Abstract
Chiral 1,1'-binaphthyl-linked diporphyrin 'tweezers' (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2/(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units.
Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and H-1 nuclear magnetic resonance (H-1-NMR) methods.
Chiral configurations could also be differentiated using CD or H-1-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10(-6) mol center dot L-1).
The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest.
This work demonstrates the utility of 1,1'-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers.