[(thf)Li₂{H₂CS(N^tBu)₂}]₂: Synthesis, Polymorphism, and Experimental Charge Density to Elucidate the Bonding Properties of a Lithium Sulfur Ylide

Abstract

Sulfur ylides (R 2 S + --CR 2 ) are widely used in organic synthesis for stereoselective epoxidations, cyclopropane formations, and ring expansion reactions. Nevertheless, their electronic properties are still under debate, because their ylenic textbook formulation (R 2 SdCR 2 ) contradicts the reactivity. In order to elucidate the electronic situation in a sulfur ylide, we present an experimental charge density study via multipole refinement and subsequent topological analysis based on high-resolution X-ray data of [(thf)Li 2 {H 2 CS(N t Bu) 2 }] 2 (1). The title compound is of special interest, since additionally the formal hypervalency can be investigated along with the controversial interaction between a carbanion with a Li 3 triangle. As a prerequisite for these studies, the polymorphism and synthesis of 1 were investigated. The findings clearly support the ylidic, non-hypervalent description of the molecule. The ylidic carbanion was determined to be 6-fold coordinated with three single bonds to the sulfur atom and both hydrogen atoms and three closed-shell interactions to the lithium atoms of the Li 3 triangle.

Electron density distribution in tetralithium hypodiphosphate hexahydrate, Li4P2O6·6H2O

“…The Bader and Hirshfeld charges of the water oxygen OW atom are higher than the respective charges of the P-bonded O atom. The Bader Li charges are practically the same as reported earlier (Deuerlein et al, 2008;Mermer & Starynowicz, 2011), whereas the Hirshfeld ones are slightly lower than the previously reported and the theoretical values. It may also be noticed that Q H of the hexacoordinate Li2 is somewhat higher than Q H of the tetrahedral Li1 -probably because of larger Li-O distances in the former case.…”

Meaningful Structural Descriptors from Charge Density

“…The use of the density-related bonding angles leads to a higher agreement with those anticipated from the VSEPR theory (Figure 8). [73][74][75][76][77] Covalent bonds are characterized by an overlapping of the valence shells, more specific the VSCCs, which refer to the valence shell regions of the bonding partners. This causes an accumulation of charge density (5 2 1A C H T U N G T R E N N U N G (r BCP ) < 0) in the bonding region and therefore at the BCP.…”

“…is especially interesting, [77] as in addition to the formal hypervalency discussed above, the controversial interaction of a carbanion with a Li 3 triangle can be investigated. The coordination of a carbanion to a Li 3 triangle, [109] a structural motif wellknown throughout organolithium chemistry, is also present…”

Catalytic Abilities of [(C6F5)2BR] (R=NC4H4and NC4H8) Deduced from Experimental and Theoretical Charge‐Density Investigations

“…[9] These charges originate from bond polarization effects as well as from charge transfer between the atoms. [18] The integrated charges are given in Table 2, together with the atomic net charges, which are calculated from the difference in the number of valence electrons and the refined mono-A C H T U N G T R E N N U N G pole populations of the atoms. The integrated charges of the nitrogen atoms are about one order of magnitude higher than the net charges.…”