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

Alkyl hex-1-ynyl tellurides, n-C4H9C drop CTeR, where R=CH3, CH(CH3)(2), cy clo-C6H11, CH2CH(CH3)(2), CH2(CH2)(6)CH3, CH2(CH2)(10)CH3, CH2CH2CH(Br)CH3, CH2C6H5, 4-CH2C6H4NO2, CH2CH2C6H5 and CH2CH2OC6K5, have been prepared in g ood 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 degreesC the reaction with cy clo-hexyl halide has been conducted at lower temperature (- 30 degreesC). A lkyl chloro, bromo and iodo derivatives have provided the same products in the same yields. The reaction has produced n-C4H9C drop CTe(CH2)(5)TeC drop CC4H9-n when Br(CH2)(5)Br has been used as alkylating agent, while BrCH2CH 2CH(Br)CH3 has produced only the monotelluride compound n-C4H9C drop CTeCH2 CH2CH(Br)CH3 even when employing excess lithium hex-1-ynyl tellurolate. In contrast (n-C4H9C dropC)(2)Te has been the major tellurium-containing produ ct when (C6H5)(3)CCl, 4-BrC6H4C(=O)CH2Br CH2=CHCH2Br ClCH2C(=O)CH2Cl and Cl CH2CI drop CCH2Cl have been employed. The H-1-NMR spectra of alkyl hex-1-yn yl tellurides display deshielded resonances for the CHx (x = 1, 2. 3) group directly bound to tellurium. In many cases, specific couplings between tel lurium and hydrogen are observed around these resonances. Characteristic fe atures in the C-13-NMR spectra include a shielding effect of the sp(3) and sp carbons directly bound to tellurium, and a deshielding effect to the oth er sp carbon. Closer analysis of the C-13{H-1}-NMR spectra reveals satellit es due to coupling with tellurium. Nuclear magnetic resonances measurements of the Te-125 nucleus show a correlation of 125Te chemical shift to the al kyl group of n-C4H9C drop CTeR. In addition, the Te-125-NMR spectra show a splitting of the Te-125 nuclear magnetic resonances due to coupling through up to three bonds with H-1 nuclei. (C) 2001 Elsevier Science B.V. All righ ts reserved.