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Are bis(pyridine)iodine(I) complexes applicable for asymmetric halogenation?
Daniel von der Heiden1, Flóra Boróka Németh2, Måns Andreasson3
1Department of Chemistry - BMC, Uppsala University, SE-751 23 Uppsala, Sweden. mate.erdelyi@kemi.uu.se.
Chiral iodine(I) complexes show efficient iodenium transfer to alkenes but lack enantioselectivity. Achieving stereoselective halofunctionalization requires catalyst-induced substrate preorganization.
Area of Science:
- Organic Chemistry
- Asymmetric Catalysis
Background:
- Enantiopure halogenated molecules are crucial synthetic intermediates.
- Enantioselective halofunctionalization methods are underdeveloped.
Purpose of the Study:
- To explore chiral trans-chelating bis(pyridine)iodine(I) complexes for catalytic enantioselective halofunctionalization.
- To design and synthesize novel chiral bidentate pyridine donor ligands and their iodine(I) complexes.
Main Methods:
- Synthesis of six novel chiral bidentate pyridine donor ligands.
- Formation and characterization of [N-I-N]+-type halogen bond complexes using 15N NMR and DFT.
- Investigation of iodenium transfer to alkenes.
Main Results:
- Chiral iodine(I) complexes facilitated efficient iodenium transfer to alkenes.
- The developed complexes did not provide enantioselectivity in the halofunctionalization reactions.
- Multiple ligand conformations and insufficient steric hindrance were identified as reasons for the lack of stereoselectivity.
Conclusions:
- Substrate preorganization by the chiral catalyst is necessary for enantioselective halofunctionalization.
- Current chiral bis(pyridine)iodine(I) complexes are not suitable for enantioselective halofunctionalization without modification.
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