Non-Covalent Synthesis of Calix[4]arene-Capped Porphyrins in Polar Solvents via Ionic Interactions.

Non-covalent synthesis of calix[4]arene capped porphyrins can be achieved in polar solvents (up to 45% molar fraction of water) via ionic interaction. Thus tetracationic meso-tetrakis(N-alkylpyridinium-3-yl) porphyrins 1a–d and tetra anionic 25,26,27,28-tetrakis(2-ethoxyethoxy)-calix[4]arene tetrasulfonate 2 self-assemble in an entropy driven process in 1:1 stoichiometry with association constants K1·2 as high as 107 M−1 in methanol. The thermodynamic stability remains high even in the presence of competing salts: 10−2 M Bu4NClO4 (4500 times the concentration of the building blocks) gives a reduction in K1·2 of only 10 times. Ternary complexes 1a·2·L using 1-methylimidazole or pyridine as axial ligands (L) have been obtained with L residing outside the assembly cavity.