Complex Formation Involving Calixarenes

Complex Formation Involving Calixarenes 7.1 Solid State Complexes with Neutral Molecules... 

Chloroform solutions of calixarenes (33 38)293,354 show high affinity for Au111 and good selectivity over Fe111 in some cases.293 Spectroscopic data indicate that complex formation with thioethoxy calix[4]arenes involves formation of inner-sphere complexes with Au—S bonds.354... 

Supramolecular catalysis may also involve the combination of a host cavity and a metal active site as in the bis(diphenylphosphino)calix[4]arene nickel(II) complex 12.40 which acts as an efficient catalyst for ethylene and propylene polymerisation, and in tandem with zirconocene dichloride, for the formation of linear low-density polyethylene. In the latter case the complex gives very little branching - a significant advantage. The key to the effectiveness of the catalyst involves calixarene-induced changes in the bite angle at the Ni(II) centre, which is square planar in the active form of the catalyst.29... 

There is only eight crystal structures of calix[7]arenes deposited in CSD. The reason for this is much more difficult synthesis of seven-membered calixarenes and/or difficulties in obtaining monocrystals of this compounds and their complexes/co-crystals. Like for smaller calixarenes discussed above also here the self-inclusion of one of the substituent may occur like in para-t-hvXy -carboxymethoxycalix[7]arene/deuterochloroform clathrate (Fig. 38.25a) [52] or inclusion complexes are obtained. For the later, due to a great degree of flexibility, many conformations of calixarene host molecule is possible but the most observed is a double partial cone, e.g. 1 2 para-t-butyl-calix[7]arene/pyridine inclusion complex where one guest molecule is located in each partial cone cavity (Fig. 38.25b) [53]. In one case the flattened cone conformation was found where the (Fig. 38.25c). In this crystal structure one toluene and one disordered benzene/ toluene molecule are involved in inclusion complex formation with one para-t-butyl-calix[7]arene molecule [54]. 

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