Supporting Information

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1 Supporting Information Complete Series of {FeNO} 8, {FeNO} 7 and {FeNO} 6 complexes stabilized by a tetracarbene macrocycle Claudia Kupper, Julian A. Rees, Sebastian Dechert, Serena DeBeer, Δ and Franc Meyer * Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, D Göttingen, Germany. Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D Mülheim an der Ruhr, Germany. Department of Chemistry, University of Washington, Box , Seattle, WA, , USA. Δ Department of Chemistry and Biochemistry, Cornell University, Ithaca, NY, 14853, USA. Contents 1 NMR Spectroscopy... S2 2 ESI Mass Spectrometry... S4 3 UV/vis/NIR Spectroscopy... S6 4 IR Spectroscopy... S7 5 XES Spectroscopy... S9 6 EPR Spectroscopy... S10 7 Cyclic Voltammetry... S11 8 Crystallographic Details... S12 9 DFT Calculations... S15 10 References... S23 S1

2 1 NMR Spectroscopy * CoCp 2 Figure S1. 1 H NMR (top) and HSQC (bottom) spectra of compound 2. The concentration of the sample could not be increased due to limited solubility. The signal for residual cobaltocene (0.7 eq) is marked with an asterisk. S2

3 Figure S2. 1 H NMR (top) and HSQC (bottom) spectra of compound 3. S3

4 2 ESI Mass Spectrometry Figure S3. Left: ESI(+)-MS of 2 in MeCN. The peak at m/z = can be assigned to [( NHC L)Fe] 2+, the peak at m/z = to [( NHC L)Fe(NO)] 2+, at m/z = to [( NHC L)Fe(NO)] + and the peak at m/z = to [( NHC L)Fe(NO)(OTf)] +. The relative intensity of the signal at is higher compared to the signal at with respect to the non-reduced compound 1. Right: The isotopic pattern shows the peak at m/z = 434.1, both experiment (top) and the corresponding simulated pattern (bottom). A labeling experiment with 15 N was performed. Therfore, nitric oxide gas was generated in situ by reaction of L-ascorbic acid with sodium 15 N-nitrite in dioxygen-containing water. The gas was purified using a KOH column and a cooling trap ( 80 C). However, we observed a mixture of {FeNO} 7 compound 1 and the corresponding {FeNO} 6 (ONO) 3. Below, the ESI-MS of the product mixture is depicted. Moreover, in chapter 4 the IR spectrum of this mixture is shown as well as the IR spectrum after treatment of the solution with reducing agent. Since about 1 eq of CoCp 2 was used, the solution contains the reduced {FeNO} 8 compound 2 as well as 1. S4

5 Figure S4. ESI(+)-MS of 15 N-labeled 1 in MeCN. The peak at m/z = can be assigned to [( NHC L)Fe] 2+, the peak at m/z = to [( NHC L)Fe( 15 NO)] 2+, the peak at m/z = to [( NHC L)Fe( 15 NO)] + and the peak at m/z = to [( NHC L)Fe( 15 NO)(OTf)] +. The insets show the isotopic pattern for the labelling experiment with 15 NO (top) and the simulated pattern (bottom). Figure S5. ESI(+)-MS of 3 in MeCN. The peak at m/z = can be assigned to [( NHC L)Fe] 2+, the peak at m/z = to [( NHC L)Fe(NO)] 2+ and the peak at m/z = to [( NHC L)Fe(NO)(OTf)] +. The insets show the isotopic pattern for the peak at m/z = assigned to [( NHC L)Fe(NO)(ONO)(OTf)] + from the experiment using 16 O2 (top), the experiment using 18 O2 (middle) and the simulated pattern for the 16 O isotopomer of [( NHC L)Fe(NO)(ONO)(OTf)] + (bottom). S5

