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

Abstract

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 CD spectroscopy, and a high stability constant K21 of 1.59  1011 M-2 for the assembled host-guest ensemble has been determined with a substantial cooperativity factor  of 6.4. DFT analysis has been used to investigate the origin of the stability of the host-guest system and the experimental CD spectrum compared with the calculated ones 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.