Preparations Involving Organometallic Precursors

Impr nation of Phosphine-Based Cold Complexes 

One advantage of using phosphine organogold complexes or clusters is that they do not contain chlorides, but one drawback is that they must be synthesized, and handled with care because of toxicity. Moreover, depending on the nature of the compounds, they are more or less stable in air and light. 

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All of the attempted generations of this type of aryne to date have involved organometalic precursors or strongly basic reaction conditions, either of which is incompatible with the presence of the N-H group of the indole nucleus. Consequently only the preparation of the iV-methyl derivative 31 has been investigated. Decomposition of the mercury compound 231 in the presence of tetracyclone (151) gave both the expected aryne adduct (232) and 3-chloro-A -methylindole (233). The isolation of the latter compound indicates that the precursor 231 decomposes by a stepwise process probably via the radical 234. Reaction of tetracyclone (151) with either this radical or directly with the... 

A number of low temperature routes to the preparation of oxides have begun to receive attention. In many cases these involve the decomposition of organometallic precursors such as oxalates. These alternative ceramic approaches will be discussed elsewhere in this volume. 

X HE USE OF CHEMICAL APPROACHES to improve the processing, properties, and performance of advanced ceramic materials is a rapidly growing area of research and development. One approach involves the preparation of organometallic polymer precursors and their controlled pyrolysis to ceramic materials. This chapter will review the preparation and application of silicon-, carbon-, and nitrogen-containing polymer systems. However, the discussion is not exhaustive the focus is on systems with historical significance or that demonstrate key technological advances. 

A number of techniques have been used for producing nanoparticles, including vapour phase techniques [72], sol-gel methods [73], sputtering [74], coprecipitation [75] etc. Two main methods can be employed for the preparation of metal nanoparticles coprecipitation and chemical reduction. In both cases, the presence of surfactant is required to govern the growth process. Typically, the coprecipitation reactions involve the thermal decomposition of organometallic precursors [76 ]. The chemical reduction occurring in colloidal assemblies... 

Erkey and co-workers [59-61] prepared Pt- and Ru-doped carbon aerogels using a supercritical deposition method. This involved dissolution of an organometallic precursor in a supercritical fluid and the exposure of a solid substrate to this solution. After impregnation of the support with the metal precursor, it was converted to the metal form by different methods. Dimethyl(l,5-cyclooctadiene) platinum(ll) was used as a precursor for Pt [59,60], and two different Ru complexes, trisacetylacetonate Ru(lll) and Ru(cod)(tmhd)2, were used for Ru [61], Monolithic organic and carbon aerogels... 

Peng et al. [85] report the synthesis of CdSe/CdS NPs with core diameters ranging from 2.3 to 3.9nm with a shell thickness up to three monolayers. Their results indicate that in the excited state the hole is confined to the core and the electron is delocalized throughout the entire structure. ZnSe-CdS core-shell NPs are prepared via the traditional pyrolysis of organometallic precursors. The two-step synthesis involves the fabrication of 4.5-6nm ZnSe seeds followed by a subsequent deposition... 

In this chapter are presented, two different liquid phase chemical synthesis methods for the preparation of M50 steel and iron nano-powders. Also, the compaction of these powders into a consolidated sample and a structural and morphological study of the powders and compacts is described here. One synthetic methodology involves the ultrasound assisted decomposition (26-28) of organometallic precursors and the other involves the use of a reducing agent to produce the fine particles from the elemental halides. In addition, the ultrasound-assisted synthesis of pure iron nanopowders, its compaction and the physical properties are reported. 

Applications involving ring transfer or loss. The kinetic lability, volatility, and Lewis acidity of heavy alkaline earth metallocenes have been the properties most important to their applications. The gas-phase decomposition of volatile metallocenes is useful in the preparation of thin films of alkaline earth-containing materials and in doping semiconductors. Reviews are available on the use of group 2 organometallic compounds as precursors for chemical-vapour deposition (CVD).2 3... 

In this section, some recent uses of pyrans in synthesis are described. Much of the chemistry of this class of compounds involves Diels-Alder cycloadditions, metal- and thermal-assisted reorganization reactions, and the preparation and reactions of organometallic derivatives. The chemistry of the pyrylium salts, useful precursors to substituted aromatics (B-64MI11600), will not be discussed here. 

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