New insights about the host-guest chemistry of the tungsten oxo complex of calix[4]arene, and novel 'one pot' difunctionalizations of calix[4]arene using tetrachlorometal(VI) oxide (M = Mo, W)

The strong Lewis acid tungsten oxo complex of calix[4]arene can be obtained in both hydrated and nonhydrated forms. This complex coordinates a water molecule inside the cavity via strong O ... W interactions with relatively short distances of 2.284(4) and 2.329(2) [Angstrom] for the tungsten oxo complex of calix[4]arene*[H.sub.2]O *aniline (1), and the tungsten oxo complex of calix[4]arene*[H.sub.2]O *toluene (2*toluene), respectively. The strong interactions are also deduced by the relatively high [H.sub.2]O elimination temperature observed by TGA and DSC (above 200 [degrees]C). The coordinated water molecule inside the calix[4]arene cavity is characterized by a strong IR absorption at 3616 [cm.sup.-1], and a narrow resonance at ~1.2 ppm (the chemical shifts of the uncoordinated water are 1.55 and 1.60 ppm in [C.sub.6][D.sub.6] and CD[Cl.sub.3], respectively). This water molecule gives rise to H-bonds with aniline in 1. The tungsten oxo complex of 5,11,17,23-tetrabromocalix[4]arene (4), also binds [H.sub.2]O as the characteristic signatures are observed. The successful removal of [H.sub.2]O in 2, is performed under mild conditions using bis(tetrahydrofuran)-uranyl nitrate as a competitive Lewis acid. When this reaction is performed in acetonitrile, butyronitrile or tert-butylnitrile, the corresponding tungsten oxo complexes of calix[4]arene*acetonitrile (3), *butyronitrile (5), and *tert-butylnitrile (6) are obtained. The use of uranyl as a [H.sub.2]O abstractor is unprecedented. The X-ray structure of 3 consists of a tungsten oxo complex of calix[4]arene coordinated by an acetonitrile molecule (d(W ... N = 2.412(2) [Angstrom]). The tetra-5,11,17, 23-choromethyl-25,26,27,28-tetrahydroxycalix[4]arene reacts with M(O) [Cl.sub.4] (M = Mo, W) in a 1:1 stoichiometry, via a tetra Friedel--Crafts addition of benzene or toluene, followed by a lower-rim complexation of the metal oxide, to form "flower-shaped" calix[4]arenes. This "one pot" double functionalization is unprecedented. Key words: calix[4]arene, tungsten, molybdenum, X-ray, host-guest, Friedel--Crafts, Lewis acid, uranyl, DSC, TGA.