Organometallic species

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

Grignard reagents are a very important class of organometallic compounds. For their preparation an alkyl halide or aryl halide 5 is reacted with magnesium metal. The formation of the organometallic species takes place at the metal surface by transfer of an electron from magnesium to a halide molecule, an alkyl or aryl radical species 6 respectively is formed. Whether the intermediate radical species stays adsorbed at the metal surface (the A-modelf, or desorbs into solution (the D-model), still is in debate ... 

Mechanistically the reaction can be divided into two steps. Initially the alkyl halide 1 reacts with sodium to give an organometallic species 3, that can be isolated in many cases. In a second step the carbanionic R of the organometallic compound 3 acts as nucleophile in a substitution reaction with alkyl halide 1 to replace the halide ... 

Ionic liquids possess a variety of properties that make them desirable as solvents for investigation of electrochemical processes. They often have wide electrochemical potential windows, they have reasonably good electrical conductivity and solvent transport properties, they have wide liquid ranges, and they are able to solvate a wide variety of inorganic, organic, and organometallic species. The liquid ranges of ionic liquids have been discussed in Section 3.1 and their solubility and solvation in... 

The optically active iodide 153 (Scheme 43) can be conveniently prepared from commercially available methyl (S)-(+)-3-hydroxy-2-methylpropionate (154) (see Scheme 41). At this stage of the synthesis, our plan called for the conversion of 153 to a nucleophilic organometallic species, with the hope that the latter would combine with epoxide 152. As matters transpired, we found that the mixed higher order cuprate reagent derived from 153 reacts in the desired and expected way with epoxide 152, affording alcohol 180 in 88% yield this regioselective union creates the C12-C13 bond of rapamycin. 

Despite the undefined nature of the organometallic species, chirally modified organotita-nium reagents are useful tools in enantioselective synthesis. In particular, the binaphthol-mod-ified phenyltitanium reagent 41 shows excellent enantioselectivity in additions to aromatic aldehydes34-40,41. 

One of the most general preparative routes to allyl- and 2-butenylboranes involves the reaction of an allylic organometallic species and an electrophilic borylating reagent. Various esters of allylboronic acid have been prepared in this way2,4-5. 

Richards et at. carried out extensive studies on the use of mercury,2 6 277 lead278 279 and silver compounds to terminate anionic polymerization and form polymeric organometallic species which can be used to initiate polymerization. 

The transmetallation reaction involves the transfer of the organic group from an organometallic species to a Pd(II) species and produces a trails Pd(II) species. Isomerization from the trans arrangement to a cis one is necessary prior to the reductive elimination step. Reductive elimination yields the coupled product and regenerates the transition metal catalyst. Because the reductive elimination is very fast, competing reactions leading to by-products are usually not observed. 

Arylboronic acids have traditionally been prepared via the addition of an organomagnesium or organolithium intermediate to a trialkyl borate. Subsequent acidic hydrolysis produces the free arylboronic acid. This limits the type of arylboronic acids one can access via this method, as many functional groups are not compatible with the conditions necessary to generate the required organometallic species, or these species may not be stable intermediates. 

Recent organometallic studies have been reported. Mossbauer spectra have shown that the Fej dimer reacts at 4K with CH4 to oxidatively cleave the C—H bond to form HFe2CH3. Zirconium atoms have also been shown to oxidatively cleave the C—H and C—C bonds of alkanes to form discrete organometallic species. ... 

Prange A, Jantzen E (1995) Determination of organometallic species using GC-ICP-MS. Journal of Analytical Atomic Spectrometry, 10 105-109. 

Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing 0x0 or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the 0x0 and imido complexes is beyond the scope of the review and will not be covered here. 

The first series of soluble oligo(para-phenylene)s OPVs (20) were generated by Kern and Wirth 1331 and shortly thereafter by Heitz and Ulrich [34]. They introduced alkyl substituents (methyls) in each repeat unit and synthesized oligomers (20) up to the hexamer. Various synthetic methods, like copper-catalyzed Ullmann coupling, copper-catalyzed condensation of lithium aryls, and twofold additon of organometallic species to cyclohexan-l,4-dione, have been investigated. 

The authors developed two general methodologies for the synthesis of these monodisperse, defined oligomers. They can be built up stepwise, e. g. via additon of organometallic species to cyclohexan-1,4-dione, followed by aromatization to the oligoarylene (e.g. for 21). 

Nolan, M. Porchia, G. Sishta, T. J. Marks in Energetics of Organometallic Species, J. A. Martinho Simoes (ed.), Kluwer Dordrecht, 1992, pp 35-51. 

Two challenging, but very difficult tasks have been tackled mainly or increasingly during the last two decades the certification of organometallic species and valency states of elements (see Section 3.3), and organic compounds (see Section 3.4). But doubtless this was just the beginning and a wealth of work waits in the future to serve all needs of the analytical community (Quevauviller and Maier 1999)-... 

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