The Influence of Secondary Interactions on the [N−I−N]⁺ Halogen Bond

Abstract

[Bis(pyridine)iodine(I)]+ complexes offer controlled access to halonium ions under mild conditions. The reactivity of such stabilized halonium ions is primarily determined by their three‐center, four‐electron [N−I−N]+ halogen bond. We studied the importance of chelation, strain, steric hindrance and electrostatic interaction for the structure and reactivity of halogen bonded halonium ions by acquiring their 15N NMR coordination shifts and measuring their iodenium release rates, and interpreted the data with the support of DFT computations. A bidentate ligand stabilizes the [N−I−N]+ halogen bond, decreasing the halenium transfer rate. Strain weakens the bond and accordingly increases the release rate. Remote modifications in the backbone do not influence the stability as long as the effect is entirely steric. Incorporating an electron‐rich moiety close by the [N−I−N]+ motif increases the iodenium release rate. The analysis of the iodine(I) transfer mechanism highlights the impact of secondary interactions, and may provide a handle on the induction of stereoselectivity in electrophilic halogenations.

Ligand exchange among iodine(i) complexes

“…It should be noted that despite the increasing asymmetry of the N 1 -I-N 2 bond, the N 1 -I-N 2 angle remains strictly linear (Table S2 †) even for [I(1)( 16)] + , enforced by the nature of the 3c-4e [N 1 ⋯I⋯N 2 ] + halogen bond in all halogen(I) complexes. [36][37][38][39][40]42,50,53 Mechanism of ligand exchange Similar to proposed mechanisms for halogen(I) transfer using three-centre iodine(I) complexes in organic synthesis, [54][55][56][57][58][59] the ligand exchange process in iodine(I) complexes can be addressed (Scheme 2). The reversible dissociation of the threecentre complex (e.g., [I( 7 It should be noted that the dynamic character of the bis(acyloxy)iodates(I)-related axles in rotaxanes was also studied by the group of Šindelář, in which the carbonyl hypoiodite was analogously suggested to be the key intermediate in the transfer of the iodine(I) ion among different axles.…”

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

“…The mechanism of iodine( i ) transfer from bis(pyridine) complexes, such as 1 , has been recently described based on UV-kinetic and computational data. 31 Herein we assess whether chiral analogues of 1 presenting chiral functionalities near the coordinating nitrogen may influence the enantioselectivity of iodocyclisation.…”

Construction of Halogen-Bonded Organic Frameworks (XOFs) as Novel Efficient Iodinating Agents

“…To date, the halogen bond (XB), the directional, noncovalent interaction between the electron-poor region of halogens and Lewis bases, − has been applied in extensive different fields like material sciences, , crystal engineering, − anion recognition and transportation, − medicinal chemistry, , organic synthesis, and organocatalysis. , Among the XBs, the three-center–four-electron [N···X + ···N] halogen bonds, stabilized by simultaneous coordination of the halogen to two nitrogen electron donors, are widely applicable as novel tools for the construction of functional supramolecular aggregates. , Many [N···I + ···N] halonium complexes with ingenious structures have been constructed so far. − Recently, [N···I + ···N] halogen bonds have been employed to construct two-dimensional halogen-bonded organic frameworks (XOFs). , As a novel member of APMs, XOFs aroused our great interest in exploring their new structures and potential applications.…”