to occur significantly. The electrodeposition of Pt nanoparticles could be carried out on a GC electrode in DEMEBF(4) containing [PtCl(6)](2-) by holding the potential at -3.5 or -2.0 V. At -3.5 V, the four-electron reduction of [PtCl(6)](2-) to Pt can take place, while at -2.0 V the two-electron reduction of [PtCl(6)](2-) to [PtCl(4)](2-) occurs. The results obtained demonstrate that the electrodeposition of Pt at -3.5 V may occur via a series of reductions of [PtCl(6)](2-) to [PtCl(4)](2-) and further [PtCl(4)](2-) to Pt and at -2.0 V via a disproportionation reaction of [PtCl(4)](2-) to [PtCl(6)](2-) and Pt. Furthermore, the deposition potential of Pt nanoparticles was found to largely influence their size and morphology as well as the relative ratio of Pt(110) and Pt(100) crystalline orientation domains. The sizes of the Pt nanoparticles prepared by holding the electrode potential at -2.0 and -3.5 V are almost the same, in the range of ca. 1-2 nm. These small nanoparticles are "grown" to form bigger particles with different morphologies: In the case of the deposition at -2.0 V, the GC electrode surface is totally, relatively compactly covered with Pt particles of relatively uniform size of ca. 10-50 nm. On the other hand, in the case of the electrodeposition at -3.5 V, small particles of ca. 50-100 nm and the grown-up particles of ca. 100-200 nm cover the GC surface irregularly and coarsely. Interestingly, the Pt nanoparticles prepared by holding the potential at -2.0 and -3.5 V are relatively enriched in Pt(100) and Pt(110) facets, respectively.     

Metal-catalyzed chemoselective cycloisomerization of cis-2,4-dien-1-als to 3-cyclopentenones and 4-alkylidene-3,4-dihydro-2H-pyrans

[reaction: see text] PtCl(2) (5 mol %) catalyst effected cycloisomerization of cis-2,4-dien-1-al (1) to 3-cyclopentenone (3) efficiently in hot toluene. In the presence of p-TSA, this PtCl(2) catalysis gave 2-cyclopentenone (5) exclusively because of the secondary isomerization reaction. Although the 1-2 equilibrium state greatly favors aldehyde (1), PdCl(2)(PhCN)(2) (5 mol %) catalyzed cycloisomerization of aldehyde (1) to 4,6,7,8-tetrahydro-3H-isochromene (4) smoothly in hot toluene. A plausible mechanism is proposed on the basis of reaction observation and isotope-labeled experiment.     

Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl2 and Au(I) complexes

The intramolecular [4C+3C] cycloaddition reaction of allenedienes catalysed by PtCl(2) and several Au(I) complexes has been studied by means of DFT calculations. Overall, the reaction mechanism comprises three main steps: (i) the formation of a metal allyl cation intermediate, (ii) a [4C(4π)+3C(2π)] cycloaddition that produces a seven-membered ring and (iii) a 1,2-hydrogen migration process on these intermediates. The reaction proceeds with complete diastereochemical control resulting from a favoured exo-like cycloaddition. Allene substituents have a critical influence in the reaction outcome and mechanism. The experimental observation of [4C+2C] cycloadducts in the reaction of substrates lacking substituents at the allene terminus can be explained through a mechanism involving Pt(IV)-metallacycles. With gold catalysts it is also possible to obtain [4C+2C] cycloaddition products, but only with substrates featuring terminally disubstituted allenes, and employing π-acceptor ligands at gold. However the mechanism for the formation of these adducts is completely different to that proposed with PtCl(2), and consists of the formation of a metal allyl cation, subsequent [4C+3C] cycloaddition and a 1,2-alkyl shift (ring contraction). Electronic analysis indicates that the divergent pathways are mainly controlled by the electronic properties of the gold heptacyclic species (L-Au-C(2)), in particular, the backdonation capacity of the metal center to the unoccupied C(2) (pπ-orbital) of the intermediate resulting from the [4C+3C] cycloaddition. The less backdonation, (i.e. using P(OR)(3)Au(+) complexes), the more favoured is the 1,2-alkyl shift.     

