Alkyl hex-1-ynyl tellurides: Syntheses and multinuclear NMR (125Te-, 13C{1H}-, 1H-) studies

Alkyl hex-1-ynyl tellurides, n-C4H9CCTeR, where R=CH3, CH(CH3)2, cyclo-C6H11, CH2CH(CH3)2, CH2(CH2)6CH3, CH2(CH2)10CH3, CH2CH2CH(Br)CH3, CH2C6H5, 4-CH2C6H4NO2, CH2CH2C6H5 and CH2CH2OC6H5, have been prepared in good yields by the anaerobic reaction of lithium hex-1-ynyl tellurolate with the appropriate alkyl halides in the absence of light. While most of these reactions have been performed at −5 to −10°C the reaction with cyclo-hexyl halide has been conducted at lower temperature (−30°C). Alkyl chloro, bromo and iodo derivatives have provided the same products in the same yields. The reaction has produced n-C4H9CCTe(CH2)5TeCCC4H9-n when Br(CH2)5Br has been used as alkylating agent, while BrCH2CH2CH(Br)CH3 has produced only the monotelluride compound n-C4H9CCTeCH2CH2CH(Br)CH3 even when employing excess lithium hex-1-ynyl tellurolate. In contrast (n-C4H9CC)2Te has been the major tellurium-containing product when (C6H5)3CCl, 4-BrC6H4C(O)CH2Br, CH2CHCH2Br, ClCH2C(O)CH2Cl and ClCH2CCCH2Cl have been employed. The 1H-NMR spectra of alkyl hex-1-ynyl tellurides display deshielded resonances for the CHx (x=1, 2, 3) group directly bound to tellurium. In many cases, specific couplings between tellurium and hydrogen are observed around these resonances. Characteristic features in the 13C-NMR spectra include a shielding effect of the sp3 and sp carbons directly bound to tellurium, and a deshielding effect to the other sp carbon. Closer analysis of the 13C{1H}-NMR spectra reveals satellites due to coupling with tellurium. Nuclear magnetic resonances measurements of the 125Te nucleus show a correlation of 125Te chemical shift to the alkyl group of n-C4H9CCTeR. In addition, the 125Te-NMR spectra show a splitting of the 125Te nuclear magnetic resonances due to coupling through up to three bonds with 1H nuclei.