6 3 UV/vis/NIR Spectroscopy Figure S6. UV/vis spectra of 2 and 3 in MeCN solution (c = 0.1 mm). Figure S7. Top: UV/vis monitoring of the fast reaction of a mixture of 2 (0.14 mm, MeCN) and 1 eq of 1,5-bis(dimethyl)- piperidinium with excess of dioxygen at RT. Bottom: UV/vis monitoring of the slower reaction of 2 (0.14 mm, MeCN) with excess of dioxygen at RT (in the absence of acid). The inset in both spectra shows the kinetic trace of the absorbance at 340 nm; additon of dioxygen is marked with an arrow. S6

7 4 IR Spectroscopy Figure S8. ATR-IR spectrum of 2 (solid state). The band at 1590 cm -1 (1604 cm -1 in MeCN solution) is assigned to the N O streching frequency. Esfe ν Figure S9. Left: ATR-IR (black line) and dial path IR spectrum (orange line) of 3. The band at 1887 cm -1 (1882 cm -1 in MeCN solution) is assigned to the N O streching frequency. Right: Dial path IR spectrum of 3 (black) and partially 18 O labelled complex (red) with a new signal at 1841 cm -1. S7

8 Figure S10. Dial path IR spectrum in acetonitrile of a mixture of 1 and 3 after reaction with 15 NO (formed through reaction of L-ascorbic acid with 15 N-sodium nitrite in oxygen-containing water, detailed information see chapter 2). The gas was purified using a KOH coloumn and a cooling trap ( 80 C). The bands at 1844 cm -1 and 1708 cm -1 are assigned to the 15 N O streching frequencies in 15 N-labeled 3 and 1, respectively. Figure S11. Dial Path IR spectrum of 1 and 2 generated by reaction of 3 and 1 with CoCp2 (detailed information see chapter 2). The new signal at 1573 cm -1 is assigned to compound 2 with 15 NO. S8

9 5 XES Spectroscopy Figure S12. Fe Kβ mainline XES spectra of 1-3 and the iron(ii) precursor [ NHC LFe II (MeCN)2](OTf)2. The spectra of 1-3 exhibit no low-energy Kβ' shoulder, indicative of low-spin iron in all three complexes. S9

10 6 EPR Spectroscopy Figure S13. X-band electron paramagnetic resonance spectrum of {FeNO} 6 3 in frozen MeCN solution at 159 K. The red line represents a simulation with the parameters g = , , with A( 14 N) = [ ] MHz. Figure S14. X-Band Electron paramagnetic resonance spectra of {FeNO} 6 3 (10 mm) in frozen MeCN solution (black trace) and a reference spectrum of CuSO4 (1 mm) with NaClO4 (200 mm) in HClO4 (1 mm) in water (red trace) at 158 K and 10.0 mw each. Taking into account the differences in concentration, integration assigns the detected EPR active species in 3 to represent less than 5% of the sample. S10

11 7 Cyclic Voltammetry Figure S15. Cyclic voltammogram of 3 in MeCN/0.1 M Bu4NPF6 at RT and scan rate v = 100 mv s 1 ; potentials given vs. Fc/Fc +. Figure S16. Cyclic voltammogram of 1 (blue, in MeCN/0.1 M Bu4NPF6, scan rate v = 50 mv s 1 ) and 1 with additional [NBu4]NO2 (red, in MeCN/0.1 M Bu4NPF6, scan rate v = 100 mv s 1 ) at RT; potentials given vs. Fc/Fc +. The blanc sample with NBu4NO2 (black, in MeCN/0.1 M Bu4NPF6, scan rate v = 100 mv s.1) clearly shows that the irreversible oxidation at 0.1 (marked with an asterisk) is due to a nitrite redox process. S11

12 8 Crystallographic Details Crystal data and details of the data collections are given in Table S1. X-ray data were collected on a STOE IPDS II diffractometer (graphite monochromated Mo-Kα radiation, λ = Å) by use of ω scans at 140 C. The structures were solved by direct methods (SHELXS-2013/14) and refined on F 2 using all reflections with SHELXL-2013/14. [S1] Nonhydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions and assigned to an isotropic displacement parameter of 1.2 Ueq(C). Face-indexed absorption corrections were performed numerically with the program X-RED. [S2] Figure S17. Plot (50% probability thermal ellipsoids) of the molecular structure of the cationic part of 2 (hydrogen atoms omitted for clarity). Selected distances [Å] and angles [ ]: Fe1 N (2), Fe1 C (2), Fe1 C (2), Fe1 C (2), Fe1 C (2), N9 O1 ; N9 Fe1 C (9), N9 Fe1 C (10), C10 Fe1 C (9), N9 Fe1 C (9), C10 Fe1 C (9), C1 Fe1 C (9), N9 Fe1 C (9), C10 Fe1 C (9), C1 Fe1 C (10), C14 Fe1 C (9), O1 N9 Fe (18). S12

