Amidomethylation of elemental tellurium: synthesis and solid state structures of N-substituted amidomethyltellurium(IV & II) derivatives.

Amidomethylation of Te(0) (elemental tellurium) as well as Te(II) (aryltellurium bromide, in situ) proceeds readily under mild conditions. It involves oxidative insertion of low valent tellurium into the C-Br bond of N-substituted alpha-bromoacetamides and provides a direct synthetic route to the stable, crystalline amidomethyltellurium(IV) dibromides, (RR'NCOCH2)(2)TeBr2 (RR'N = Et2N (1b), MePhN (2b), Me(c-Hex)N (3b), O(CH2CH2)(2)N (4b)) and (Et2NCOCH2)ArTeBr2 (Ar = mesityl, 5b; 1-naphthyl, 6b). Biphasic bisulfite reduction of the dialkyltellurium dibromides afforded yellow to orange coloured amido functionalized symmetrical telluroethers, (RR'NCOCH2)(2)Te (RR'N = Et2N (1), MePhN (2), Me(c-Hex) N ( 3), O( CH2CH2) 2N ( 4)), of which compound 2 was isolated as a crystalline solid. Oxidation of the new dialkyltelluroethers with dihalogens (Br-2, I-2) or SO2Cl2 afforded the corresponding amidomethyltellurium(IV) dihalides, (RR'NCOCH2)(2)TeX2 (RR'N = Et2N, X = Cl (1a), Br (1b), I (1c); RR'N = MePhN, X = Cl (2a), Br (2b), I (2c); RR'N = Me(c-Hex)N, X = Cl (3a), Br (3b), I (3c); RR'N = O( CH2CH2) 2N, X = Cl (4a), Br ( 4b), I (4c)) that were characterized by elemental analyses and multinuclear (H-1, C-13, Te-125) NMR. Single crystal X-ray data on 1b, 1c, 2, 2b, 2c, 4b, 5b and 6b suggest that the N-substituted amidomethyl group acts as a small-bite chelating ligand, via intramolecular 1,4-Te center dot center dot center dot O coordination, towards the Te( IV) centre. Steric congestion around Te(IV) due to intramolecular secondary bonding interaction(s), reduced electrophilicity of Te(II) and the partial positive charge on N due to the resonating character of the amido group presumably prevents these atoms from participating in the intermolecular associative forces in the solid state. Instead, weak C-H center dot center dot center dot O and C-H center dot center dot center dot X H-bonding interactions take centre-stage in the self assembly.