Accelerated photorelease of NO from {Ru-NO}6 nitrosyls containing carboxamido-N and carboxylato-O donors: Syntheses, structures, and photochemistry

Article abstract of DOI:10.1021/ic801748t

Three ruthenium nitrosyls, namely, [(Me₂bpb)Ru(NO)(OAc)], [(Me₂bpb)Ru(NO)(OBz)] (1), and [(Me₂Qb)Ru-(NO)(qca)] (BF₄) (2), have been synthesized from designed ligands with carboxamido-N donors. In all three compl

Full text of DOI:10.1021/ic801748t

Inorg. Chem. 2009, 48, 1490-1497
6
Accelerated Photorelease of NO from {Ru-NO} Nitrosyls Containing
Carboxamido-N and Carboxylato-O Donors: Syntheses, Structures, and
Photochemistry
Genevieve M. Halpenny and Pradip K. Mascharak*
Department of Chemistry and Biochemistry, UniVersity of California,
Santa Cruz, California 95064
Received September 15, 2008
Three ruthenium nitrosyls, namely, [(Me
2 2 2
bpb)Ru(NO)(OAc)], [(Me bpb)Ru(NO)(OBz)] (1), and [(Me Qb)Ru-
(NO)(qca)](BF ) (2), have been synthesized from designed ligands with carboxamido-N donors. In all three complexes,
4
a carboxylato-O donor is trans to the bound NO. The structures of 1 and 2 have been determined by X-ray
crystallography. The nearly linear Ru-N-O bond angles [175.18(18)° and 175.0(3)°, respectively] and diamagnetism
6
of the two nitrosyls are indicative of the {Ru-NO} configuration. All three complexes exhibit νNO in the range
-1
1
830-1890 cm . When solutions of 1 and 2 are exposed to low-intensity (milliwatts) UV light, rapid release of
NO is observed. The results of photochemical measurements indicate that the placement of the carboxylato-O
-
donor trans to NO promotes the photorelease of NO in these nitrosyls much like Cl and py. The presence of the
carboxamido-N donor is, however, essential for the observed NO photolability because the structurally similar
2
nitrosyl [(pyca) Ru(NO)(Cl)] (3) (with carboxylato-O trans to NO) does not release NO upon exposure to UV light.
Extension of conjugation in the ligand frame (quinoline rings in place of pyridine rings) increases both the rate of
NO photorelease and the quantum yield of 2 compared to 1. The results of this investigation confirm that the
combination of carboxamido-N donor(s) in the ligand frame and carboxylato-O trans to NO is a new structural motif
6
in photoactive {Ru-NO} nitrosyls.
7
-9
Introduction
for the treatment of various diseases.
Such attempts have
10,11
afforded novel NO donors such as diazeniumdiolates
and
In recent years, nitric oxide (NO) has been shown to play
key roles in several physiological and pathological pathways.
For example, NO participates in blood pressure control,
neurotransmission, inflammatory responses, and cell apop-
12
S-nitrosothiols, which release NO in cellular environments.
The extent of NO delivery by such systemic NO donors,
however, can hardly be controlled in biological systems
because the drug goes everywhere and releases NO via
relatively ubiquitous enzymatic or pH-dependent processes.
In order to deliver NO to selected target areas under the
control of light, we have developed a series of metal nitrosyls
1
-6
tosis.
The discovery of these biological effects of NO
has prompted research in the area of development of
exogenous NO donors that can deliver NO at desired locales
n+
*
To whom correspondence should be addressed. E-mail: pradip@
(NO complexes) of the type [(L)M(NO)(L′)] [L ) mul-
chemistry.ucsc.edu.
(
(
(
1) Ignarro, L. J. Nitric Oxide: Biology and Pathobiology; Academic Press:
San Diego, CA, 2000.
2) Feelisch, M., Stamler, J. S., Eds. Nitric Oxide Research; John Wiley
and Sons: Chichester, U.K., 1996.
3) Moncada, S., Higgs, E. A., Bagetta, G., Eds. Nitric Oxide and the
Cell: Proliferation, Differentiation and Death; Portland Press: London,
(7) Wang, P. G; Cai, T. B.; Taniguchi, N. Nitric Oxide Donors for
Pharmaceutical and Biological Applications; Wiley-VCH: Weinheim,
Germany, 2005.
(8) Chiueh, C. C., Hong, J.-S., Leong, S. K., Eds. Nitric Oxide: NoVel
Actions, Deleterious Effects, and Clinical Potential; New York
Academy of Sciences: New York, 2002.
1
998.
(
(
(
4) Lincoln, J.; Burnstock, G. Nitric Oxide in Health and Disease;
Cambridge University Press: New York, 1997.
5) Kalsner, S., Ed Nitric Oxide Free Radicals in Peripheral Neurotrans-
mission; Birkhauser: Boston, 2000.
6) Ko, G. Y.; Fang, F. C. Nitric Oxide and Infection; Kluwer Academic/
Plenum Publishers: New York, 1999.
(9) Wang, P. G.; Xian, M.; Tang, X.; Wu, X.; Wen, X.; Cai, T.; Janczuk,
A. J. Chem. ReV. 2002, 102, 1091–1134.
(10) Keefer, L. K. Curr. Top. Med. Chem. 2005, 5, 625–636.
(11) Hrabie, J. A.; Keefer, L. K. Chem. ReV. 2002, 102, 1135–1154.
(12) Wang, K.; Zhang, W.; Xian, M.; Hou, Y.-C.; Chen, X.-C.; Cheng,
J.-P.; Wang, P. G. Curr. Med. Chem. 2000, 7, 821–834.
