Atranes are a class oftricyclic molecules that are fused to a common central bond. Unlike thepropellanes, the central bond is atransannulardative bond from aLewis base—typically nitrogen—at one bridgehead to aLewis acidic atom such as silicon or boron at the other bridgehead.[1] Each of the three rings is thereforeheterocyclic. Each of the rings is typically five atoms, or sometimes six atoms.[2] The name "atrane" was first proposed byMikhail Grigorievich Voronkov [ru].[1]
Various atranes are named depending on the centralelement, e.g. "silatrane" (E =silicon); "boratrane" (E =boron); "phosphatrane" (E =phosphorus),stannatrane (E =tin), etc. It is also proposed that when Y = nitrogen, the prefix "aza" be inserted beforeelement + "atrane" (azasilatrane, for example) because atranes wherein E = silicon and Y =oxygen have been referred to as just "silatranes".[4]
Bis-atranes are two atrane cages that are fused end-to-end, sharing the same Lewis-acid donor atom in two co-axial dative interations.[5]
Silatranes exhibit unusual properties, as the transannular coordinate bond in atranes can be stretched (quasiatranes) and even broken (proatranes). The strength (and multiplicity) of the central bond depends on thestereoelectronic properties of the surrounding ligands, theelectronegativity of the participating atoms, and the size of the rings. A strong driving force for the formation of the central bond is relief ofring strain from the otherwise-formed 8-membered rings.[4]
Atranes exhibit biological activity in which the coordination of nitrogen tosilane plays an important role. Some derivatives such asphenylsilatrane are highly toxic.
Proazaphosphatrane is a very strong non-ionicbase and is utilized in various types oforganicsynthesis as an efficientcatalyst.
