| Abstrakt: |
Alkyl(2,6-dimethoxyphenyl)tellurium dihalides, RArTeX2 [Ar = 2,6-(MeO)2C6H3; X = Cl 2ac, Br 3ac, I 4ac; R = Me a, Et b, i-Pr c] were prepared by the reactions of alkyl 2,6-dimethoxyphenyl telluride, RArTe 1, with SOCl2, Br2 or I2, respectively. The rotational barrier ΔG of the Ar-group around the TeC bond in 2ac, 3ac and 4ac estimated by variable temperature 1H NMR spectra was dependent on the alkyl (R) group as well as on the halogen atoms. It decreased in the order R = Me > Et > i-Pr as well as X = Cl > Br > I. The 125Te resonances of 1 were observed at higher magnetic fields than those of RPhTe, and those of 1ac, 2ac, 3ac and 4ac shifted to lower magnetic field in the order R = Me > Et > i-Pr. The X-ray crystallographic analyses of 2ac, 3a, 3b and 4a showed that the geometry around tellurium was pseudo-trigonal bipyramidal with the alkyl group, the Ar group and a lone pair of electrons in the equatorial positions and with two halogen atoms in the apical positions. Whereas each of the TeC(Ar) bond distances were very similar [2.10 ± 0.01 Å], the TeC(R) bonds of 2ac were longer than TeC(Ar) and increased in length in the order R = Me < Et < i-Pr. The C(Ar)TeC(R) bond angles also increased in the order R = Me < Et < i-Pr. These molecules were bridged by intermolecular Te⋯X bonding to form dimers or polymers. Based on these results and VSEPR theory, the dependence of the rotational barrier ΔG of the Ar-group in RArTeX2 on the R-group is discussed. |
