Low‐Temperature X‐ray Crystal‐Structure Analysis of the Thermally Unstable Lithiated 2‐Butenyl tert‐Butyl Sulfide: A comparison with model ab initio MO calculations

Abstract

AbstractSingle crystals of the N,N,N′,N′‐tetramethylethylenediamine (TMEDA) complex 6 of the title compound have been isolated. Compound 6 decomposes in the crystalline state above −20°. From the bond lengths and angles obtained by X‐ray crystal‐structure analysis (data collected at −70°), compound 6 is best described as a (E)‐1‐(tert‐butylthio)‐1‐lithio‐2‐butene with the double bond acting as an additional ligand on lithium (unsymmetrical allylic group). The S‐atom is in a cisoid arrangement in a common plane with the four C‐atoms of the butenyl system. The t‐Bu group and the Li‐atom are located above and below this plane. The structure is discussed with respect to the reactivity of 6 (α/γ reactivity). The gross structure is reproduced surprisingly well by an ab initio SCF MO calculation of the model lithiopropene‐1‐thiol 7(HS instead of t‐BuS, CH2 instead of CHCH3, no solvation of Li). The prominent difference is the symmetry of the allyllic moiety in the calculated structure.