An official website of the United States government
Abstract The interaction of diiodine with quinuclidine (QN) and 4‐dimethylaminopyridine (DMAP) in solutions with 1 : 1 molar ratio of reactants at room temperature produced (in essentially quantitative yields) pure charge‐transfer QN⋅I2adducts and iodine(I) salt [DMAP‐I‐DMAP]I3, respectively. In comparison, the quantitative formation of pure iodine (I) salt [QN‐I‐QN]I5was observed for the room‐temperature reactions of QN with a 50 % excess of I2, and the charge‐transfer adducts of I2with DMAP (and other pyridines) were formed when reactions were carried out at low temperatures. Computational analysis related the switch from the formation of charge‐transfer adducts to iodine(I) complexes in these systems to the strength of the halogen bonding of diiodine to the N‐donor bases. It shows that while the halogen‐bonded adducts represent critical intermediates in the formation of iodine(I) complexes, exceedingly strong halogen bonding between diiodine and the base prevents any subsequent transformations. In other words, while halogen bonding usually facilitates electron and halogen transfer, the halogen‐bonded complexes may serve as “black holes” hindering any follow‐up processes if this intermolecular interaction is too strong.
more »
« less
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 their15N 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.
more »
« less
- Award ID(s):
- 1903581
- PAR ID:
- 10449011
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 27
- Issue:
- 55
- ISSN:
- 0947-6539
- Page Range / eLocation ID:
- p. 13748-13756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The lone pair of the N atom is a common electron donor in noncovalent bonds. Quantum calculations examine how various aspects of the base on which the N is located affect the strength and other properties of complexes formed with Lewis acids FH, FBr, F2Se, and F3As that respectively encompass hydrogen, halogen, chalcogen, and pnicogen bonds. In most cases the halogen bond is the strongest, followed in order by chalcogen, hydrogen, and pnicogen. The noncovalent bond strength increases in the sp23order of hybridization of N. Replacement of H substituents on the base by a methyl group or substituting N by C atom to which the base N is attached, strengthens the bond. The strongest bonds occur for trimethylamine and the weakest for N2.more » « less
-
Abstract The effects on the C−I⋅⋅N halogen bond between iodobenzene and NH3of placing various substituents on the phenyl ring are monitored by quantum calculations. Substituents R=N(CH3)2, NH2, CH3, OCH3, COCH3, Cl, F, COH, CN, and NO2were each placed ortho, meta, and para to the I. The depth of the σ‐hole on I is deepened as R becomes more electron‐withdrawing which is reflected in a strengthening of the halogen bond, which varied between 3.3 and 5.5 kcal mol−1. In most cases, the ortho placement yields the largest perturbation, followed by meta and then para, but this trend is not universal. Parallel to these substituent effects is a progressive lengthening of the covalent C−I bond. Formation of the halogen bond reduces the NMR chemical shielding of all three nuclei directly involved in the C−I⋅⋅N interaction. The deshielding of the electron donor N is most closely correlated with the strength of the bond, as is the coupling constant between I and N, so both have potential use as spectroscopic measures of halogen bond strength.more » « less
-
The relationship between solid-state supramolecular interactions and crystal habits is highlighted based on experimental and computational analysis of the crystal structure of strong halogen-bonded (HaB) associations between iodine-containing dihalogens (ICl, IBr) with 1,4-diazabicyclo[2,2,2]octane (DABCO) as well as with substituted pyridines and phenazine. The pattern of the energy frameworks and the interplay of the attractive and repulsive interactions in the solid-state associations involving these HaB donors and acceptors directly correlated with their crystal habits. This correlation suggests that analysis of the energy framework serves as a useful tool (complementary to the earlier developed methods) to rationalize and predict the crystal habit. The X-ray structural analysis also revealed that the I⋯N distances in the complexes were in the 2.24–2.54 Å range, i.e. they were much closer to the I⋯N covalent bond length than to the van der Waals separation. The computational analysis of the nature of halogen bonding in these complexes showed delocalization of their molecular orbitals' between donor and acceptors resulting in a substantial charge transfer from the nucleophiles to dihalogens and elongation of the I⋯X bond. As a result, both I⋯N and I⋯X bonds in the strongest complexes ( e.g. , ICl with DABCO or 4-dimethylaminopyridine) are characterized by the comparable Mayer bonds orders of about 0.6, along with the electron and energy densities at their bond critical points of about 0.1 a.u. and −0.02 a.u., respectively. These data as well as the density overlap regions indicator (DORI) point to the covalency of the I⋯N bonding and suggest that the interaction within the IX complexes can be described as (unsymmetrical) hypervalent 3c/4e N⋯I⋯X bonding akin to that in trihalide or halonium ions.more » « less
-
Abstract The escape of heavy ions from the Earth atmosphere is a consequence of energization and transport mechanisms, including photoionization, electron precipitation, ion‐electron‐neutral chemistry, and collisions. Numerous studies considered the outflow of O+ions only, but ignored the observational record of outflowing N+. In spite of 12% mass difference, N+and O+ions have different ionization potentials, ionospheric chemistry, and scale heights. We expanded the Polar Wind Outflow Model (PWOM) to include N+and key molecular ions in the polar wind. We refer to this model expansion as the Seven Ion Polar Wind Outflow Model (7iPWOM), which involves expanded schemes for suprathermal electron production and ion‐electron‐neutral chemistry and collisions. Numerical experiments, designed to probe the influence of season, as well as that of solar conditions, suggest that N+is a significant ion species in the polar ionosphere and its presence largely improves the polar wind solution, as compared to observations.more » « less
