Strukturbestimmung von Di-tert-butyldiphosphatetrahedrane im Festkörper und in der Gasphase
Zusammenfassung der Projektergebnisse
Di-tert-butyldiphosphatetrahedrane, (PCCMe3)2, contains a tetrahedron consisting of two carbon and two phosphorus atoms. This simple hetero-tetrahedrane has a composition between those of the extremely strained tetra-tert-butyltetrahedrane (CCMe3)4 and the spherically aromatic molecules of white phosphorus P4. It is thus of fundamental interest for chemistry. The determination of an experimental structure of di-tert-butyldiphosphatetrahedrane turned out to be outstandingly challenging. Despite numerous attempts to determine the structure of the free molecule in the gas phase by gas electron diffraction, all effort failed due to the extreme combination of sensitivity of the compound towards temperature and light. Obtained diffraction patterns could not be described by di-tertbutyldiphosphatetrahedrane nor by its decomposition products or likely impurities or of mixtures thereof. Also challenging was the determination of a molecular structure in the crystalline state. A crystal of the liquid di-tert-butyldiphosphatetrahedrane, grown from a mixture with n-pentane at low temperatures and largely under exclusion of light, served as specimen for X-ray diffraction. The P−P bond length of di-tert-butyldiphosphatetrahedrane at 2.205(1) Å is similar to that in P4. The P−C bond lengths range from 1.845(2) to 1.849(2) Å and the C−C bond in the tetrahedron has a length of 1.458(2) Å, similar to that found in (tBuC)4. Di-tert-butyldiphosphatetrahedrane is a spherically aromatic molecule with a magnetically induced ring current of 19 nA T^−1, in between those of P4 and (tBuC)4 and exceeding that of benzene, the prototype of an aromatic molecule, at 12 nA T^−1.