Platinum-catalyzed aromatization of enediynes via a C-H bond insertion of tethered alkanes

[STRUCTURE: SEE TEXT] PtCl2 (5 mol%) is an effective catalyst for aromatization of enediynes via a C-H bond insertion of tethered alkanes. The reaction mechanism of this cyclization is proposed to involve platinum-pi-alkyne intermediates. This cyclization works not only for terminal alkynes but also for internal alkynes.     

Unusual reaction between (nitrile)Pt complexes and pyrazoles: substitution proceeds via metal-mediated nitrile-pyrazole coupling followed by elimination of the nitrile

The reaction of platinum(IV) complex trans-[PtCl4(EtCN)2] with pyrazoles 3,5-RR'pzH (R/R' = H/H, Me/H, Me/Me) leads to the formation of the trans-[PtCl4{NH=C(Et)(3,5-RR'pz)}2] (1-3) species due to the metal-mediated nitrile-pyrazole coupling. Pyrazolylimino complexes 1-3 (i) completely convert to pyrazole complexes cis-[PtCl4(3,5-RR'pzH)2] by elimination of EtCN upon reflux in a CH2Cl2 solution or upon heating in the solid state; (ii) undergo exchange at the imino C atom with another pyrazole different from that contained in the pyrazolylimino ligand. The reaction of trans-[PtIICl2(EtCN)2] and 3,5-RR'pzH, conducted under conditions similar to those for trans-[PtIVCl4(EtCN)2], is much less selective, and the composition of the products strongly depends on the pyrazole employed: (a) with pzH, the reaction gives a mixture of three products, i.e., [PtCl2NH=C(Et)pz-kappa2N,N}] (4), [PtCl(pzH){NH=C(Et)pz-kappa2N,N}]Cl (5), and [Pt(pzH)2{NH=C(Et)pz-kappa2N,N}]Cl2 (6) (complexes 5 and 6 are rather unstable and gradually transform to trans-[PtCl2(pzH2] and [Pt(pzH)(4)]Cl(2) and free EtCN); (b) with 3,5-Me(2)pzH, the reaction leads to the formation of [PtCl2NH=C(Et)(3,5-Me2pz)-kappa2N,N}] (7) and [PtCl(3,5-Me2pzH)3]Cl (8); (c) in the case of asymmetric pyrazole 3(5)-MepzH, which can be added to EtCN and/or bind metal centers by any of the two nonequivalent nitrogen sites, a broad mixture of currently unidentified products is formed. The reduction of 1-3 with Ph3P=CHCO2Me in CHCl3 allows for the formation of corresponding platinum(II) compounds trans-[PtCl2{NH=C(Et)(3,5-RR'pz)}2] (9-11). Ligands NH=C(Et)(3,5-RR'pz) (12-14) were almost quantitatively liberated from 9-11 with 2 equiv of 1,2-bis-(diphenylphosphino)ethane in CDCl3, giving free imines 12-14 in solution and the precipitate of trans-[Pt(dppe)2](Cl)2. Pyrazolylimines 12-14 undergo splitting in CDCl3 solution at 20-25 degrees C for ca. 20 h to furnish the parent propiononitrile and the pyrazole 3,5-RR'pzH, but they can be synthetically utilized immediately after the liberation.     

