Clathrates of allene dimers. X-ray crystal structures of two inclusion compounds with p-xylene and phenyloxirane

Allene dimers of the 1,2-dimethylenecyclobutane-type with bridged aromatic groups (fluorenylidene units) and extra substituents (Me, t-Bu)2a-c have been synthesized and characterized by elemental analysis and spectroscopic data. Their crystal inclusion properties are reported. The unsubstituted compound 2a yields only an inclusion compound with p-xylene, while methyl-substituted 2b enclathrates a broad range of molecules. On the other hand, the t-butyl-substituted 2c does not form clathrates, crystallizing as a pure compound. Complete structural descriptions of the two inclusion compounds 2a-p-xylene (2:1) and 2b-phenyloxirane (1:1) are given. They represent interstitial clathrates. Crystallographic data of the 1:1 p-xylene clathrate of 2b (which is isomorphous to its phenyloxirane analog) and of unsolvated 2c are also reported. As indicated by the results, substitutional effects critically influence the inclusion properties of the new clathrate family.