Anionic Platinum Complexes Research Articles

Piperidinium and Pyrrolidinium Ionic Liquids as Precursors in the Synthesis of New Platinum Catalysts for Hydrosilylation

Six new air-stable anionic platinum complexes were synthesized in simple reactions of piperidinium [BMPip]Cl or pyrrolidinium [BMPyrr]Cl ionic liquids with platinum compounds ([Pt(cod)Cl2] or K2[PtCl6]). All these compounds were subjected to isolation and spectrometric characterization using NMR and ESI-MS techniques. Furthermore, the determination of melting points and thermal stability of the above derivatives was performed with the use of thermogravimetric analysis. The catalytic performance of the synthesized complexes was tested in hydrosilylation of 1-octene and allyl glycidyl ether with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The study has shown that they have high catalytic activity and are insoluble in the reaction medium which enabled them to isolate and reuse them in consecutive catalytic cycles. The most active complex [BMPip]2[PtCl6] makes it possible to conduct at least 10 catalytic runs without losing activity which makes it an attractive alternative not only to commonly used homogeneous catalysts, but also to heterogeneous catalysts for hydrosilylation processes. The activity of the studied catalysts is also affected by the kind of anion and, to some extent, the kind of cation.

The surface modification of Ag3PO4 using anionic platinum complexes for enhanced visible-light photocatalytic activity

The surface modification of Ag3PO4 using anionic platinum complexes was successfully prepared. The starting materials of chloroplatinic chloride hydrate, silver nitrate, and sodium dihydrogen phosphate dodecahydrate were used in the experiments. The Ag3PO4 (AP) and defect-Ag3PO4 (DAP) were firstly synthesized using the coprecipitation method. These samples were suspended in chloroplatinic chloride solution under sonication to obtain the doping of anionic platinum complexes in Ag3PO4 (AP/Pt) and defect-Ag3PO4 (DAP/Pt). Anionic platinum complexes successfully substituted the phosphate site of Ag3PO4 and significantly improved the photocatalytic activity.

Bone invasion‐targeted chemotherapy with a novel anionic platinum complex (3Pt) for oral squamous cell carcinoma

Cisplatin (CDDP) is an important drug for chemotherapy in patients with head and neck squamous cell carcinoma. Nephrotoxicity and lack of an effect on bone invasion are limitations of CDDP. To increase its antitumor effect on bone invasion and reduce toxicity problems, anionic Pt complex (3Pt) has been developed. The present study aimed to characterize the basis of the cytotoxicity of the novel platinum complex 3Pt in comparison with that of CDDP for oral squamous cell carcinoma. The ionic platinum complex was prepared to increase solubility and avoid platinum nephrotoxicity. Furthermore, 3Pt was designed to target bone hydroxyapatite and has germinal bisphosphonate moieties for drug delivery. In vitro antitumor activity was assayed in two oral squamous cell carcinoma cell lines. To investigate the antitumor and nephrotoxic effects of 3Pt, nude mice with OSC‐19 were given 3Pt and CDDP. The in vitro growth‐inhibitory effect of 3Pt was significantly less than that of CDDP. However, both 3Pt and CDDP showed equivalent antitumor effects in vivo. Mice injected with CDDP developed renal cell apoptosis; however, those injected with 3Pt were almost free of renal cell injury. In addition to similar in vivo antitumor effects, 3Pt decreased the volume of bone resorption compared to that with CDDP in a bone invasion model using OSC‐19. In conclusion, considering the potential advantages in terms of noticeable antitumor activity on bone invasion and reduced nephrotoxicity, 3Pt represents a significant improvement in the development of bone‐targeting platinum drugs.

