Disproportionation of Low Valent Indium Bromide: Synthesis and Molecular Structure of Bis (2,6-Dimesityl-Phenyl) Indium Bromide,(2,6-Mes 2 C 6 H 3 ) 2 InBr (Mes = 2,4,6-Me 3 C 6 H 2 ). When does Trigonal Planar Become T-Shaped?

Abstract

Bis(2, 6-dimesitylphenyl) indium bromide, (2, 6-Mes₂C₆H₃)₂ InBr (Mes = 2, 4, 6-Me₃C₆H₂), I, has been prepared and characterized by ¹H NMR, elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. I may be approached by either of two synthetic routes. Whereas I may be readily prepared from reaction of indium (III) bromide with (2, 6-dimesitylphenyl) lithium in Et₂O, it may also be approached by an interesting disproportionation of Br₂In-hBr₂ in the presence of (2, 6-Mes₂C₆H₃)Li. The title compound crystallizes in the monoclinic space group P2₁/n (No. 14) with unit cell parameters a = 12.341 ((2)Å, b = 20.799 (4) Å, c = 16.512 (2) Å, β = 101.18 (1)°, D_calcd = 1.31 g cm⁻³, and V = 4158 (l)ų for Z = 4. Refinement, based on 1661 observed reflections, converged at R = 0.072, R_w = 0.071. The In-Br bond distance is 2.505 (4) Å. As the steric demands of the two bulky ligands are sufficient to result in a C-In-C bond angle of 157.3 (8)° — the widest angle reported for a three-coordinate indium atom — the coordination about the metal center may be described as T-shaped.