Irreversible and reversible formation of a [2]rotaxane containing platinum(II) complex with an N-alkyl bipyridinium ligand as the axis component

An N-Alkyl bipyridinium having a polymethylene chain and a bulky aryl group at the end, [4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2]Cl (Cl), reacts with K[PtCl3(dmso)] to produce the Pt complex with the N-alkyl bipyridinium ligand [Cl2(dmso)Pt{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}][PtCl3(dmso)] as a 6:1 mixture of trans and cis isomers ([trans-][PtCl3(dmso)] and [cis-][PtCl3(dmso)]). Addition of alpha-cyclodextrin (alpha-CD) to a solution of Cl in dmso-d6/D2O (3:1) forms [2]pseudorotaxane [{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}.(alpha-CD)]Cl (Cl) which is equilibrated with Cl and alpha-CD in solution. The reaction of K[PtCl3(dmso)] with Cl affords the [2]rotaxane [trans-Cl2(dmso)Pt{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}.(alpha-CD)][PtCl3(dmso)] ([trans-][PtCl3(dmso)]) which contains alpha-CD and [trans-][PtCl3(dmso)] as the cyclic and axis components, respectively. Dissolution of a mixture of [trans-][PtCl3(dmso)], [cis-][PtCl3(dmso)] and alpha-CD in dmso-d6/D2O (3:1) forms a mixture of the rotaxanes containing [trans--d6][PtCl3(dmso)] and [cis--d6][PtCl3(dmso)]. The reaction involves partial dissociation of the bipyridinium from Pt of [trans-][PtCl3(dmso)] or [cis-][PtCl3(dmso)] to yield [PtCl3(dmso)] and formation of pseudorotaxane with alpha-CD, followed by recoordination of the bipyridinium to the Pt. The reversible formation of the Pt-N coordination bond is studied in a dmso solution of the N-butyl compounds [trans-Cl2(dmso)Pt{4,4'-bpy-N-nBu}][PtCl3(dmso)] ([trans-][PtCl3(dmso)]).     

Hydrolysis Process of the Anticancer Agents Novel Non-classical trans-Platinum(Ⅱ) with Aliphatic Amines

The hydrolysis process of the anticancer agents novel non-classical trans- platinum(Ⅱ ) with aliphatic amines and the influence of solvent models therein have been studied by using hybrid density functional theory (B3LYP). In this study, the stepwise hydrolysis, trans- [PtCl2(Am)(isopropylamine)] + 2H2O → trans-[Pt(Am)(isopropylamine)(OH2)2]2+ + 2Cl-, was explored. Implicit solvent effects were incorporated through polarized continuum models. The stationary points on the potential energy surfaces for the first and second hydrolysis steps, proceeding via a general SN2 pathway, were fully optimized and characterized. It was found that the first hydrolysis reaction is easier than the second one and the hydrolysis of trans-[PtCl2- (isopropylamine)2] is the easiest in our studying systems. The result can assist in under-tanding the hydrolysis mechanism of trans-[PtCl2(Am)(isopropylamine)] and designing novel Pt-based anticancer drugs.     

Solvent-free mechanochemical synthesis of two Pt complexes: cis-(Ph3P)2PtCl2 and cis-(Ph3P)2PtCO3

Cis-(Ph3P)2PtCl2 and cis-(Ph3P)2PtCO3 were prepared mechanochemically from solid reactants in the absence of a solvent; cis-(Ph3P)2PtCl2 was obtained in 98% yield after ball-milling of polycrystalline PtCl2 and Ph3P; the mechanically induced solid-state reaction of cis-(Ph3P)2PtCl2 with an excess of anhydrous K2CO3 produced cis-(Ph3P)2PtCO3 in 70% yield; the formation of transition metal complexes as a result of mechanochemical solvent-free reactions has been confirmed by means of solid-state 31P MAS NMR spectroscopy, X-ray powder diffraction and differential thermal analysis.     

