Ruthenium nitrosyls derived from tetradentate ligands containing carboxamido-N and phenolato-O donors: Syntheses, structures, photolability, and time dependent density functional theory studies

Article abstract of DOI:10.1021/ic9017129

In order to examine the role(s) of designed ligands on the NO photolability of {Ru-NO}⁶ nitrosyls, a set of three nitrosyls with ligands containing two carboxamide groups along with a varying number of phenolates have been synthesized. The nitrosyls namely, (NEt₄)₂[(hybeb) Ru(NO)(OEt)] (1), (PPh₄)[(hypyb)Ru(NO)(OEt)] (2), and [(bpb)Ru(NO)(OEt)] (3) have been characterized by X-ray crystallography. Complexes 1-3 are diamagnetic, exhibit ^vNO in the range 1780-1840 cm^-1 and rapidly release NO in solution upon exposure to low power UV light (7mW/cm²). Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations on 1-3 indicate considerable contribution of ligand orbitals in the MOs involved in transitions leading to NO photolability. The results of the theoretical studies match well with the experimental absorption spectra as well as the parameters for NO photorelease and provide insight into the transition(s) associated with loss of NO.

Full text of DOI:10.1021/ic9017129

Inorg. Chem. 2010, 49, 1487–1495 1487
DOI: 10.1021/ic9017129
Ruthenium Nitrosyls Derived from Tetradentate Ligands Containing Carboxamido-N and
Phenolato-O Donors: Syntheses, Structures, Photolability, and Time Dependent Density
Functional Theory Studies
Nicole L. Fry, Michael J. Rose, David L. Rogow, Crystal Nyitray, Manpreet Kaur, and Pradip K. Mascharak*
Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064
Received August 28, 2009
6
In order to examine the role(s) of designed ligands on the NO photolability of {Ru-NO} nitrosyls, a set of three nitrosyls with
ligands containing two carboxamide groups along with a varying number of phenolates have been synthesized. The nitro-
syls namely, (NEt ) [(hybeb)Ru(NO)(OEt)] (1), (PPh )[(hypyb)Ru(NO)(OEt)] (2), and [(bpb)Ru(NO)(OEt)] (3) have been
4
2
4
-
1
characterized by X-ray crystallography. Complexes 1-3 are diamagnetic, exhibit ν in the range 1780-1840 cm and
NO
2
rapidly release NO in solution upon exposure to low power UV light (7 mW/cm ). Density Functional Theory (DFT) and Time
Dependent DFT (TDDFT) calculations on 1-3 indicate considerable contribution of ligand orbitals in the MOs involved in
transitions leading to NO photolability. The results of the theoretical studies match well with the experimental absorption
spectra as well as the parameters for NO photorelease and provide insight into the transition(s) associated with loss of NO.
Introduction
and S-nitrosothiols (SNAP) have been used clinically as
11,12
vasodilators.
These compounds are systemic donors that
In recent years, the unique chemistry of nitric oxide (NO)
has drawn much attention because of its regulatory role in
several biological processes.
by nitric oxide synthase (NOS) has been shown to participate
as a signaling molecule in vasodilation and neurotransmis-
sion (both in low nM concentrations) and in cell apoptosis
release NO in response to stimuli such as heat, pH change, or
enzymatic activity. As a consequence, they cannot be used in
site-specific controlled delivery of NO, and there is a clear
need for compounds that can provide high doses of NO at
selected targets under controlled conditions.
1
-6
Endogenous NO produced
7,8
9
,10
The photolability of NO-containing transition metal com-
(in high μM concentrations).
These findings have spurred
13
plexes (metal nitrosyls) has recently been exploited in
controlled delivery of NO. Among metal nitrosyls, ruthe-
nium nitrosyls are a promising class of NO donor because of
their increased thermal stability in biological media com-
the development of several synthetic exogenous NO donors
that mimic and even enhance the utility of endogenous NO
production. For example, organic nitrites (trinitroglycerol)
1
4,15
pared to other metal (Mn and Fe) nitrosyls.
