Metal ions as external stimuli in stereoselective self-sorting of koneramines and thiokoneramines

Abstract

Stereoselective self-sorting of hemiaminal ethers (koneramines) and hemiaminal thioethers (thiokoneramines), which are N3 ligands, evolved from the system of pyridine-2-carboxaldehyde, mono-N-substituted ethylenediamine, primary alcohol or thiol, is observed when metal ions such as nickel(II), copper(II), zinc(II) and cadmium(II) are added as external stimuli to isolate the emergent molecule. Interestingly, copper(II) and zinc(II) ions are found to specifically coordinate with syn-hemiaminal ether or anti-hemiaminal thioether equatorially, while nickel(II) and cadmium(II) ions coordinate specifically with anti-hemiaminal ether facially or anti-hemiaminal thioether equatorially. Another system of pyridine-2-carboxaldehyde, N-phenylethylenediamine, methanol, copper(II) and cadmium(II) shows a beautiful example of emergent phenomena, where anti-cadmium complex precipitates out cleanly from the system while syn-copper(II) complexes stay in the solution, whereas the same system yields only syn-copper(II) complex when the amount of metal ions is doubled. Interestingly, nickel(II) is the emergent complex when Ni(II) and Cd(II) are used, while copper(II) is the emergent complex when Ni(II) and Cu(II) are used. Amazingly, copper(II) is the sole emergent complex when a mixture of Ni(II), Cu(II), Cd(II) and Zn(II) is used. Only anti forms of thiokoneramine are found to coordinate equatorially with Ni(II), Cu(II), Cd(II) or Zn(II) when the stereoselective self-sorting is performed in ethanethiol. This stereoselective self-sorting process has been substantiated by the analysis of isolated molecules with analytical techniques such as electrospray mass ionisation spectrometry, nuclear magnetic resonance spectroscopy and single crystal X-ray diffraction analysis.