含磷硫杂配位原子的Pt(Ⅱ)金属有机配合物的合成及其对苯的C-H键活化

本文合成了含磷硫杂配位原子配体的Pt金属有机配合物,并对PtCl~2[Ph~2P(CH~2)~2SCH~3]配合物进行了晶体和分子结构测定,研究了这些Pt 金属配合物对苯的C-H键的活化作用,考察了对苯的光羰化反应性能     

用从头算研究Shilov反应的机理

Shilov反应在CH~4活化中占有中心地位,它有氧化加成和σ迁移两种可能的机理。本文用较大基组的从头算研究了这两种机理的反应过程,认为Shilov反应应按氧化加成机理进行。     

Hydrolysis process of the second generation platinum-based anticancer drug cis-amminedichlorocyclohexylamineplatinum(II)

The hydrolysis process of the anticancer drug cis-amminedichlorocyclohexylamineplatinum(II) (JM118 or cis-[PtCl2(NH3)cyclohexylamine]) and the influence of solvent models therein have been studied using hybrid density functional theory (B3LYP). The aquation reactions leading to the activated drug forms a key step for the reaction with the target DNA. In this study, the stepwise hydrolysis, cis-[PtCl2(NH3)cyclohexylamine] + 2 H2O --> cis-[Pt(NH3)cyclohexylamine(OH2)2]2+ + 2 Cl- was explored, using three different models. Implicit solvent effects were incorporated through polarized continuum models. The stationary points on the potential energy surfaces for the first and second hydrolysis steps, proceeding via a general S(N)2 pathway, were fully optimized and characterized. It was found that the explicit solvent effects originating from the inclusion of extra water molecules into the system are significantly stronger than those arising from the bulk aqueous medium, especially for the second aquation step, emphasizing the use of appropriate models for these types of problems. In comparison with previous work on the parent compound cisplatin, a slower rate of hydrolysis is determined for the first (rate determining) reaction. The results furthermore imply that the doubly aquated form of JM118 will be the main DNA binding form of the drug. The results provide detailed energy profiles for the mechanism of hydrolysis of JM118, which may assist in understanding the reaction mechanism of the drug with the DNA target and in the design of novel Pt-containing anticancer drugs.     

Kinetics and mechanism for reversible chloride transfer between mercury(II) and square-planar platinum(II) chloro ammine, aqua, and sulfoxide complexes. Stabilities, spectra, and reactivities of transient metal-metal bonded platinum-mercury adducts

The Hg2+aq- and HgCl+aq-assisted aquations of [PtCl4]2- (1), [PtCl3(H2O)]- (2), cis-[PtCl2(H2O)2] (3), trans-[PtCl2(H2O)2] (4), [PtCl(H2O)3]+ (5), [PtCl3Me2SO]- (6), trans-[PtCl2(H2O)Me2SO] (7), cis-[PtCl(H2O)2Me2SO]+ (8), trans-[PtCl(H2O)2M32SO]+ (9), trans-[PtCl2(NH3)2] (10), and cis-[PtCl2(NH3)2] (11) have been studied at 25.0 degrees C in a 1.00 M HClO4 medium buffered with chloride, using stopped-flow and conventional spectrophotometry. Saturation kinetics and instantaneous, large UV/vis spectral changes on mixing solutions of platinum complex and mercury are ascribed to formation of transient adducts between Hg2+ and several of the platinum complexes. Depending on the limiting rate constants, these adducts are observed for a few milliseconds to a few minutes. Thermodynamic and kinetics data together with the UV/vis spectral changes and DFT calculations indicate that their structures are characterized by axial coordination of Hg to Pt with remarkably short metal-metal bonds. Stability constants for the Hg2+ adducts with complexes 1-6, 10, and 11 are (2.1 +/- 0.4) x 10(4), (8 +/- 1) x 10(2), 94 +/- 6, 13 +/- 2, 5 +/- 2, 60 +/- 6, 387 +/- 2, and 190 +/- 3 M-1, respectively, whereas adduct formation with the sulfoxide complexes 7-9 is too weak to be observed. For analogous platinum(II) complexes, the stabilities of the Pt-Hg adducts increase in the order sulfoxide < aqua < ammine complex, reflecting a sensitivity to the pi-acid strength of the Pt ligands. Rate constants for chloride transfer from HgCl+ and HgCl2 to complexes 1-11 have been determined. Second-order rate constants for activation by Hg2+ are practically the same as those for activation by HgCl+ for each of the platinum complexes studied, yet resolved contributions for Hg2+ and HgCl+ reveal that the latter does not form dinuclear adducts of any significant stability. The overall experimental evidence is consistent with a mechanism in which the accumulated Pt(II)-Hg2+ adducts are not reactive intermediates along the reaction coordinate. The aquation process occurs via weaker Pt-Cl-Hg or Pt-Cl-HgCl bridged complexes.     

