Effect of Chirality on the Binding of Viologen Guests in Porphyrin Macrocycles

Abstract

As part of a project aimed at the development of chiral processive catalysts that can write information on a polymer chain we describe the synthesis of two optically active porphyrin macrocycles, which are prepared in 3 steps from an achiral precursor compound. Fluorescence and 1 H‐NMR studies show that one of the macrocycles displays selectivity in the binding of chiral viologen guest molecules.

Enantioselective synthesis of chiral porphyrin macrocyclic hosts and kinetic enantiorecognition of viologen guests

“…To investigate whether enantiomeric viologens with chiral N -substituents would exhibit stereoselective threading behavior through the cavities of the enantiomers of H23 , we examined the threading and de-threading processes of chiral viologens ( R , R )- 15 and ( S , S )- 15 ( Table 1 , entries 7–12). 23 The threading experiments ( Fig. 4A and B ) revealed that the enantiomers of H23 display no kinetic preference for the binding of either ( R , R )- 15 or ( S , S )- 15 .…”

“… 21 The enantiomers of H22 could be resolved by chiral HPLC 22 and by installing a chiral auxiliary on the corresponding amino-functionalized host. 23 The enantiopure hosts investigated earlier were shown to have small differences in affinity for chiral viologen guests (up to 3-fold difference in binding constant K assoc ). 22,23 In this paper we report an alternative approach to synthesize a chiral C 2 -symmetric porphyrin cage compound, i.e.…”

Molecular motor-functionalized porphyrin macrocycles

“…To this end, free base porphyrin cage compound H 2 1 26 , 27 was regioselectively mononitrated at one of its xylylene sidewalls via our recently developed procedure 28 to afford H 2 9 (50–75%). This compound was subsequently reduced to monoamino cage H 2 10 with stannous chloride and HCl 29 . The aniline derivative was readily transformed into azide H 2 11 via the diazonium intermediate.…”

Host–Guest Exchange of Viologen Guests in Porphyrin Cage Compounds as Studied by Selective Exchange Spectroscopy (1D EXSY) NMR

“…[14] More recently, we have started a program to write digital information onto single polymer chains in the form of chiral epoxides (R,R-epoxide = digit 1, S,Sepoxide = digit 2) with the help of chiral porphyrin cage compounds derived from glycoluril. [15] As part of this project we are studying the threading and binding of viologen-based guest molecules, which are blocked on one side with a bulky stopper, in these host molecules, [16,17] and we have observed unidirectional binding depending on the type of viologen guest. These studies are a first important step in the design of porphyrin cage catalysts that can thread onto a polymer chain containing alkene double bonds and move along it, while converting the alkene functions into epoxides (digital printing process).…”