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)

Abstract

The strong Lewis acid tungsten oxo complex of calix[4]arene can be obtained in both hydrated and non-hydrated 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) Å for the tungsten oxo complex of calix[4]arene··H2O·aniline (1), and the tungsten oxo complex of calix[4]arene·H2O·toluene (2·toluene), respectively. The strong interactions are also deduced by the relatively high H2O elimination temperature observed by TGA and DSC (above 200 °C). The coordinated water molecule inside the calix[4]arene cavity is characterized by a strong IR absorption at 3616 cm–1, and a narrow resonance at ~1.2 ppm (the chemical shifts of the uncoordinated water are 1.55 and 1.60 ppm in C6D6 and CDCl3, 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 H2O as the characteristic signatures are observed. The successful removal of H2O 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 H2O 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) Å). The tetra-5,11,17,23-choromethyl-25,26,27,28-tetrahydroxycalix[4]arene reacts with M(O)Cl4 (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.

Molybdocalixarene Structure Control via Rim Deprotonation. Synthesis, Characterization, and Crystal Structures of Calix[4]arene Mo(VI) Monooxo Complexes and Calix[4]arene Alkali Metal/Mo(VI) Dioxo Complexes

“…The scarcity of oxomolybdenum(VI) calixarene complexes has been noted, despite the fact that they “are of interest as models of heterogeneous metal-oxide catalyst surfaces, centers capable of supporting organometallic transformations, and as building blocks for supramolecular structures.” , One dioxomolybdenum(VI) dimethylcalixarene has been reported, as well as some monooxomolybdenum(VI) calixarenes, − one of which is virtually insoluble in organic solvents and therefore intractable …”

Organic guests inclusion by tungsten-calix[4]arene hosts

“…However, the first one is a molybdenum complex, 17 whereas the second is a tungsten calix [4]arene complex in which a disordered aniline molecule is present in the second coordination sphere. 14 This prevents any other speculation on the intermolecular interaction occurring in this latter complex.…”

Detection and Differentiation of Neutral Organic Compounds by 19F NMR with a Tungsten Calix[4]arene Imido Complex

“…8 Among the various metallated calixarene complexes, tungsten-oxo complex stands out as being particularly stable and has a restrictive binding site capable of binding small Lewis basic organic molecules. 9 Despite the highly specific recognition properties of these complexes, their application in sensing is largely unexplored. In 2002, we reported a conducting polymer incorporated with calixarene tungsten-oxo complex and observed a change of polymer’s conductivity in the presence of certain organic molecules.…”

“…12 These methods necessitated the preparation of air-sensitive intermediates, and as an alternative we attempted to incorporate the imido moiety by direct imination of the corresponding calix[4]arene tungsten-oxo which is stable and readily prepared. 9 Although WOCl 4 can be transformed to W(=NR)Cl 4 by reaction with isocyanates, 13 no conversion was observed under the same conditions with calix[4]arene tungsten-oxo as a result of the increased electron density on tungsten metal and rigid geometry imposed by the calix[4]arene. In analogy to Wittig reactions, which are driven to completion by the strong phosphorous oxygen bond, 14 we envisioned the direct imination of the calix[4]arene tungsten-oxo could be achieved by an analogous iminophoshorane (Ph 3 P=NR) reagent.…”

“…In contrast, metalated calixarene complexes tend to be higher affinity receptors as a result of the presence of the Lewis acidic metal centers . Among the various metalated calixarene complexes, tungsten–oxo complex stands out as being particularly stable and has a restrictive binding site capable of binding small Lewis basic organic molecules . Despite the highly specific recognition properties of these complexes, their application in sensing is largely unexplored.…”