Organometallic selenium

The wide substrate tolerance of lipases is demonstrated by the resolution of organometallic substrates [129-131]. The presence of tin, selenium, or tellurium in the structure of secondary alcohols does not inhibit the lipase activity and enantiopure organometallic alcohols were obtained by acylation in organic media (Figure 6.48). 

A direct synthesis of the thiophene nucleus has been achieved by allowing air-stable cobaltacyclopentadiene complexes (66) to react with sulfur the organometallic complexes are prepared in variable yields in a stepwise fashion from f75-cyclopentadienyIbis(triphenylphosphine)cobalt (65) (Scheme 82) 147,148 Reactions of the complexes 66 with selenium and nitrosobenzene give rise to selenophenes and pyrroles, respectively. 

It is now well established that organometallic compounds are formed in the environment from mercury, arsenic, selenium, tellurium and tin and hence were also deduced on the basis of analytical evidence for lead, germanium, antimony and thallium. Biological methylation of tin has been demonstrated by the use of experimental organisms. Methylgermanium and methyllead were widely found in the environment but it is debatable whether germanium and lead are directly methylated by biological activity in natural environment. 

The application of high temperatures to increase the speed of HPLC separation extends to ion chromatography and to inorganic analysis. Le et al. [18,19] reported a 50% reduction in analysis time when a number of selenium and arsenic species including inorganic forms, organometallics, and compounds with amino acids and sugars were analyzed at 70°C. 

Gas chromatography and mass spectroscopy (GC/MS) of inorganic and organometallic compounds, 18 273-276 Gaseous hydroxides, 5 215-258 dimerization of, 5 224 mass spectrometric study of, 5 220-225 metalic, 5 220 nonmetallic, 5 217-220 study of in oxyhydrogen flame, 5 225-226 types of, 5 215-217 Gases, see also specific substances high ternperamre species from, 14 137-139 thermal decomposition of, 17 90-93 Gas phase electron resonance spectra, of sulfur and selenium fluorides, 24 190... 

Since dioxiranes are electrophilic oxidants, heteroatom functionalities with lone pair electrons are among the most reactive substrates towards oxidation. Among such nucleophilic heteroatom-type substrates, those that contain a nitrogen, sulfur or phosphorus atom, or a C=X functionality (where X is N or S), have been most extensively employed, mainly in view of the usefulness of the resulting oxidation products. Some less studied heteroatoms include oxygen, selenium, halogen and the metal centers in organometallic compounds. These transformations are summarized in Scheme 10. We shall present the substrate classes separately, since the heteroatom oxidation is quite substrate-dependent. 

C.R. Johnson, Sulfoximides, in D. Barton u. W.D. Ollis, Comprehensive Organic Chemistry, Bd. 3, D.N. Jones, Sulphur, Selenium, Silicon, Boron, Organometallic Compounds, S. 223, Pergamon Press, Oxford New York Toronto Sydney Paris - Frankfurt 1979. 

Jones, Sulphur, Selenium, Silicon, Boron, Organometallic Compounds, S. 237, Pergamon Press, Oxford New York Toronto. Sydney Paris Frankfurt 1979. 

The reaction of bis-phenylpropargyl ether (321) with tris(triphenylphosphine)rhodium chloride in benzene or toluene led to the formation of the unusual organometallic compound (322), which can be viewed as a derivative of an oxygen-rhodium pentalene system. Reaction of the rhodium complex (322) with sulfur leads to the corresponding 4,6-diphenyl-l,3-dihydro[3,4-c]furan (323). The selenium and tellurium analogs (324) and (325) were made in a similar manner (Scheme 111) (76LA1448). 

NLO properties, 12, 128 organometallic complexes, 3, 318 as reaction materials, 3, 368 and selenium nucleophiles, 9, 471 surface chemistry on oxides, 12, 502 in triruthenium cyclopentadienyl clusters, 6, 799 trivalent halides, with metal carbonyl monoanions, 3, 347 Group 14 elements... 

Since sulfur chemistry lies beyond the scope of this review and organo-tellurium chemistry so far has not been of any impact on organometallic chemistry in general, this section will be restricted to the discussion of redistribution equilibria on selenium. 

Capillary electrophoresis (CE) provides high resolution for separation of chemical compounds. Separations of metal ions, of metal ions in different oxidation states and of organometallic compounds are all possible with appropriate CE conditions. This technique is being investigated for speciation. Since sample volumes in CE are generally very small, a detector capable of very low detection limits is desirable. Thus, ICP-MS has been combined with CE to provide a means for studying metal speciation. CE-ICP-MS procedures have been described for the separations of platinum species (Michalke and Schramel, 1996), selenium species (Kumar et al., 1995 Michalke and Schramel, 1996) and arsenic species (Magnuson et al., 1997). Detection limits were about 1 mgl 1 (platinum species) and 10 and 24 pg for Sclv and Scvl, respectively. An application of CE-ICP-MS to platinum species in soils is described in Section 15.8.6. 

This chapter concentrates on the developments in organoselenium chemistry from 1993 to 2004 and is therefore a continuation and extention of the chapter Selenium by Krief in the previous edition of Comprehensive Organometallic Chemistry,18 During that period many aspects of organoselenium chemistry have been covered in review articles19-35 and in books completely devoted to different areas of selenium.36-40 These reports highlight the current activities in selenium chemistry and stress the importance of selenium-containing molecules in different areas. 

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