Inclusion of quinolines by binaphthol: structures and selectivity

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Crystallography

Background:

• Host-guest chemistry explores the selective binding of guest molecules within host structures.
• 2,2'-dihydroxyl-1,1'-binaphthyl (BINAP) is a chiral host known for forming inclusion compounds.
• Quinoline derivatives are common guests in host-guest systems.

Purpose of the Study:

• To investigate the enclathration selectivity of BINAP towards various methylquinoline guests.
• To elucidate the structural basis of BINAP-methylquinoline inclusion compounds.
• To explore the impact of pH on the selectivity of BINAP enclathration.

Main Methods:

• Competition experiments were used to determine relative enclathration affinities.
• X-ray crystallography was employed to determine the structures of inclusion compounds.
• Thermal analysis was performed to assess the relative stabilities of the complexes.
• pH control was utilized to investigate its effect on selectivity.

Main Results:

• The enclathration selectivity order was established as BINAP·2(2MeQ) > BINAP·2Q > BINAP·2(8MeQ) > BINAP·2.5(6MeQ).
• Crystal structures revealed stabilization through (host)O-H···N(guest) hydrogen bonds.
• Thermal analysis confirmed the observed selectivity sequence.
• Significant modification of the selectivity profile was achieved by controlling pH, particularly for 2-methylquinoline and 8-methylquinoline.

Conclusions:

• BINAP exhibits distinct enclathration selectivity towards methylquinolines, influenced by guest structure.
• Hydrogen bonding plays a crucial role in stabilizing the BINAP-methylquinoline inclusion complexes.
• pH manipulation offers a powerful strategy to tune the enclathration selectivity of BINAP, enabling control over guest binding.