Structure and nitrite reduction reactivity study of bio-inspired copper(i)-nitro complexes in steric and electronic considerations of tridentate nitrogen ligands

Article abstract of DOI:10.1039/c7dt03843g

Two copper(i)-nitro complexes [Tpm^3-tBuCu(NO₂)] (1) and [(Ph₃P)₂N][Tp^3-tBuCu(NO₂)] (2), containing steric bulky neutral tris(3-tert-butylpyrazolyl)methane and anionic hydrotris(3-tert-butylpyrazolyl)borate ligands, have been synthesized and characterized. Complex 2 adopts a unique κ²-binding mode of Tp^3-tBu around the copper(i)-nitro environment in the solid state and shows a four-coordinated tetrahedral geometry surrounded by a nitro and three pz^3-tBu groups in solution. Both complexes 1 and 2 allow for the stoichiometric reduction of NO₂^- to NO with H⁺ addition. The results of this effort show that increasing steric bulk and electron donation properties on the nitrogen ancillary ligand will improve the nitrite reduction ability of the copper(i)-nitro model complexes.

Full text of DOI:10.1039/c7dt03843g

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PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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PAPER
Structure and Nitrite Reduction Reactivity Study of Bio-inspired
Copper(I)-nitro Complexes in Steric and Electronic Considerations of
†
Received 00th January 20xx,
Accepted 00th January 20xx
Tridentate Nitrogen Ligand
a,b
a,c
a
a,b
a
DOI: 10.1039/x0xx00000x
Yu-Lun Chang , Ya-Fan Lin , Wan-Jung Chuang , Chai-Lin Kao , Manmath Narwane ,
a
a,b
,a,d
Hsing-Yin Chen , Michael Y. Chiang , Sodio C. N. Hsu*
www.rsc.org/
3
-tBu
3-tBu
Two copper(I)-nitro complexes [Tpm Cu(NO
2 3 2 2
)] (1) and [(Ph P) N][Tp Cu(NO )] (2), containing steric bulky neutral
tris(3-tert-butylpyrazolyl)methane and anionic hydrotris(3-tert-butylpyrazolyl)borate lignads, have been synthesized and
2
3-tBu
characterized. Complex 2 adopts a unique
κ
-binding mode of Tp
around copper(I)-nitro environment in solid state
3
-tBu
and shows four-coordinated tetrahedral geometry surrounded by a nitro and three pz
groups in solution. Both
2
to NO with H addition. The results of this efforts show
-
+
complexes 1 and 2 allow for the stoichiometric reduction of NO
the increasing steric bulky and electronic donation properties on the nitrogen ancillary ligand will improve the
nitrite reduction ability on the copper(I)-nitro model complexes.
ligands in model copper(I)-nitro complexes (Scheme 1).
Recently, the first example of a monomeric copper(I)-nitrito
complex, containing two bidentate nitrogen ligands, was
Introduction
-
Copper-containing nitrite reductases (Cu-NIRs) catalyze the
reduction of nitrite to nitric oxide (NO), a key step in
described, but its reduction ability of NO
evaluated.
2
to NO was not
2
9
1
-5
denitrification.
Base on numerous spectroscopic and
A
B
C
crystallographic studies, the catalysis mechanisms of Cu-NIRs
will involve formation of copper(I)-nitro (N-bound) or -nitrito
O
O
O
O
N
N
6
-18
O
O
N
Cu
(O-bound) core species in type 2 center.
site of Cu-NIRs contains a copper ion ligated by three histidines
The type 2 active
N
Cu
N
N
N
N
Cu
N
N
N
N
3
that are in a facial conformation. Due to the complexity of the
Cu-NIRs enzyme structures, chemists have tried to use some
relatively simple ligands to model the environment of the type
*
*
First bio-inspired complex for * Release NO under acid condition
Cu-NIR
Release NO under acid
condition (Tolman)
* No report in NO releasing
(Walton)
(Yokoyama)
2
copper center. However, because of the instability of
copper(I)-nitro complexes, only few copper(I)-nitro
complexes have been synthesized and fully characterized.
Despite the instability issue, using simple ligands, Tolman and
D
E
F
a
-
1
9-27
O
O
O
O
O
N
O
N
N
N
R
R
R
R
N
Cu
Cu
Cu
R
R
N
N
N
N
N
N
N
N
i
20
N
N
N
co-workers successfully synthesized [( Pr-TACN)Cu(NO
2
)],
N
N
N
N
N
N
N
R'
N
R'
which forms NO(g) by reaction with acid, generating the first
functional biomimetic model of the copper center in Cu-NIRs.
