Experimental evidence for hypercoordination in triorganotelluronium halides with 2-(Me2NCH2)C6H4 groups

Abstract

Heteroleptic triorganotelluronium chlorides of the type [RPh₂Te]⁺Cl⁻ (1) and [R₂PhTe]⁺Cl⁻ (4) [R = 2-(Me₂NCH₂)C₆H₄] were obtained by reacting Ph₂TeCl₂ with RLi in 1 : 1 and 1 : 2 molar ratios. The reaction of TeCl₄ with RLi (a 1 : 3 molar ratio) afforded a mixture of [R₃Te]⁺Cl⁻ (7) and [R₂Te(OH)]⁺Cl⁻ (10) after separation by column chromatography. Halogen exchange reactions using KX resulted in the corresponding [RPh₂Te]⁺X⁻ [X = Br (2), I (3)], [R₂PhTe]⁺X⁻ [X = Br (5), I (6)] and [R₃Te]⁺X⁻ [X = Br (8), I (9)]. The compounds were characterized by multinuclear NMR spectroscopy and mass spectrometry. The NMR spectra are similar for each series of triorganotelluronium halides (1–3, 4–6 and 7–9, respectively) and no clear evidence for N→Te interactions in solution could be concluded at room temperature, except in the case of compounds 4–6 for which the ¹H resonance of the CH₂N protons in the pendant arms appears as an AB spin system. For compounds 7 and 10 the low temperature ¹H and ¹³C NMR spectra are consistent with intramolecularly coordinated pendant arms. The solid state structures for compounds 1, 1·0.5CH₂Cl₂, 3, 4·H₂O, 5·H₂O, 6, 7·H₂O and 10 were determined by single-crystal X-ray diffraction. For all compounds the nitrogen atom of a pendant arm is involved in an intramolecular N→Te interaction in the range 2.571(3)–2.839(8) Å. This results in hypercoordinated triorganotelluronium(IV) cations with different distorted coordination geometries: “see saw” in 1–3, square pyramidal in 4–6 and 10, and octahedral in 7. Further secondary interactions between cations, anions and water molecules were observed in the crystals of these species, resulting in different supramolecular associations.