1490 Inorganic Chemistry, Vol. 48, No. 4, 2009
10.1021/ic801748t CCC: $40.75  2009 American Chemical Society
Published on Web 01/21/2009

6
Accelerated Photorelease of NO from {Ru-NO} Nitrosyls
30,31
metal nitrosyls.
Greene and Richards have suggested that
the presence of two lone pairs on the carboxamido-N donor
allows greater electron donation (more covalent character)
2
+
to the Fe-N bond in [(PaPy
release of NO upon illumination. In the case of {Ru-NO}
nitrosyls derived from Schiff bases, NO photolability also
arises from a d (M)-π*(NO) transition (photoband), which
has some ligand (phenolato-oxo)-π*(NO) character as
3
)Fe(NO)] and facilitates the
30
6
π
Figure 1. Examples of multidentate ligands (L) employed to isolate
photoactive metal nitrosyls.
3
2,33
well.
In our search for other donor centers that could
6
tidentate ligands (Figure 1); M ) Ru, Fe, and Mn; L′ )
promote such a transition in {M-NO} nitrosyls, we have
now looked into the role of a carboxylato-O donor (an
anionic σ donor with two lone pairs) in introducing NO
photolability in metal nitrosyls. As examples of the simplest
-
monodentate ligands like py and Cl ] that rapidly release
13-20
NO upon exposure to light of various wavelengths.
The
utility of such NO donors in delivering NO at cellular targets
2
1-28
6
via triggering with light has also been established.
One interesting feature of these photoactive {M-NO}
type, we have synthesized two {Ru-NO} nitrosyls,
6
2-
[(Me
Me bpbH
benzene); R ) CH
2
bpb)Ru(NO)(RCOO)] [Me
2
bpb
) deprotonated
2
9
metal nitrosyls is the presence of one (or two) carboxa-
mido-N donors in the donor set of the ligand L. Our work
has clearly shown that the presence of this strongly σ-donat-
ing anionic N donor either in the equatorial plane of the metal
nitrosyl or trans to the bound NO makes these nitrosyls
susceptible to light of low intensity (milliwatts to watts).
2
2
, 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-
and Ph], in which the carboxylate ligand
3
acts as a monodentate ligand bound through one O atom.
As part of a more involved second type, we have employed
-
quinoline carboxylate (qca ) as a bidentate ligand (bound
through quinoline-N and carboxylato-O) to isolate
6
3+
Although {Ru-NO} nitrosyls such as [Ru(NH
L ) py, NH , Im, etc.) and K [Ru(NO)(Cl)
photolability, the intensity of UV light required for NO
3
)
4
(L)(NO)]
[(Me
mination of [(Me
PhCOO ) and [(Me
2
Qb)Ru(NO)(qca)]BF
4
. Following the structural deter-
bpb)Ru(NO)(OBz)] (1; OBz ) benzoate,
Qb)Ru(NO)(qca)]BF (2), we investi-
(
3
2
5
] exhibit NO
2
-
2
4
2
7
release is usually high (300-500 W). In addition, the
gated the capacity of NO photorelease of these two structur-
6
6
designed {Ru-NO} nitrosyls with carboxamido-N donor(s)
ally similar {Ru-NO} nitrosyls (both with carboxylato-O
6
exhibit high quantum yield (φ) values compared to nitrosyls
trans to NO) along with that of another {Ru-NO} nitrosyl
-
34
derived from typical N-donor ligands such as NH
3
, py, bpy
2
[(pyca) Ru(NO)(Cl)] (3; pyca ) picolinate ligand) that
2
7
(
2,2′-bipyridine), and phen (1,10-o-phenanthroline). The
is devoid of carboxamido-N coordination (but with carboxy-
lato-O trans to NO). The results of such studies are reported
in this article. As discussed in the following sections, both
1 and 2 exhibit excellent photolability while 3 (no carboxa-
mido-N coordination) does not. Also, coordination of car-
results of recent theoretical work indicate that electronic
transition from a molecular orbital (MO), which is predomi-
nantly metal and carboxamido-N in character, to a M-NO
π*-antibonding MO promotes NO photolability in these
boxylates increases the capacity of NO photorelease from
(
13) Patra, A. K.; Afshar, R. K.; Olmstead, M. M.; Mascharak, P. K. Angew.
Chem., Int. Ed. 2002, 41, 2512–2515.
6
the {Ru-NO} nitrosyl 1 compared to [(Me
(
2
bpb)Ru(NO)-
1
8
Cl)]. Extension of conjugation in the ligand frame in 2
(
14) Patra, A. K.; Rowland, J. M.; Marlin, D. S.; Bill, E.; Olmstead, M. M.;
Mascharak, P. K. Inorg. Chem. 2003, 42, 6812–6823.
results in significant enhancement of the quantum yield
(
15) Patra, A. K.; Mascharak, P. K. Inorg. Chem. 2003, 42, 7363–7365.
16) Ghosh, K.; Eroy-Reveles, A. A.; Avila, B.; Holman, T. R.; Olmstead,
M. M.; Mascharak, P. K. Inorg. Chem. 2004, 43, 2988–2997.
17) Eroy-Reveles, A. A.; Leung, Y.; Mascharak, P. K. J. Am. Chem. Soc.
(
compared to 1), a phenomenon reported by us in previous
(
18,19
reports.
Scrutiny of the literature reveals that to date one
O(OAc) (pic)
(pic ) 4-methylpyridine), has been shown to
(
(
(
(
(
(
(
trinuclear carboxylato cluster, namely, [Ru
(NO)]PF
release NO upon irradiation.
3
6
2
-
2
006, 128, 7166–7167.
