Platinum cationic species

The proposed mechanism starts with a methyl group abstraction on platinum complex 416 with the borane reagent in the presence of diyne 414 (Scheme 105). The square-planar cationic diyne-platinum(n) complex 417 is converted to the octahedral platinum(rv) hydride intermediate 418 through oxidative addition of the hydrosilane. This complex decomposes rapidly with methane release to form another tetracoordinated platinum(n) species 419, followed by platinasilylation of the triple bond. The resulting vinylplatinum 420 undergoes an intramolecular carboplatination to... 

Many of the recent efforts in this area of chemistry have been designed to explore the chemistry of the trifluoromethyl species prepared by these reactions. Among the more interesting results have been the construction of carbene and tetramethylcyclobutadiene ligands affixed to trifluoromethyl platinum cations (78), the synthesis of difluoro-carbene complexes like (Cp)Mo(CO)3CF2+ (79), the formation of (CF3)2CS from CF3Re(CO)5 (38), and the insertion reaction of S02 into CF3-metal bonds (80). 

More work is needed to clearly establish the role of outer-sphere association in DNA-platination. We can infer its influence on the rate of platination according to the relation kp = kK0 [N]/(l + K0 [N]) (with N = nucleotide-binding sites of Pt, i.e., N G, [N] [Pt]) (Scheme 3). It could also influence the selectivity of platination via selective association between the cationic species and the sites of higher negative electrostatic potential. To test this hypothesis one will have to analyze the influence of various sequences, of different types of platinum ligands, and of the ionic status of the DNA medium. 

The palladium(II) and platinum(II) ions form stable complexes with a variety of chelating diolefins.1-"5 These may be either neutral or cationic in character. The preparative routes to the former type are, in general, well-documented. The spedies (I) through (IV) include all the presently known cationic species, and the preparation of each type is discussed and exemplified. 

Fluoride derivatives of palladium(II) and platinum(II), all of which are phosphine derivatives, can be most simply grouped into one of two subsections, namely neutral or cationic species. The neutral species are all of the form [MXF(PPh3)2] (M = Pd, Pt) where X can be Cl, Br, I, H, methyl, phenyl and C6F5. The synthetic route into these compunds involves either addition of HF to a metal phosphine dihalide or... 

Recent studies indicate the reaction of platina-/3-diketone with bipyridines via oxidative addition yields the diacyl hydrido Pt(IV) complex. Further ligand abstraction may result in H bond bridged dimer and a double-deck dimer through Pt Pt interaction (Scheme 17). On the other hand, the prototype of unsupported cis- diacyl platinum(II) species was obtained either via nucleophilic addition to cationic acyl carbonyl complexes or CO insertion into a trans acyl alkyl complex (Scheme 18). In the latter process for propionyl methyl or acetyl ethyl complex. 

The -allenyl/propargyl platinum cations generally exhibit electrophilicity at the central carbon. The unsubstituted rj -allenyl/propargyl species is particularly reactive and is subject to addition to a wide variety of nncleophiles (see Nucleophile). The reactions of the -allenyl/propargyl species with alcohol,... 

First, a direct extension of this thinking leads to the conclusion that high oxidation states are most likely to be achieved in an anion, where, as a consequence of the electron-rich environment, the electronegativity of the high oxidation state is lower than in neutral or cationic species. This thought led to the discovery of the room temperature oxidation of gold and the platinum metals (all except rhodium react) using F2 in aHF made basic with alkali fluorides, described in Ref. 112. 

An electrochemical study of the behavior of the dinuclear complex [Rh2(CO)2(PPh3)2(/x-dmpz)2, 84, was described (98). This species undergoes two consecutive oxidation processes at a platinum electrode. The first oxidation gives the corresponding cationic species, [Rh2(CO)2(PPh3)2(/i-dmpz)2]+, as inferred from electrochemical and spectroscopic examination of the oxidized product. 

Taylor et al.8 were the first to report an electrochemical method for preparation of MEAs for PEMFCs. In their technique, Pt was electrochemically reduced and deposited at the electrode membrane interface, where it was actually utilized as an electrocatalyst. Nation, which is an ion exchange polymer membrane, is first coated on a noncatalyzed carbon support. The Nafion-coated carbon support is then immersed into a commercial acidic Pt plating solution for electrodeposition. Application of a cathodic potential results in diffusion of platinum cations through the active Nation layer. The migrated platinum species are reduced and form Pt particle at the electrode/membrane interface only on the sites which are both electronically and ionically conductive. The deposition of Pt particles merely at the electrode/membrane interface maximizes the Pt utilization. The Pt particles of 2-3.5 nm and a Pt loading of less than 0.05 mg cm-2 were obtained employing this technique.8 The limitation of this method is the difficulty of the diffusion of platinum... 

The oxidation of methane with molecular oxygen is catalyzed by the atomic platinum cation [11b]. A key step in the catalytic cycle is the reaction of PtCHi with molecular oxygen to mainly (70%) regenerate PF via liberation of neutral species [C,Hi,Oil which either represents vibrationally excited formic acid and/or its decomposition products (CO-f-HiO) and (CO2+H2). Final oxygenates are methanol, formaldehyde as well as higher oxidation products (Scheme V.4). Experimentally determined reaction energies for the elemental steps are summarized in Table V.2 [11b]. The coupling of carbon dioxide and aromatic C-H bonds mediated by ion SiFs" has also been observed [11c]. 

Meanwhile, the mechanism proposed for the hydroxylation of aromatics catalyzed by cationic complexes of platinum(ll) involves an electrophilic meta-lation of the aromatic ring to yield platinum-aryl intermediates followed by oxygen transfer from a platinum-hydroperoxy species (Scheme X.3) [23b]. Finally, the oxidation [26a] of aromatic compounds by hydrogen peroxide catalyzed by the peroxovanadium complex VO(02)(Picolinate)(H20)2 is proposed to occur via oxygenation of the arene by this complex, which is restored under the action of H2O2. 

Abe, Y., Mochizuki, A., Kawashima, T., Yamashita, S., Asaka, K. and Oguro, K. (1998). Effect on bending behavior of counter cation species in perflu-orinated sulfonate membrane-platinum composite, Polymers for Advanced Technologies 9, 8, pp. 520-526. 

The main contaminants for the membrane are cationic species, such as metal ions, which may come from contaminated air and fuel streams when moisture is present, metal fuel cell components, balance-of-plant components, or nonmetal contaminated component materials. Other organic and inorganic materials can also contaminate the membrane, but the effects of these are less well documented. Component materials supplying contaminants may include the platinum catalyst or alloying metals, such as ruthenium or cobalt, which may leach out into the membrane the raw material source for the carbon materials (in the catalyst support, microporous layer, gas diffusion layer, or plate materials) may also have inherent metal or other chemical impurities and seal and gasketing materials, such as silicone, can decompose and contaminate the membrane. All of the membrane contaminants can also impact the ionomer materials present in the catalyst layers. 

Platinum RDE with Nafion Film Exchanged with Cation Species... 

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