Platinum and Palladium

Palladium and Platinum. - The reader is referred to the exhaustive review by Sheppard and Nguyen as far as the literature about CO adsorption up to 1978 is concerned. The most accurate work was, at that time, that 

Vannice et have made a comparative i.r. study of Pd supported 

Moriki, Y. Inoue, E. Miyazaki, and I. Yasumori, J. Chem. Soc., Faraday Trans. 

As shown by Sheppard,such a band almost always accompanies the major peak of linear species on supported Pt. 

Morrow and Cody studied the adsorption of NHa and pyridine on Pt/Si02. For NH3, no evidence was found for dissociation up to 250 °C, as shown by isotopic exchange. To the contrary, pyridine adsorbs by dissociation of the a-C-H bond. The interaction of the N atom with a nearby Pt probably forces the molecule to lie perpendicular to the surface. Other molecules have been studied including ethylene,cyclohexanol, cyclohexanone, and cyclohexane ° on Pt/Al203 and formic acid and ethanoic 

Palladium and platinum are the longest known and most studied of the six platinum metals [1-11], a reflection of their abundance and consequent availability. Platinum occurs naturally as the element, generally with small amounts of the other platinum metals. It was used as a silver substitute by Colombian Indians and first observed there by Ulloa (1736), who called it platina del Pinto ( little silver of the Pinto river ) but the first sample was actually brought to Europe in 1741 by Charles Wood, Assay Master of Jamaica. Palladium was isolated in 1803 by W.H. Wollaston, who was studying the aqua regia-soluble portion of platinum ores (he announced his discovery by an anonymous leaflet advertising its sale through a shop in Soho) and named it after the newly discovered asteroid Pallas [12], 

There are many more examples of cis- and trans-isomers for platinum (a consequence of (2)). 

Platinum in particular forms numbers of stable er-bonded alkyls and aryls in both the +2 and +4 states. 

Palladium and Platinum. The reaction in equation (48), when carried out in aqueous methanol, follows rate law (49), which indicates preliminary dissociation of Cl  

Rotondo, G. Tresoldi, F. Faraone, and R. Pietropaolo, Inorg. Chem., 1976, 15, 2102. 

Natile, L. Marisca, L. Cattalani, U. Belluco, P. Uguagliati, and U. Croatto, Inorg. Chim. Acta, 1976, 20, 49. 

In aqueous methanol a rapid first-order reaction results in preferential chloride ion ejection [equation (50)] followed on addition of excess Cl by reaction (51) which 

19 Palladium and Platinum. NMR spectroscopy has been used to study chloride binding to [(qLC3H5)Pd bis(oxazoline)phenylphosphonite ]. The 

Crowley and B. Bosnich, Helv. Chim. Acta, 2001, 84, 2971. 

Wheate, L.K. Webster, C.R. Brodie and J.G. Collins, Anti-Cancer Drug Des., 2000, (Pub. 

The spectrum of Pd(IT) has been recorded in the and Li2S04 Na2S04-K2S04 eutectic melts (cf. Fig. 46 and Table XLV). An increase in temperature from 400 to 600 C caused a red shift of 0.2 kK 266) chloride melt spectrum. The spectrum in the chloride melt 

The spectrum of a solution of K2PtCl4 in the LiCl-KCl eutectic has been reported by two The two sets of results are col- 

Substantial agreement exists between the two groups as far as band positions are concerned. The extinction coefficients of the spin-allowed bands, on the other hand, differ by a factor of ten almost exactly. 

Both groups argued that in the LiCl-KCl eutectic there was evidence of some interaction between the square-planar PtCl ion and solvent anions oriented above and below the molecular plane. However, further work remains to be done to substantiate this interpretation. 

1 Preparation of Highiy Reactive Palladium and Piatinum and Some Oxidative Addition Chemistry 

Three general approaches for the preparation of highly reactive palladium and platinum metal powders have been developed [1,2], As will be seen, each successive approach leads to more reactive metal powders. 

Initially we tried the standard approach of reduction of NU2, NiBr2, or NiCl2 with potassium in refluxing THE Finely divided black nickel powders were obtained however, they showed rather limited reactivity toward oxidation insertion into carbon-halogen bonds. Similar results were found with palladium and platinum. 

We have demonstrated with several of the main group elements that the reactivity of the resulting metal is highly dependent on such factors as the solvent, reducing agent, anion, or in the case of some metals the presence of additional alkali salts [2, 9, 10]. In the case of the transition metals, the presence of a triaryl- or trialkylphosphine during the reduction yields a highly reactive metal slurry. 

Chemical Synthesis Using Highly Reactive Metals, First Edition. Reuben D. Rieke. 2017 John Wiley Sons, Inc. Published 2017 by John Wiley Sons, Inc. 

In general, the chemistry of pincer derivatives of palladium and platinum is very closely related, affording in many cases analogous species and reactivity. Thus, for the sake of discussion, the chemistry ofboth metals is included in this section and we will be switching from one metal to another unless a specific reaction or product refers to one metal solely. 

