Investigations of the TeCl4−tBuNHLi Reaction: Synthesis, X-ray Structures, and Fluxional Behavior of the Tellurium−Nitrogen Compounds [Li2Te(NtBu)3]2, {[LiTe(NtBu)2(NHtBu)]2LiCl}2, and {Te2(NtBu)4[LiTe(NtBu)2(NHtBu)]LiCl}2

Abstract

The reaction of ^tBuNHLi with TeCl₄ in toluene at −78 °C produces ^tBuNTe(μ-N^tBu)₂TeN^tBu (1) (55%) or [(^tBuNH)Te(μ-N^tBu)₂TeN^tBu]Cl (2) (65%) for 4:1 or 7:2 molar ratios, respectively. The complex {Te₂(N^tBu)₄[LiTe(N^tBu)₂(NH^tBu)]LiCl}₂ (5) is obtained as a minor product (23%) from the 4:1 reaction. It is a centrosymmetric dimer in which each half consists of the tellurium diimide dimer 1 bonded through an exocyclic nitrogen atom to a molecule of LiTe(N^tBu)₂(NH^tBu) which, in turn, is linked to a LiCl molecule. Crystals of 5 are monoclinic, of space group C2/c, with a = 27.680(6) Å, b = 23.662(3) Å, c = 12.989(2) Å, β = 96.32(2)°, V = 8455(2) ų, and Z = 4. The final R and R_w values were 0.046 and 0.047. At 65 °C in toluene solution, 5 dissociates into 1, LiCl, and {[LiTe(N^tBu)₂(NH^tBu)]₂LiCl}₂ (4), which may also be prepared by treatment of [Li₂Te(N^tBu)₃]₂ (6) with 2 equiv of HCl gas. The centrosymmetric structure of 6 consists of a distorted hexagonal prism involving two pyramidal Te(N^tBu)₃^2- anions linked by four Li atoms to give a Te₂N₆Li₄ cluster. Crystals of 6 are monoclinic, of space group P2₁/c, with a = 10.194(2) Å, b = 17.135(3) Å, c = 10.482(2) Å, β = 109.21(1)°, V = 1729.0(5) ų, and Z = 2. The final R and R_w values were 0.026 and 0.023. VT ¹H and ⁷Li NMR studies reveal that, unlike 1, compounds 2, 4, and 6 are fluxional molecules. Possible mechanisms for these fluxional processes are discussed.