Deprotonation of calixarenes 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) calixarene complexes. In these complexes a central Ti(iv)/Zr(iv) coordinated in the exo-position connects the two calixarenes 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 calixarene dimer was also prepared wherein the calixarenes are in the 1,3-alternate conformation with each coordinating one endo- and one exo-barium centre. The exo-barium cations connect the two calixarenes through bridging methanol ligands. In this and the heterometallic complexes, cation–π complexation of the Ba2+ ion within the 1,3 alternate conformation of calixarene 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 calixarenes, and (ii) a synergistic endo–exo binding behaviour.
|Number of pages||7|
|Journal||Journal of the Chemical Society. Dalton Transactions|
|Publication status||Published - 8 Jan 2004|
- Alkaline-earth metals
- Calixarenes, crown ethers, cryptands, cyclophanes
- Coordination chemistry