Insight into one-electron oxidation of the {Fe(NO)2}9 dinitrosyl iron complex (DNIC): Aminyl radical stabilized by [Fe(NO) 2] motif

Article abstract of DOI:10.1021/ic302537d

A reversible redox reaction ({Fe(NO)₂}⁹ DNIC [(NO)₂Fe(N(Mes)(TMS))₂]^- (4) ? oxidized-form DNIC [(NO)₂Fe(N(Mes)(TMS))₂] (5) (Mes = mesityl, TMS = trimethylsilane)), characterized by IR, UV-vis, ¹H/¹⁵N NMR, SQUID, XAS, single-crystal X-ray structure, and DFT calculation, was demonstrated. The electronic structure of the oxidized-form DNIC 5 (S_total = 0) may be best described as the delocalized aminyl radical [(N(Mes)(TMS))₂]₂ ^-? stabilized by the electron-deficient {Fe ^III(NO^-)₂}⁹ motif, that is, substantial spin is delocalized onto the [(N(Mes)(TMS))₂] ₂^-? such that the highly covalent dinitrosyl iron core (DNIC) is preserved. In addition to IR, EPR (g ≈ 2.03 for {Fe(NO) ₂}⁹), single-crystal X-ray structure (Fe-N(O) and N-O bond distances), and Fe K-edge pre-edge energy (7113.1-7113.3 eV for {Fe(NO) ₂}¹⁰ vs 7113.4-7113.9 eV for {Fe(NO)₂} ⁹), the ¹⁵N NMR spectrum of [Fe(¹⁵NO) ₂] was also explored to serve as an efficient tool to characterize and discriminate {Fe(NO)₂}⁹ (δ 23.1-76.1 ppm) and {Fe(NO)₂}¹⁰ (δ -7.8-25.0 ppm) DNICs. To the best of our knowledge, DNIC 5 is the first structurally characterized tetrahedral DNIC formulated as covalent-delocalized [{Fe^III(NO^-) ₂}⁹-[N(Mes)(TMS)]₂^-?]. This result may explain why all tetrahedral DNICs containing monodentate-coordinate ligands isolated and characterized nowadays are confined in the {Fe(NO) ₂}⁹ and {Fe(NO)₂}¹⁰ DNICs in chemistry and biology.

Full text of DOI:10.1021/ic302537d

Supporting Information
Insight into One-Electron Oxidation of the {Fe(NO)2}9 Dinitrosyl Iron
Complex (DNIC): Aminyl Radical Stabilized by [Fe(NO)2] Motif
,
,
‡
ChihꢀChin Tsou,† FuꢀTe Tsai,† HuangꢀYeh Chen,‡ IꢀJui Hsu,* and WenꢀFeng Liaw* †
† Department of Chemistry, National TsingꢀHua University, Hsinchu, 30013, Taiwan.
‡ Department of Molecular Science and Engineering, National Taipei University of
Technology, Taipei 10608 Taiwan.
Eꢀmail: wfliaw@mx.nthu.edu.tw; Eꢀmail: ijuihsu@ntut.edu.tw

Table S1. The IR νNO of the reversible redox {Fe(NO)2}9 and {Fe(NO)2}10 DNICs.
{Fe(NO)2}9
{Fe(NO)2}10
{Fe(NO)2}9
{Fe(NO)2}10
ꢁνNO
Ref. a
4c
νNO cm–1
νNO cm–1
cm–1
1808,
1739 (THF)
1814,
1746 (MeCN) 1622 (MeCN)
1815,
1687,
1633 (THF)
1679,
121
106
135
124
129
109
+
+ e-
NO
N
NO
NO
N
Fe
Fe
Fe
- e-
N
N
NO
1686,
1632 (THF)
1673
this
work,
4b
+
N
N
N
N
+ e-
- e-
NO
NO
N
1741 (THF)
N
N
NO
NO
Fe
N
1616 (CH2Cl2)
N
N
+
+
+ e-
- e-
N
N
N
NO
NO
NO
NO
1789,
1733 (THF)
1667,
1624 (THF)
122
109
4f
4f
Fe
Fe
N
N
N
N
iPr
NO
N
iPr
N
N
+ e-
- e-
iPr
iPr
1791,
1723 (THF)
1664,
1619 (THF)
127
104
NO
iPr
Fe
N
Fe
iPr
NO
iPr
NO
N
N
N
iPr
+ e-
- e-
+
Ph3P
Ph3P
Ph3P
Ph3P
NO
NO
NO
NO
1814,
1714,
100
98
4a
Fe
Fe
1766 (CH2Cl2) 1668 (CH2Cl2)
_
1761,
1709 (C6D6)
1755,
1705 (KBr)
1715,
1674 (THF)
1721,
1676 (KBr)
1773,
1721 (MeCN) 1633 (MeCN)
1768,
1729 (KBr)
1791,
1627,
1567 (C6D6)
1632,
1559 (KBr)
1614,
1571 (THF)
1604,
134
142
123
146
101
103
117
116
89
iPr
iPr
iPr
iPr
+ e-
- e-
N
N
NO
N
N
NO
NO
4d
Fe
iPr
Fe
NO
iPr
iPr
iPr
_
_
2
+ e-
- e-
NO
NO
EtS
EtS
EtS
NO
NO
5f, 8
4e
Fe
Fe
EtS
1560 (KBr)
1684,
_
_
2
N
N
+ e-
NO
S
S
88
S
N
NO
NO
S
S
S
Fe
Fe
N
- e-
NO
1654,
1609 (KBr)
1665,
114
120
126
114
S
S
_
_
2
S
S
+ e-
- e-
O
O
N
N
O
O
N
1723 (MeCN) 1609 (MeCN)
4e
NO
NO
NO
NO
Fe
Fe
N
1786,
1696 (KBr)
1664,
1606 (KBr)
122
90
S
S
a References are shown in the text.

