Atrane

An Atrane is a tricyclic molecule with three five-membered rings. It has a transannular dative bond by a nitrogen atom, depicted as A. The name "atrane" was first proposed by Mikhail Grigorievich Voronkov.

Various atranes are named depending on the central element, e.g. "silatrane" (E = silicon); "boratrane" (E = boron); "phosphatrane" (E = phosphorus), etc. It is also proposed that when Y = nitrogen, the prefix "aza" be inserted before "element" + "atrane" (azasilatrane, for example) because atranes wherein E = silicon and Y = oxygen have been referred to as just "silatranes". [John G. Verkade "Main group atranes: chemical and structural features" Coordination Chemistry Reviews volume 137 (1994) 233-295 233.]

Silatranes exhibit unusual properties as well as biological activity in which the coordination of nitrogen to silane plays an important role.

The transannular coordinate bond in atranes can be stretched (quasiatranes, B) and even broken (proatranes, C) by controlling their stereoelectronic properties. Proazaphosphatrane is a very strong non-ionic base and is utilized in various types of organic synthesis as an efficient catalyst.

In 2000, Robert R. Holmes and his co-workers reported a new class of silatranes that contain three six-membered rings and revealed that these atranes have weaker nitrogen donor interaction in comparison with corresponding ones bearing three five-membered rings. The degree of the interaction depends mainly on the electronegativity effects of an exocyclic ligand.

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