Highly efficient hydrosilylation catalysts based on chloroplatinate “ionic liquids”

The reaction between ionic liquid [Cat]+Cl− (where Cat stands for 1-butyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium or 1-butyl-4-methylpyridinium) and the metal precursor ([PtCl2(cod)], PtCl4, K2[PtCl4] or K2[PtCl6]) yielded two groups of derivatives: [Cat]+[PtCl4]− and [Cat]+[PtCl6]−, which formally are counted among halometallate ionic liquids, however, due to their high melting points they should be classified into anionic platinum complexes rather than into ionic liquids. All the derivatives were isolated and characterized spectroscopically (NMR, ESI-MS) and crystallographic structures were determined for three derivatives: ([BMPy]2[PtCl4], [BMIM]2[PtCl6] and [BMMIM]2[PtCl6]. Moreover, their melting points were measured and thermal stability was assessed. The above derivatives were employed as catalysts for hydrosilylation of olefins with diverse properties. All the studied catalysts showed high activity and their insolubility in the reaction medium made easy their isolation and multiple use in subsequent catalytic runs. The most effective catalysts did not lose their activity even after ten runs, thereby they make a very good alternative to commonly used homogeneous catalysts. Their simple synthesis and stability make them interesting both for economic and ecological reasons.

Electric Field Induced Molecular Assemblies Showing Different Nanostructures and Distinct Emission Colors

AbstractApplication of external stimuli in self‐assembly processes would offer greater degrees of freedom to regulate the supramolecular nanostructures and functions of self‐assembling molecules. In particular, the utilization of electric field to control molecular self‐assembly is of fundamental significance, and it contributes to the development of applications in nanofabrication and optoelectronic fields. Here, the self‐assembly of an anionic platinum complex ([Pt(tfmpy)(CN)2]−Bu4N+, tfmpy = 2‐(4‐(trifluoromethyl)phenyl)pyridine) is studied in the absence or presence of an electric field. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate an interesting morphological transformation from rod‐like to flower‐shaped nanoaggregate structures. For rod‐like nanostructure, selected area electron diffraction (SAED) and powder X‐ray diffraction (PXRD) analysis suggest that the Bu4N+ cations are squeezed between adjacent platinum(II) complex anions, forming alternating layers of two ions. In addition, SAED result suggests that the flower‐shaped nanoaggregate is constructed by a layer‐by‐layer packing through the formation of Pt⋅⋅⋅Pt and π–π stacking interactions. Importantly, confocal fluorescence imaging shows that these two different stable assemblies possess distinct emission colors and lifetimes. This unique feature might be useful in various optoelectronic applications including data recording, anti‐counterfeiting, smart windows, etc.

Phosphorescence Properties of Discrete Platinum(II) Complex Anions Bearing N-Heterocyclic Carbenes in the Solid State.

The synthesis, crystal structures, and photophysical properties of four anionic platinum complexes bearing N-heterocyclic carbenes (NHCs), n-Bu4N[Pt(CN)2(NHC)] (H2NHC+ = 1-methyl-3-phenyl-1 H-imidazolium (1), 1-methyl-3-phenyl-1 H-benzimidazolium (2), 1-methyl-3-(naphthalen-2-yl)-1 H-imidazolium (3), 1-methyl-3-(naphthalen-1-yl)-1 H-imidazolium (4)), are reported. The tetra- n-butylammonium salts afforded discrete Pt(II) complexes surrounded by the bulky cations in the crystalline states with no Pt-Pt, π-π, or solute-solvent interactions. As a result, the crystals exhibited strong phosphorescence with quantum yields of 0.24-0.72 at 298 K. The three isomeric complexes 2-4 with π-extended structures of 1 exhibited luminescence with different colors depending on the π-extension site. These complexes in a discrete and restricted space enabled the comparative investigation of the luminescent states and regioselective benzannulation effect using computational methods and luminescence spectroscopy. Blue-emissive 1 and 2 exhibited lifetime changes at temperatures of 77-298 K, suggesting the influence of dark states located 2000-3000 cm-1 above the emissive state. In contrast, yellow- and orange-emissive 3 and 4 showed no thermal deactivation effect at ambient temperature. The temperature dependence of the emission lifetimes in the low-temperature region of 4-77 K showed that blue-emissive 1 and 2 had a relatively large zero-field splittings (ZFSs) of 35 and 28 cm-1, respectively, indicating the significant contribution of triplet metal-to-ligand charge transfer character to the 3π-π* emission. On the other hand, the ZFS of 4 was less than 2 cm-1, suggesting purer 3π-π* character.