13 Figure S18. Plot (50% probability thermal ellipsoids) of the molecular structure of the cationic part of 3 (hydrogen atoms omitted for clarity). Selected bond lengths [Å] and angles [ ]: Fe1 N (4), Fe1 O (3), Fe1 C (4), Fe1 C (4), Fe1 C (4), Fe1 C (4), N9 O (4), N10 O (5), N10 O (4); N9 Fe1 O (13), N9 Fe1 C (16), O2 Fe1 C (14), N9 Fe1 C (15), O2 Fe1 C (13), C1 Fe1 C (15), N9 Fe1 C (16), O2 Fe1 C (14), C1 Fe1 C (15), C5 Fe1 C (15), N9 Fe1 C (15), O2 Fe1 C (13), C1 Fe1 C (15), C5 Fe1 C (17), C10 Fe1 C (15), O1 N9 Fe (3), N10 O2 Fe (2), O2 N10 O (4). Table S1. Crystal data and refinement details for 2 and 3. compound 2 3 empirical formula C 19H 20F 3FeN 9O 4S C 20H 20F 6FeN 10O 9S 2 formula weight crystal size [mm³] crystal system monoclinic triclinic space group P2 1/c P1 a [Å] (6) (9) b [Å] (4) (10) c [Å] (8) (11) α [ ] (7) β [ ] (4) (7) γ [ ] (7) V [ų] (18) (2) Z 4 2 ρ [g/cm³] F(000) µ [mm 1 ] T min / T max / / S13

14 θ-range [ ] hkl-range 16-15, ±15, ±19 ±12, 13-14, ±17 measured refl unique refl. [R int] 4713 [0.0611] 5991 [0.0729] observed refl. (I > 2σ (I)) data / restraints / param / 0 / / 0 / 433 goodness-of-fit (F²) R1, wr2 (I > 2σ (I)) , , R1, wr2 (all data) , , resid. el. dens. [e/å³] / / S14

15 9 DFT Calculations Table S2. Coordinates of the energy-optimized structure of complex 2. Fe N O C C C C N N N N N N N N C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H Table S3. Coordinates of the energy-optimized structure of complex 3. Fe N O O C C C C N N N S15

16 N N N N N N O C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H Figure S19. Energetic order of α and β frontier orbitals of 2 (left) and 3 (right) generated by Chemcraft and calculated with BP86 functional, RI approximation def2-tzvp and def2-tzvp/j basis sets. S16

17 Figure S20. Calculated absorption spectra of complex 2 (top) and 3 (bottom) generated by Chemcraft and calculated with B3LYP functional, RIJCOSX approximation def2-tzvp and def2-tzvp/j basis sets using a Gaussian line shape function with a half-width of 30 nm. S17

18 2 352 nm: 650 nm nm: 344 nm: Figure S21. Calculated transition densities (green/yellow indicate gain/loss of electron density) of complex 2 (top, states 21 and 5) and 3 (bottom, states 48 and 34) generated by Chemcraft and calculated with B3LYP functional, RIJCOSX approximation def2-tzvp and def2-tzvp/j basis sets. In case of compound 2, the dd-transition around 350 nm shows interaction between the iron center and the tetracarbene ligand while the broad band around 650 nm is assigned to the lowest energy HOMO LUMO transition. The main transitions in compound 3 are mainly ONO Fe related (302 nm) and ON Fe related (344 nm), respectively. Figure 22. Natural transition orbitals (spin-up, occupied/unoccupied pair) that mainly contribute to state 5 (top, n= , cm 1, nm) and state 21 (bottom, n= , cm 1, nm) of 2 (contour value = 0.08, color code: C = white, N = blue, O = pink, Fe=red). Hydrogen atoms not shown. S18

