The Six Platinum Group Metals

All the six platinum-group metals are highly resistant to corrosion by most acids, alkalis, and other chemicals. Their high nobility is the main factor determining their chemical resistance, and the formation of. complex ions in solution is principally responsible for their dissolution under certain conditions. 

Ruthenium was the last of the six platinum group metals to be isolated, and was discovered in Kazan (now capital of the Tatarstan Republic, Russian Federation) by Karl Karlovich Klaus (1796-1864) in 1844. The original papers were published in Russian journals which are difficult to obtain now, but were published in Western Europe in 1845 [1,2] with a summary in English [3]. Klaus made the metal by reduction of RuOj with H3 and named it Ruthenium in honour of his native land (Ruthenia, Latin for Russia) there are short biographies of him [4, 5],... 

The six platinum group metals, platinum, palladium, ruthenium, osmium, rhodium, and iridium, usually occur together in nature. These metals are not often found in artifacts. These metals are rare and have only been widely used in industry and for ornaments since the early twentieth century. Most platinum used today is as a catalyst in the systems used to control car exhaust emissions, in dentistry, and to make surgical tools, jewelry, and electrical equipment. 

Delepine and Horeau also compared the activating effects of the six platinum group metals on Raney Ni in the hydrogenation of carbonyl compounds. Osmium, iridium, and platinum were the most effective, ruthenium and rhodium followed them, and palladium was the least effective.66... 

Sen Gupta, J. G. Determination of microgram amounts of the six platinum-group metals in iron and stary meteorites. Anal. Chim. Acta 42, 481 (1968)... 

Electrochemists early on observed that noble and precious metals were stiff materials, with good tensile properties and machinability, high electronic conductivity, and exceptional chemical and electrochemical inertness in most corrosive media, all combined with intrinsic electrocatalytic properties/ Consequently, the first industrial anodes used in electrochemical processes requiring an excellent dimensional stabihty were made of the noble and precious metals (e.g., Au and Ag), the six platinum-group metals (PGMs) (e.g., Ru, Rh, Pd, Os, Ir, and Pt), or their alloys (e.g., Pt- lr and °Pt- °Rh) . Of these, the PGMs, especially platinum and iridium, occupied a particular place owing to their electrochemical inertness... 

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). 

Aromatic compounds are reduced over the six platinum metal group catalysts at widely different rates, as expected, but additionally the products of reduction frequently vary with the metal used. Many of these results may be correlated in terms of two parameters not obviously connected to aromatic properties the relative tendencies of these catalysts to promote double bond migration in olefins and to promote hydro-genolysis of vinylic and allylic functions. 

Nishimura et al. studied the hydrogenation of 19-21 over the six unsupported platinum group metals in f-butyl alcohol at 26°C and 1 atm H2.138 The hydrogenations of 19 over iridium and osmium have been found to be highly stereoselective, affording... 

The marked dependence of 7( P—M— P) on stereochemistry for complexes of the platinum group metals has been used in NMR spectroscopy for several years 109,115). For methyl or tert-h xty tertiary phosphines, when the two phosphines are mutually trans then a triplet pattern results, but if the two phosphines are mutually cis, then a doublet pattern results as a consequence of the spectrum being of the AA X X type and the dependence of V( P—M— P) on stereochemistry. Exactly the same behavior is found in NMR spectroscopy with the advantage that the technique is far more versatile and is not normally troubled by resolution problems. Thus for cr-[RhCl3(CO)(PBu"2Ph)2] triplet patterns have been observed for six of the eight different carbon atoms in the tertiary phosphine ligand 164). When —M—is... 

The corresponding Pt-Pt and Ru-Ru coordination numbers were found to be 2.0 and 4.0, respectively, indicating that slight agglomeration of the metal took place, and the clusters incorporated, on average, less than three and six Pt and Ru atoms, respectively. These appear to be the smallest supported bimetallic clusters of platinum-group metals yet reported. 

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