18) Patra, A. K.; Rose, M. J.; Murphy, K. A.; Olmstead, M. M.; Mascharak,
P. K. Inorg. Chem. 2004, 43, 4487–4495.
6
3
5
19) Rose, M. J.; Olmstead, M. M.; Mascharak, P. K. Polyhedron 2007,
2
6, 4713–4718.
20) Rose, M. J.; Patra, A. K.; Alcid, E. A.; Olmstead, M. M.; Mascharak,
P. K. Inorg. Chem. 2007, 46, 2328–2338.
21) Afshar, R. K.; Patra, A. K.; Mascharak, P. K. J. Inorg. Biochem. 2005,
9
9, 1458–1464.
22) Szundi, I.; Rose, M. J.; Sen, I.; Eroy-Reveleas, A. A.; Mascharak,
P. K.; Einarsdottir, O. Photochem. Photobiol. 2006, 82, 1377–1384.
23) Madhani, M.; Patra, A. K.; Miller, T. W.; Eroy-Reveles, A. A.; Hobbs,
A.; Fukuto, J. M.; Mascharak, P. K. J. Med. Chem. 2006, 49, 7325–
7
330.
(
(
(
(
24) Eroy-Reveles, A. A.; Leung, Y.; Beavers, C. M.; Olmstead, M. M.;
Mascharak, P. K. J. Am. Chem. Soc. 2008, 130, 4447–4458.
25) Rose, M. J.; Fry, N. L.; Marlow, R.; Hinck, L.; Mascharak, P. K.
J. Am. Chem. Soc. 2008, 130, 8834–8846.
Experimental Section
26) Rose, M. J.; Mascharak, P. K. Curr. Opin. Chem. Biol. 2008, 12, 238–
2
44.
27) Rose, M. J.; Mascharak, P. K. Coord. Chem. ReV. 2008, 252, 2093–
Materials and Reagents. 4,5-Dimethyl-1,2-diaminobenzene,
picolinic acid, triphenyl phosphate, and sodium benzoate were
purchased from Aldrich Chemical Co. and used without further
2
114.
(
28) Rose, M. J.; Mascharak, P. K. Chem. Commun. 2008, 3933–3935.
29) The {M-NO}n notation used in this paper is that of Feltham and
Enemark. See: Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV.
(
purification. RuCl
3
2
·xH O (Aldrich Chemical Co.) was treated
1
974, 13, 339–406.
several times with concentrated HCl to prepare the starting metal
Inorganic Chemistry, Vol. 48, No. 4, 2009 1491

Halpenny and Mascharak
salt, RuCl
3
·3H
2
O. Potassium pentachloronitrosylruthenate(II) was
Table 1. Summary of Crystal Data and Intensity Collection and
3
Structural Refinement Parameters for 1·2CHCl and 2
purchased from Alfa Aesar and used without further purification.
NO gas was purchased from Spectra Gases Inc. and was purified
by passing through a long KOH column prior to use. The nitrosyls
1
2
formula
fw
cryst color, habit
T (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
29 6 5 5 28 4 5 4
C H23Cl N O Ru C H22BF N O Ru
[
(Me
2
bpb)Ru(NO)(Cl)], [(Me
2
bQb)Ru(NO)(Cl)], and [(pyca)
2
Ru-
835.29
680.39
red, blade
153(2)
P1
(
NO)(Cl)] (3) were synthesized by following the published proce-
1
8,34
150(2)
dures.
All solvents were purified and/or dried by standard
jP1j
techniques and distilled.
triclinic
triclinic
Syntheses of Compounds. [(Me
2
bpb)Ru(NO)(OBz)] (1). A
in 5 mL of MeCN
was added to a stirred solution of 0.14 g (0.268 mmol) of
11.6052(6)
11.8863(6)
14.0099(7)
77.5810(10)
66.2400(10)
72.0440(10)
1673.43(15)
2
7.3221(17)
12.982(3)
15.497(4)
98.244(3)
99.337(3)
101.954(3)
1397.9(6)
2
solution of 0.057 g (0.274 mmol) of AgBF
4
1
8
[
2
(Me bpb)Ru(NO)(Cl)] in 20 mL of MeCN, and the reaction
ꢀ
(deg)
mixture was heated to reflux for 8 h. The precipitate of AgCl that
separated during this period was then removed by filtration through
a sintered-glass frit with a Celite pad on top. Next, a batch of 0.050
g (0.348 mmol) of sodium benzoate was added to the filtrate, and
the reaction mixture was heated to reflux for 4 h. Finally, the clear
red-brown solution was concentrated to 10 mL and filtered through
a sintered-glass frit with a Celite pad on top, as above. The filtrate
was then stored at -20 °C for 16 h, resulting in precipitation of a
fine red powder that was collected by filtration. Crystalline solid
γ (deg)
3
V (Å )
Z
d
calcd (g cm-3)
1.658
1.616
abs coeff, µ (mm-1)
0.994
0.632
a
2
GOF on F
final R indices [I > 2σ(I)] R1
1.028
1.017
b
0.0313
0.0428
c
wR2 0.0781
0.0903
b
R indices all data
R1
0.0369
0.0663
c
wR2 0.0818
0.0995
a
2
2
2
1/2
GOF ) [∑w(F
o
- F ) /(M - N)] (M ) number of reflections, N )
c
(
suitable for diffraction measurements) was obtained via slow
evaporation of the solution of this red solid in a CHCl /toluene
mixture (yield: 0.034 g, 21%). Anal. Calcd for C29 Cl
1·2CHCl ): C, 41.69; H, 2.78; N, 8.39. Found: C, 41.58; H, 2.71;
N, 8.12. Selected IR frequencies (KBr disk, cm ): 1833 (νNO, vs),
630 (vs), 1594 (vs), 1484 (m), 1355 (m), 1319 (s), 756 (w), 723
w), 682 (m). Electronic absorption spectrum in MeCN, λmax (in
b
c
2
number of parameters refined). R1 ) ∑|F
F
o c o
| - |F |/∑|F |. wR2 ) [∑w(F
o
3
2
2
2 1/2
-
c
) /∑w(F
o
) ]
.
