Zero-valent group 10 metals

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

The chemical state of the metal can play a decisive role on the reaction mechanism. In TWC, Rh is thought to remain in the zero-valent state, which favors NO dissociation [77,78], However, the role of the OSC materials is complex, and it is not inert with respect to NO activation. Ranga Rao et al. [79] showed that, when bulk oxygen vacancies are formed in a reduced Ce06Zr04O2 solid solution, NO was efficiently decomposed on the support to give N20 and N2. Further studies by the same group... 

In principle, any type of particle can be prepared inside a dendrimer template if a means can be found first to sequester the components and then to transform them chemically into the desired product. As discussed earlier, the simplest way to accomplish this goal is to take advantage of strong interactions between functional groups within the dendrimer and ions in solution, and then chemically reduce the ions to the zero-valent metal. In certain cases, Ag for example, this approach does not work (at least not with dendrimers having interiors dominated with tertiary amines) because the partition coefficient is too small. However, in that case it was possible first to prepare a less noble metal nanoparticle, and then to displace it with Ag. 

Historically, vinylidene complexes of zero-valent pentacarbonyl Group 6 metals appeared as a fleeting intermediate for the preparation of Fischer-type carbene complexes. Probably the first example of the formation of such a pentacarbonyl vinylidene complex of a Group 6 metal was proposed in 1974 by Fischer et al, who examined the reaction of pentacarbonyl[hydroxy(methyl)carbene] chromium 1 with dicyclohexylcarbodiimide(DCC) [3]. Thus, treatment of 1 with DCC in CH2CI2 at —20°C rt gave a novel azetidinylidene complex 2 in 47% yield. As a possible... 

The active catalyst is presumably formed through reduction of the Ni species, aided by hydrogen or group VIB metals and their carbonyls, to the nickel carbonyl. Nickel carbonyl is converted to the active catalyst by ligand dissociation. The exact nickel species is the result of complex equilibria, equations 11-17. The zero valent complex adds methyl iodide, after CO dissociation. This is believed to be the rate-determining step and has first order kinetics with respect to both iodide and Ni. It was found that temperature greater than 100 C is needed for the oxidative addition (29). 

Hydrides of Pt(II) are the most numerous of any transition metal hydride group. In addition to the presence of the hydride ligand, the complexes invariably have a coordinated phosphine, and synthetic routes to these compounds using both hydridic and protonic reagents have been reported (I). The pure complexes are usually both air stable and kinetically inert. The purpose of this chapter is to show the diversity of hydrides that can be obtained from protonation reactions on zero-valent and di-valent triphenylphosphine platinum compounds, and to rationalize the type and nature of the product formed from the character of the acid HX. 

A further class of embodiments is any of the above-described compositions, wherein the silver particles comprise both silver in the zero-valent, that is, metallic, oxidation state [Ag(0)] and a coating of silver in an ionic oxidation selected from the group consisting of Ag(I), Ag(II), and Ag(III). 

Such complexes have been referred to as nitrene complexes but, strictly, nitrenes are RN species and while zero valent NR compounds have been reported, none has been isolated. Imido compounds are commonly found in transition metal complexes with oxidation states 3 and above. The high capacity for electron donation by the imido group does of course, like that of O2-, act to stabilize high oxidation states prime examples of this are Os(NBu )4 vs. 0s04 and (Bu N)3MnCl vs. 03MnCl. 

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