Dialkoxy Tellurium Tetrafluorides

Refluxing a mixture of boron tris[methoxo(oxo)tetrafluorotellurates(VI)] with an excess of arsenic trifluoride yielded arsenic tris[methoxo(oxo)tetrqfiuorotellurates (VI)Y. 

Dialkoxy tellurium tetrafluorides with the same or two different alkoxy groups have been prepared. These compounds may exist as cis- and tra 5-isomers. Both isomers are colorless liquids that can be distilled under reduced pressure. They are only slowly hydrolyzed by concentrated alkali.  

Fluorination of tetraalkoxy tellurium compounds in fiuorotrichloromethane at —78° with fluorine diluted with nitrogen produced dialkoxy tellurium tetrafluorides among other alkoxy tellurium fluorides. The reactions were carried out as described on page 123. The mixture of products was characterized by F-NMR spectroscopy.  

Irgolic Organo-tellurium Compounds without a C,Te-Bond 

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Dialkoxy tellurium tetrafluorides may react in chloroform with an excess of alcohol in the presence of pyridine to form trialkoxy tellurium trifluorides. Whether or not these reactions produce trialkoxy tellurium trifluorides depends on the nature of the alkoxy groups in the dialkoxy tellurium tetrafluoride and only secondarily on the nature of the alkyl groups of the alcohol. 

The following dialkoxy tellurium tetrafluorides did not react with the corresponding alkanols (alkyl group given R1 = R2 = R3) methyl, ethyl, propyl, prop-2-en-l-yl, 2-phenylethyl, 2-acetylethyl, 2-(methoxycarbonyl)ethyl, 2-t-butoxyethyl, 2-phenoxy-ethyl, 2-iodoethyl, and 3-bromopropyl1. 

The reactivities of the R groups in the alcohols correlated with the combined Taft constants, Iff, of the substituents in the Alkoxy groups. When the Zo values for X and Y in the dialkoxy tellurium tetrafluorides were greater than + 1.75 further reaction with alcohols occurred, however, when Zo was less than + 1.75 no reaction was observed1. 

Tellurium hexafluoride reacted with primary monohydroxyalkanes in the presence of pyridine as hydrogen fluoride scavenger to form predominantly cw-dialkoxy tellurium tetrafluorides. The trans-isomer, detected in a few cases by 19F-NMR spectroscopy, never occurred in the products in more than a few percent2. 

When tellurium hexafluoride was heated at 90° with at least 4.5 moles of a primary alcohol per mole of tellurium hexafluoride for 9 days in the presence of excess sodium fluoride, cis-dialkoxy tellurium tetrafluorides were only produced in reactions with 2-bromoethanol or propanol4. 

The reactions of alkoxy tellurium pentafluorides with alcohols in the presence of pyridine were used to prepare dialkoxy tellurium tetrafluorides with two different alkoxy groups in the molecule1. These unsymmetrical compounds are suspected to be predominantly in the cis-form. 

Dialkoxy tellurium tetrafluorides reacted with primary monohydric alcohols to give trialkoxy tellurium trifluorides1. 

Alcohols other than methanol reacted only slowly with tellurium hexafluoride in the presence of sodium fluoride as the HF-acceptor. The reactions proceeded much faster with 0.5 mole of pyridine per mole of tellurium hexafluoride. Under these conditions, small quantities of dialkoxy tellurium tetrafluorides are also formed3. 

Methoxyethanol, 2-chloroethanol, and 2,2,2-trifluoroethanol did not form any dialkoxy tellurium tetrafluorides ... 

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