TY - JOUR
T1 - A paradigm shift in the construction of heterobimetallic complexes
T2 - Synthesis of group 2 & 4 metal–calix[6]arene complexes
AU - Petrella, Antonella J.
AU - Craig, Donald C.
AU - Lamb, Robert N.
AU - Raston, Colin L.
AU - Roberts, Nicholas K.
PY - 2004/1/8
Y1 - 2004/1/8
N2 - 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.
AB - 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.
KW - Alkaline-earth metals
KW - Calixarenes, crown ethers, cryptands, cyclophanes
KW - Coordination chemistry
KW - Titanium
KW - Zirconium
UR - http://www.scopus.com/inward/record.url?scp=85034343039&partnerID=8YFLogxK
U2 - 10.1039/b312919e
DO - 10.1039/b312919e
M3 - Article
AN - SCOPUS:85034343039
SN - 1477-9226
VL - 4
SP - 327
EP - 333
JO - Journal of the Chemical Society. Dalton Transactions
JF - Journal of the Chemical Society. Dalton Transactions
IS - 2
ER -