To explore the electronic influences of compounds of this type,
various N3 donating ancillary ligands have been made and
their complexes have been fully characterized by neutral
C
H
C
R'
B
H
OH
R = Et, iPr
R = R' = Me, Et, iPr
* No X-ray Structure
* Release NO under acid condition
(Lehnert and co-workers)
*
Release NO under acid condition (Fujii)
G
H
I
-
n
O
N
O
O
O
O
2
4, 25
N
O
N
N
ligand such as tris(pyrazolyl)methane (Tpm),
and tris(4-
or by negative ligand such
O
Cu
H
H
O
Cu
2
4
imidazolyl)carbinol (TIC),
tris(pyrazolyl)borate (Tp) or tris(triazolyl)borate tridentate
H
N
N
N
N
N
N
O
N
2
5
28
N
Cu
N
N
N
N
N
N
N
B
H
X
H
X = C, n = 0; X = B, n = -1
*
*
First bio-inspired activity complex
bearing a negtive ligand
Release NO under acid condition
* No X-ray Structure
* Release NO by the second
coordination sphere
* First bio-inspired activity complexes
in steric and electronic consideration
* Release NO under acid condition
(This work)
(
Hsu)
consideration (Szymczak)
Scheme 1. Structural Illustrations of specific Tpm, Tp, and
other Cu(I) nitrite complexes bearing in N3 ligand
environment.
A few Cu(II)-nitrito complexes with Tp ligand have been
characterized by X-ray crystallography showing either a symmetric
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ARTICLE
Journal Name
2
-
tBu
38
or asymmetric
η
-O,O coordination mode of the NO
2
ligand
However, these (triphenylphosphine)iminium] in THF yielded a yellow solution
Cu]
2
react with [(Ph
3
P)
2
N](NO
2
)
[(Ph
3
P)
2
N
=
bis-
3
0, 31
depending on the pyrazolyl substituents.
compounds do not support nitric oxide formation from nitrite.
Very recently, electron-deficient β-diketiminate copper(II)- [(Ph
nitrito complex also show the activation of nitrite through the cooling to -20 °C (Scheme 2). The anionic copper(I)-nitro
3
2
that deposited an mononuclear copper(I)-nitro complex
3
-tBu
3
2 2
P) N][Tp Cu(NO )] (2) as pale yellow prism upon
2
7, 33
oxygen atom transfer pathway or thiol reduction.
Two species is rarely reported due to their instability and air-
phosphine ligands supported copper(I)-nitrito complexes, have sensitivity. Only two examples were described separately by
21
2
8
25
described by our group and others, could release NO under Lehnert and his co-workers and our lab , but only our lab
3
4, 35
acidic condition act as functional model of Cu-NIRs.
reported crystallographic structure of anionic copper(I)-nitro
complex [(Ph
a positive molecular ion peaks (m/z = 445.16) which is
Me2
3 2 2
P) N] [Tp CuNO ]. The FAB-MS data of 1 shows
In order to understand how electronic issue will affect the
nitrite reduction ability in the bio-inspired copper(I)-nitro
model of Cu-NIRs, we first reported and examined the
-
corresponding to the loss of coordinated NO
2
(Fig. S1, ESI
On the other hand, the ESI-MS data of anionic complex
†
).
Me2
2
displays a negative molecular ion peaks (m/z = 490.37)
3 2 2
electronic rich anionic [(Ph P) N][Tp Cu(NO )] complex
which is more effective model compound for nitrite reduction
-
Me2
to NO than neutral [Tpm Cu(NO
25
contains coordinated NO
and contain diagnostic metal-to-ligand charge-transfer bands
Me2 at 320 nm (
2
(Fig. S2, ESI†). UV-vis spectra of 1
2
)] analogue. However,
RR
2
steric hindrance influences discussion in Tp type copper(I)-
nitro complexes still remains an unknown entity. Since Tp
-
1
-1
-1
-1
ε
= 4200 M cm ) and 295 nm (ε = 4292 M cm ),
3
-tBu
respectively.
and Tp
ligands have similar electronic donating ability, as is
evident from similar value in the [Tp Cu(CO)] stretching
R,R
Complexes
investigated by X-ray crystallography (see Table 1), indicating
will be chosen to explore how the steric that both complexes are mononuclear. As shown in Fig. 1,
1
and 2 were obtained as single crystals and
−1
Me2
CO: 2066 cm for Tp ; 2069 cm for Tp ).