Table S2. Comparisons of different exchange functionals results on complex 5.
Table S3. IR vibrational frequencies of experimental and B3LYP* results.
νNO (cm–1)
Expt.
B3LYP*
Complex
Symmetry
1707
Asymmetry
1652
Symmetry
1724.43
1828.96
Asymmetry
1673.73
1770.88
4
5
1786
1733

Table S4 Summary of crystal data, intensity collection and structure refinement parameters
for [(NO)2Fe(NPh2)2]– (2), [(NO)2Fe(N(TMS)2)2]– (3), [(NO)2Fe(N(mesityl)ꢀ(TMS))2]– (4)
and [(NO)2Fe(N(mesityl)(TMS))2] (5).
Complex number
2
3
4
5
Chemical formula
Formula Mass
C32H36 FeKN4O9•2(C4H8O)
899.92
C24H60FeKN4O8Si4
740.07
C44H80FeKN4O10Si2•2(C4H8O)
976.25
C24H40FeN4O2Si2
528.63
Crystal system
Monoclinic
14.256(3)
13.064(3)
24.449(5)
90.00
Monoclinic
23.2705(8)
15.7542(6)
24.0988(9)
90.00
Orthorhombic
15.8975(9)
22.4576(12)
30.9214(17)
90.00
Orthorhombic
13.1256(10)
11.3614(9)
19.5259(14)
90.00
a/Å
b/Å
c/Å
α/°
β/°
95.777(4)
90.00
111.731(2)
90.00
90.00
90.00
γ/°
90.00
90.00
Unit cell volume/Å3
4530.4(16)
200(2)
8206.9(5)
200(2)
11039.5(11)
200(2)
2911.8(4)
200(2)
Temperature/K
Space group
P 2/c
P 21/n
P b c a
P n n a
No. of formula units per unit cell, Z
Radiation type Synchrotron
Absorption coefficient, ꢀ/mmꢀ1
No. of reflections measured
No. of independent reflections
Rint
4
8
8
4
MoKα
MoKα
MoKα
MoKα
0.477
0.627
0.443
0.626
26327
54135
62208
14571
7925
14412
9717
2570
0.0704
0.0738
0.0656
0.0430
Final R1 values (I > 2σ(I))
Final wR(F2) values (I > 2σ(I))
Final R1 values (all data)
Final wR(F2) values (all data)
Goodness of fit on F2
CCDC number
0.0619
0.0770
0.0505
0.0435
0.1540
0.2042
0.1194
0.1146
0.1161
0.1374
0.0860
0.0603
0.1722
0.2275
0.1386
0.1268
0.966
1.099
1.014
1.023
CCDCꢀ876478
CCDCꢀ876479
CCDCꢀ876480
CCDCꢀ876481
Scheme S1. Oneꢀelectron oxidation of thiolateꢀcoordinate {Fe(NO)2}9 DNICs, presumably,
–•
occurs from thiolate ligands to yield [{Fe(NO)2}9ꢀ(SR)2 ] intermediate, followed by
dimerizing to yield [(NO)2Fe(ꢂꢀSR)]2 and disulfide.

