Tin—Tin π Bonding as a Conduit for Alkali-Metal Reduction

Reactions of the doubly reduced distannynes, [Ar′SnSnAr′M2], (Ar′ = C6H3-2,6-Dipp; M = Li, Na, K), with the successively heavier group 1 elements (M′) result in reduction of M and the isolation of [Ar′SnSnAr′M′2]. Although the viability of these observations, along with the reversible formation of [Ar′SnSnAr′K2] by treatment of [Ar′SnSnAr′Rb2] with potassium, is successfully predicted by a combined theoretical and thermochemical analysis, assessment of the bonding within [Ar′SnSnAr′M2] suggests that any M+ ns valence orbital contribution should be too high in energy to effect M+ reduction. Based on a consideration of the Sn─Sn π bonding and theoretical assessment of the resultant frontier orbitals, however, we suggest that the electron transfer necessary for M+ reduction, occurs intramolecularly and via a suitably disposed π* SOMO of the putative radical anions, [Ar′SnSnAr′M2]•−.