Self-Sorting Chiral Subcomponent Rearrangement During Crystallization

Abstract

Abstract:The incorporation of enantiopure 1-amino-2,3-propanediol as a subcomponent into a dicopper double helicate resulted in perfect chiral induction of the helicate's twist. DFT calculations allowed the determination of the helicity of the complex in solution. The same helical induction, in which S amines induced a Λ helical twist, was observed in the solid state by X-ray crystallography. Electronic structure calculations also revealed that the unusual deep green color of this class of complexes was due to a metalto-ligand charge transfer excitation, in which the excited state possesses a valence delocalized Cu2 3+ core. The use of a racemic amine subcomponent resulted in the formation of a dynamic library of six diastereomeric pairs of enantiomers. Surprisingly, this library converted into a single pair of enantiomers during crystallization. We were able to observe this process reverse upon redissolution, as initial ligand exchange was followed by covalent imine metathesis.

The use of X‐ray crystallography to determine absolute configuration

“…Clearly although this technique is of no help for detecting racemic conglomerates, it is very helpful for other solid mixtures. 26 As the presence of diastereoisomers has the capability of invalidating the determination of absolute configuration, any method which establishes the number and relative concentration of these isomers should be used to characterize the bulk compound and if possible the single crystal used for the diffraction studies.…”

Helicate Extension as a Route to Molecular Wires

“…We note that the TD-B3LYP level has been shown previously to predict UV/Vis spectral transitions for 1 a 2 + in good agreement with those measured experimentally for 1. [29] The longest wavelength transitions in 2 a 4 + are well described as being one-electron excitations from the HOMO and HOMOÀ1 to the LUMO, LUMO + 1, and LUMO + 2. The HOMO is dominated by a combination of d orbitals on all four copper atoms, with somewhat larger amplitude on the outermost two compared with the innermost (Figure 3).…”

History and Principles of Dynamic Combinatorial Chemistry

“…(Scheme 1.8 ) [9] . A library of six pairs of enantiomers of different diastereomers of metal helicates was generated from the reaction of a racemic mixture of amine 16 with dialdehyde 17 in the presence of Cu(NCMe) 4 BF 4 .…”

“…Although an increase in the proportion of the building blocks that have been specially designed may make the outcome of equilibration more predictable, it may also increase the probability that one or more of the library members formed will respond to external infl uences upon the library. Scheme 1.8 Selection via crystallization of a single pair of enantiomeric Cu(I) helicates from among a complex library of diastereomers [9] .…”