Electronic Configuration and Ligand Nature of Five-Coordinate Iron Porphyrin Carbene Complexes: An Experimental Study

Yulong Liu; Wei Xu; Jing Zhang; William Fuller; Charles E Schulz; Jianfeng Li

doi:10.1021/jacs.7b01722

Electronic Configuration and Ligand Nature of Five-Coordinate Iron Porphyrin Carbene Complexes: An Experimental Study

J Am Chem Soc. 2017 Apr 12;139(14):5023-5026. doi: 10.1021/jacs.7b01722. Epub 2017 Mar 29.

Authors

Yulong Liu¹, Wei Xu², Jing Zhang², William Fuller³, Charles E Schulz³, Jianfeng Li¹

Affiliations

¹ College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences , Yanqi Lake, Huairou District, Beijing 101408, China.
² Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing 100049, China.
³ Department of Physics, Knox College , Galesburg, Illinois 61401, United States.

PMID: 28339195
DOI: 10.1021/jacs.7b01722

Abstract

The five-coordinate iron porphyrin carbene complexes [Fe(TPP) (CCl₂)] (TPP = tetraphenylporphyrin), [Fe(TTP) (CCl₂)] (TTP = tetratolylporphyrin) and [Fe(TFPP) (CPh₂)] (TFPP = tetra(pentafluorophenyl)porphyrin), utilizing two types of carbene ligands (CCl₂ and CPh₂), have been investigated by single crystal X-ray, XANES (X-ray absorption near edge spectroscopy), Mössbauer, NMR and UV-vis spectroscopies. The XANES suggested the iron(II) oxidation state of the complexes. The multitemperature and high magnetic field Mössbauer experiments, which show very large quadrupole splittings (QS, ΔE_Q), determined the S = 0 electronic configuration. More importantly, combined structural and Mössbauer studies, especially the comparison with the low spin iron(II) porphyrin complexes with strong diatomic ligands (CS, CO and CN^-) revealed the covalent bond nature of the carbene ligands. A correlation between the iron isomer shifts (IS, δ) and the axial bond distances is established for the first time for these donor carbon ligands (:C-R).