Figure S1. ORTEP drawing and labeling scheme of [(NO)2Fe(NPh2)2]– (2) in [(THF)2ꢀKꢀ
18ꢀcrownꢀ6ꢀether)]+ salt with thermal ellipsoids drawn at 50 % probability. Selected bond
distances (Ǻ) and angles (deg): Fe(1)ꢀN(1) 1.689(3), Fe(1)ꢀN(2) 1.693(4), Fe(1)ꢀN(3)
1.983(3), Fe(1)ꢀN(4) 1.973(3), N(1)ꢀO(1) 1.178(4), N(2)ꢀO(2) 1.163(4), N(1)ꢀFe(1)ꢀN(2)
110.73(17), N(3)ꢀFe(1)ꢀN(4) 109.75(12), Fe(1)ꢀN(1)ꢀO(1) 161.7(3), Fe(1)ꢀN(2)ꢀO(2)
163.9(4).
Figure S2. ORTEP drawing and labeling scheme of [(NO)2Fe(N(TMS)2)2]– (3) in [Kꢀ18ꢀ
crownꢀ6ꢀether)]+ salt with thermal ellipsoids drawn at 30 % probability. Selected bond
distances (Ǻ) and angles (deg): Fe(1)ꢀN(1) 1.700(6), Fe(1)ꢀN(2) 1.686(6), Fe(1)ꢀN(3)
2.010(5), Fe(1)ꢀN(4) 1.971(5), N(1)ꢀO(1) 1.190(7), N(2)ꢀO(2) 1.152(8), N(3)ꢀSi(1) 1.683(6),
N(3)ꢀSi(2) 1.709(6), N(4)ꢀSi(3) 1.708(5), N(4)ꢀSi(4) 1.713(6), K(1)ꢀO(1) 2.778(6), Fe(2)ꢀ
N(5) 1.706(7), Fe(2)ꢀN(6) 1.695(7), Fe(2)ꢀN(7) 2.009(6), Fe(2)ꢀN(8) 1.976(5), N(5)ꢀO(16)
1.184(8), N(6)ꢀO(16) 1.175 (8), N(7)ꢀSi(5) 1.701(6), N(7)ꢀSi(6) 1.712(6), N(8)ꢀSi(7)
1.704(5), N(8)ꢀSi(8) 1.712(5), N(1)ꢀFe(1)ꢀN(2) 110.5(3), N(3)ꢀFe(1)ꢀN(4) 117.5(2), Fe(1)ꢀ
N(1)ꢀO(1) 152.1(7), Fe(1)ꢀN(2)ꢀO(2) 170.0(6), N(5)ꢀFe(2)ꢀN(6) 104.2(3), N(7)ꢀFe(2)ꢀN(8)
116.1(2), Fe(2)ꢀN(5)ꢀO(15) 150.9(7), Fe(2)ꢀN(6)ꢀO(16) 163.0(7).

(a)
(b)
3390
3400
3410
3420
3430
3440
3450
3360
3380
3400
3420
3440
3460
3480
3500
Field [G]
Field [G]
Figure S3. Xꢀband EPR spectra of complex 2 in THF (a) at 298 K (solid line) and the
simulation curve (dash line) with gav = 2.019 and AN(NO) = 2.40 G, AN(amide) = 4.64 G; (b) at
77K with g1 = 2.023, g2 = 2.016, g3 = 2.010.
(a)
(b)
3360
3380
3400
3420
3440
3460
3480
3390
3400
3410
3420
3430
3440
Field [G]
Field [G]
Figure S4. Xꢀband EPR spectra of complex 3 in THF (a) at 298 K (solid line) and the
simulation curve (dash line) with gav = 2.020 and AN(NO) = 2.45 G, AN(amide) = 3.75 G; (b) at
77K with g1 = 2.024, g2 = 2.017, g3 = 2.011.

(a)
(b)
2.0
0.20
0.15
0.10
0.05
0.00
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
ꢀeff
χM
0
50
100
150
200
250
300
0
50
100
150
200
250
300
T(K)
T (K)
(c)
0.5
data
fit
0.4
0.3
0.2
0.1
0.0
χMT
Data: Data1_B
Model: user29
Chi^2/DoF
= 2.3855E-6
R^2
= 0.99274
P1
P2
P3
2.049 ±--
-0.14625
2.25765
±0.00543
±0.01329
0
50
100
150
200
250
300
T (K)
Figure S5. (a) The magnetic susceptibility (χM) of complex 4 under 0.5 Tesla applied field.
(b) Effective magnetic moment (ꢀeff) vs temperature (T) plot. (c) Curie Law fitting of χMT vs
T plot gives g = 2.049, θ = –0.146 ± 0.005 K and TIP = (226 ± 1.3) × 10ꢀ6 cm3 molꢀ1 (R2 =
0.993).

