Carlsson Anna-Carin C, Mehmeti Krenare, Uhrbom Martin, Karim Alavi, Bedin Michele, Puttreddy Rakesh, Kleinmaier Roland, Neverov Alexei A, Nekoueishahraki Bijan, Gräfenstein Jürgen, Rissanen Kari, Erdélyi Máté
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Gothenburg, Sweden.
Department of Chemistry, Nanoscience Center, University of Jyvaskyla , P.O. Box 35, Jyvaskyla FI-40014, Finland.
J Am Chem Soc. 2016 Aug 10;138(31):9853-63. doi: 10.1021/jacs.6b03842. Epub 2016 Jun 17.
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.
我们研究了电子密度对三中心N-I-N卤键的影响。合成了一系列在吡啶氮的对位被吸电子和供电子官能团取代的双(吡啶)碘和1,2-双((吡啶-2-乙炔基)苯)碘BF4(-)配合物，并通过光谱和计算方法进行了研究。通过(15)N NMR以及氮原子的自然原子布居和π电子布居的计算，证实了对位取代基(NO2、CF3、H、F、Me、OMe、NMe2)改变时吡啶氮电子密度的系统变化。N-I-N卤键的形成导致(15)N NMR配位位移>100 ppm。取代基对(15)N NMR化学位移的影响由π布居而非氮原子上的总电子布居决定。平衡NMR研究的同位素微扰以及DFT水平的计算表明，所有研究的体系都具有静态、对称的N-I-N卤键，与它们的电子密度无关。4-取代双(吡啶)碘配合物的单晶X射线衍射数据进一步证实了这一点。如紫外动力学和计算所示，卤键受体电子密度的增加稳定了N···I···N键，而电子不足则降低了配合物的稳定性。相比之下，N-I键长实际上不受电子密度变化的影响。对N-X-N卤键电子效应的理解有望为调节双(吡啶)卤素型合成试剂的反应性提供有用的方法。
