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2. E. Niecke and D.Gudat, Imino(oxo, thio and selenoxo)phosphoranes, in Multiple Bonds and Low Coordination in Phosphorus Chemistry, ed. M. Regitz and O. J. Scherer, Thieme Verlag, Stuttgart, 1990, pp. 405–410.
3. Das erste stabile Methylenoxophosphoran
4. The First Stable Methyleneoxophosphorane
5. V. von der Gönna , M.Nieger, E.Niecke, H.Beckmann, K.Krieger, G.Ohms and G.Großmann, XIIIth International Conference on Phosphorus Chemistry, Jerusalem, Israel, July 16–21, 1995, Abstr. 178.