Synthesis and first X-ray structure analysis of a stabilized chiral chlorobismuthine: fixation of molecular geometry induced by the intramolecular coordination of a sulfonyl group

Abstract

A sulfonyl-stabilized chiral chlorobismuthine 1a was synthesized by the selective fluorodearylation of compound 3a with boron trifluoride–diethyl ether, followed by halogen exchange of the resulting fluorobismuthine 4a with brine. The ¹H NMR spectrum of compound 1a showed an unusually large downfield shift of a proton signal (δ 9.16), and X-ray structure analysis revealed that this unique shift was due to the anisotropic deshielding of the proton adjacent to the bismuth atom by the chlorine atom in close proximity. The bismuth centre of compound 1a was found to adopt a distorted pseudotrigonal bipyramidal geometry, probably through the formation of a hypervalent 3-centre 4-electron bond with the oxygen and chlorine atoms at apical positions. This is in marked contrast to the bismuthine 3a which has a pyramidal configuration characteristic of trivalent organobismuth compounds. A quite short Bi–O distance [2.592(5)Å] of compound 1a, compared with that [2.914(6)Å] of the bismuthine 3a, indicates that the introduction of an electronegative chlorine atom onto the bismuth atom enhances the Lewis acidity of the metal centre, leading to the pronounced intramolecular Bi-O interaction.