An interesting feature of the chemistry of monomeric organoplatinum(II) hydroxides and alkoxides is that CO inserts into the Pt—O bond more readily than into the Pt—C bond. Thus in 1993, Bennett and coworkers in an effort to examine the structures and properties of Pt(II)-hydroxycarbonyls with trans-arranged phosphines explored the reaction of the monomeric pincer Pt(II)-hydroxo species (14) with CO [9]. Hence, treating the (PCP)Pt(OH) pincer complex (14) with CO in benzene under ambient conditions caused the formation of the hydroxycarbonyl complex (15) as a 

As it has been shown so far, many of the species presented are the result of research focused in the most interesting water gas shift reaction. A different approach with similar consequences is the electrochemical reduction of CO2 catalyzed by (PCP)Pd (II) pincer complexes. Of particular interest is the study by DuBois in 1994 [10] in which several different pincer complexes were evaluated as potential catalyst for the electrochemical reduction of CO2. Thus, because CO is the main product of the CO2 reduction electrochemical process, the effect of CO on complex (16) was investigated. 

Given the already mentioned importance that 0 H, CO, and CO2 derivatives have had as potential intermediates in the water gas shift reaction and the relevance that late transition metal complexes containing metal-oxygen covalent bonds have in 

One striking difference to the reactivity of complex (32) is that the normal arm PCN-based carbonyl complex (33) does not react vdth dihydrogen under the same conditions and remains unchanged. This result clearly reflects the influence of the amine arm length on its hemilability properties and, as a consequence, on the alternative reactivity patterns. 

Interest has centred almost exclusively on square-planar complexes of palladium(ii) and platinum(ii), and a number of topics have attracted particular attention. The structural /ron -influence has been frequently discussed in platinum(ii) complexes the effect is now rather well documented, and comparative data on palladium(ii) compounds are beginning to accumulate. The kinetic and thermodynamic effects of intramolecular overcrowding, a popular subject in the 1950 s, are again beginning to interest co-ordination chemists and have motivated a number of structural studies. Several papers have been concerned with chelate complexes involving S-donor ligands. A review of crystal structures of compounds of the platinum-group metals has appeared.  

The only structural study of a non-organometallic compound of palladium(iv) or platinum(iv) appears to be that on platinum tetrachloride, PtCU. Powder data for PtCl suggest that it is isostructural with PtBr, and a-Ptl4, in both of which PtXg octahedra are linked through edges to form an infinite polymer. Previously, tetrahedral co-ordination had been proposed for PtCl4.  

A general impression of trends in bond lengths may be obtained from Table 3, in which a selection of metal-ligand distances in square-planar 

Compounds with Hetcronuclear Transition Metal Bonds 

Due to a the limitation of space a discussion of individual publications in this section is not feasible. Hence for both binuclear and polynuclear complexes, lists of relevant examples will be given followed by a brief discussion of those examples which, in the authors opinion, represent the more interesting and novel reports. 

The room temperature reaction of [Pd(N02)2(PMePh2)2] with CO gives [Pd4(PMePh2)40w-CO)5], which has been shown to adopt a butterfly metal skeleton.  

The A-frame complex [PtH2( -H)(M-dppm)2]+ reacts with CO to give [Pt2(CO)(H)C -dppm)2]+, which is transformed back to the original trihydrocomplex on reaction with H2. A related complex, [Pt2Me2(iM-H)(/M-dppm)2]+, 

An unusual cluster, [Pt7(2,6-Me2CeH3NQi2], which has been structurally characterized, results on reaction of 2,6-xylyl isocyanide with [Pt(cod)2].  

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Broadly speaking, the differences in effectiveness of palladium and platinum catalysts are very small the choice will generally be made on the basis of availability and current price of the two metals. Charcoal is a somewhat more efficient carrier than asbestos. 

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

Palladium and platinum (5—10 wt % on activated carbon) can be used with a variety of solvents as can copper carbonate on siHca and 60 wt % nickel on kieselguhr. The same is tme of nonsupported catalysts copper chromite, rhenium (VII) sulfide, rhenium (VI) oxide, and any of the Raney catalysts, copper, iron, or nickel. 

Figure 27.1 Flow diagram for refining palladium and platinum by solvent extraction.

Table 27.1 Some properties of the elements nickel, palladium and platinum...

The mechanism by which this low oxidation state is stabilized for this triad has been the subject of some debate. That it is not straightforward is clear from the fact that, in contrast to nickel, palladium and platinum require the presence of phosphines for the formation of stable carbonyls. For most transition metals the TT-acceptor properties of the ligand are thought to be of considerable importance and there is... 

The cyclometallated palladium and platinum derivatives of trimesityl phosphine or arsine react with pyrazole or 3,5-dimethylpyrazole to form metal chelates 243 (E = P, As M = Pd, Pt R = H, Me) having the trans configuration (81TMC24). 

Organonickel derivatives also offer cases of the -coordination of the substituted hydrotrisfpyrazol- l-yl)borate ligand. For the palladium and platinum complexes, the M(II) M(IV) (M = Pd, Pt) transformation is facile. Organopalla-dium chemistry offers anew type of agostic interactions, C—H - - - Pd, where the C—H bond belongs to one of the pyrazolate rings. Cyclopalladation of various pyrazol-l-ylborates and -methanes does not modify their structure. 

Cationic BINAP-palladium and platinum complexes 30a,b can catalyze highly enantioselective cycloaddition reactions of arylglyoxals with acyclic and cyclic... 

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