Palladium IV compound

Just as many palladium(IV) complexes are produced by halogen oxidation of the corresponding palladium(II) complex, so the palladium(IV) compounds tend to decompose by the reverse process, usually on heating ... 

The decomposition of the dimethyl palladium(II) carbene complex with excess methyl iodide is a stepwise process. Although the authors [282] propose oxidative addition of methyl iodide on the palladium centre forming an octahedral palladium(IV) complex, it seems much more likely, with respect to the rarity of palladium(IV) compounds [284,285], that the first step is reductive elimination of an imidazolium salt, a decomposition pathway found to be fairly common after the initial publication of McGuinness et al. [283], Oxidative addition of methyl iodide followed by reductive elimination of ethane would account for the accumulation of iodide ligands on the palladium centre and a Pd(0)/Pd(II) redox couple. However, in the last step, a six coordinate Pd(IV) centre still seems to be necessary (see Figure 3.91). 

Finally, a third means of ligand formation from an imidazolium cation, described by Dupont and co-workers, should be mentioned here [34]. They investigated the hydrodimerization/telomerization of 1,3-butadiene with palladium(II) compounds in [BMIM][BF4] and described the activation of the catalyst precursor complex [BMIM]2[PdCl4] by a palladium(IV) compound formed by oxidative addition of the imidazolium nitrogen atom and the alkyl group with cleavage of the C-N bond of the [BMIM]+ ion, resulting in bis(methylimidazole) dichloropalladate (Scheme 5.2-5). However, this reaction was only observed in the presence of water. 

In contrast to the synthetic approach to all known organopalladium(iv) complexes through (isolated) palladium(ii) complexes, the dialkyl-dialkoxy-palladium(iv) compound 196 was formed in a single step from [Pd2(dba)3], norbor-nene, and ( -chloranil." Gomplexes 197 and 198 were obtained from 196 by treatment with THE or pyridine, respectively. The coordination number seems to depend on the basicity of the monodentate donor molecules 196 and 197 are five-coordinate but 198 is distorted octahedral, as confirmed by X-ray structures of the latter two. The palladaspirocycle fragments have C2 symmetry. 

Compared with the plethora of platinum(IV) compounds, the palladium(IV) complexes are as yet relatively few in number [10, 11]. When isolable, they tend to resemble the corresponding platinum compounds. 

The anionic palladium(IV) species (NPr4)[PdCl5(SMe2)] has been prepared by chlorine oxidation of the corresponding palladium(II) species. It undergoes facile decomposition at room temperature like the phosphine analogue.346 The neutral compound h-ans-[PdCU(SMe2)2] could not be characterized, however, because of thermal decomposition. 

Palladium(II) sulfide is precipitated as a brown powder by adding H2S to a solution of palladium(II) ion. When this sulfide is heated with sulfur at 400°C, the insoluble disulfide is formed. The excess sulfur can be extracted with CS2 to yield the gray-black crystalline palladium(IV) sulfide. This compound is not soluble in single acids but is soluble in aqua regia. 

Palladium(IV) and platinum(IV) compounds are accessible by oxidative addition of organic halides to the corresponding divalent species. In general, the Pt(IV) derivatives are more stable, but a number of organopalladium(IV) compounds have been isolated. 

Palladium (Pd, at. mass 106.42) is a platinum-group metal, and occurs in the II and IV oxidation states. Palladium(II) compounds are the more stable. Unlike the other platinum metals, palladium is soluble in cone. HNO3. Brown-red Pd(OH)2 precipitates at pH 4, but dissolves in excess of an alkali-metal hydroxide. Palladium(ll) gives stable nitrite, ammine, cyanide, chloride, bromide, and iodide complexes. Palladium(ll)- and (IV) are reduced to the metal by SO2, Fe(II), and ethanol. 

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