First Isolation and Characterization of Sodium and Potassium Tellurocarboxylates: Structural Analysis of Te-Alkyl Telluroester

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Abstract
The first synthesis and characterization of sodium and potassium tellurocarboxylates were achieved by the reaction of acyl chlorides with the corresponding alkali metal tellurides. The salts are yellow to red solids or oils. The aliphatic derivatives are very sensitive toward oxygen and very thermally sensitive. However, the aromatic derivatives are relatively stable and can be stored for 1 week below −5 °C and under oxygen-free conditions. The most practical method for the synthesis of Te-alkyl telluroesters was established by the reaction of the sodium and potassium tellurocarboxylates with alkyl iodides at 0 °C. The first X-ray structural analysis of telluroesters (RCOTeR‘) was carried out for Te-methyl 4-chlorobenzenecarbotelluroate (4-ClC6H4COTeCH3), whose crystals are monoclinic (P21/a) with a = 5.975(3) Å, b = 14.517(2) Å, c = 10.617(3) Å, β = 92.74(3)°, V = 919.8(4) Å3, and Z = 4. The molecule was nearly planar. The CO and C−Te bond lengths are 1.204(3) and 2.153(3) Å, respectively, indicating CO double and C−Te single bonds. The C−Te−C angle of the C(O)TeCH3 moiety is close to a right angle (92.3°), much more narrow compared with those [C−E−C, E = O (>105°), S (>102°), Se (>95)] of common esters and thio- and selenoesters (ArC(O)ER‘, E = O, S, Se; R‘ = alkyl). The ν(CO) bands and the 13CO and 125Te NMR spectra of the sodium and potassium tellurocarboxylates are discussed in comparison with those of other alkali metal or oxygen, sulfur, and selenium isologues.