Organometallic synthetic approach

Several samples of CdSe/ZnS QDs with a CdSe core size of 4 nm and different thickness of ZnS shell measured in monolayers (ML) have been studied at RT. The QDs were prepared by an organometallic synthetic approach in a three-component hexadecylamine - trioctylphosphine oxide - trioctylphosphine mixture [1], All samples exhibited a PL in the region of 594-600 tun with quantum yield above 50%. The size of the core (4 nm) and the width of the QD size distributions (from 8% to 12%) were estimated from absorption spectra as described in Ref [1]. 

As an extension of the reaction of sulphinates with organometallic compounds, the Claisen-type condensation between ketone enolate anions 101 and arenesulphinates may be considered. It was found161,162 that this reaction provides an interesting synthetic approach to a-ketosulphoxides 102 (equation 54 Table 9). 

Organometallic polymer precursors offer the potential to manufacture shaped forms of advanced ceramic materials using low temperature processing. Polysilazanes, compounds containing Si-N bonds in the polymer backbone, can be used as precursors to silicon nitride containing ceramic materials. This chapter provides an overview of the general synthetic approaches to polysilazanes with particular emphasis on the synthesis of preceramic polysilazanes. 

In this unusual and new synthetic approach the surface of the inorganic oxide does not behave as a new medium for dispersion of reagents but as a particular kind of ligand that by binding, in various ways, surface organometallic molecular fragments or species controls both the kinetic and the selectivity of the reactions taking place on the surface. 

A variant on the ship-in-a-bottle approaches described above is to react a preformed catalyst with the zeolite framework. This is analogous to procedures developed for immobilizing organometallic and coordination compounds on surfaces, but occurs within zeolite pores. These compounds that have reacted with the external surface must be removed, along with those adsorbed on the surface, to produce a true single-site catalyst. Two examples, illustrating different synthetic approaches, are discussed below. 

An alternate synthetic approach to organometallic polymers is to perform reactions where the metal atom is not the reaction site. An example is a polyesterification between an organometallic monomer containing two carboxyl groups and a diol (Eq. 2-238). Reaction of the diacid with a diamine would yield an organometallic polymer via polyamidation. A wide range of other reactions covered in this chapter can be used to synthesize organometallic polymers. 

Alternative synthetic approaches include enantioselective addition of the organometallic reagent to quinoline in the first step of the synthesis [16], the resolution of the racemic amines resulting from simple protonation of anions 1 (Scheme 2.1.5.1, Method C) by diastereomeric salts formation [17] or by enzymatic kinetic resolution [18], and the iridium-catalyzed enantioselective hydrogenation of 2-substituted quinolines [19]. All these methodologies would avoid the need for diastereomer separation later on, and give direct access to enantio-enriched QUINAPHOS derivatives bearing achiral or tropoisomeric diols. Current work in our laboratories is directed to the evaluation of these methods. 

Another synthetic approach to p.-methylene complexes originates from the very simple idea that there might be an analogy with olefin cyclo-propanation (146) in organometallic chemistry if one had starting materials at hand that contain metal-metal double bonds (147). This type... 

The first step in this synthetic approach is to form a metal-metal dimer. Numerous organometallic dimers have been prepared, and examples of the reaction types that appear most useful are tabulated here [Eqs. (58) (160), (59) (16), (60) (131), (61) (61), and (62) (122).. ... 

Vinyl isoxazolines 48 can be prepared by cycloaddition of nitrile oxide to 1,3-butadiene. An alternative synthetic approach has been recently described. The method is based on domino nucleophilic addition-anionic C-O-heterocyclization of nitrile oxides with allyl organometallics derived from trans-1,4-dihalobutene and a metal such as zinc, magnesium or indium. In the case of indium an aqueous media could be used <07SL1449>. 

Many of the synthetic approaches that are used for the preparation of fluoroalkenes can be adopted for the synthesis of polyfluorodienes. Examples of other processes such as reductive coupling methods and syntheses based on organometallic precursors [265] or phosphorous ylids are also included in Table 7.16. 

It will become clear that, in some cases, the classical routes to organometallics are not available but, compensating for this, the different chemistry of, for example, unsaturated fluorocarbons has often been exploited to provide quite new synthetic approaches. 

The majority of the known heterocyclic dienes are pentadienes, largely as a result of the discovery that alkynes react with alkali metals and form dianions via dimer addition of the acetylene anion radical. A method that has become useful for the generation of larger cyclic dienes is the addition of an organometallic dihydride to a suitable dialkyne. Synthetic approaches to six-membered dienes tend to be unique for each system, and no general method has been developed. Some of the six-membered heterocyclic dienes have been converted to trienes for the study of systems that may be aromatic. 

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