A Remarkable Solvent Effect on the Nuclearity of Neutral Titanium(IV)‐Based Helicate Assemblies. Issue 17 (18th March 2014)

• Record Type: Journal Article
• Authors: Weekes, David Michael; Diebold, Carine; Mobian, Pierre; Huguenard, Clarisse; Allouche, Lionel; Henry, Marc
• Is Part Of: Chemistry. Volume 20:Issue 17(2014)
• Page Start: 5092
• Page End: 5101
• Publication Date: 2014-03-18
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201304317
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The spontaneous self‐assembly of a neutral circular trinuclear Ti<sup>IV</sup>‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of <italic>n</italic>‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, <sup>13</sup>C CP‐MAS NMR and <sup>1</sup>H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by Δ<italic>H</italic>(toluene)=−30 kJ mol<sup>−1</sup> and Δ<italic>S</italic>(toluene)=+357 J K<sup>−1</sup> mol<sup>−1</sup>, whereas these values were Δ<italic>H</italic>(CH<sub>2</sub>Cl<sub>2</sub>)=−75 kJ mol<sup>−1</sup> and Δ<italic>S</italic>(CH<sub>2</sub>Cl<sub>2</sub>)=−37 J K<sup>−1</sup> mol<sup>−1</sup> for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by Δ<italic>H</italic>(CH<sub>2</sub>Cl<sub>2</sub>)=+127 kJ mol<sup>−1</sup> and Δ<italic>H</italic>(<italic>n</italic>‐pentane)=+644 kJ mol<sup>−1</sup> associated with a large positive entropy change Δ<italic>S</italic>=+1115 J K<sup>−1</sup>⋅mol<sup>−1</sup>. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to <italic>n</italic>‐pentane. Suggestions for increasing the stability of the ring helicate are given.</p> </abstract>