Chalcogen alkylation

Fig. 8. Sensitizing dyes of the cyanine class. K. = N — alkyl or chalcogens (O, S, Se, Te) R = chloro, phenyl, or additional benzene ring R = methyl, ethyl, or hydrogen n = 0, 1, 2 and RPRIME, R " = alkyl or sulfoalkyl. Solubihty in methanol for a carbocyanine dye n = 1 X = S R = Cl R = ethyl. Cationic dye (R" = R " = ethyl anion = bromide) 9.5 mmol/T. neutral dye (R" = ethyl R " = sulfopropyl) 3.6 mmol/L anionic dye (R" = R = sulfopropyl ...

As described previously, the two dimethyl amino methyl groups on the 2,6-position of the phenyl ring of teluride 161 act as internal ligands (Koten s arms) and stabilize the cation generated at the central Te atom (see Equation 44). Furukawa and co-workers subsequently showed that these Koten s arms also activate the molecule to release alkyl substituents which are attached to the central chalcogen atom <1995JA10153> and <1997BCJ2571>. For example,... 

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

Thiophene and its derivatives, however, have become the most-studied chalcogen-containing monomers. Doped (oxidised) PT is highly conducting, and 3-alkyl-substituted PTs are soluble, easily characterised polymers,83 85 see Figure 7. Self-assembly is an important consideration in these substituted PTs, allowing control of the degree of planarity, n-orbital overlap, and hence optical... 

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. 

Due to the reduced availability of the lone pair at the chalcogen atom, the sulfur or selenium atom in p -chalcogenoaldehyde or -ketone complexes cannot be alkylated by the usual alkylating agents. 

By varying the conditions of the methylation reaction it is possible to prepare both N-methyl and Te-methyl derivatives of 2-phenylbenzotellurazole. The iodide of./V-methyl-2-phenylbenzotellurazole 17 is formed in 91% yield when heated in excess methyl iodide. When an equimolar amount of AgC104 is added, the methylation reaction provides the perchlorate of Te-methyl-2-phenylbenzotellurazole 18 in almost quantitative yield (88KGS136 89KGS989). The reaction represents the first known example of alkylation of a benzochalcogenazole on the chalcogen atom. It is easy... 

The molecular constraint which precludes ligand exchange unambiguously ensures that the tricyclic compounds undergo nucleophilic attack exclusively at the pseudo-equatorial carbon atom, irrespective of the nature of the carbon atom situated in the apical ligand of the TBP. The compounds 1-4 were obtained by alkylation of the chalcogen atom of the corresponding bicyclic (thio)phosphate, 6 and 7, with trialkyloxonium tetrafluoroborate at -78 °c (2). 

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