H
23RuN
5
O
5
6
(
3
(
cluster of thick needles) were obtained after 5 days (0.035 g, 28%
yield). Anal. Calcd for C28 BF : C, 49.45; H, 3.27; N,
0.30. Found: C, 49.23; H, 3.19; N, 10.27. Selected IR frequencies
-1
H
22RuN
5
O
4
4
1
(
1
(
1
-1
KBr disk, cm ): 1872 (νNO, vs), 1680 (vs), 1650 (vs), 1386 (m),
325 (s), 1174 (m), 1082 (s), 875 (w), 764 (m). Electronic
-1
-1
1
nm) (ꢀ in M cm ): 300 (13 000), 390 (6700). H NMR (500
MHz. CDCl , δ from TMS): 2.35 (s, 6H), 7.09 (t, 2H), 7.23 (t,
H), 7.49 (d, 2H), 7.68 (t, 2H), 8.14 (t, 2H), 8.29 (d, 2H), 8.54 (s,
3
-1
-1
absorption spectrum in MeCN, λmax (in nm) (ꢀ in M cm ): 240
(
1
2
67 000), 320 (16 000), 600 (br, 2000). 1H NMR (500 MHz.
H), 9.13 (d, 2H).
CD CN, δ from TMS): 2.25 (s, 3H), 2.35 (s, 3H), 6.65 (d, 1H),
3
2
The acetate analogue of 1, namely, [(Me bpb)Ru(NO)(OAc)],
7
.04 (s, 1), 7.10 (t, 1H), 7.58 (t, 1H), 8.14 (m, 3H), 8.44 (m, 3H),
was also synthesized in the present study by following the same
procedure (except for the use of sodium acetate in place of
benzoate). The reddish-orange microcrystalline product was isolated
in 70% yield. Anal. Calcd for C22
N, 13.10. Found: C, 49.33; H, 3.49; N, 13.37. Selected IR
8
.53 (s, 1H), 8.65 (d, 1H), 8.88 (d, 1H), 8.94 (d, 1H).
Physical Measurements. Absorption spectra were recorded on
a Cary 50 Varian spectrophotometer. IR spectra were obtained with
a Perkin-Elmer 1600 FTIR spectrophotometer. Electron paramag-
netic resonance (EPR) spectra of the photoproducts were monitored
on a Bruker ELEXSYS 500 spectrometer. A Varian 500 MHz
5 5
H19RuN O : C, 49.43; H, 3.59;
-1
frequencies (KBr disk, cm ): 1841 (νNO, vs), 1639 (vs), 1598 (vs),
484 (m), 1358 (s), 1292 (s), 1097 (vw), 760 (w), 684 (m). This
nitrosyl is sparingly soluble in most solvents [MeCN, N,N-
1
1
spectrometer was employed to record the H NMR spectra at 298
K.
dimethylformamide (DMF), and CHCl
any solution study.
3
] and has not been used for
Photolysis Experiments. The apparent rates of NO release (kNO
)
from 1 and 2 were determined by electronic absorption spectroscopy
[
(Me
mmol) of AgBF
of 0.10 g (0.164 mmol) of [Ru(Me
2
Qb)Ru(NO)(qca)]BF
4
(2). A solution of 0.041 g (0.211
18
using a Varian Cary 50 spectrophotometer. Solutions of the
4
in 5 mL of DMF was added to a stirred solution
complexes (100-500 µM) in MeCN were used. The cuvette was
held at a fixed distance of 1 cm from the light source (5 mW UV
lamp). Absorption spectra were taken after certain time intervals
1
8
2
bQb)(NO)(Cl)] in 25 mL of
DMF, and the reaction mixture was heated to 60 °C for 16 h. The
precipitate of AgCl that separated during this period was then
removed by filtration through a sintered-glass frit with a Celite pad
on top. DMF was removed by short-path distillation, and the solid
was triturated four times with 10 mL of MeCN. The residue was
finally dissolved in 30 mL of MeCN, and diethyl ether was allowed
to diffuse into it slowly at room temperature. X-ray-quality crystals
(
usually 15-20 s), and the absorbance values at specific wave-
lengths (585 nm for 1 and 590 nm for 2) were noted. The apparent
rates of NO photorelease (kNO) were calculated from plots of the
concentrations of the photoproducts (absorbing at the 550-650 nm
range) versus the total time of exposure using the equation c ) c
a exp(-kNOt). The quantum yields at 300 nm were determined
0
+
2
2
by standard ferrioxalate actinometry. An Oriel Apex illuminator
(
(
30) Greene, S. N.; Richards, N. G. J. Inorg. Chem. 2004, 43, 7030–7041.
31) Sizova, O. V.; Ivanova, N. V.; Lyubimova, O. O. Russ. J. Gen. Chem.
1
(
8
150 W Xe lamp) with an Oriel / m Cornerstone monochromator
2
004, 74, 155–163.
was used as the light source. The NO amperogram was recorded
with an amiNO-2000 electrode (part of an inNO Nitric Oxide
Measuring System, Innovative Instruments, Inc.).
X-ray Crystallography. Diffraction data were collected on a
Bruker Apex II system at 150 K. Mo KR (0.710 73 Å) radiation
was used, and the data were corrected for absorption (Table 1).
