Oxoiron(IV) motifs are found in important intermediates in many enzymatic cycles that involve oxidations. Over half of the reported synthetic nonheme oxoiron(IV) analogs incorporate heterocyclic donors, with a majority of them comprising pyridines. Herein, we report 1H-NMR studies of oxoiron(IV) complexes containing pyridines that are arranged in different configurations relative to the Fe = O unit and give rise to paramagnetically shifted resonances that differ by as much as 50 ppm. The strong dependence of 1H-NMR shifts on the different configurations and orientation of pyridines relative to the oxoiron(IV) unit demonstrates how unpaired electronic spin density of the iron center affects the chemical shifts of these protons.
Bibliographical noteFunding Information:
We gratefully acknowledge the support of the U.S. National Science Foundation (Grants CHE-1665391 to L.Q. and CHE-1654060 to Y.G.). The Bruker Avance III HD nanobay 400?MHz spectrometer used in this study was purchased from funds provided by the Office of the Vice President of Research, the College of Science and Engineering, and the Department of Chemistry at the University of Minnesota. The Bruker-AXS D8 Venture Diffractometer was purchased through a grant from NSF/MRI 1229400 and the University of Minnesota. We thank Dr. Letitia Yao for her help with NMR experiments and Dr Victor G. Young and Shuangning Xu for their valuable input on X-ray crystallography. We also thank the Pittsburgh Supercomputing Center for granting us computational resources (CHE180020P to R.F. and Y.G.).
- Iron(IV)-oxo complexes
- Nonheme iron