Trapping an Ester Hydrate Intermediate in a π-Stacked Macrocycle with Multiple Hydrogen Bonds.

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Coordination Chemistry

Background:

• Ester hydrates are transient intermediates in esterification reactions, making their isolation and structural characterization difficult.
• Previous studies have rarely reported the crystal structures of ester hydrates due to their instability.

Purpose of the Study:

• To present a method for trapping and stabilizing mono-deprotonated ester hydrates.
• To characterize the crystal structure of a novel self-assembled macrocycle incorporating ester hydrates.
• To investigate the templating role of ester hydrates in supramolecular assembly.

Main Methods:

• Single-crystal X-ray diffraction analysis was employed to determine the structure of the complex.
• The synthesis involved the reaction of cobalt(II) chloride, a tris(benzimidazolylmethyl)amine ligand, and sulfuric acid in methanol.
• In situ formation and trapping of ester hydrates within a macrocyclic host structure.

Main Results:

• A novel π-stacked boat-shaped macrocycle was synthesized and characterized: (CH3OSO2(OH)2)0.67(CH3OSO3)1.33@{[ClLCoII]6}·Cl4·13CH3OH·9H2O.
• Mono-deprotonated ester hydrates, [CH3OSO2(OH)2]-, were successfully trapped within the macrocycle via hydrogen bonding.
• The ester hydrate intermediate and its product, [CH3OSO3]-, acted as templates for the macrocycle's self-assembly.

Conclusions:

• The study demonstrates a successful strategy for stabilizing and characterizing short-lived ester hydrates.
• The self-assembled macrocycle provides a unique host environment for trapping reactive intermediates.
• This work advances the understanding of templated synthesis and the structural characterization of transient species.