Issue 2, 2004

A paradigm shift in the construction of heterobimetallic complexes: Synthesis of group 2 & 4 metal–calix[6]arene complexes

Abstract

Deprotonation of calix[6]arenes with barium in methanol followed by the addition of [Ti(OPri)4] or [Zr(OBun)4] is effective in the formation of novel dimeric 2 ∶ 1 barium–titanium(IV)/zirconium(IV) calix[6]arene complexes. In these complexes a central Ti(IV)/Zr(IV) coordinated in the exo-position connects the two calix[6]arenes in the 1,3-alternate conformation, each with an endo-barium sharing common phenolate groups with the titanium/zirconium centre and participating in cation–π interactions. A homometallic barium calix[6]arene dimer was also prepared wherein the calix[6]arenes are in the 1,3-alternate conformation with each coordinating one endo- and one exo-barium centre. The exo-barium cations connect the two calix[6]arenes through bridging methanol ligands. In this and the heterometallic complexes, cation–π complexation of the Ba2+ ion within the 1,3 alternate conformation of calix[6]arene facilitates the formation of the dimeric complexes in methanol. In contrast, the smaller Sr2+ ion did not form similar complexes in methanol, and the formation of an analogous 2 ∶ 1 strontium–titanium calixarene complex required the use of the more sterically demanding donor alcohol, isopropanol, the resulting complex being devoid of cation–π interaction. The results show (i) that a subtle interplay of solvation strength, coordination array type and cavity/cation size influences the accessibility of heterobimetallic complexes based on calix[6]arenes, and (ii) a synergistic endoexo binding behaviour.

Graphical abstract: A paradigm shift in the construction of heterobimetallic complexes: Synthesis of group 2 & 4 metal–calix[6]arene complexes

Article information

Article type
Paper
Submitted
15 Oct 2003
Accepted
01 Dec 2003
First published
11 Dec 2003

Dalton Trans., 2004, 327-333

A paradigm shift in the construction of heterobimetallic complexes: Synthesis of group 2 & 4 metal–calix[6]arene complexes

A. J. Petrella, D. C. Craig, R. N. Lamb, C. L. Raston and N. K. Roberts, Dalton Trans., 2004, 327 DOI: 10.1039/B312919E

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