−1
3-tBu 36
frequencies (
ν
Therefore, the Tp
3
-tBu
Me2
3-tBu
to Tp
change in the ligand from Tp
alters the structures complex 1 has a C3 pseudoaxis along the Cmethine···Cu···N atoms
and the spectral properties of copper(I)-nitro complexes (Chart with a symmetric disorder of nitrite molecule. The Tpm
3
-tBu
3
-tBu
3
1). The electronic effect between the neutral Tpm
anionic Tp
copper(I)-nitro complexes [Tpm
3-tBu
N][Tp Cu(NO
and tridentate ligand bound to copper ion in a
was also investigated. The synthesis of two new nitrite ion is bound to copper in a N coordination manner. The
κ -manner and the
3
-tBu
3
-tBu
Cu(NO
2
)]
(
1
)
and coordination geometry of copper atom in complex
) are described here, both could described as tetrahedral environment. The Cu-Nnitrite distance
1
is
[(Ph
evolve NO(g) upon protonation and act as bio-inspired of 1.921(9) Å in complex
3
P)
2
2
)] (2
Me2
1
is longer than the [Tpm Cu(NO
2
)]
2
4
compounds for Cu-NIRs.
[1.833(6) Å] due to the steric hindrance of 3-tert-butyl compared
to 3-methyl.
Complex 2 shows a Y-shape coordinated environment by
3
-tBu
2
two nitrogen of the anion Tp
ligand in a
κ -manner and the
N-bound nitrite ion as shown in Fig. 2, is a new binding mode
for Tp ligand in copper-nitrite chemistry. Very recently, a
potential relevance anionic three coordinate Cu(I) nitro
complex bearing a
Warren. Two pyrazolyl rings of Tp
β-dikitiminate ligand was reported by
2
7
3-tBu
ligand are binding to
copper(I)-nitro core and the third pyrazolyl ring is hanging
away from the copper(I) core. The steric hindrance and charge
3
-tBu
consideration of the Tp
for adoption of this unusual binding mode. The average
distance of Cu-N of complex is 1.993 Å which is shorter than
related bis(pyrazolyl)methane ligand Cu(II) (bis-nitrito) complex
ligand presumably are responsible
Me2
Chart 1. Comparisons of the Tpm , Tp , Tpm
Me2
3-tBu
3-tBu
38
and Tp
ligand sets.
L
2
3
2
(
2.005
Å) due to the electronic consideration of ligand effect.
The IR analysis (KBr pellets) also supports the different
Results and discussion
-
3
-tBu
structural properties between
1
and
2
. The NO
at 1319, 1293 cm
are due to the three-
coordinated copper(I)-nitro environment.
2
stretching
The neutral copper(I)-nitro complex [Tpm
Cu(NO
2
)] (
was prepared through the reaction of [Tpm
1
)
-1
-
3
-
bands of appear at 1306, 1282 cm , and 2
1
1
-
tBu
37
Cu(CH CN)](BF ) with NaNO and isolated as a yellow solid.
For comparison to neutral Tpm ligand, the mononuclear
complex [Tp Cu(CH CN)] or the binuclear complex [Tp
2
. The higher NO frequencies in 2
3
4
2
3
-tBu
3
-tBu
38
3-
3
Scheme 2. Method for synthesis of copper(I)-nitro complexes 1 and 2
2
| J. Name., 2012, 00, 1-3
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3
-
Fig. 2 ORTEP drawing of an anion of the X-ray structure of
[(Ph P) N][Tp Cu(NO )] (2) (50% ellipsoids; hydrogen atoms
3 2 2
not shown for clarity).
Fig. 1 ORTEP drawing of the X-ray structure of [Tpm
Cu(NO
clarity) and the projections along their C3-pseudoaxis.
