Lewis-acid receptors

Maruoka, K. Synthetic Utility of Bulky Aluminum Reagents as Lewis Acid Receptors. In Lewis Acid Reagents-, Yamamoto, H., Ed. Oxford University Press Oxford, 1999 pp 5-29. 

In order to quantify the transition metal ion concentration, Jones et al. [107] developed a highly sensitive fluorescent chemosensor in the form of dialkoxy-phenyleneethynylene-thiophene copolymers 68/69. The PAEs were functionalized on the thiophene unit with terpyridine (68), and included 2,2 -bipyridine (69) as a Lewis acid receptor. The terpyridine polymers [108] were found to respond quantitatively to transition metal ions at concentrations as low as 4x10 M (NP, Hg, Cr ", and Co " ). The additionally used bpy-PAE demonstrates that variation in the chelation at the receptor site is an important variable in tuning selectivity. The observed dynamic quenching mechanism, combined with the solubility of this material, provides the opportunity to extend these initial investigations to thin solid films for use in real-time monitoring applications. 

Because of this selective Lewis acid-base complex formation, molecular recognition chemistry with MAD as a Lewis-acid receptor for carbonyls enables other types of chemoselectivity. For example, the successful utilization of reactive nucleophiles... 

The authors reported that the Lewis-acid receptor ATPH and its congeners self-assemble with a dicarbonyl guest molecule in organic solvents to form a dimeric capsule the X-ray crystal structure of such a complex with l,4-dimethyl-2,5-piperazine-dione as a model guest is shown in Fig. 1 [166]. 

V. INORGANIC APPROACHES TO ANION BINDING A. Neutral, Lewis Acidic Receptors... 

Although technically a heteroelement rather than a metal, some interesting Lewis acidic receptors for anions have been based on boron-containing systems. The first evidence for this type of anion receptor was published in 1967, one of the earliest examples of anion binding. Compound 21, when compared with 22, exhibited a chelate effect in the binding of methoxide anions (3). 

Scheme 4-14 Formation of capsule 56 from Lewis acid receptor ATPH (55).

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