Chalcogen, arylation

It has, however, also been reported that the reaction of aryl ditellurides with Ni°, Pd°, and Pt° may result in the cleavage of the carbon-chalcogen bond. The oxidative addition of... 

Figure 1 Nomenclature of phosphorus-chalcogen compounds (names in brackets refer to the anionic deprotonatedform). R = alkyl, aryl E — S, Se, Te...

The arylmethylselenides ArSeMe and tellurides ArTeMe pose somewhat of a special case in the alkyl aryl compounds, due to the comparatively low reactivity of their radical cations, which do not easily undergo cleavage of the chalcogen-methyl bond, due to the low stability of the resulting methyl radical or cation. 

Unlike the aryl methyl selenides, the alkyl aryl selenides with alkyl groups of two carbons or more are able to undergo scission of the radical cation at the Cgp-Se bond, yielding the ArSe radical (Fig. 35). This can impact product distribution, particularly under conditions in which water is not present to react with the radical cation. Trends in ease of oxidation typically seen in series of chalcogen compounds can still be observed, and are consistent with trends in the diaryl chalcogenides and aryl methyl chalcogenides. 

Aryl iodides, in Grignard reagent preparation, 9, 35 Aryl isocyanides, chalcogen—chalcogen additions, 10, 752 Aryl isonitriles, in insertion reactions, 1, 106-107 Aryl ketones, via intramolecular G—H functionalizations,... 

In view of the preference of the tetrasilabuta-1,3-diene 139 for the s-cis form, it seemed worthwhile to examine its behavior in [4 + 2] cycloadditions of the Diels-Alder type. Since 139, like many disilenes, should behave as an electron-rich diene, we attempted to react it with various electron-poor and also with some electron-rich olefins. No reaction was detected in any case. Only in the presence of water did 139 react with quinones to furnish the unsymmetrically substituted disilenes 36 and 37 (see Section III.A). The effective shielding of the double bonds by the bulky aryl groups and, above all, the 1, 4-separation of the terminal silicon atoms of about 5.40 A appear to be responsible for these failures. Thus, it was surprising that treatment of 139 with the heavier chalcogens afforded five-membered ring compounds in a formal [4 + 1] cycloaddition (see below). 

Compounds with a nucleophilic sulphur are readily arylated by iodonium salts in their anionic form, and less readily in other cases, notably in sulphides triaryl sulphonium salts are useful photoinitiators in cationic polymerizations. A list of chalcogen compounds arylated by iodonium salts appears in Table 8.7. 

The reactions of aryl tellurium bromides with bromomagnesium benzeneselenolate11, sodium bcnzenethiolate, or sodium benzeneselenolate12 yield aryl phenyl tellurium chalcogen compounds (p. 208). 

Antimony forms nnmerons stable pentavalent organo-metallic componnds among these are penta alkyls and aryls, mixed organohalides, and varions chalcogen and nitrogen derivatives. 

Ge amidinate complexes are susceptible to oxidation of elemental chalcogens. Many of these complexes are excellent catalysts for the cycUzation of aryl isocyanates. ... 

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