3
-tBu
tBu
2
)] (1) (50% ellipsoids; hydrogen atoms not shown for
Me2
-
The solution structures of complex
by NMR and IR analysis. Interestingly, measurements of
carried out in solution and solid states give consistent results, consideration of solvent effects. According to the crystal
1 and 2 were confirmed and [Tp Cu(NO )] are respectively about 8 and 12 kcal/mol
2
1
more stable than the tri-coordinated isomers with/without the
whereas the structure of
2
in solution disagrees with that in structural analysis of
the solid state (see Table 2). The H NMR spectrum of complex uncoordinated pz
2
, interaction between the N atom on the
+
and the H atom on [(Ph P) N] can be
1
3-tBu
3
2
3
-tBu
+
2
symmetrical
reveals only one type of pz
3
signals, implying the found. Therefore, the effect of the counterion [(Ph P)
3-tBu
in solution. To further taken into account in the gas-phase calculation. To our
3
2
N] was
κ -coordinated nature of Tp
+
obtain better understanding of its solution behavior, complex surprise, in the presence of [(Ph
was then subjected to the variable temperature NMR studies structure of is not a minimum on the energy surface. Instead,
as NMR solvent). The chemical shifts the equilibrium geometry obtained after optimization shows
3 2
P) N] , the tetra-coordinated
2
2
8
(333 K to 173 K; THF-d
3
-tBu
3-tBu
for pz
were observed to be temperature independent (Fig. the dissociation of one of the pz
). Furthermore, the IR spectrum of
recorded in DMSO leading to a trigonal planar arrangement of the Cu(I) center.
fragments, thereby
S4, ESI
exhibits the NO
the peaks shown in [(PPh
with a more electron-rich copper center. The facts suggest that tetra-coordinated structure of [(Ph
†
2
-
-1
Me2
-
)] and [(Ph
+
stretching bands at 1299 and 1270 cm , similar to The shortest distance between [Tp Cu(NO
P) N]
3 2
2
2
Me,Me
14
25
)
2
N][Tp
Cu( NO
2
)] , consistent was found to be 2.432 Å (Fig. S5, ESI†). On the other hand, the
3
Me2
P)
calculated to be 18.7 kcal/mol more stable than the tri-
group thus adopts a distorted tetrahedral coordinated one (Fig. S6, ESI ). Consequently, the structural
geometry (see Scheme 2).
variation of can be attributed to both the steric effect and
N][Tp Cu(NO )] was
2 2
3
3
-tBu
complex
2 in solution has a Cu(I) center surrounded by three pz
-
moieties and a NO
2
†
2
The dispersion-corrected DFT calculations were performed the necessity to neutralize the negative charge on the ligand.
to shed more light on the structural variation from solid state For the tetra-coordinated isomers, the average Cu–N bond
3
-tBu
3-tBu
in [Tp Cu(NO
-
to solution. The B3LYP-D3/6-31g* approach in Gaussian 09 length between Cu and pz
program was exploited to obtain the optimized structures. The longer than that in [Tp Cu(NO
)] is 0.06 Å
). Hence, the
2
Me2
-
)] (Fig. S7, ESI
2
†
3
-tBu
polarized continuum model (PCM) was employed to mimic anionic Tp
solvation. The tetra-coordinated structures of [Tp
ligand is much easier to be attracted by
arm.
3
-tBu
-
)] [(Ph
+
N] and undergo dissociation of one pz
3-tBu
Cu(NO
2
3
P)
2
Table 1. Selected Bond Distance (Å) and Angles (deg) for
1, 2, and Known Relevant Copper(I)-Nitro Complexes
Cu-Nnitro
N-O
Cu-N
L
O-N-O
N
L
-Cu-Nnitro
N
L
-Cu-N
L
ref
3
-tBu
Tpm Cu(NO
[
2
)] (
1
)
1.921(9)
1.264(9)
.264(9)
2.112(4)
2.112(4)
96.2(7)
125.93(9)
125.93(9)
125.93(9)
89.06(13) this work
89.06(13)
89.06(13)
1
2.112(4)
3-tBu
N][Tp Cu(NO
[(Ph
3
P)
2
2
)] (
2
)
1.925(4)
1.883(6)
1.224(3)
.224(4)
1.176(7)
.278(7)
1.985(3)
2.001(3)
2.051(3)
2.051(3)
122.8(3)
117.4(5)
131.53(13) 96.33(12) this work
131.98(13)
1
Me,Me
24
[Tpm
Cu(NO )]
2
126.7(1)
126.7(1)
128.4(2)
86.2(2)
87.6(1)
87.6(2)
1
2.124(5)
Me,Me
25
[
(PPh
3
)
2
N][Tp
Cu(NO
2
)]
1.927(5)
1.212(9)
.290(12)
2.070(3)
2.078(5)
2.103(4)
116.7(7)
116.8(8)
121.07(19) 89.17(16)
126.38(19) 90.19(14)
128.2(2)
a
1
a
1
1
.161(10)
.332(13)
90.51(17)
a
3
9
NaNO
a
1.240(3)
Oxygen atoms in the copper-bound nitro were found to be disordered.