Probing the Solvent Shell with 195Pt Chemical Shifts: Density Functional Theory Molecular Dynamics Study of PtII and PtIV Anionic Complexes in Aqueous Solution

Ab initio molecular dynamics (aiMD) simulations based on density functional theory (DFT) were performed on a set of five anionic platinum complexes in aqueous solution. (195)Pt nuclear magnetic shielding constants were computed with DFT as averages over the aiMD trajectories, using the two-component relativistic zeroth-order regular approximation (ZORA) in order to treat relativistic effects on the Pt shielding tensors. The chemical shifts obtained from the aiMD averages are in good agreement with experimental data. For Pt(II) and Pt(IV) halide complexes we found an intermediate solvent shell interacting with the complexes that causes pronounced solvent effects on the Pt chemical shifts. For these complexes, the magnitude of solvent effects on the Pt shielding constant can be correlated with the surface charge density. For square-planar Pt complexes the aiMD simulations also clearly demonstrate the influence of closely coordinated non-equatorial water molecules on the Pt chemical shift, relating the structure of the solution around the complex to the solvent effects on the metal NMR chemical shift. For the complex [Pt(CN)(4)](2-), the solvent effects on the Pt shielding constant are surprisingly small.

Anionic clay–Pt metal nanoparticle composite through intercalation of hexachloroplatinate in nickel zinc hydroxysalt

Nickel zinc hydroxysalt–Pt metal nanoparticle composite was prepared by intercalation of the anionic platinum complex, [PtCl 6] 2− in nickel zinc hydroxysalt through ion exchange reaction and subsequent reduction of the platinum complex by ethanol. Powder X-ray diffraction and microscopy studies indicate that the process of reduction of the platinum complex in the interlayer region of the anionic clay takes place topotactically without destroying the layers.

Supramolecular recognition: association of palladium molecular clefts with planar platinum complexes

The crystal structures of two new molecular recognition adducts formed between a dicationic, di-terpyridyl-Pd–Cl molecular cleft and two square planar platinum complexes are reported. In both structures, the planar platinum-containing guests are located within the molecular cleft formed by the two parallel disposed terpyridyl-Pd–Cl + units of the receptor. The crystal structure of the adduct formed between the molecular cleft and a neutral platinum complex has interplanar distances between the host and guest of 3.24 Å, a distance shorter than that usually ascribed to π-stacking interaction (∼3.45 Å). The short distance is likely the result of metal–metal interaction between the host and guest. The second adduct, that between the dicationic molecular receptor and an anionic platinum complex, also bears the guest within the molecular cleft. The interplanar distances between the cationic terpyridyl-Pd–Cl units of the host and the anionic guest (3.21 and 3.29 Å) are also shorter than typical π-stacking distances but no metal–metal interaction is present. Coulombic attraction between the host and guest is believed to be responsible for the short interplanar separation. These data are discussed in relation to analogous systems that associate through π–π and metal–metal interaction.

Anionic platinum complexes with 2-pyridylphosphines as ligands for rhodium: synthesis of zwitterionic Pt-Rh organometallic compounds.

Bimetallic zwitterionic platinum(II)-rhodium(I) complexes of the type [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)Rh(CO)(2))] and [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)())Rh(diene))] (n = 2, 3; Py = 2-pyridyl) have been prepared. The P end of the bridging ligands (micro-PPy(n)Ph(3)(-)(n)) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving metallacycles comparable to pyrazolylborate-Rh complexes. These metallacycles can adopt two conformations, either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically demanding Rh-carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(COD)] (COD = 1,5-cyclooctadiene) and [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(CO)(2)] are reported.

