Diorganotellurides

The oxidative addition of iodine to diorganotellurides has also been examined by stopped-flow spectroscopy. The initial fast reaction of iodine with diphenyltellur-ide (23), di-4-methoxyphenyltelluride (24), A,V-dimethyl-2-(aminomethyl)phenyl-telluride (17), and 2,6-di-tert-butyltelluropyran-4-one (25) displays inverted Arrhenius behavior (negative values of E ), which is consistent with a preequilibrium involving higher-order iodine species as shown in equation (6). The I4 species is the actual oxidant for diorganotellurides as shown in equation (7). Thus, the initial reaction is formation of the r i-association complex of I4 with the... 

Fig. 13 A plausible mechanism for the debromination of v/cma/-dibromides with diorganotellurides.

In contrast to the rate of debromination of 30 with telluride 26, the debromination of dibromide 30 with iodide is much more rapid. In general, the rate of debromination with the anionic iodide is several orders of magnitude faster than with the uncharged dihexyltelluride 26. The debromination with iodide most likely proceeds via the E2-like transition state 32 (Fig. 12), which avoids the strain associated with bromonium ion 31." " Diorganotellurides should also be capable of following a similar mechanism. 

Fig. 14 Plausible E2-like transition state for the debromination of 1,2-dibromoalkanes with either diorganotellurides or iodide.

Polymer stabilization is another area in which the peroxide-decomposing and chain-breaking antioxidant properties of diorganotellurides has found utUity. Alone or in combination with phenol and phosphate antioxidants, electron-rich dialkylamino-substirnted diaryltellurides and alkylaryltellurides provided greatly enhanced polymer stability for a thermoplastic elastomer and for polypropylene. The effects were unique to the tellurides, with selenides not providing similar protective effects. ... 

Chlorine, addition/reduction from diorganotellurides, 82 CID spectrometry... 

A modification of an earlier procedure for debromination of v/c-dibromides in the presence of catalytic amounts of diorganotellurides has allowed the synthesis of terminal alkenes and cis- and frani-l,2-disubstituted alkenes from appropriate precursors the relative substrate reactivities suggest that, as for the stoichiometric reaction, the catalytic reaction involves intermediate bromonium ion formation. The Te(IV) dibromides formed in the debrominative elimination are reduced back to the catalysts by either sodium ascorbate or the thiol glutathione. 

Diorganotellurides form complex compounds of the type (TeR2)m MA , of which compound [TeR2 M(CO)5] (M = Cr R = C6H4CH2NMe2-o) [633-635] is a clear example. 

Diorganotellurium dichlorides 6 (X = Cl) are odorless viscous oils or colorless crystalline solids. These compounds are more stable than the corresponding diorganotellurides 3, and most of them are not moisture or air sensitive. The analogous diorganotellurium dibromides or diiodides are less common than the diorganotellurium dichlorides. 

Diorganotellurium oxides 8 are prepared by oxidation of diorganotellurides. The dialkyl derivatives are prone to air oxidation specially when they are in solution. The diaryl tellurides 3 are more stable being oxidized to the corresponding tellurium oxides 8 by sodium periodate32 or A -chlorosuccinimide followed by alkaline hydrolysis82 (Scheme 14). Alternatively, diaryltellurium dichlorides 6, prepared by electrophilic aromatic substitution (Section 9.13.6.2, Scheme 70), can be hydrolyzed in alkaline medium to the corresponding tellurium oxide 883 (Scheme 14). 

Diorganotellurides are themselves nucleophiles and react with alkyl halides to give triorganotelluronium salts.118... 

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