The structure was solved by direct methods (standard SHELXS-97
package).
(
(
(
(
32) Works, C. F.; Jocher, C. J.; Bart, G. D.; Bu, X.; Ford, P. C. Inorg.
Chem. 2002, 41, 3728–3739.
33) Bordini, J.; Hughes, D. L.; Da Motta Neto, J. D.; da Cunha, J. C.
Inorg. Chem. 2002, 41, 5410–5416.
34) Bottomley, F.; Hahn, E.; Pickardt, J.; Schumann, H.; Mukaida, M.;
Kakihana, H. J. Chem. Soc., Dalton Trans. 1985, 2427–2431.
35) Toma, H. E.; Alexiou, A. D. P.; Formiga, A. L. B.; Nakamura, M.;
Dovidauskas, S.; Eberlin, M. N.; Tomazela, D. M. Inorg. Chim. Acta
2
005, 358, 2891–2899.
1492 Inorganic Chemistry, Vol. 48, No. 4, 2009

6
Accelerated Photorelease of NO from {Ru-NO} Nitrosyls
Scheme 1
Results and Discussion
2
[(Me bQb)Ru(NO)(Cl)] is 25.2° due to strong steric interac-
tions among the H atoms of the quinaldic acid moieties. Once
hydrolyzed, the quinoline-2-carboxylate (qca ) ligand reori-
ents itself and coordinates in a bidentate fashion by displacing
the weakly bound solvent molecule. This series of events
finally affords the mixed-ligand nitrosyl 2 in moderate yield
within 4-5 days.
Syntheses of the Nitrosyls. Both 1 and [(Me
2
bpb)Ru-
bpb)Ru-
-
(
(
NO)(OAc)] have been synthesized from [(Me
2
1
8
NO)(Cl)] by a ligand displacement reaction. Following
bpb)Ru(NO)(Cl)]
in MeCN, the reaction with sodium benzoate
or acetate) affords the desired nitrosyls with carboxylato-O
the removal of the chloride ligand of [(Me
with AgBF
2
4
(
coordination trans to NO (vide infra). We have employed
Structure of 1. The structure of the benzoate complex 1
is shown in Figure 2, and selected bond distances and angles
are listed in Table 2. Much like [(Me bpb)Ru(NO)(Cl)], the
2
+
this method to synthesize other [(X
2
bpb)Ru(NO)(L)] (X )
H, Me, and OMe; L ) py, im, and 4-vpy) nitrosyls in
1
8,25,36
previous work.
The mixed-ligand nitrosyl 2 was
Ru center is ligated to the four N atoms of the deprotonated
obtained in a somewhat unexpected reaction when we
attempted the removal of the chloride ligand from
2-
2
Me bpb ligand in the equatorial plane, while NO and
benzoate occupy the axial positions. The overall geometry
is distorted octahedral. In 1, the average Ru-Namide distance
1
8
[
2 4
(Me bQb)Ru(NO)(Cl)] with AgBF in hot DMF (the
starting chloride species is insoluble in MeCN). The synthesis
has now been modified to make it reproducible. IR measure-
ments on the dried product of this reaction reveal that one
(
1.9888 Å) is shorter than the average Ru-Npy (2.1263 Å)
distance. All of these distances are, however, comparable to
those of [(Me bpb)Ru(NO)(Cl)] (Ru-Namide ) 1.988 Å and
2 4
indeed obtains [(Me bQb)Ru(NO)(DMF)]BF as the initial
2
1
8
species (see Figure S1 in the Supporting Information), which
upon further storage in MeCN/diethyl ether during the
crystallization step is converted into 2. Hydrolysis of one
Ru-Npy ) 2.122 Å). Also, the Ru-N-O bond angle of 1
[175.18(18)°] is nearly linear, as in the case of the chloride
6
[173.90(3)°]. These bond angles are typical of {Ru-NO}
2
-
27
amide linkage of the ligated Me
2
bQb
frame in
nitrosyls. The short Ru-N(O) bond distance [1.7384(18)
+
[
(Me
2
bQb)Ru(NO)(DMF)] by trace amounts of water in
Å] is indicative of multiple bond character between the Ru
and NO moieties. The Ru-O bond distance in 1 [2.0039(14)
Å] is comparable to distances noted in other ruthenium
carboxylate complexes. For example, in trans- and cis-
such a solution and coordination of quinoline-2-carboxylate
eventually affords 2 (Scheme 1). Hydrolysis of -CdN-
37
38
38
bonds of ligated Schiff bases by Ru, Pd, and Pt centers
have been reported. In most cases, part of the initial ligand
frame remains coordinated to the metal center in the final
2
-
2
product. In contrast, both fragments of the initial Me bQb
ligand frame remain coordinated in 2. Singh and Mukherjee
III
have reported a similar cleavage reaction in a Co complex
39
derived from a carboxamide ligand with a thioether linkage.
In this case, the coordinated 1,4-bis[o-pyrazine-2-carboxa-
midophenyl)]-1,4-dithiobutane ligand undergoes C-S bond
III
cleavage, and both fragments remain coordinated to the Co
center in the final product. Coordination of the carboxamide
moiety to metal centers generally makes the amide bond
susceptible to hydrolysis. In the case of [(Me
2
bQb)Ru-
+
(
NO)(DMF)] , hydrolysis of the amide linkage of the ligated
2
-
2
Me bQb frame is further facilitated by steric strain in the
1
8
equatorial plane of the complex. As reported earlier, the
dihedral angle between the two quinoline rings in
(
(
(
(
36) Halpenny, G. M.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
007, 46, 6601–6606.