114.9(5)
2
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Table 2. Comparisons on the Vibrational Frequencies of 1, 2, and Known Relevant Copper(I)-Nitro Complexes
-
1
-1
FT-IR cm (Solution, DMSO)
FT-IR cm (KBr)
(NO2)
a
compound
ν
ν
(NO2)
ref
3
Tpm Cu( NO )] (
-tBu
14
[
[
1
)
1306, 1282, 821
1285, 1256, 814
1319, 1293, 812
1300, 1265, 820
1312, 1289, 824
1289, 1262, 814
1302, 1284, 806
1284, 1265, 805
1303, 1283
1299, 1270
-
this work
2
3
-tBu
Tpm Cu( NO
15
2
)]
3
N][Tp Cu( NO
-tBu
14
[(Ph
3
P)
2
2
)] (
2)
this work
3
(Ph P) N][Tp Cu( NO )]
-tBu
15
[
3
2
Me,Me
2
14
Cu( NO
24
[Tpm
2
2
)]
)]
Me,Me
15
Cu( NO
Me,Me
[
Tpm
(PPh
(PPh
14
b
25
[
[
a
3
3
)
)
2
N][Tp
N][Tp
Cu( NO
2
)]
)]
1299, 1268
s
ν (N-O) and νas(N-O) values.
Me,Me
15
Cu( NO
2
2
Due to the complexity on the fingerprint region, only show the
This work.
b
1
or
temperature, color change observed from yellow to blue-
green. The results show that complex is highly reactive
2 was treated with 4 equiv. of acetic acid at ambient
Table 3. Yields of NO generation of 1, 2 and known copper(I)-
nitro complexes.
2
toward acids, as shown by the immediate color change that
occurs when the complex is subjected to acidic conditions. In
Complex
NO yield
Ref
a
a
c
Me2
Tpm CuNO
52.3±3.7
32.0
24, 25
contrast,
toward oxygen, we observed complex
sensitive and that is air- and moisture-stable in the solid
state but air-sensitive in solution. These properties may be a
consequence of the different electronic nature of the Cu-NO
cores of and which has been observed earlier in the studies
1
reacts more slowly with acid. For the reactivity
2
b
2
is extremely air
1
Me2
N][Tp Cu(NO
25
[(Ph
3
P)
2
2
)]
83.3±2.3
a
2
3-tBu
Tpm Cu(NO ) (
80.0
86.4±0.5
1
)
This work
1
2
2
Me2
Me2
25
2 3 2 2
of [Tpm CuNO ] and [(PPh ) N][Tp CuNO ].
a
To confirm the NO generation ability from these reactions,
the generating NO gas was trapped with Co(TPP) (TPP = tetra-
phenylporphyrinato) complex that has high affinity for NO (Fig.
S10). From the vial-to-vial gas-trapping experiment and UV
detection, it was estimated that about 86% and quantitative
3
-tBu
93.0
quantitative
[
(Ph P) N][Tp Cu(NO )] (
2
)
c
This work
3
3
2
2
2
3
-tBu,5Me
c
28
[(Ph
P)
N][Ttz
Cu(NO
2
)]
93.0
a.
Addition of 6 equiv. acetic acid and detection from GC-TCD
method.
Addition of 4 equiv. acetic acid and detection from the
intensities of the EPR signals.
Addition of 4 equiv. acetic acid and detection from UV band
of Co(TPP).
yield of NO were trapped for complexes
Comparisons of the NO evolution results demonstrate that the
more steric bulky and electron-rich complex is a more
effective model compound for nitrite reduction than the
1 and 2, respectively.
b
2
c
25
neutral complex
Table 3), and is a good functional bio-inspired Cu-NIRs model.
1 and known copper(I)-nitro complexes (see
2
5
Importantly, no N
2
O gas is found by known GC-TCD method
3
-tBu
Cyclic voltammetry measurements were conducted to and the blue-green copper(II) product [Tpm
Cu(OAc)
are generated as products in the
and (Fig. S11 and S12, ESI ).
] (3) as
2
3
-tBu
31
assess the ligand properties of the neutral and anionic well as [Tp Cu(OAc)] (
copper(I)-nitro complexes. Complex
exhibits an irreversible respective reaction of
wave with an Epa of 0.08 V (Fig. S8, ESI
), which is nearly the Complexes and
copper(I)-nitro analogue. These results UV-vis, IR, and ESI-MS, S11-S14) with samples prepared
4)
2
1
2
†
†
3
4 prepared via these routes are identical (by
Me2
25
Me2
same as the Tp
3
-tBu
provide another evidence that Tp
and Tp
have identical directly from copper(II) acetate.