Skeletal reorganization of enynes into 1-vinylcycloalkenes in ionic liquids

The skeletal reorganization of enynes catalyzed by transition metal chlorides, such as PtCl(2), [RuCl(2)(CO)(3)](2), [RhCl(CO)(2)](2), and AuCl(3), in ionic liquids proceeds under milder conditions (at lower reaction temperatures and for shorter reaction times) than those needed for ordinary solvents. The products produced by the skeletal reorganization of enynes were easily removed from the catalyst by a simple extraction with Et(2)O or distillation. The PtCl(2) can be reused up to five times.     

Direct synthesis of (imine)platinum(II) complexes by iminoacylation of ketoximes with activated organonitrile ligands

The metal-mediated iminoacylation of ketoximes R1R2C=NOH (1a R1 = R2 = Me; 1b R1 = Me, R2 = Et; 1c R1R2 = C4H8; 1d R1R2 = C5H10) upon treatment with the platinum(II) complex trans-[PtCl2(NCCH2CO2Me)2] 2a with an organonitrile bearing an acceptor group proceeds under mild conditions in dry CH2Cl2 to give the trans-[PtCl2{NH=C(CH2CO2Me)ON=CR1R2}2] 3a-d isomers in moderate yield. The reaction of those ketoximes with trans-[PtCl2(NCCH2Cl)2] 2b under the same experimental conditions gives a 1 : 1 mixture of the isomers trans/cis-[PtCl2{NH=C(CH2Cl)ON=CR1R2}2] 3e-h and 4e-h in moderate to good yield. These reactions are greatly accelerated by microwave irradiation to give, with higher yields (ca. 75%), the same products which were characterized by IR and 1H, 13C and 195Pt NMR spectroscopies, FAB-MS, elemental analysis for the stable trans isomers, and X-ray diffraction analysis (3f). The diiminoester ligand in 3a was liberated upon reaction of the complex with a diphosphine.     

Platinum(IV) analogues of AMD473 (cis-[PtCl2(NH3)(2-picoline)]): preparative, structural, and electrochemical studies

The preparation and oxidation of the anticancer drug AMD473, cis-[PtCl2(NH3)(2-pic)] (2-pic = 2-methylpyridine), has been investigated. cis-[PtCl2(NH3)(2-pic)] is readily oxidized with peroxide to give the trans-dihydroxoplatinum(IV) complex cis,trans,cis-[PtCl2(OH)2(NH3)(2-pic)]. The crystal structure of this complex reveals that it is highly strained as a result of a steric clash between the methyl group of the 2-picoline ligand and an axial hydroxo ligand, with the Pt-N-C angle adjacent to this clash opened up to an unprecedented 138.6(6) degrees . Attempts at converting the dihydroxoplatinum(IV) complex to dichloro and diacetato analogues were unsuccessful with reaction with HCl leading to loss and protonation of the 2-picoline ligand to form the salt (2-picH)[PtCl5(NH3)] and the platinum(II) complex cis-[PtCl2(NH3)(2-pic)], both confirmed by crystallography. Electrochemical studies revealed that cis,trans,cis-[PtCl2(OH)2(NH3)(2-pic)] is reduced more readily (-714 mV vs Ag/AgCl) than its pyridine analogue cis,trans,cis-[PtCl2(OH)2(NH3)(pyridine)] (-770 mV vs Ag/AgCl) consistent with the steric clash in the former complex destabilizing the platinum(IV) oxidation state.     

