Bicyclic cage molecules with large (usually more than 20-membered) rings consisting of flexible methylene groups or similar heteroatoms show unique properties regarding their stereochemistry since they are able to undergo in/out isomerization which provides a greater difference in reactivity than other isomers of those compounds. This conformational inversion process, the so-called homeomorphic isomerization, is documented for only a few dibridgehead hydrocarbons and amines.
To the best of our knowledge, methylene group-bridged cage diphosphines with larger rings have never been described in the literature so far. We report on the first dibridgehead diphosphine (2) with 30-membered rings which is obtained by demetallation of the gyroscope-like platinum(II) complex 1 in high yields. The single crystal X-ray structure determination of 2 reveals the out/out conformation in solid state whereas the precursor complex 1, due to the coordination of the platinum center, bears the in/in isomeric arrangement of the cage diphosphine. Thermal inversion of one bridgehead phosphorous atom of 2 leads to the in/out isomer 3, which represents the only conformationally stable isomer retaining the basic cage structure. The binuclear gold(I) complexes 4 and 5, readily available from the dibridgehead diphosphine 2 and (Me2S)AuCl, together with their single crystal X-ray structures, are also presented.