2
fragment in
coordination modes toward the Cu(I)-NO
solution. Besides, the two ligands are evaluated to possess
similar electronic donating abilities according to the Summary and conclusions
electrochemical data. In contrast, the cyclic voltammetry of
contains an irreversible wave at Epa = 0.16 V (Fig. S9, ESI
1
†
In summary, two copper(I)-nitro complexes bearing steric
3
-tBu
3-tBu
bulky neutral Tpm
exam their nitrite reduction ability. Crystallographic evidence
of complex shows a four-coordinated distorted tetrahedral
environment and moderate NO generation ability. Complex
and anionic Tp
were synthesized and
)
,which is significantly higher than that of . This finding
2
indicates the electronic influences of the tridentate ligands
dominate the redox properties of the copper(I)-nitro
complexes. The irreversible oxidation behavior (Cu ) of
1
I/II
2
contains a copper(I)-nitro core in a unique three-coordinated
environment in solid state, protonation of which to release NO
gas quantitatively is of interest within the context of the
chemistry of the biological denitrification process. Our work
complexes
changed via a classical EC mechanism.
In order to probe the viability of
NIRs models under anaerobic conditions, the CH
1 and 2 may due to the coordinate geometry
1
and
2
as functional Cu-
Cl solution of
2
2
4
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ARTICLE
shows that the steric bulky on the ancillary ligand will improve Method B: In glove box, a solution of [(Ph P) N](NO ) (0.361 g,
3
2
2
3
-
the nitrite reduction ability on the copper(I)-nitro model 0.618 mmol) in 6 mL acetone was added to a solution [Tp
complexes.
tBu
Cu(CH CN)] (0.300 g, 0.618 mmol) in 5 mL THF followed by
3
stirring 2 hrs. The solution was kept at -20°C for 3 days under a
N atmosphere to yield yellow crystals (0.128 g, 0.125 mmol,
Experimental section
2
2
0 %).
General considerations
All manipulations involving copper(I) complexes were
carried out under an atmosphere of purified dinitrogen in the
dry box, or using standard Schlenk techniques. Chemical
reagents were purchased from Aldrich Chemical Co. Ltd.,
Lancaster Chemicals Ltd., or Fluka Ltd. All the reagents were
used without further purification, apart from all solvents that
3-tBu
[
Tpm
2 3 2
Cu(O CCH ) ] (3)
3
-tBu
To a stirred methanol solution (15 mL) of Tpm (0.200 g,
.522 mmol) at r.t. and under nitrogen, Cu(O CCH ) (0.063 g,
2 3 2
.348 mmol) was added. After approximately 12 h the solvent
was removed by a rotary evaporator. The residue was
extracted with diethyl ether, and undissolved powder was
filtered off using Celite. The filtrate was evaporated under
reduced pressure to give a blue-green solid 0.121 g (41%) of
0
0
2 2 2 2 3
were dried over Na (Et O, THF) or CaH (CH Cl , CH CN) and
then thoroughly degassed before use. The mononuclear
)
3
-tBu
37
3-
copper(I) complexes [Tpm
Cu(CH CN)] or the dinuclear complex [Tp
Cu(CH
3
CN)](BF
4
and [Tp
-
1
tBu
38
3-tBu
38
product. IR (solution, CH
3
CN, cm ): 3377br [
(COO)], 1456 [ (COO)], 1365, 1252, 1160,
2 3
056, 803, 759. ESI-MS: m/z = 504.16 [Tpm CCH )] .
ν(O-H)], 2961,
3
Cu]
2
were
2
1
916, 2866, 1528 [
ν
ν
prepared as described in the literature. IR spectra were
recorded on a Varian FT-IR 640 or Brucker Alpha FT-IR
3
-tBu
+
Cu(O
, cm M )]: 223 (10714), 253 (2192),
-
1
-1
spectrometer. UV-vis spectra were recorded on an Agilent 8453 UV-vis (CH
spectrophotometer. H NMR and C NMR spectra were 672 (53).
acquired on a Varian Gemini-200 proton/carbon FT NMR or a
3
CN)[λ
max, nm(
ε
1
13
X-ray Crystal Structure Determinations
Varian Gemini-500 proton/carbon FT NMR spectrometer.