37) Sukanya, D.; Evans, M. R.; Zeller, M.; Natarajan, K. Polyhedron 2007,
6, 4314–4320.
38) Bravo, J.; Cativiela, C.; Navarro, R.; Urriolabeitia, E. P. J. Organomet.
Chem. 2002, 650, 157–172.
39) Singh, A. K.; Mukherjee, R. Dalton Trans. 2008, 2, 260–270.
2
2
Figure 2. Thermal ellipsoid plot (probability level 50%) of 1 with an atom-
labeling scheme. H atoms are omitted for the sake of clarity.
Inorganic Chemistry, Vol. 48, No. 4, 2009 1493

Halpenny and Mascharak
Ru-N-O bond angle [175.0(3)°] and the Ru-Namide distance
[1.977(3) Å] of 2 are similar to those noted for 1. However,
the Ru-O distance [1.997(2) Å] is shorter than that in 1
2.0039(14) Å] because of the chelate effect of the bidentate
[
-
II
qca ligand. It is also shorter than the Ru -O distance
4
1
[2.106(12) Å] observed in [(6-carboxylato-bpy)
2
Ru].
Spectroscopic Properties. Coordination of the carboxa-
mido-N donor to the Ru center in 1 and 2 is evidenced by
the shift of the carbonyl stretching frequency (νCO) to low
-
1
energy, at 1630 and 1650 cm , respectively, compared to
-
1
the free ligands (Me
2
bpbH
2
, νCO ) 1666 cm ; Me
2 2
bQbH ,
-
1
ν
CO ) 1689 cm ). The benzoate ligand in 1 exhibits strong
-
1
IR bands at 1320 and 1297 cm
(both νC-O).
[
1
2
(Me bpb)Ru(NO)(OAc)] exhibits its νC-O bands at 1358 and
-
1
-1
292 cm . In addition to νCO at 1650 cm , 2 displays νNH
-
1
Figure 3. Thermal ellipsoid plot (probability level 50%) of
at 3256 and 3188 cm and bands at 1680, 1386, and 1325
cm for the coordinated qca ligand. The latter bands are
also exhibited by 3 at 1682, 1318, and 1286 cm because
of the presence of coordinated pyca ligands. In previous
+
[
(Me
2
Qb)Ru(NO)(qca)] (cation of 2) with an atom-labeling scheme. H
-1
-
atoms are omitted for the sake of clarity.
-
1
-
Table 2. Selected Bond Distances and Angles
6
bond distances (Å)
bond angles (deg)
accounts, we have reported that for {Ru-NO} nitrosyls
derived from the bpbH
frequency (νNO) appears in the range 1830-1870 cm .
Quite in line with this trend, the four nitrosyls
Ru(Me bpb)(NO)(OAc)] and 1-3 exhibit νNO at 1841, 1834,
872, and 1890 cm , respectively.
2
-type ligands, the N-O stretching
Complex 1
Ru1-N5-O3
-
1
18
Ru1-N1
2.1327(17)
1.9876(16)
1.9899(16)
2.1198(16)
1.7384(18)
2.0039(14)
1.341(3)
1.416(3)
1.417(2)
1.339(2)
1.229(2)
175.18(18)
127.15(13)
80.02(6)
114.98(7)
93.11(7)
86.72(6)
83.64(7)
97.89(8)
84.13(6)
80.10(7)
96.60(7)
84.11(6)
90.82(7)
87.37(6)
177.91(7)
Ru1-N2
Ru1-N3
Ru1-N4
Ru1-N5
Ru1-O4
N2-C6
Ru1-O4-C21
N1-Ru1-N2
N1-Ru1-N4
N1-Ru1-N5
N1-Ru1-O4
N2-Ru1-N3
N2-Ru1-N5
N2-Ru1-O4
N3-Ru1-N4
N3-Ru1-N5
N3-Ru1-O4
N4-Ru1-N5
N4-Ru1-O4
N5-Ru1-O4
[
1
2
-
1
1
The clean H NMR spectra of 1 (see Figure S2 in the
Supporting Information) and 2 (Figure 4, panel b) in CD CN
3
N2-C7
6
confirm the S ) 0 ground state of these two {Ru-NO}
N3-C12
N3-C13
O1-C6
1
nitrosyls. As shown in panel a of Figure 4, the H NMR
2
spectrum of [(Me bQb)Ru(NO)(Cl)] consists of six reso-
nances in the range of 7-9.5 ppm. In contrast, 2 exhibits 12
resonances (14 in total), in addition to two broad ones from
O2-C13
O3-N5
O4-C21
O5-C21
1.230(3)
1.150(2)
1.296(3)
1.221(3)
the coordinated NH
of the Me
2
2
group, in the aromatic region. Cleavage
bQb ligand removes the symmetry of the bound
ligand frame in [(Me bQb)Ru(NO)(Cl)] and makes the
2-
Complex 2
Ru1-N1
Ru1-N2
Ru1-N3
Ru1-N4
Ru1-N5
Ru1-O2
N2-C10
N2-C11
N3-H3N1
N3-H3N2
N5-O4
2.135(3)
1.977(3)
2.077(4)
2.174(3)
1.737(3)
1.997(2)
1.353(5)
1.409(5)
0.91(4)
Ru1-N5-O4
N1-Ru1-N2
N1-Ru1-N4
N1-Ru1-N5
N1-Ru1-O2
N2-Ru1-N3
N2-Ru1-N5
N2-Ru1-O2
N3-Ru1-N4
N3-Ru1-N5
N3-Ru1-O2
N4-Ru1-N5
N4-Ru1-O2
N5-Ru1-O2
175.0(3)
2
80.88(14)
102.82(12)
91.18(14)
85.70(11)
82.78(13)
97.21(12)
83.07(11)
90.67(12)
96.90(14)
86.31(11)
101.78(12)
78.21(10)
176.79(13)
aromatic protons (14 in total) almost distinct. The lift in
symmetry is nicely reflected in the two resonances at 2.25
and 2.35 ppm arising from the two Me groups on the
-
Me
2
Qb ligand frame of 2 (see the inset in Figure 4). With
2
[(Me bQb)Ru(NO)(Cl)], one observes a single peak at 2.27
ppm for the two Me groups on the ligand frame of
0.82(4)
2-
2
Me bQb .
