Experimental and theoretical investigations of tellurium(IV) diimides and imidotelluroxanes:: X-ray structures of B(C6F5)3 adducts of OTe(μ-NtBu)2TeNtBu, [OTe(μ-NtBu)2Te(μ-O)]2 and tBuNH2

The hydrolysis of 'BuNTe(mu-(NBu)-Bu-t)(2)TeN'Bu (1) with 1 or 2 equiv of (C6F5)(3)(BH2O)-H-. results in the successive replacement of terminal imido groups by oxo ligands to give the telluroxane-Lewis acid adducts (C6F5)(3)(BOTe)-O-.(mu-(NBu)-Bu-t)(2)TeN'Bu (2) and [(C6F5)(3)(BOTe)-O-.(mu-N'Bu)(2)Te(mu-O)](2) (3), which were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Te=O distance in 2 is 1.870(2) Angstrom. The di-adduct 3 involves the association of four (BuNTeO)-Bu-t monomers to give a tetramer in which both terminal Te=O groups [d(TeO) = 1.866(3) Angstrom] are coordinated to B(C6F5)(3). The central Te2O2 ring in 3 is distinctly unsymmetrical [d(TeO) = 1.912(3) and 2.098(2) Angstrom]. The X-ray structure of (C6F5)(3)(BNH2Bu)-N-.-Bu-t (4), the byproduct of these hydrolysis reactions, is also reported. The geometries and energies of tellurium(IV) diimides and imido telluroxanes were determined using quantum chemical calculations. The calculated energies for the reactions E(NR)(2) + Te(NR)(2) (E = S, Se, Te; R = H, Me, Bu-t, SiMe3) confirm that cyclodimerization of tellurium(IV) diimides is strongly exothermic. In the mixed-chalcogen systems, the cycloaddition is energetically favorable for the Se/Te combination. The calculated energies for the further oligomerization of the dimers XE(mu-NMe)(2)EX (E = Se, Te; X = NMe, O) indicate that the formation of tetramers is strongly exothermic for the tellurium systems but endothermic (X = NMe) or thermoneutral (X = O) for the selenium systems, consistent with experimental observations.