Elemental analyses were performed using a Heraeus CHN-OS
Rapid Elemental Analyzer. ESI mass spectra were collected on
a Waters ZQ 4000 mass spectrometer. Cyclic voltammetry
All single-crystal X-ray diffraction data were accumulated using
a Bruker Nonius Kappa CCD diffractometer using Mo Kα
radiation (λ = 0.71073 Å). The data collection was executed
-4
4
0
measurements were taken in 10 M MeCN solutions using 0.1 M
using the SMART program. Cell refinement and data
reduction were made with the SAINT program. The structure
+
/0
4
1
(
4 6
Bu N)(PF ) as supporting electrolyte and referenced to Fc . A
4
2
platinum wire counter electrode, a glassy carbon working electrode,
and an Ag/AgCl (MeCN) reference electrode were used. Gas
chromatography thermal conductivity detector (GC-TCD)
experiments were performed by using a Agilent/HP 6890 GC with
was determined using the SHELXTL/PC program and refined
using full-matrix least squares. All non-hydrogen atoms were
refined anisotropically, whereas hydrogen atoms were placed
at calculated positions and included in the final stage of
refinement with fixed parameters.
°
TCD & FID, Porpak Q column (6 ft, 20 mL/min flow rate, 30 C,
nitrogen carrier gas), and TCD detector.
3
-tBu
Computational Details
[
Tpm
A solution of [Tpm
in 15 mL methanol was added to a solution of sodium nitrite
0.150 g, 2.175 mmol) in 10 mL methanol followed by stirring 1
2
Cu(NO )] (1)
3
-tBu
All calculations were executed using Gaussian 09 program
package at the B3LYP–D3 level with the 6–31g* basis set.
Cu(CH
3
CN)](BF
4
) (0.203 g, 0.435 mmol)
43-45
The polarized continuum model (PCM) was employed to mimic
The vibrational
(
46-48
systems in solution of acetone and DMSO.
frequencies were analyzed at the same level to confirm all the
optimized structures are corresponding to the local minima.
hr. The reaction mixture was evaporated under vacuum at
room temperature to remove solvent. The resulting
precipitates formed were washed by MeOH to give a yellow
solid 0.160 g (75%) of product. 1H-NMR(d
3
-acetonitrile):
δ
8.25
pz ),
.29(s, 27H, Me2pz ). IR(KBr, cm ; ν(NO )): 1306, 1282. IR
3
-tBu
Detection of NO generated from 1 or 2
(
s, 1H,
H
C(Tpm
)
3
), 7.57 (d, 3H, 5-
H
pz ), 6.27 (d, 3H, 4-H
-
1
Method A : A solution of
mL) was prepared in a small vial capped with a rubber septum.
A solution of acetic acid (21 L) in CH Cl (0.1 mL) was then
1 (0.029 g, 0.059 mmol) in CH Cl (0.9
1
2 2
2
-1
(solution, DMSO, cm ;
ν
(NO
45.16 [Tpm Cu] . Anal. Calcd for C22
.96; N, 19.92. Found: C, 53.76; H, 7.01; N, 19.89.
2
)): 1303, 1283. ESI-MS: m/z =
3
-tBu
+
μ
4
6
H34CuN
7
O
2
: C, 53.70; H,
2
2
introduced with a syringe at room temperature. The solution
changed immediately from light-yellow to blue-green. A
3
-tBu
solution of
prepared in a small vial capped with a rubber septum. A
solution of acetic acid (21 L) in CH Cl (0.1 mL) was then
2 2
2 (0.061 g, 0.059 mmol) in CH Cl (0.9 mL) was
[
(Ph
Method A: In glove box, a solution of [(Ph
.672 mmol) in 1.4 mL acetone was added to a solution [Tp
3
P)
2
N][Tp
2
Cu(NO )] (2)
3
2 2
P) N](NO ) (0.393 g,
3
-
μ
2
2
0
tBu
introduced with a syringe at room temperature. The solution
changed immediately from light-yellow to blue-green. Analysis
of the headspace gas by a TCD indicated that NO had been
Cu]
hrs. The solution was kept at -20°C for 3 days under a N
atmosphere to yield yellow crystals (0.276 g, 0.269 mmol, 40
). 1H NMR (d -acetone ): 7.58~7.78 (m), 6.9 (d, 3H, 5-
(pz)), 6.01 (d, 3H, 4- (pz)), 1,31(s, 27H, CMe). IR (KBr, cm ;
(NO )): 1319, 1293. IR (solution, DMSO, cm ;
270. ESI-Mass(-): m/z = 490.37 [Tp
: C, 66.50; H, 6.27; N, 10.88. Found: C,
6.38; H, 6.57; N, 10.45.
