Mechanochemically Driven Transformations in Organotin Chemistry: Stereochemical Rearrangement, Redox Behavior, and Dispersion-Stabilized Complexes

Ball milling a mixture
of the bulky allyl K­[A′] {[A′]
= [1,3-(SiMe3)2C3H3]−} and SnCl2 in a 2:1 ratio for 5 min leads
to the tris­(allyl) stannate [SnA′3K]∞, which forms a coordination polymer in the solid state. Longer grinding
of the 2:1 mixture (15 min), or the use of a 3:1 ratio of reagents,
initiates a disproportionation reaction and the chiral tetra­(allyl)­tin
species [SnA′4] is produced. A small amount of a
diastereomeric [SnA′4] complex with meso symmetry can also be isolated with extended grinding. These products
have been structurally authenticated with single-crystal X-ray crystallography.
The tetra­(allyl) species [SnA′4] are sterically
crowded and decompose relatively quickly (<1 h) in hydrocarbon
solvents. In the solid state, they are much more persistent (several
months) and evidently owe their stability to internal London dispersion
interactions, as evidenced by multiple close H···H′
interligand contacts. Dispersion-corrected DFT calculations have been
used to confirm the critical contribution of dispersion interactions
to their stability. None of these products are available in their
isolated forms from solution-based reactions, demonstrating the ability
of mechanochemical activation to access otherwise unobtainable transformations
in organotin chemistry.