Reactions of some ortho-tellurated compounds with intramolecular co-ordinate bonds

Abstract

Reaction of 2-(Br₃Te)C₆H₄CHNC₆H₄Me-p1 with BH₄^– results in reduction at both the tellurium and double-bond centres to afford 2-(BrTe)C₆H₄CH₂NH(C₆H₄Me-p)2, however substitution of p-tolyl by a more sterically demanding group such as 2,4,6-tri-tert-butylphenyl precludes reduction of the double bond. The crystal and molecular structure of 2 has been determined: monoclinic, space group P2₁/n, with a= 11.010(4), b= 9.231(2), c= 14.862(7)Å, β= 110.80(4)° and Z= 4; R= 0.0533 for 1180 observed reflections. The tellurium atom is three-co-ordinate with Br–Te–N 165.3(3), Br–Te–C(1) 91.5(4) and N–Te–C(1) 74.9(5)° and Te–C(1) 2.125(16), Te–Br 2.663(3)Å and a Te ⋯ N interaction of 2.375(13)Å. A survey of available structural data for ortho-tellurated compounds suggests this interaction to be stronger when the donor nitrogen atom is sp² rather than sp³ hybridised. A multinuclear (¹H, ¹³C, ¹²³Te, ¹²⁵Te) and variable-temperature (¹H) NMR study of compound 2 in chloroform solution is interpreted in terms of an equilibrium between N(sp³) co-ordinated and non-co-ordinated forms. New multinuclear (¹H, ¹⁹F, ¹²³Te) NMR together with Raman data for related compounds containing Te ⋯ N(sp²) interactions e.g. 2-XTeC₆H₄CHNC₆H₄Me-p(X = F, Cl, Br or I) provide further support for the reality of the intramolecular co-ordination and ν(Te–N) is assigned in the region 206–219 cm^–1.