Are bis(pyridine)iodine() complexes applicable for asymmetric halogenation?

• Published in: Organic & biomolecular chemistry 2021-10, Vol.19 (38), p.837-8323
• Main Authors: von der Heiden, Daniel, Németh, Flóra Boróka, Andreasson, Måns, Sethio, Daniel, Pápai, Imre, Erdelyi, Mate
• Format: Article
• Language: English
• Subjects: 2-bis(2'-pyridylethynyl)benzene; Alkenes; Biochemistry; bonds; bromonium; Catalysts; Chelation; Chemistry; Enantiomers; Flavors; Functional materials; Halogenation; Intermediates; iodination; Iodine; Ligands; Natural products; NMR; Nuclear magnetic resonance; Organic Chemistry; organic-synthesis; Organisk kemi; participation; Pesticides; Physical and Theoretical Chemistry; Pyridines; reduction; stable carbonium-ions; Stereoselectivity; Substrates
• ISSN: 1477-0520; 1477-0539; 1477-0539
• DOI: 10.1039/d1ob01532j

Enantiopure halogenated molecules are of tremendous importance as synthetic intermediates in the construction of pharmaceuticals, fragrances, flavours, natural products, pesticides, and functional materials. Enantioselective halofunctionalizations remain poorly understood and generally applicable procedures are lacking. The applicability of chiral trans -chelating bis(pyridine)iodine( i ) complexes in the development of substrate independent, catalytic enantioselective halofunctionalization has been explored herein. Six novel chiral bidentate pyridine donor ligands have been designed, routes for their synthesis developed and their [N-I-N] + -type halogen bond complexes studied by 15 N NMR and DFT. The chiral complexes encompassing a halogen bond stabilized iodenium ion are shown to be capable of efficient iodenium transfer to alkenes; however, without enantioselectivity. The lack of stereoselectivity is shown to originate from the availability of multiple ligand conformations of comparable energies and an insufficient steric influence by the chiral ligand. Substrate preorganization by the chiral catalyst appears a necessity for enantioselective halofunctionalization. The enantioselectivity of the iodine( i ) transfer process from chiral bis(pyridine)iodine( i ) complexes to alkenes is explored.