Reversibility in Reactions of Linker-Bridged Distannenes with Terminal Alkynes at Ambient Temperature

The
linker-bridged distannene [(2,6-Mes2)­C6H3Sn]2C12H8 (1) featuring an acenaphthene linker and the sterically demanding terphenyl
substituent ArMe (= C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3) was
prepared and characterized by single-crystal analysis, NMR spectroscopy,
as well as elemental analysis. Furthermore, the reactivity of distannene 1 and previously reported distannenes 2 and 3, bearing either a naphthalene or a 9,9-dimethylxanthene
backbone and the terphenyl substituent ArMe, as well as
bis­(stannylene) 4, featuring a 9,9-dimethylxanthene backbone
and the terphenyl substituent AriPr (= C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3), toward terminal alkynes at ambient temperature
was investigated, leading to the formal [2 + 2] cycloaddition products 5–9. The reactions of distannene 1 with trimethylsilylacetylene and phenylacetylene, the reaction
of distannene 2 with trimethylsilyl–acetylene,
as well as the reaction of bis­(stannylene) 4 with phenylacetylene
show reversibility, while distannenes 2 and 3 react irreversibly with phenylacetylene at room temperature. A van’t
Hoff analysis of variable-temperature 1H NMR spectra of
the cycloadduct of the reaction of distannene 1 with
trimethylsilylacetylene afforded a dissociation enthalpy (ΔHdiss) of 71.6 kJ·mol–1, which is in surprisingly good agreement with the results of accompanying
DFT calculations (ΔHdiss = 70.9
kJ·mol–1).