Reduction of Organometallic Precursors

5 [HAuC14.3H20] Ascorbate Various shapes and diameters  

PFg [HAuC14.3H20] Imidazolium cation Prismatic particles  

In relation to the reducing agent, hydrogen gas, metal hydrides, and irradiation methods are the most investigated approaches used to produce metal NPs in ILs. 

Interestingly, in some cases the IL itself can act as the reductive agent. Spherical metal silver NPs were prepared in a hydroxyl-functionalized IL (2) (entry 30, Table 1.1) [17]. In this case, the hydroxyl moiety of the IL plays a reductive role, being oxidized to the corresponding aldehyde. In a similar manner, for Au(III) precursors, the imidazolium cation itself can act as a reducing agent to yield prismatic particles in BMI.PF6 with a very broad size range of diameter 3-20 pm and thickness 

10-400 nm (entry 10, Table 1.1) [18]. Moreover, single-crystal nano- and microprisms with larger sizes of diameter 100 [tm were prepared using BMI.NTf2. 

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Rare Earth Arene-Bridged Complexes Obtained by Reduction of Organometallic Precursors... 

CHAPTER 266. RARE EARTH ARENE-BRIDGED COMPLEXES OBTAINED BY REDUCTION OF ORGANOMETALLIC PRECURSORS... 

Besides the common alkali-metal reduction method for the production of anion-radicals, other electron-transfer reagents have been used for the production of radicals relevant in this section. Todres and co-workers have used cyclooctatetraene dianion and have examined the redox equilibria of this reductant and various substituted substrates. Radical 225 has also been produced by reduction of the precursor with organometallic reagents in the presence of transition-metal ions. ... 

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... 

The formation of active catalysts and nanostructures requires technology capable of producing finely divided materials. In fact, sonolysis of organometallic precursors enables the preparation of catalysts, amorphous powders, and intercalation compounds. o These sonolytic reactions can be applied when the metal atom is bound to neutral ligands, requiring no reduction. 

Two approaches for the synthesis of nanostructured M50 type steel (composed of 4.0% Cr, 4.5% Mo, 1.0% V, 0.8% C and balance Fe) powders and their consolidation are reported in this chapter. One approach involved the sonochemical decomposition of organometallic precursors and the other involved the reduction of the metal halides with lithium triethyl borohydride followed by vaccum sublimation of the powders to remove lithium chloride. The as-synthesized powders are amorphous by X-ray diffraction (XRD) but the peaks corresponding to bcc a-Fe are observed in the compacts. The morphology and composition of the powders synthesized by both techniques, as well as the compacts, were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness, density, particle size and impurity contents were also determined for the compacts. In addition, pure nanosized iron particles obtained by the ultrasound decompositon of iron pentacarbonyl were consolidated and the properties of the latter were studied. 

There have been a number of synthetic protocols for the preparation of transition-metal nanoparticles, for example, vapor condensation, sonochemical reduction, chemical liquid deposition, reflux alcohol reduction, decomposition of organometallic precursors, hydrogen reduction, etc. Of these, the colloidal reduction route provides a powerful platform for the ready manipulation of particle structure and functionalization. One excellent example is the biphasic Brust method, in which nanoparticles are formed by chemical reduction of a metal salt precursor in the presence of stabilizing ligands. In a typical reaction, a calculated amount of a metal salt precursor is dissolved in water, and the metal ions are then transferred into the toluene phase by ion-pairing with a... 

Generally, stable and well-dispersed metal NPs have been prepared in ILs by the simple reduction of the M(I-IV) complexes or thermal decomposition of the organometallic precursors in the formal zero oxidation state. Recently, other methods such as the phase transfer of preformed NPs in water or organic solvents to the IL and the bombardment of bulk metal precursors with deposition on the ILs have been reported. However, one of the greatest challenges in the NPs field is to synthesize reproducibly metal NPs with control of the size and shape. Selected studies of the preparation of metal NPs in ILs that, in some cases, provide NPs with different sizes and shapes are considered in this section. 

Transmission infrared spectroscopy is an important tool in catalyst preparation to study the decomposition of infrared-active catalyst precursors as a result of drying, calcination or reduction procedures. In particular, if catalysts are prepared from organometallic precursors, infrared spectroscopy is the indicated technique for investigation [26]. 

Scheme 15.3 Preparation of soluble iridium nanoparticles from in situ reduction of the organometallic precursor [ir(COD)Cl]2 in imidazolium ionic liquids.

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