19 Figure 23. Natural transition orbitals (spin-up, occupied/unoccupied pair) that mainly contribute to state 34 (top, n= , cm 1, nm) and state 35 (bottom, n=0.4549, cm 1, nm) of 3 (contour value = 0.08, color code: C = white, N = blue, O = pink, Fe=red). Hydrogen atoms not shown. Figure 24. Natural transition orbitals (spin-up, occupied/unoccupied pair) that mainly contribute to state 48 (top: n= , bottom: n=0.1337, cm 1, nm) of 3 (contour value = 0.08, color code: C = white, N = blue, O = pink, Fe=red). Hydrogen atoms not shown. S19

20 The described method for structural optimization of 2 and 3 leads to the following IR stretching frequencies: 2: ν N-O = 1698 cm -1, ν Fe-NO = 635 cm -1 3: ν N-O = 1859 cm -1 ; ν Fe-NO = 663 cm -1, ν O-NO = 887 cm -1, ν ON-O = cm -1, ν Fe-ONO = 366 cm -1 A calculation optimized for IR frequencies (UKS BP86, def2-tzvp def2-tzvp/j DecontractAux D3BJ ZORA Grid5 NoFinalGrid SlowConv TightSCF RI) lead to the following values: 2: ν N-O = 1601 cm -1 1: ν N-O = 1752 cm -1 However, the intensity of the Fe NO and Fe ONO stretching frequencies, as it is shown in Figure S22, are very low and the signals are not detectable. νfe-no = 635 cm -1 νn-o = 1698 cm -1 S20

21 νfe-no = 663 cm -1 νn-o = 1859 cm -1 Figure S25. Calculated infrared spectra of complex 2 (top) and 3 (bottom) generated by Chemcraft and calculated with BP86 functional, RI approximation def2-tzvp and def2-tzvp/j basis sets. Figure S26. Plot of the DFT-calculated Mössbauer IS vs the experimental values for {FeNO} 6 (red), {FeNO} 7 (blue), {FeNO} 8 (green) and a related tetracarbene ( NHC L) coordinated Fe III -S-Fe III species. [S3] The straight line represents perfect agreement of calculation and experiment. In comparison to the described DFT calculations for geometry optimization, XES spectra were calculated with the same basis sets and functional. As typical for XES calculation, ZORA and the D3BJ dispersion correction, a larger grid size, decontracted auxiliary basis set and a special core properties basis set on Fe were used. Valence-to-Core XES spectra were calculated within a single-electron approximation, according to a protocol described S21

22 previously. [S4] Spectral intensity reflects a 3 ev FWHM Gaussian broadening of the combined electric dipole, magnetic dipole, and electric quadrupole transition moments. A scalar correction of 55.6 ev was added to the calculated transition energies to align the calculated spectra with experimental data. A sample input file for XES calculations follows.! Opt UKS BP86 def2-tzvp def2-tzvp/j DecontractAux D3BJ ZORA Grid5 NoFinalGrid SlowConv TightSCF Normalprint RI! PAL8! COSMO(Acetonitrile) %basis NewGTO Fe "CP(PPP)" end end %method SpecialGridAtoms 26 SpecialGridIntAcc 7 end %xes CoreOrb 0,0 OrbOp 0,1 DoSOC true CoreOrbSOC 0,1 End S22

23 10 References [S1] Sheldrick, G. M. Acta Cryst. 2015, C71, 3 8. [S2] X-RED; STOE & CIE GmbH, Darmstadt, Germany, [S3] Meyer, S.; Krahe, O.; Kupper, C.; Klawitter, I.; Demeshko, S.; Bill, E.; Neese, F.; Meyer, F. Inorg. Chem. 2015, 54, [S4] Lee, L.; Petrenko, T.; Bergmann, U.; Neese, U.; DeBeer, S. J. Am. Chem. Soc. 2010, 132, S23