Antiaromatic Character of 16 pi Electron Octaethylporphyrins: Magnetically Induced Ring Currents from DFT-GIMIC Calculations

作者：Fliegl Heike^*; Pichierri Fabio; Sundholm Dage

来源：Journal of Physical Chemistry A, 2015, 119(11): 2344-2350.

DOI：10.1021/jp5067549

The magnetically induced current density susceptibility, also called current density, has been calculated for a recently synthesized octaethylporphyrin (OEP) zinc(II) dication with formally 16 pi electrons. Numerical integration of the current density passing selected chemical bonds yields the current pathway around the porphyrinoid ring and the strength of the ring current. The current strengths show that the OEP-Zn(II) dication is strongly antiaromatic, as also concluded experimentally. The calculation of the ring current pathway shows that all 24 pi electrons participate in the transport of the ring current because the current splits into inner and outer branches of practically equal strengths at the four pyrrolic rings. The corresponding neutral octaethylporphyrinoid without Zn and inner hydrogens is found to be antiaromatic, sustaining a paratropic ring current along the inner pathway with 16 pi electrons. The neutral OEP-Zn(II) molecule with formally 18 pi electrons is found to be almost as aromatic as free-base porphyrin. However, also in this case, all 26 pi electrons contribute to the ring current, as for free-base porphyrin. A comparison of calculated and measured H-1 NMR chemical shifts is presented. The current strength susceptibility under experimental conditions has been estimated by assuming a linear relation between experimental shielding constants and calculated current strengths.

• 出版日期2015-3-19