Abstract
The thioester moiety is introduced as a lithium binding unit for the hierarchical formation of titanium(IV) catecholate‐based lithium‐bridged helicates. In solution, the coordination compounds show a monomer–dimer equilibrium which —in comparison to the oxo esters— is significantly shifted towards the monomers. In addition, the influence of the thioester side chain on the dimerization behavior is investigated and an expansible/compressible molecular switch is synthesized. In the latter case expansion and compression are performed reversibly in methanol, whereas in DMSO spontaneous expansion occurs.
Highlights
Thioesters are the „little brothers“ of oxoesters
In 2005, we described the first examples of hierarchically formed helicates[3] based on triple lithium-bridged titanium(IV) triscatecholates with carbonyl moieties in 3-position of the catechol ligand
This equilibrium can be well observed by NMR spectroscopy and kinetic as well as thermodynamic parameters can be obtained for dimer association/dissociation
Summary
Thioesters are the „little brothers“ of oxoesters. In comparison to the oxygen homologous, they are more reactive regarding the cleavage of the C(=O)ÀS bond. In the present study a series of thioester-substituted catechols has been synthesized and has been used to prepare the corresponding titanium(IV) complexes.[8] It is expected that the thioesters show some distinct differences in the stability of the hierarchical helicates compared to the ester complexes. This is due to the lower polarization of C=O of the thioester and a corresponding weaker binding of the lithium cations in the dimer.[9]. An example for an expansible/compressible helicate based on an alkyl-bridged bis(catechol thioester) is described and a special spontaneous expansion behavior is observed in [D6]DMSO
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