Wide rim urethanes derived from calix[4]arenes: synthesis and self-assembly

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Macrocyclic Chemistry

Background:

• Calixarenes are versatile macrocyclic hosts capable of forming self-assembled structures.
• Urea and urethane functionalities can participate in hydrogen bonding, influencing self-assembly.
• Controlling the formation of specific supramolecular architectures is a key challenge.

Purpose of the Study:

• To synthesize novel calixarene derivatives with varying urethane and urea substitutions.
• To investigate the self-assembly behavior of these derivatives in solution.
• To explore the influence of guest molecules and co-hosts on capsule formation.

Main Methods:

• Synthesis of functionalized calix[4]arenes via N-tolyl-urethane and N-tolyl-urea linkages.
• Nuclear Magnetic Resonance (NMR) spectroscopy in CDCl3 and benzene-d6 to study self-assembly.
• Investigation of guest-induced dimerization and heterodimerization with other calixarene structures.

Main Results:

• Calixarene urethanes (4) and mixed urea-urethanes (10a,b) were synthesized.
• Unlike tetra-urea analogues, urethane derivatives did not spontaneously form dimeric capsules.
• Dimerization of triurea derivative 10b was induced by tetraethylammonium cations.
• Quantitative heterodimerization occurred between urethanes (4, 10a,b) and a "tetra-loop" tetraurea (14).
• "Bisloop" tetraureas (13) required di- or triurea derivatives (10a,b) for efficient heterodimerization.

Conclusions:

• The substitution pattern on calixarene rims significantly impacts self-assembly behavior.
• Specific guest molecules can template the formation of dimeric capsules from urea-functionalized calixarenes.
• Selective heterodimerization can be achieved by carefully selecting complementary calixarene co-hosts.