Molecules and macromolecules can undergo topologically complex dynamic processes such as knot-forming and multi-step folding sequences. However, there are only few examples of molecules that are able to turn themselves inside out. Dibridgehead diphosphine cages, e.g. P[(CH2)14]3P, can undergo such an isomerization by a ‘pull-through’ mechanism and the isomers thus obtained differ in the position of the lone pairs on the phosphorus atoms.1 Three isomers, namely, in,in, in,out and out,out have been identified with NMR studies. Here, the concept is further extended to asymmetric diphosphine dioxide cages with different chain lengths within one cage (Fig. 1). One example with two C14 and one C8 chain is shown below. Preliminary results suggest a similar pull-through mechanism with the oxygen atoms bound to phosphorus pointing in or out of the cage, in analogy to the lone pairs in the diphosphine cages. Variable-temperature and solid-state NMR studies of these diphosphine dioxide cages to investigate isomer interconversion are of utmost interest. Then, guest molecules with hydrogen bond donating abilities will be subjected to the diphosphine dioxide cages to examine host/guest interactions. Finally, the adsorption and mobility of dibridgehead diphosphine dioxide cages on silica surfaces will be explored by 31P solid-state NMR. The advantage of the diphosphine dioxide cage systems as compared to monofunctional phosphine oxides is that due to the sterics only one P=O group can interact with the surface (Fig. 1), while the other serves as an internal chemical shift and mobility standard.

Dibridgehead diphosphine dioxide cages: Syntheses and unusual structural features

249th National Meeting (2015)

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