2
(0.300 g, 0.336 mmol) in 0.5 mL THF followed by stirring
2
2
generated (80.0 for
1 and 93.0 for 2). The NO generation data
%
H
6
δ
-1
are obtained by using three different experiments (see Table 3).
NO concentrations were determined by using a calibration
curve correlating responses to known concentrations of NO
gas mixed with N (120, 100, 80, 60, and 40 ppm of NO in N );
2 2
molar quantities were calculated using the ideal gas equation.
H
-
1
ν
1
2
ν
(NO
2
)): 1299,
3
-tBu
-
Cu(NO )] . Anal. Calcd
2
8 2 2
for C57H64BCuN O P
6
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-
6
Method B : A mixture of
[
1
Co(TPP)] (0.004 g, 5.955 X 10 mol ) in MeOH (4 mL) was
(0.003 g, 5.955 X 10 mol) and 14.
Y. Zhao, D. A. Lukoyanov, Y. V. Toropov, K. Wu, J. P.
Shapleigh and C. P. Scholes, Biochemistry, 2002, 41, 7464-
7474.
-
6
-5
placed in a septum sealed vial. Acetic acid (2.2 ꢀL, 3.573 X 10
mol) was injected to this solution via a syringe. The mixture 15.
was kept for 60 minutes at room temperature and then the
UV/Vis spectrum of the resultant mixture was recorded. The 16.
E. I. Tocheva, F. I. Rosell, A. G. Mauk and M. E. P. Murphy,
Science, 2004, 304, 867.
S. V. Antonyuk, R. W. Strange, G. Sawers, R. R. Eady and S.
S. Hasnain, Proc. Natl. Acad. Sci. USA, 2005, 102, 12041–
12046.
data showed the formation of [Co(NO)TPP]. A mixture of
2
-6
-6
(0.006 g, 5.95 X 10 mol) and [Co(TPP)] (0.004 g, 5.95 X 10
mol) in MeOH (4 mL) was placed in a septum sealed vial. Acetic 17.
S. Ghosh, A. Dey, Y. Sun, C. P. Scholes and E. I. Solomon, J.
Am. Chem. Soc., 2009, 131, 277-288.
-5
acid (2.2 ꢀL, 3.57 X 10 mol) was injected to this solution via a
syringe. The mixture was kept for 60 minutes at room 18.
M. Nojiri, H. Koteishi, T. Nakagami, K. Kobayashi, T. Inoue,
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temperature and then the UV/Vis spectrum of the resultant
mixture was recorded. The data showed the formation of 19.
[Co(NO)TPP].
2
2
0.
1.
1
16, 5475-5476.
J. A. Halfen, S. Mahapatra, E. C. Wilkinson, A. J.
Gengenbach, V. G. J. Young, L. J. Que and W. B. Tolman, J.
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Conflicts of interest
There are no conflicts to declare.
2
2
2.
3.
H. Yokoyama, K. Yamaguchi, M. Sugimoto and S. Suzuki,
Eur. J. Inorg. Chem., 2005, 2005, 1435-1441.
A. K. Nairn, S. J. Archibald, R. Bhalla, C. J. Boxwell, A. C.
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Acknowledgements
We gratefully acknowledge financial support from the Ministry of
Science and Technology of Taiwan (MOST 102-2113-M-037-008-
MY3; MOST 104-2632-M-037-001), NSYSU-KMU Joint Research
Project (NSYSUKMU 105-P006), and Kaohsiung Medical University
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2
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M. Kujime, C. Izumi, M. Tomura, M. Hada and H. Fujii, J.
Am. Chem. Soc., 2008, 130, 6088-6098.
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M. Y. Chiang, C.-L. Kao and H.-Y. Chen, Inorg. Chem., 2012,
“
Aim for the Top University Grant, grant No. KMU-TP105PR12”. We
thank Mr Ting-Shen Kuo, National Taiwan Normal University for X-
ray structural determinations and Mr Min-Yuan Hung, Center for
Research Resources and Development of KMU for their facilities.
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Table of contents entry:
3
-tBu
3-tBu
Two bio-inspired cooper(I)-nitro complexes bearing steric bulky neutral Tpm
synthesized to release NO gas under acid condition.
and anionic Tp
were