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The role of halogen bonding (HaB) in the reactions of N-chlorosuccinimide (SimCl), a versatile reagent in organic synthesis, was investigated through experimental and computational analyses of its interactions with halides. The reactions of SimCl with Br− or I− resulted in the crystallization of HaB complexes of chloride with N-iodosuccinimide (SimI) or N-bromosuccinimide (SimBr). Computational analysis revealed that halogen rearrangements, which occurred even at −73 °C, were facilitated by halogen bonding. The dissociation of SimCl∙Y− (Y = I or Br) complexes into a Sim− + ClY pair (followed by the rotation and re-binding of the interhalogen molecules) bypassed the formation of the high-energy Sim− + Cl+ pair and drastically (about tenfold) reduced the dissociation energy of the N–Cl bond. Furthermore, while the dissociation energy of individual SimCl is higher (and its HaB is weaker) compared to that of SimI or SimBr, the dissociation of the N-Cl bond in SimCl∙Y− requires less energy than in the complexes of SimBr or SimI. The facile cleavage of such bonds in HaB complexes explains the high reactivity of SimCl and its effectiveness as a halogenating agent. 

The first structures containing bonds between chlorines and tertiary nitrogen atoms and very strong halogen bondsviachlorine (with a substantial contribution of orbital interactions) are reported. 

To develop synthetic strategies to construct ligands containing secondary sphere acids, we demonstrate that an appended borane of low Lewis acidity (–BPin) can be upgraded to a strong Lewis acid (–BF2). Using a pyridine-pyrazole ligand coordinated to Mo(CO)4, we show that a pendent –BPin group undergoes exhaustive fluorination to –BF3K, a precursor to a highly acidic –BF2 unit (acceptor number ~15x greater than –BPin). 

Introducing CF₃between two^tBu groups creates steric crowding that destabilizes the conformations of copper–pyrazolate tetramers. The impact of conformational behavior on luminescence is examined by low-temperature X-ray and photophysical studies.