Borophosphonate Cages

The borophosphonate cages described in what follows are also analogues of silasesquioxanes 93. In contrast to the cage-like borasiloxanes discussed above. 

All borophosphonates obtained so far are air and thermally stable (m.p. 210 °C). They are soluble in all common organic solvents if they carry bulky groups either on phosphorus or on boron. Borophosphonates that contain only methyl or phenyl groups show poor solubility [140]. H-, B-, and P-NMR spectra are in agreement with the highly symmetric silasesquioxane-type structure in solution [140, 141]. 

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Waiawalkar. M, G, Murugavel, R, Roesky. H, W, Schmidt, H,-G, The first molecular borophosphonate cage Synthesis, spectroscopy. and single-crystal X-ray structure, Organometallics 1997. 16, 516-51B,... 

Severin and co-workers have demonstrated that borophosphonate cages of the general formula [f-BuP03BR]4 (376) could be obtained in good to excellent yields by condensation of te/t-butylphosphonic acid with boronic acids (Scheme 131). ... 

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