Counterintuitive Interligand Angles in the Diaryls E{C6H3-2,6-(C6H2-2,4,6-iPr3)2}2 (E = Ge, Sn, or Pb) and Related Species: The Role of London Dispersion Forces

Abstract

The straightforward reaction of two equivalents of the lithium salt of the bulky terphenyl ligand Li(OEt2)C6H3-2,6-(C6H2-2,4,6-iPr3)2 with suspensions of GeCl2·dioxane, SnCl2, or PbBr2 in diethyl ether resulted in the isolation of the very crowded σ-bonded diaryl tetrylenes of formula E{C6H3-2,6-(C6H2-2,4,6-iPr3)2}2 (E = Ge (1), Sn (2), Pb (3)) as blue crystalline solids. Despite their high level of steric congestion, X-ray crystallography showed that compounds 1–3 possess Cipso–E–Cipso interligand bond angles in the range 107.61–112.55°, which are narrower than those observed in analogous species with less bulky terphenyl substituents. Compounds 1–3 were characterized by 1H, 13C{1H} (1–3), and 119Sn{1H} (2) NMR spectroscopy, whereas solution 207Pb{1H} NMR spectroscopy of 3 has not yet afforded a signal under ambient conditions. FT-IR and UV–vis spectra of 1–3 were also recorded. The relatively narrow interligand angles displayed by 1–3 are attributed in part to the increase in London dispersion force int...