Direct addition of alcohols to organonitriles activated by ligation to a platinum(IV) center

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with R'OH (R' = Me, Et, n-Pr, i-Pr, n-Bu) at 45 degrees C in all cases allowed the isolation of the trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] imino ester complexes, while the reaction between cis-[PtCl(4)(RCN)(2)] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R/R' = Me/Me) or trans-[PtCl(4)[(E)-NH=C(Et)OR'](2)] (R' = Me, Et), the latter being formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction between alcohols R'OH and cis-[PtCl(4)(RCN)(2)] (R = Me, R' = Et, n-Pr, i-Pr, n-Bu; R = Et; R' = n-Pr, i-Pr, n-Bu), exhibiting greater R/R' steric congestion, allowed the isolation of cis-[PtCl(4)[(E)-NH=C(R)OR'][(Z)-NH=C(R)OR']] as the major products. The alcoholysis reactions of poorly soluble [PtCl(4)(RCN)(2)] (R = CH(2)Ph, Ph) performed under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R = Ph, with heating led to trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R = CH(2)Ph, R' = Me, Et, n-Pr, i-Pr; R = Ph, R' = Me) isolated in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R'OH to the organonitrile platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph(3)P=CHCO(2)Me, to the corresponding isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino ester ligands. Furthemore, the imino esters NH=C(R)OR' can be liberated from both platinum(IV) and platinum(II) complexes [PtCl(n)[H=C(R)OR'](2)] (n = 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine, respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass spectrometry, IR, and (1)H, (13)C[(1)H], and (195)Pt (metal complexes) NMR spectroscopies; the E and Z configurations of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray structure determinations were performed for trans-[PtCl(4)[(E)-NH=C(Me)OEt](2)] (2), trans-[PtCl(4)[(E)-NH=C(Et)OEt](2)] (10), trans-[PtCl(4)[(E)-NH=C(Et)OPr-i](2)] (11), trans-[PtCl(4)[(E)-NH=C(Et)OPr-n](2)] (12), and cis-[PtCl(4)[(E)-NH=C(Et)OMe](2)] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both platinum(II) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.     

Dielectrophoretic growth of platinum nanowires: concentration and temperature dependence of the growth velocity

The growth velocity of platinum nanowires in an aqueous solution of K(2)PtCl(4) is investigated as a function of the metal complex concentration and temperature. The solution is specially prepared to provide mainly the neutral complex cis-[PtCl(2)(H(2)O)(2)] for growing nanowires by dielectrophoresis. The measured growth velocities indicate diffusion-limited nanowire growth at low concentration and high temperature in qualitative agreement with a theoretical analysis that includes the diffusion of metal complexes and the dielectrophoretic force on the complexes. At concentrations greater than 100 μM and low temperature, different behavior is observed, suggesting the growth rate to be limited by the deposition reaction of platinum at the nanowire tip. The enhancement of the K(+) concentration is found to support nanowire growth. Possible reasons for a rate limitation and for the difference between observed and calculated nanowire growth velocities are discussed.     

Microwave spectroscopy of platinum monofluoride and platinum monochloride in the X 2Π(3/2) states

Platinum monofluoride (PtF) and platinum monochloride (PtCl) were detected in the gas phase using a source-modulated microwave spectrometer. The PtF and PtCl radicals were generated in a free space cell using the sputtering reaction from a platinum sheet placed on the inner surface of a stainless steel cathode through a dc glow discharge plasma of CF(4) and Cl(2), respectively, diluted with Ar. Rotational transitions were measured in the region between 150 and 313 GHz. Rotational, centrifugal distortion, and several fine- and hyperfine-structure constants were determined by a least-squares analysis. The observed fine-structure spectral patterns indicate that both PtF and PtCl radicals have the (2)Π(3/2) electronic ground states, while the related cyanide PtCN and hydride PtH radicals have the (2)Δ(5/2) electronic ground states.