Substituent Effects on the [N-I-N](+) Halogen Bond.
We have investigated the influence of electron density on the three-center [N-I-N](+) halogen bond. A series of [bis(pyridine)iodine](+) and [1,2-bis((pyridine-2-ylethynyl)benzene)iodine](+) BF4(-) complexes substituted with electron withdrawing and donating functionalities in the para-position of their pyridine nitrogen were synthesized and studied by spectroscopic and computational methods. The systematic change of electron density of the pyridine nitrogens upon alteration of the para-substituent (NO2, CF3, H, F, Me, OMe, NMe2) was confirmed by (15)N NMR and by computation of the natural atomic population and the π electron population of the nitrogen atoms. Formation of the [N-I-N](+) halogen bond resulted in >100 ppm (15)N NMR coordination shifts. Substituent effects on the (15)N NMR chemical shift are governed by the π population rather than the total electron population at the nitrogens. Isotopic perturbation of equilibrium NMR studies along with computation on the DFT level indicate that all studied systems possess static, symmetric [N-I-N](+) halogen bonds, independent of their electron density. This was further confirmed by single crystal X-ray diffraction data of 4-substituted [bis(pyridine)iodine](+) complexes. An increased electron density of the halogen bond acceptor stabilizes the [N···I···N](+) bond, whereas electron deficiency reduces the stability of the complexes, as demonstrated by UV-kinetics and computation. In contrast, the N-I bond length is virtually unaffected by changes of the electron density. The understanding of electronic effects on the [N-X-N](+) halogen bond is expected to provide a useful handle for the modulation of the reactivity of [bis(pyridine)halogen](+)-type synthetic reagents.
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Anna-Carin C
AC
Carlsson
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Krenare
K
Mehmeti
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Martin
M
Uhrbom
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Alavi
A
Karim
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Michele
M
Bedin
Department of Chemistry, Nanoscience Center, University of Jyvaskyla , P.O. Box 35, Jyvaskyla FI-40014, Finland.
Rakesh
R
Puttreddy
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Roland
R
Kleinmaier
Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
Alexei A
AA
Neverov
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Bijan
B
Nekoueishahraki
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Jürgen
J
Gräfenstein
Department of Chemistry, Nanoscience Center, University of Jyvaskyla , P.O. Box 35, Jyvaskyla FI-40014, Finland.
Kari
K
Rissanen
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.|The Swedish NMR Centre , Medicinaregatan 5, SE-413 90 Gothenburg, Sweden.
Máté
M
Erdélyi