Titanium complexes with calixarene

The unsubstituted para-t-butyl calixarenes themselves complex metals via their aryloxide groups. Since aryloxide complexes are frequently oligomeric, the simple calixarenes do not give monomeric complexes. Aryloxides are hard ligands, therefore they readily form complexes with oxo-philic hard metal ions such as alkali metals, early transition metals, lanthanides, and actinides. Complexation is often inferred because the calixarene acts as a carrier for the metal ion from an aqueous to an organic phase. With the /wa-/-butylcalix[ ]arenes in alkaline solution, a value of n = 6 gives the best carrier for lithium(I), sodium(I), and potassium(I), with a value of n 8 giving the best carrier for rubidium(I) and caesium(I).15,16 Titanium(IV) complexes have been characterized,17-19 as well as those of niobium(V) and tantalum(V).20-22 These complexes are classified as... 

X-Ray crystallographic structures of solid state complexes of several of the parent calixarenes with metal ions have been obtained, early examples including the titanium complexes of 4 and 6 , a complex containing two Eu ... 

Inherently chiral derivatives are also known from calix[8]arenes. Dimetalla complexes were obtained with titanium (as well as with Zr, V, Sn) in which the two titanium atoms have a pseudooctahedral environment bonded to all of the eight calixarene oxygens, two of which are bridging, and two isopropoxide oxygens. The C2 symmetry was proved by single crystal X-ray analysis and in solution by two-dimensional H-NMR spectroscopy [28]. Various complexes of r-butylcalix[8]arene with lanthanide ions have a similar structure [29]. 

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