1.158(3)
1.234(4)
1.298(4)
1.220(4)
O1-C10
O2-C28
O3-C28
Both 1 and 2 dissolve in solvents like MeCN, DMF, and
DMSO to afford reddish-brown solutions. The electronic
absorption spectra of 1 and 2 in MeCN are shown in Figure
5
along with that of 3. Much like [(Me
2
bpb)Ru(NO)(Cl)], 1
[
2
Ru(OAc)(2cqn)
.042(3) and 2.017(5) Å, respectively.
Structure of 2. The crystal structure of 2 is composed of
2
(NO)], the Ru-OAc bond distances are
-
1
-1
exhibits one moderately strong band (ꢀ ) 6700 M cm )
4
0
18-20,27
32,33
with λmax at 390 nm. We
this band to a metal-to-ligand charge-transfer (MLCT)
transition from a MO that is predominantly metal [d (Ru)]
and carboxamido-N in character to a M-NO π*-antibonding
MO. In the case of 2, this MLCT band overlaps with the
intense (ꢀ ) 16 000 M cm ) ligand-centered absorption
band at 320 nm (Figure 5). 2 also displays a broad absorption
with λmax at ∼600 nm. The overall increase in the absorption
and others
have assigned
+
both isomers of [(Me
2
Qb)Ru(NO)(qca)] (cation of 2), and
π
the structure of one isomer is shown in Figure 3. Selected
bond distances and angles are listed in Table 2. The Ru center
is in a pseudooctahedral geometry. Three N atoms from the
-
1
-1
Me
2
Qb ligand and one N atom from the quinoline-2-
-
carboxylate (qca ) ligand are coordinated in the equatorial
plane, while the carboxylato-O donor is trans to NO. The
(
41) Norrby, T.; B o¨ rje, A.; Åkermark, B.; Hammarstr o¨ m, L.; Alsins, J.;
Lashgari, K.; Norrestam, R.; Mårtensson, J.; Stenhagen, G. Inorg.
Chem. 1997, 36, 5850–5858.
(
40) Wang, H.; Tomizawa, H.; Miki, E. Inorg. Chim. Acta 2004, 357, 4291–
4
296.
1494 Inorganic Chemistry, Vol. 48, No. 4, 2009

6
Accelerated Photorelease of NO from {Ru-NO} Nitrosyls
1
Figure 4. H NMR spectra (500 MHz) of [(Me
2
bQb)Ru(NO)(Cl)] in (CD
3
)
2
SO and 2 in CD
3
CN at 298 K.
higher than that of both 1 and 3 (both containing pyridine
rings only).
Photochemistry. We have previously reported that ex-
6
posure of solutions of {Ru-NO} nitrosyls of the type
n+
-
[(X
2
bpb)Ru(NO)(L′)] (X ) H, Me, and OMe; L′ ) Cl
and py; n ) 0 and 1) in MeCN (or DMF) to low-intensity
(
3-5 mW) UV light results in the rapid photorelease of NO
III
with concomitant generation of Ru photoproducts of the
general composition [(X O
and MeCN; eq 1).
bpb)Ru(solv)(L′)]n+ (solv ) H
2
2
1
8,20,25-27
In the present work, we have
investigated the effects of carboxylate ligands on the NO
6
photolability of two structurally similar {Ru-NO} nitrosyls
Figure 5. Electronic absorption spectra of 1 (red trace), 2 (green trace),
and 3 (blue trace) in MeCN.
of light in the 450-250 nm region by 2 (Figure 5) results
from the extended conjugation in the ligand frame in 2. We
have previously reported a similar increase in absorption in
6
{
Ru-NO} nitrosyls of this type due to replacement of
1 and 2 in which a carboxylato-O donor has been placed
trans to NO (structures shown in Figures 2 and 3). Exposure
of a solution of 1 in MeCN to UV light (5 mW, 290-310
nm band-filtered) brings about rapid and significant changes.
1
8,19
pyridine rings with quinoline rings in the ligand frame.
Because 2 contains quinoline rings in both Me
ligand frames, the overall absorption of 2 is significantly
-
-
2
Qb and qca
Inorganic Chemistry, Vol. 48, No. 4, 2009 1495

Halpenny and Mascharak
the Supporting Information). Also, no NO is detected by
the NO electrode. The reddish-brown residue, obtained
by evaporation of the photolyzed solution, exhibits a very
weak νNO stretch in its IR spectrum. In addition, a strong
-
1
band at 1384 cm
due to free picolinate ligand is
observed. Clearly, exposure to UV light causes damage
to 3 and no NO photolability is observed with this {Ru-
6
NO} nitrosyl. It is important to note that all three nitrosyls
(
1-3) contain a carboxylato-O donor trans to NO.
However, the simple presence of a carboxylato-O donor
trans to NO does not promote NO photorelease (as in 3).
NO photolability is observed only when additional car-
boxamido-N donor atom(s) is (are) present (as in 1 and
2
2
). In this regard, 1 resembles [(Me bpb)Ru(NO)(Cl)],
1
8
reported by us previously.
