and of a trace of the 2:1 host-guest complex with as guest the symmetrical diurea-diammonium ion resulting from the reaction of the diisocyanate with two equiv. of cadaverine (Figure ). The formation of this minor by-product is probably due to the reaction between the two hostguest complexes Ox3⸧CadNH 3 + and Ox3⸧CadNH 3 + NCO upon the addition of the diisocyanate. Note that attempts to totally prevent the formation of this by-product (either through slow addition of complex Ox3⸧CadNH 3 + to the diisocyanate or fast addition of the diisocyanate to the complex Ox3⸧CadNH 3 + ) failed. The 1 H NMR spectrum of Ox3⸧CadNH 3 + NCO remained unchanged after 20h, indicating the remarkable stability of the included guest. The preparation and stabilization of such an ammonium-isocyanate derivative illustrates the power of the supramolecular protection approach. Further reaction of Figure . H NMR spectra (298 K, 400 MHz, CDCl 3 /CD 3 CN 9:1) of Ox3 (3 mM) + 0.9 equiv. cadaverine + 0.9 equiv. PicH + 0.9 equiv. 1,3-phenylene diisocyanate (a); Ox3 (3 mM) + 0.9 equiv. putrescine + 0.9 equiv. PicH (b) and protected diamino-diurea derivative 4.2H + (c). S: residual solvents; w: residual water; g: grease; *: symmetrical diurea-diammonium by-product.