Platinum halide

Among the second- and third-row transition metal halide complexes, those of platinum have received considerable study. Both the octahedral platinum(IV) complex PtCli and the square planar platinum(II) complex PtCl have been investigated. Both complexes are substitution inert under thermal conditions, and kinetic studies of their substitution chemistry have been important in the development of a general understanding of the mechanisms of substitution reactions in transition metal chemistry. The photochemistry of PtCli was one of the earliest such studies to be made, and the early discoveries of the photosensitive nature of platinum halides led to these salts being used in photographic processes. The subsequent decision to use a silver-based process was based more on economical rather than on technical reasons. 

The photolysis of PtCle in the presence of an alkene provides a convenient route to the synthesis of 7C-alkene complexes of divalent platinum  

High yields of the alkene complex are obtained after 1 h irradiation with a halogen tungsten lamp. If the irradiation is carried out in the presence of an aliphatic or an aromatic hydrogen, products resulting from the cleavage of a carbon-hydrogen bond are formed. Examples are the formation of alkene platinum(II) complexes 

No mechanistic details have been given for these reactions, but the data suggest a pathway whereby photoreduction of PtCli to PtCls is the first step. Support for such a mechanism comes from our own personal observation that small quantities of chloroalkanes are formed by photolysis of a mixture that contains PtCU and an alkane. Such a radical mechanism contrasts, however, with the generally accepted 

A catalyst comprised of H2PtCl6 and CuCb can be used for the photooxidation of primary and secondary alcohols to the corresponding aldehyde and ketone  

Ptp2 is unknown, presumably unstable with respect to the disproportionation 

All the trihalides are mixed valence compounds. PtFs is isostructural with PdF3 PtX3 (X = Cl, Br, I) cannot be made by straightforward thermal decomposition of PtX4 [22] under open conditions but by routes involving continuous decomposition and formation under closed, equilibrium conditions. 

The iodide is polymorphic, with the a-and 7-forms known to have this Structure bond lengths are 2.65-2.72 A (7-Ptl4), 2.62-2.78 A (a-Ptl4) 2.41-2.54A (PtBr4 . 

Evaporation of solutions of platinum in aqua regia gives yellow crystals of the hydrates rram-[PtCl4(H20)2].3H20 and /oc-[Pta3(H20)3]Cl. H20 [25]. 

made by fluorination of PtCl2 at 350°C disproportionates above its m.p. 

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CVD Reactions. The platinum halides are volatile with a decomposition pointtooclose to thevaporizati on pointtomakethempracticalfor C VD transport. Platinum canbe deposited by the decomposition of the acetylacetonate, although carbonaceous impurities remain in the deposit. The carbonyl halides, specifically dicarbonyl dichloride, are more satisfactory precursors. The decomposition reaction is as follows ... 

Batsanov et al. 23) reacted sulfur with PtCU and PtBr2 by heating mixtures of the reactants in evacuated, sealed ampoules. At 100 -200°C after 12-24 h, sulfide chlorides PtCljS (1.70 < x < 2 0.6 s y < 3.35) and sulfide bromides PtBr S (1.87 < x 2.06 0.84 y s 1.80) were formed. The compositions depended on the initial PtX2 S ratio, and the temperature. At 320-350°C, loss of chlorine led to the compounds PtClS (1.7 y 1.9). According to their X-ray powder patterns, all of these products retained the main structural features of the original platinum halides. From considerations of molar volumes, the authors deduced the presence of polysulfide anions. 

Shortly after Trost s works, two investigations demonstrated the high reactivity of platinum halide salts for this type of reactions. Blum reported a PtCU-catalyzed rearrangement of allyl propargyl ethers to 3-oxabicyclo[4.1.0]-heptenes (Scheme 79).294 This series of reactions also represented the premiere entry into the versatile formation of cyclopropyl products based on skeletal rearrangements of enynes.295 This intriguing aspect is discussed further. 

Platinum-group minerals, classes of, 79 603 Platinum halides, 79 657 Platinum-iridium alloy electrodes, medical applications for, 79 629... 

The chloride curve usually is not a straight line the stability diagram then is more complicated than for the platinum halides, but it always shows, as typical features, the non-existence of the lower fluorides and the instability, or non-existence, of the highest iodides. Some typical examples are given in Table XXV. There are a few cases in which there are deviations from this rule, e.g. in the... 

The interaction of platinum halides with boron hydrides has been used to couple boranes. In the presence of PtBr2 at 25 °C the compound 1,2 -(B5H8)2 can be formed from B5H9 (equation 91). 2... 

Since these substitution reactions follow a two-term rate law, it is clear that solvent effects are very significant. Poorly coordinating solvents are benzene, carbon tetrachloride and sterically hindered alcohols and strongly coordinating solvents are water, lower alcohols, DMF, DMSO, acetonitrile and nitromethane. The first-order rate constants are greater in DMSO than in water. Since the majority of precursor platinum complexes used in synthetic and mechanistic studies are halo complexes, the replacement of halide ligands by solvent and the reversibility of this reaction are important features of platinum halide chemistry. 

Ethylene derivatives of organophosphines and organoarsines [75a] are used as cr, 71-chelating donors. Thus, 4-pentenediphenylphosphine reacts (3.61) with platinum halides in boiling chloroform, forming complexes of the type 623 ... 

The electronic character of the stacked aromatic systems makes it possible for atoms or molecules to slip between these layers, either accepting or donating electrons to bond with the carbon system, a process referred to as intercalation. Platinum metal graphite intercalates have been prepared by reducing platinum halide graphite intercalates. These catalysts are particularly useful for the selective hydrogenation of acetylenes to cis alkenes (Eqn. 9.3).22... 

A platinum- and Lewis acid catalyzed enyne metathesis was used as the key step in the formal total synthesis of antibiotics streptorubin B and metacycloprodigiosin by A. Furstner. The electron-deficient enyne was cyclized with either a platinum halide or a hard Lewis acid (e.g., BF3-OEt2) to the desired mefa-pyrrolophane core of the target molecules. A few more steps completed the formal synthesis. 

One way of overcoming this limitation has recently been described. In this procedure a dried chloroplatinic-acid-impregnated silica gel is thermally pyrolysed at 625 K. It was shown that the divalent platinum halide formed under these conditions was sufficiently volatile and reactive as to react subsequently with and become dispersed on the support surface. 

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