Platinum-group metals reactivity

A large number of papers has been devoted to the influence of substituents upon the reactivity of benzene nucleus. Extensive studies concerning various benzene derivatives and catalysts from the platinum group metals have been published by H. A. Smith and his co-workers (for a summary see 36). The most consistent sets of data on alkylbenzenes are available from him and other groups of authors. Table VI summarizes the influence of the structure of a single alkyl group Table VII (94, 95, 97-103) summarizes the influence of the number and position of the methyl groups. Both series show very similar behavior on all metal catalysts, a decrease in rate with the size... 

We might also expect to find oxide ores for the s-block metals and sulfide ores for the more electronegative p-block metals. In fact, sulfide ores are common for the p-block metals, except for A1 and Sn, but oxides of the s-block metals are strongly basic and far too reactive to exist in an environment that contains acidic oxides such as CO2 and SiC>2. Consequently, s-block metals are found in nature as carbonates, as silicates, and, in the case of Na and K, as chlorides (Sections 6.7 and 6.8). Only gold and the platinum-group metals (Ru, Os, Rh, Ir, Pd, and Pt) are sufficiently unreactive to occur commonly in uncombined form as the free metals. 

A An answer to this question may be found by consulting Chapters 25, 26, 27 and 28 in the first edition of Chemistry of the Elements, by N. N. Greenwood and A. Earnshaw (1984). A possible separation process which exploits the differing reactivities and solubilities of the platinum group metals (Box l.l) is shown in Scheme 1.1. 

Most elements, in their pure elemental form are metals. But almost all elements are also quite chemically reactive and thus not found naturally in their elemental form. Metals that do occur naturally as pure elements include the noble metals, so-called because they are not chemically reactive, i.e., gold, silver, platinum, and rare platinum-group metals such as osmium and iridium, and copper. Copper is more reactive and more common and thus sometimes called a base metal. 

TABLE 3. Chemical Reactivities of Platinum Group Metals in Various Media (mg/cm -hr at I00°C)... 

We bave previously prepared and described binuclear orthometallated complexes of palladium(II) which could be used as precursors to prepare potoitially mixed-valence compounds. Hie presence of unusual Pd-N amido bonds in these complexes adds further interest based cm the reactivity shown by amides of the platinum group metals. ... 

A comparison of platinum group metal complexes is illustrative of the relatively narrow window of reactivity and stability which generates complexes with suitable antitumour activity. Table 6.1 collects some comparative data of structurally analogous complexes, containing only ammonia and chloride ligands. The palladium complex, like the octahedral iridium analogue, shows little activity, while those of rhodium and ruthenium are somewhat intermediate. Palladium complexes are more labile than those of platinum, reacting approximately 10 times faster, and it is reasonable to accept that the palladium complex will be too reactive in vivo for any... 

The range of chemical reactivity of metals is wide, from the inertness of the platinum group to the extreme reactivity of some alkali metals. The order of metal reactivity follows essentially the order of the electrochemical series which is shown in Table 17.4 for the metals commonly deposited by CVD. 

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