(a)
10
5
0
-5
-10
-15
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
Potential vs Fc+/Fc (V)
30
20
(b)
10
0
-10
-20
-30
-40
-50
-60
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Potential vs Fc+/Fc (V)
Figure S6. (a) Cyclic voltammogram of DNIC 2 in a 20 mM THF with 0.2 M [nꢀ
Bu4N][PF6] as the supporting electrolyte at room temperature and scan rate of 100 mV/s
showing a psuedoꢀreversible redox wave with E1/2 = –0.581 V and ipa/ipc = 0.80. (b) Cyclic
voltammogram of DNIC 3 in the same condition showing an oxidation wave at –0.270 V.

(a)
(b)
1.4
2
270 nm
265 nm
315 nm
1
1
Abs
Abs
318 nm
340 nm
0.5
465 5n1m6 nm
380 nm
760 nm
495 nm
630 nm
600
0
-0.1
240
-0.1
250
400
600
800
1000
1200
400
800
1000
1200
Wavelength [nm]
Wavelength [nm]
(c)
(d)
0.75
1.5
269 nm
0.6
624 nm
664 nm
1
285 nm
374 nm
0.4
0.2
0
Abs
Abs
380 nm
0.5
942 nm
442 nm
0
250
634 nm
600
265
400
600
800
1000
1200
400
800
1000
1200
Wavelength [nm]
Wavelength [nm]
Figure S7. UVꢀvis spectra of (a) [(NO)2Fe(NPh2)2]– (2), (b) [(NO)2Fe(N(TMS)2)2]– (3), (c)
[(NO)2Fe(N(mesityl)(TMS))2]– (4) and (d) [(NO)2Fe(N(mesityl)(TMS))2] (5) in THF.
Figure S8. Fe Kꢀedge spectra of complexes 2, 3 and 4 (complex 2, 7113.8 eV; complex 3,
7113.9 eV; complex 4, 7113.9 eV) (the preꢀedge absorption spectra are enlarged in the inset).

(a)
(b)
(c)
(d)
(e)
(f)

(g)
(h)
(i)
(j)

(k)
(l)
15
Figure S9. N NMR spectra of [Fe(ꢂꢀSEt)(15NO)2]2 (a) in D8ꢀTHF and (b) in CD3CN; 15N
NMR spectra of [(15NO)2Fe(sparteine)] (c) in D8ꢀtoluene, (d) in D8ꢀTHF and (e) in CD3CN;
(f) [(TMEDA)Fe(15NO)2] in D8ꢀTHF; (g) [(EtS)2Fe(15NO)2]2–
in D8ꢀTHF; (h)
2–
[(EtS)2Fe(15NO)2]2– in CD3CN; (i) [Fe(ꢂꢀSEt)(15NO)2]2
in CD3CN; (j) [Fe(ꢂꢀ
StBu)(15NO)2]22– in CD3CN; 15N NMR spectra of complex 5 (k) in D8ꢀtoluene and (l) in D8ꢀ
THF. Peak at ꢀ132 ppm is assigned to solvent CD3C15N.
Figure S10. 1H NMR spectrum of [(NO)2Fe(N(mesityl)(TMS))2] (5) in D8ꢀtoluene.

(a)
(b)
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.0030
0.0025
0.0020
0.0015
0.0010
0.0005
0.0000
ꢀeff
χM
0
50
100
150
200
250
300
0
50
100
150
200
250
300
T (K)
T(K)
(c)
0.055
0.050
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
Data: Data1_B
Model: user5
χMT
Chi^2/DoF
= 1.9664E-8
R^2
= 0.99969
P1
P2
P3
P4
P5
P6
2.015 ±--
±--
2647.34096
0.03192
-4.44991
0.81792
2
±97.52167
±0.00007
±0.0551
±0.00367
0
50
100
150
200
250
300
T (K)
Figure S11. (a) The magnetic susceptibility of complex 5 under 0.5 T applied field, (b)
effective magnetic moment (ꢀeff) vs temperature (T) plot, and (c) the best fit gives
g({Fe(NO)2}9) = 2.015, g(L•) = 2.000, ꢁS/T = 1840 ± 68 cm–1, θ = –4.45 ± 0.06 K, p = 3.19
% and TIP = (81.8 ± 0.4) × 10–6 cm3 mol–1 (R2 = 0.999).

Figure S12. Frontier MO diagram of complex 4. Numbers shown are the compositions of Fe
3d, NO 2p and N ([N(mesityl)(TMS)]ꢀcoordinated ligands) 2p orbitals in each MO.

Figure S13. Frontier MO diagram of complex 5. Numbers shown are the compositions of Fe
3d, NO 2p and N ([N(mesityl)(TMS)]ꢀcoordinated ligands) 2p orbitals in each MO.