Highly Efficient Chirality Transfer from Diamines Encapsulated within a Self-Assembled Calixarene-Salen Host

• Published in: Chemistry : a European journal 2015-05, Vol.21 (19), p.7144-7150
• Main Authors: Martínez-Rodríguez, Luis, Bandeira, Nuno A. G., Bo, Carles, Kleij, Arjan W.
• Format: Article
• Language: English
• Subjects: calixarenes; Calixarenes - chemistry; Chemistry; Chirality; chirality transfer; Coordination Complexes - chemistry; Cotton; Density; Diamines; Diamines - chemistry; Dichroism; Encapsulation; host-guest systems; Isomers; Mathematical analysis; Models, Molecular; Phenols - chemistry; Phenylenediamines - chemistry; salens; Zinc - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500333

A calix[4]arene host equipped with two bis‐[Zn(salphen)] complexes self‐assembles into a capsular complex in the presence of a chiral diamine guest with an unexpected 2:1 ratio between the host and the guest. Effective chirality transfer from the diamine to the calix–salen hybrid host is observed by circular dichroism (CD) spectroscopy, and a high stability constant K2,1 of 1.59×1011 M−2 for the assembled host–guest ensemble has been determined with a substantial cooperativity factor α of 6.4. Density functional calculations are used to investigate the origin of the stability of the host–guest system and the experimental CD spectrum compared with those calculated for both possible diastereoisomers showing that the M,M isomer is the one that is preferentially formed. The current system holds promise for the chirality determination of diamines, as evidenced by the investigated substrate scope and the linear relationship between the ee of the diamine and the amplitude of the observed Cotton effects. The host with the most: A calix[4]arene functionalized with two [Zn(salphen)] complexes shows highly effective chirality transfer effects in the presence of chiral diamines. The operating modus of the system involves a unique encapsulation of the diamine guest. This calixarene–salphen hybrid host holds promise for the determination of the absolute configuration and ee of diamines.