Group 10 palladium and platinum

At 298 K, bulk Pd and Pt are resistant to corrosion. Palladium is more reactive than Pt, and at high temperatures is attacked by O2, F2 and CI2 (equation 22.124). 

Palladium dissolves in hot oxidizing acids (e.g. HNO3), but both metals dissolve in aqua regia and are attacked by molten alkali metal oxides. The absorption of H2 by Pd was described at the end of Section 9.7. 

The dominant oxidation states are M(II) and M(IV), but the M(IV) state is more stable for Pt than Pd. Within a given oxidation state, resemblances are close with the exception of their behaviour towards oxidizing and reducing agents. In comparing the chemistries of Ni(II), Pd(II) and Pt(II), structural similarities between low-spin square planar complexes are observed, but octahedral and tetrahedral high-spin Ni(II) complexes have only a few parallels in Pd(II) chemistry and effectively none among Pt(II) species (see Box 20.7). 

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Thus, for group 10 palladium and platinum metals, a mixture of 1,2-bis(dialkylamino)-3-halocyclopropenylium halide and a slight excess of Pd or Pt black is refluxed in MeCN for 24h, affording the corresponding dimeric cyclopropenylidene //-complexes [(R2N)2C3 MX2 2 (R = Me, Et, i-Pr, M = Pd, Pt X = Cl, I) (equation 276)340 347-352. The dimers further react with Bu3P to give the planar mononuclear complex cis-[(R2N)2C3]MX2(PBu3). 

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). 

The group 10 metals, such as palladium and platinum, are active for the conversion of methanol. However, they are much less selective than the copper-based catalysts, yielding primarily the decomposition products [123,124,133]. This catalytic property makes them less feasible for fuel cell applications. The only exception found is for Pd/ZnO, which showed selectivity close to that of a copper catalyst [105, 121]. 

Ishikawa and coworkers have studied the unique reactivity of strained cyclic disilanes (Equation 9.11) [35]. Transition metals, especially those of Group 10, readily insert into the Si—Si bond of disilacyclobutene 118 and can catalyze the addition of that bond across a variety of unsaturated acceptors. In the case of Ni(0)-catalyzed reactions of 118 with trimethylsilyl alkynes, insertion was found to occur both in a 1,2-and in a 1,1-fashion. The latter of these pathways implies a 1,2-silyl-migration, presumably occurring at the metal center. A nickel vinylidene intermediate was therefore proposed, though efforts to prove its existence were inconclusive. Similar vinylidene intermediates have been proposed by Ishikawa and coworkers to account for migrations observed in related palladium- and platinum-catalyzed reactions [36]. 

Of the Group 10 elements, nickel, palladium and platinum, only the +2 states of Ni and Pd are well characterized in aqueous acid solutions. Their + 2/0 standard reduction potentials in acid solution are given in the Latimer diagram ... 

Laboratory in Oxford, and Geoffrey Ozin at the University of Toronto in the early 1970s. With the metal atom cocondensation technique (which as described in Chaps. 6 and 7 was also used to prepare a series of zerovalent arene and olefin metal complexes), they reported simultaneously that the elusive palladium and platinum tetracarbonyls, Pd(CO)4 and Pt(CO)4, as well as the coordinatively unsaturated fragments M(CO)3, M(CO)2, and M(CO) (M = Pd, Pt) were formed by cocondensation reactions of Pd and Pt atoms with CO in inert gas matrices at 4-10 K [119-122]. The comparison of the CO bond stretching force constants for Pd(CO)ra and Pt(CO)ra (n - 1-4) revealed that, in analogy to Ni(CO) , the most stable compounds were the tetracarbonyls. In a xenon matrix, Pd(CO)4 existed up to about 80 K [120]. Ozin s group as well as others... 

H PALLADIUM AND PLATINUM GROUP 10 18-H-l General Remarks Stereochemistry1... 

A member of the first transition series of the group 10 elements, nickel, seems to have less of a tendency to form dinuclear or oligo-nuclear complexes compared with palladium and platinum. This is probably the consequence of the higher stability of the octahedral terms of nickel(II). The known quadruply bridged dinickel complexes are those of carboxylates, dithiocarboxylates, 1,3-diphenyltriazen (Hdpt), thiobenzoate, and A(,A( -di-p-tolylformamidinate (form). 

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