The photolysis of 1 and 2 has been studied in coordinating
solvents such as MeCN and DMF. The apparent NO
dissociation rates (kNO) of 1 and 2 in MeCN (100 µM) are
-
3
-1
-2 -1
(
5.75 ( 0.20) × 10
s
and (1.55 ( 0.02) × 10 s ,
2
respectively. Under the same conditions, [(Me bpb)Ru-
-
3 -1
(
NO)(Cl)] yields a kNO value of (8.08 ( 0.10) × 10 s . It
is, therefore, apparent that the benzoate ligand is as effective
as chloride in promoting the photorelease of NO from this
Figure 6. Changes in the electronic absorption spectra of 0.07 mM 1 (top
panel) and 0.1 mM 2 (bottom panel) upon exposure to a low-intensity (5
mW) UV lamp at 10 s intervals.
6
type of {Ru-NO} nitrosyl. Significant enhancement of the
As shown in Figure 6 (top panel), new bands with λmax at
rate of NO photorelease is further achieved by providing
-
5
85 and 260 nm in addition to two shoulders around 450
more conjugation to the two ligand frames of Me
2
Qb and
-
and 350 nm are developed. Isosbestic points are noted at
qca moieties in 2. The quantum yield values (φ) of
2
7
86, 271, and 244 nm. Also, a broad absorption around the
00-900 nm range arises from a ligand-to-Ru charge-
2
[(Me bpb)Ru(NO)(Cl)], 1, and 2 have also been determined
III
in the present study to compare the efficiency of NO
photorelease. In MeCN, the φ values of these three nitrosyls
are 2.5%, 3.5%, and 15%, respectively. Clearly, 2 is a very
efficient NO donor under low-intensity (3-10 mW) UV light.
It must also be noted here that 2 exhibits a broad absorption
in the 600 nm region (Figure 5). As a consequence, 2 slowly
releases NO even upon illumination with visible light. When
a solution of 2 in MeCN is exposed to visible light (100 W
incandescent lamp), the orange color slowly changes to deep
purple. This latter result indicates that it is possible to alter
the design of the ligands of 2 to further improve its NO
2
transfer transition in [(Me bpb)Ru(MeCN)(OBz)], the pho-
toproduct of this reaction. That these changes occur because
of the photorelease of NO from 1 (eq 1) is evidenced by the
response from an NO-sensitive electrode placed in the
cuvette. Very similar behavior has been noted with other
photosensitive {Ru-NO} nitrosyls reported by us
others.
observed when the solution (in MeCN) is exposed to the
same UV light (Figure 6, bottom panel). The initial orange-
brown solution of 2 exhibits one strong absorption band with
6
18,20,25
and
3
2,33
In the case of 2, more dramatic changes are
2
4
λ
max at 323 nm. Exposure to UV light shifts this peak to 317
photolability under visible light. Such studies are in
progress in this laboratory.
nm, and strong absorptions with λmax values at 375, 510,
and 590 nm appear (Figure 6, bottom panel). Also, the low-
energy absorption around 700-900 nm grows in intensity.
Overall, the loss of NO (evidenced by NO-electrode
response) causes a color change from orange brown to
deep purple. These results demonstrate that carboxylato-O
coordination in 1 and 2 retains the photoactivity of these
types of nitrosyls. In both cases, EPR spectra of the
6
In summary, two new photoactive {Ru-NO} nitrosyls
with carboxamido-N coordination, namely, 1 and 2, have
been synthesized and structurally characterized. In both
nitrosyls, a carboxylate group is present as the trans ligand
to NO. Such disposition of the carboxylato-O donor
imparts photolability of NO. Extended conjugation in the
ligand frames (quinoline rings in place of pyridine rings)
in 2 significantly enhances the capacity of the NO release
compared to 1.
III
photolyzed solutions confirm the presence of Ru pho-
1
8
toproducts (see eq 1). For example, the photoproduct
of 1 exhibits strong EPR signals with g ) 2.22 and 1.88
in MeCN/toluene glass. Interestingly, such behavior is
Acknowledgment. This research was supported by a
grant from the National Science Foundation (Grant CHE-
0553405). Experimental assistance from Dr. Allen Oliver
is gratefully acknowledged. Crystallographic data for 1
were collected at Beamline 11.3.1 at the Advanced Light
Source (ALS), Lawrence Berkeley National Laboratory.
The ALS is supported by the U.S. Department of Energy,
6
quite in contrast with the {Ru-NO} nitrosyl 3 in which
3
4
a carboxylato-O donor is also trans to NO. When a
solution of 3 in MeCN is illuminated with the same UV
light, the intensity of the initial absorption band with λmax
at 470 nm decreases progressively, and no new absorption
is evident in the entire 250-950 nm region (Figure S7 in
1496 Inorganic Chemistry, Vol. 48, No. 4, 2009

6
Accelerated Photorelease of NO from {Ru-NO} Nitrosyls
Office of Energy Sciences, under Contract DE-AC02-
(Figure S3), 1 (Figure S4), 2 (Figure S5), and [(pyca)
2
Ru(NO)-
(
Cl)] (Figure S6), electronic absorption spectra during photolysis
0
5CH11231.
of 3 (Figure S7), and X-ray crystallographic data (in CIF format).
This material is available free of charge via the Internet at
http://pubs.acs.org.
Supporting Information Available: FTIR spectrum of
1
[
(Me
2
bQb)Ru(NO)(DMF)]BF
4
(Figure S1), H NMR spectrum
of 1 (Figure S2), FTIR spectra of [(Me
2
bpb)Ru(NO)(OAc)]
IC801748T
Inorganic Chemistry, Vol. 48, No. 4, 2009 1497