Designing a Solution-Stable Distannene: The Decisive Role of London Dispersion Effects in the Structure and Properties of {Sn(C<sub>6</sub>H<sub>2</sub>-2,4,6-Cy<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(Cy = Cyclohexyl)
Cary R. Stennett, Markus Bursch, James C. Fettinger, Stefan Grimme, Philip P. Power
Abstract
The reaction of 1 equiv of the dimeric lithium salt of a new London dispersion effect donor ligand {Li(C6H2-2,4,6-Cy3)·OEt2}2 (Cy = cyclohexyl) with SnCl2 afforded the distannene {Sn(C6H2-2,4,6-Cy3)2}2 (1). The distannene remains dimeric in solution, as indicated by its room-temperature 119Sn NMR signal (δ = 361.3 ppm) and its electronic spectrum, which is invariant over the temperature range of −10 to 100 °C. The formation of the distannene, which has a short Sn–Sn distance of 2.7005(7) Å and greatly enhanced stability in solution compared to that of other distannenes, is due to increased interligand London dispersion (LD) attraction arising from multiple close approaches of ligand C–H moieties across the Sn–Sn bond. DFT-D4 calculations revealed a dispersion stabilization of dimer 1 of 38 kcal mol–1 and a dimerization free energy of ΔGdimer = −6 kcal mol–1. In contrast, the reaction of 2 equiv of the similarly shaped but less bulky, less hydrogen-rich Li(C6H2-2,4,6-Ph3)·(OEt2)2 with SnCl2 yielded the monomeric stannylene Sn(C6H2-2,4,6-Ph3)2 (2), which is unstable in solution at ambient temperature.