Salts of cationic platinum dithiolenes with anionic platinum complexes: structural characterization of [Pt(Me 2pipdt) 2][Pt(SCN) 4] (Me 2pipdt = N, N′-dimethyl-piperazine-2,3-dithione)

[Pt(Me 2pipdt) 2](BF 4) 2 salts [Me 2pipdt = N, N ′-dimethyl-piperazine-2,3-dithione] bearing cationic dithiolene complexes react with (Bu 4N) 2[Pt(X) 4] (X = SCN, CN) to form [Pt(Me 2pipdt) 2][Pt(SCN) 4 ] ( 1) and [Pt(Me 2pipdt) 2][Pt(CN) 4] ( 2) salts by metathesis. Black crystals of 1 have been structurally characterized showing that the two metals lie on inversion centers and exhibit a square planar coordination. The Pt–S bond distances in the anion complex (2.324(2) Å) are longer than in the cation complex (2.280(2) Å) whereas the C–S bond distances are shorter in SCN − (average 1.669 Å) than in Me 2pipdt (average 1.694 Å). The chelating Me 2Pipdt ligand is found disordered in the λ/ δ conformations with site occupancies of 50/50, respectively. The cation and anion complexes run parallel to a.

Catalytic activity of platinum after exchange with surface active functional groups of carbon blacks

The deposition of platinum on various carbon blacks has been carried out by forming active functional groups on the surface of the carbon support, and exchanging these active groups with different platinum complexes. Using H2PtCl6 solution, an aggregation rather than an exchange takes place. In this case, the anionic platinum complexes [PtCI6]2– involved have a tendency to form a coagulated platinum cluster after the reduction process. However, using ammonium platinum chloride, an exchange between the cationic platinum complexes and surface functional groups takes place. The exchange process involving the divalent platinum complex, [Pt(NH3)4]2+, is much faster than the one where the tetravalent platinum complex [Pt(NH3)6]4+, is involved. Transmission electron migrograph (TEM) photographs have shown that when using Pt(NH3)4Cl2 solution for the exchange, platinum particles are extremely small (0.75–1.7 nm) and highly dispersed on the surface of the carbon black. A comparison of the catalytic activities of platinum supported on various carbon blacks was also carried out. The catalytic activity mainly depends on the particle size rather than the loading amount of the catalyst.

Synthesis and structures of novel types of heteronuclear PtM (MAg, Sn or Pb) neutral or anionic organometallic complexes

Donor-acceptor Pt→Ag bonds formed by reactions between anionic platinum complexes and silver salts or complexes are the subject of this review. We discuss their structural features and the role played by the charge of the anions and by o-X…Ag interactions in the stability and spatial arrangement of the resulting heteronuclear complexes. The extension of these studies to other M→M′ systems is briefly commented.

Synthesis, 119Sn, 13C and 195Pt NMR studies of five-coordinate rhodium(I), iridium(I) and platinum(II) complexes containing three trichlorostannate ligands

The synthesis and 119Sn NMR characteristics of new five-coordinate tris(trichlorostannato) complexes of Rh I, Ir I and Pt II are reported. The Rh I and Ir I complexes are complex dianions of the form (PPN) 2[M(SnCl 3) 3L 2] where L can be CO, CN (cyclohexyl) or L 2, a diolefin such as 1,5-COD or NBD (norbornadiene). The anionic platinum complexes (PPN)[Pt(SnCl 3) 3L 2] contain similar L ligands. A number of neutral monotrichlorostannato complexes of type [M(SnCl 3)L 4] including [Ir(SnCl 3)(NBD)(1,5-COD)] have been prepared and characterized. Their δ( 119Sn), δ( 13C), δ( 195Pt) as well as 1 J( 103Rh, 119Sn), 1 J( 195Pt, 119Sn), 2 J( 119Sn, 117Sn) and 2 J( 119Sn, 13C) data are given. A trans influence series, based on 1 J( 195Pt, 119Sn), reveals the following sequence: H − > PR 3 > AsR 3 > SnCl 3 − > olefin > Cl −.