Aryl–Aryl Interactions in (Aryl‐Perhalogenated) 1,2‐Diaryldisilanes

Abstract

Three 1,2‐diaryltetramethyldisilanes X5C6‐(SiMe2)2‐C6X5 with two C6H5, C6F5, or C6Cl5 groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2‐dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X‐ray diffraction and for free molecules by gas electron‐diffraction. The solid‐state structures of the fluorinated and chlorinated derivatives are dominated by aryl–aryl interactions. Unexpectedly, Cl5C6‐(SiMe2)2‐C6Cl5 exists exclusively as an eclipsed syn‐conformer in the gas phase with strongly distorted Si‐C6Cl5 units due to strong intramolecular interactions. In contrast, F5C6‐(SiMe2)2‐C6F5 reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations.

Inter‐ and Intramolecular Aryl–Aryl Interactions in Partially Fluorinated Ethylenedioxy‐bridged Bisarenes**

“…On first sight, this parallel displaced arrangement of the aromatic groups seems to be disfavored because of the steric hindrance of the halogen substituents and the electrostatic repulsion through of the aromatic rings—although the centroid–centroid distances are quite short. Such eclipsed conformations were also found for the perhalogenated disilanes Ph X SiMe 2 SiMe 2 Ph X and are stabilized by London dispersion interactions [15] . Symmetric bisarenes without halogen substitution do not preferably arrange in folded sandwich structures.…”

“…[26] Within one column, the centroid-centroid distances alternate with 3.462(1) (A)a nd 3.550(1) (B; Figure 7). A is the shortest intermolecular aryl-aryl distance for partially fluorinated flexibly bridged bisarenes found so far for sandwich structures in the solid state [for example, shortest centroid-centroid distances:F 5 C 6 (CH 2 ) 2 SiMe 2 C 6 H 5 :3 .535(1) ; F 5 C 6 (SiMe 2 ) 2 C 6 H 5 :4 .425(1) ] [14][15] and is even shorter than in the C 6 F 6 /C 6 H 6 co-crystal (3.77 ). [16] The variation from phenyl to naphthyl group enables each group to form two aryl contacts in the solid state.…”

“…Gas-phase structures, that is, the structures of free molecules undistorted by intermolecular interactions,c an be determined by meanso fg as electron diffraction (GED).O wing to the very high effort to be spent, we chose 2 as am odel compound for the partially fluorinated ethylenedioxy-bridged bisarenes to be studied exemplarily in the contexto ft his present study.T he structure of 2 is suitable for comparison with those of other flexibly bridged bisarenes, we investigated earlier. [14,15,23] First, as earch for possible stable conformationso f2 was done theoretically by using the CREST program [19] utilizing the GFN2-xTB method [20] for solving the electronic problem. Structures with relative energies below 3kcal mol À1 were manually inspected and (symmetry) duplicates were sorted out.…”

“…Compounds with phenyl and perfluorophenyl rings bridged by (sila)propyl chains receive stabilization by intermolecular aryl–aryl stacking interactions in the solid state, [14] whereas free molecules, studied by gas electron diffraction (GED), find their energetic minima as conformers bearing intramolecular aryl–aryl interactions. 1,1,2,2‐Tetramethyldisilanes, substituted with symmetric or asymmetric pairs of phenyl and/or perhalogenated (F, Cl) phenyl groups also show strong π‐interactions [15, 16] . The aggregation in solid state was found to be significantly stabilized by intramolecular aryl–aryl interactions.…”

“…1,1,2,2-Tetramethyldisilanes, substituted with symmetric or asymmetric pairs of phenyl and/or perhalogenated (F,C l) phenylg roups also show strong p-interactions. [15,16] The aggregation in solid state was foundt ob es ignificantly stabilized by intramolecular aryl-aryl interactions. Gas electron diffraction and SAPT (symmetry-adaptedp erturbation theory) cal-culationsd emonstratet he untypical syn-conformers to be stabilized by large dispersion contributions.…”