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

Antonella J. Petrella, Donald C. Craig, Robert N. Lamb, Colin L. Raston, Nicholas K. Roberts

Research output: Contribution to journalArticle

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 endo–exo binding behaviour.

Original languageEnglish
Pages (from-to)327-333
Number of pages7
JournalJournal of the Chemical Society. Dalton Transactions
Volume4
Issue number2
DOIs
Publication statusPublished - 8 Jan 2004
Externally publishedYes

Keywords

  • Alkaline-earth metals
  • Calixarenes, crown ethers, cryptands, cyclophanes
  • Coordination chemistry
  • Titanium
  • Zirconium

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