Organochalcogen

The third class of compounds to be discussed in this chapter are those in which an RE group (E = S, Se, Te) is attached to a nitrogen centre. This category includes amines of the type (REfsN and the related radicals [(RE)2N] , as well as organochalcogen(ir) azides, REN3, and nitrenes REN (E = S, Se). Covalent azides of the type RTe(N3)3 and R2Te(N3)2, in which the chalcogen is in the +4 oxidation state, have also been characterized. 

The methodology of heteroatom-directed lithiation has been applied to the synthesis of a variety of organochalcogen compounds, including unstable, low-valent compounds (Section 15.6). ° The Se N interactions in the diselenide 15.4 activate the Se-Se bond toward insertion of a sulfur atom or a methylene group to give the derivatives 15.21a,... 

Figure 27 Oxidative addition of the organochalcogen compounds to low-valent transition metal centers most often resulting in the cleavage of the chalcogen-chalcogen bond and the formation of mono- or dinuclear complexes with anionic bridging or terminal RE- (E = Se, Te) ligands.

The single-bond compounds between Si, Ge, and Sn and chalcogens (S, Se, Te) are reactive and used as synthetic intermediates in the synthesis of organic compounds, organochalcogen compounds, organo-silicon, -germanium and -tin compounds, and transition metal-chalcogen complexes and clusters. 

The oxidations and reductions of organochalcogen compounds all involve the lone-pairs of electrons associated with the chalcogen atoms. These lone-pairs are stereochemically active, which provides well-defined geometries for many of the intermediate species described herein. Oxidized organochalcogen compounds also are stabilized by lone-pair donation from neighboring heteroatoms, which again leads to unusual structures with well-defined geometries as described herein. 

ORGANOCHALCOGEN(II) AND ORGANOCHALCOGEN(IV) COMPOUNDS WITH AN ODD NUMBER OE EIGANDS... 

Organochalcogen(II) compounds, 100-102 Organochalcogen(IV) compounds, 100-102 Organoselenium compounds dehalogenation reactions, 96 electrochemical reduction, 113-117 haloperoxidase-like activity, 108-113 with odd number of ligands, 100-102 one-electron oxidation, 117-118 oxidation of thiols, 102-106 redox reactions, 79-80 thioperoxidase-like activity, 108-113 Organotellurium compounds... 

The practical significance of the reaction depicted in Scheme 7.43 consists of the development of novel antioxidants carrying chalcogen atoms. Divalent organochalcogen compounds react readily with many types of oxidants (peroxide, peroxyl radicals, peroxynitrite, singlet oxygen, and ozone). The tetravalent organylchalcogenides formed are reduced by many mild reductants. Therefore, compounds of this sort have the potential to act as catalytic antioxidants. 

Dr. Richard Glass was born in New York City. He received his B.A. degree from New York University in 1963 with a major in chemistry. He earned his Ph.D. degree from Harvard University under Professor E. J. Corey. He then was a postdoctoral associate at Stanford University with Professor E. E. van Tamelen before joining Hoffmann-La Roche, Inc. as a senior chemist. In 1970, he was appointed assistant professor in the Department of Chemistry at the University of Arizona where he is now professor of chemistry. His research interests are in organochalcogen, organoiron, bioorganic, and heterocyclic chemistry. 

Reactions of diaryliodonium salts with organochalcogen nucleophiles... 

Reactions of diaryliodonium salts with various organochalcogen anions led to the arylchalcogen derivatives. (Table 5.7) The anions of sulfur compounds afford generally the 5-aryl derivatives. Sometimes the intermediate iodanes can be isolated. Examples are the reaction of dithiocarbamate and xanthate salts with diaryliodonium. Upon heating, the dithiocarbamate derived iodane afforded the aryldithiocarbamates.133 Thermal decomposition of the xanthate derived iodanes gave mixtures of arylxanthates and diaryldisulfides. ... 

Table 5.7 Arylation of organochalcogen anions by diaryliodonium salts...

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