Characterization of Paramagnetic Reactive Intermediates: Predicting the NMR Spectra of Iron(IV)–Oxo Complexes by DFT

Abstract

The relative energies of spin states of several iron(IV)-oxo complexes and related species have been calculated with DFT methods by employing the B3LYP* functional. We show that such calculations can predict the correct ground spin state of Fe(IV) complexes and can then be used to determine the (1) H NMR spectra of all spin states; the spectral features are remarkably different, hence calculated paramagnetic (1) H NMR spectra can be used to support the structure elucidation of numerous paramagnetic complexes. Applications to a number of stable and reactive iron(IV)-oxo species are described.

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

“…[35] Promising advances in TDDFT or DFT/CI-based (CI, configuration interaction) approaches have been made towards the calculation of various X-ray absorption and emission features relevant for iron complexes, [36,37,38,39] again with the potential of structural assigment or electronic structure calibration. [40,41] Nuclear resonance vibrational spectroscopy (NRVS), selectively probing the iron-containing vibrational modes using nuclear excitations with synchrotron radiation, has lately become an important tool in the bioinorganic chemistry of iron systems.…”

Probing the Local Magnetic Structure of the [FeIII(Tp)(CN)3]− Building Block Via Solid‐State NMR Spectroscopy, Polarized Neutron Diffraction, and First‐Principle Calculations

“…in which β e , g N , β N , and k B represent the Bohr magneton, the nuclear g ‐factor, the nuclear magneton, and the Boltzmann constant, respectively, corresponds to the Zeeman coupling matrix and is calculated either by using wave‐function theory or by using KS‐DFT, and is the hyperfine coupling matrix and is obtained from KS‐DFT calculations (see the Computational Details). Such a computational strategy has already been applied successfully to a large panel of transition‐metal complexes . To assemble the Zeeman g ‐tensors, the hyperfine coupling matrices, and the orbital shielding, we have used the pNMRShift program developed by the Autschbach's group .…”

“…[89][90][91][92][93][94][95][96][97][98][99] To assemble the Zeeman g-tensors, the hyperfine coupling matrices, and the orbital shielding, we have used the pNMRShift program developed by the Autschbach's group. Such acomputational strategy has already been applied successfully to al arge panel of transition-metal complexes.…”

NMR Reveals That a Highly Reactive Nonheme FeIV=O Complex Retains Its Six‐Coordinate Geometry and S=1 State in Solution

“…Unfortunately, there are no reported examples to date of NMR data for S =2 Fe IV =O complexes, but this notion is supported by the NMR data for mononuclear S =2 Fe II (NTB) complexes (Table S7). To fill this knowledge gap, we have turned to DFT methods (see the Supporting Information for computational details) to predict the paramagnetic shifts of 1 in the S =1 and 2 states using a protocol that Borgogno et al. have successfully applied in reproducing the paramagnetic shifts observed for the S =1 complexes [Fe IV (O)(TPA)] 2+ (TPA=tris(pyridyl‐2‐methyl)amine) and [Fe IV (O)(TMC)] 2+ (TMC=1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane) .…”

“…Unfortunately, there are no reported examples to date of NMR data for S = 2Fe IV =Oc omplexes, but this notion is supported by the NMR data for mononuclear S = 2Fe II (NTB) complexes (Table S7). To fill this knowledge gap, we have turned to DFT methods (see the SupportingI nformationf or computational details) to predict the paramagnetic shifts of 1 in the S = 1a nd 2s tates using ap rotocol [23] (TMC = 1,4,8,11-tetramethyl-1,4,8,11tetraazacyclotetradecane). [19][20][21] As shown in Ta ble 1, there is good agreement between the experimental data for 1 and 2 and values calculated for the S = 1c omplexes,b ut the shifts predicted for their S = 2c ounterparts are generally much larger,c ommensurate with the higherp aramagnetisme xpected for an S = 2c enter.T hus,t he NMR data show that 1 has an S = 1s pin state in acetone solution at 193 K. In addition, the linear Eyring plot fort he oxidation of tolueneb y1 between 193 and 233 K( FigureS5, SupportingI nformation) is consistent with the conclusion that the ground spin state of 1 does not change in this temperature range.…”