such as [Ru(salen)(Cl)] (salen
Complexes
*
To whom correspondence should be addressed. E-mail: pradip@
chemistry.ucsc.edu.
1) Ignarro, L. J. Nitric Oxide: Biology and Pathobiology; Academic Press:
San Diego, 2000.
2) Nitric Oxide Free Radicals in Peripheral Neurotransmission; Kalsner,
S., Ed.; Birkhauser: Boston, 2000.
0
=
N,N -ethylenebis-
(
(salicylideneiminato) dianion), [(bpb)Ru(NO)(Cl)] (bpb =
,2-bis(pyridine-2-carboxamido)benzene dianion), K [Ru-
1
2
(
16,17
(NO)(Cl) ] all release NO when exposed to UV light.
5
(
(
3) Fukuto, J. M.; Wink, D. A. Met. Ions Biol. Syst. 1999, 36, 547–595.
However, there is still a need to increase the efficiency
quantum yield) of NO release from ruthenium nitrosyls
4) Ko, G. Y.; Fang, F. C. Nitric Oxide and Infection; Kluwer Academic/
(
Plenum Publishers: New York, 1999.
5) Lincoln, J.; Burnstock, G. Nitric Oxide in Health and Disease; Cambridge
University Press: New York, 1997.
6) Nitric Oxide Research; Feelisch, M., Stamler, J. S., Eds.; John Wiley and
Sons: Chichester, U.K., 1996.
when exposed to lower energy light for delivery of NO to
biological targets. Progress in this area requires understand-
ing of the structural and electronic parameters that lead to the
absorption of lower energy light in ruthenium nitrosyls.
(
(
(7) Rosen, G. M.; Tsai, P.; Pou, S. Chem. Rev. 2002, 102, 1191–1199.
(8) Mocellin, S.; Bronte, V.; Nitti, D. Med. Res. Rev. 2007, 27, 317–352.
(9) (a) Whitmore, M. M.; DeVeer, M. J.; Edling, A.; Oates, R. K.; Simons,
(13) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University
Press: Oxford, U.K., 1992.
B.; Lindner, D.; Williams, B. R. Cancer Res. 2004, 64, 5850–5860. (b) Shi, Q.;
Xiong, Q.; Wang, B.; Le, X.; Khan, N. A.; Xie, K. Cancer Res. 2000, 60, 2579–
(14) Rose, M. J.; Fry, N. L.; Marlow, R.; Hink, L.; Mascharak, P. K.
J. Am. Chem. Soc. 2008, 130, 8834–8846.
2
583.
(
10) Du, C.; Guan, Q.; Diao, H.; Yin, Z.; Jevnikar, A. M. Am. J. Physiol.
(15) Szundi, I.; Rose, M. J.; Sen, I.; Eroy-Reveles, A. A.; Mascharak,
ꢀ
2
006, 290, F1044–F1054.
P. K.; Einarsd oꢀ ttir, O. Photochem. Photobiol. 2006, 82, 1377–1384.
(
11) Wang, P. G.; Cai, T. B.; Taniguchi, N. Nitric Oxide Donors for
(16) (a) Rose, M. J.; Mascharak, P. K. Coord. Chem. Rev. 2008, 252,
2093–2114. (b) Rose, M. J.; Mascharak, P. K. Curr. Opin. Chem. Biol. 2008, 12,
238–244.
Pharmaceutical and Biological Applications; Wiley-VCH: Weinheim, 2005.
12) (a) Keefer, L. K. Curr. Top. Med. Chem. 2005, 5, 625–636. (b) Hrabie,
(
J. A.; Keefer, L. K. Chem. Rev. 2002, 102, 1135–1154. (c) Wang, K.; Zhang, W.;
Xian, M.; Hou, Y.-C.; Chen, X.-C.; Cheng, J.-P.; Wang, P. G. Curr. Med. Chem.
(17) (a) Ford, P. C.; Lorkovic, I. M. Chem. Rev. 2002, 102, 993–1017.
(b) Ford, P. C.; Bourassa, J.; Miranda, K.; Lee, B.; Lorkovic, I.; Boggs, S.; Kudo,
S.; Laverman, L. Coord. Chem. Rev. 1998, 171, 185–202.
2
000, 7, 821–834.
r 2010 American Chemical Society
Published on Web 01/11/2010
pubs.acs.org/IC

1
488 Inorganic Chemistry, Vol. 49, No. 4, 2010
Fry et al.
Figure 1. Tetradentate dicarboxamide ligands containing zero, one, or two phenolato-O donors.
Theoretical studies by Franco and coworkers on simple
number of theoretical studies on closely related ruthenium
nitrosyls containing systematically modified multidentate
ligands that examine the effects of these donors. Thus, in
the present study, we were interested in examining the effects
of tetradentate ligands combining anionic carboxamido-N,
phenolato-O donors, and neutral pyridine-N donors using
density functional theory (DFT) and time dependent DFT
(TDDFT) to gain insight into the roles of specific donor
atoms involved in the absorption of lower energy light
leading to the photorelease of NO. We have therefore
synthesized three nitrosyls derived from a set of tetradentate
dicarboxamide-N ligands containing zero, one, or two
6
18
2þ
such as [Ru(NH ) NO]
{
[
RuNO} nitrosyls,
and
3
5
2þ
Ru(NH ) (Cl)NO] , suggest that the photolability of these
3
4
complexes are likely initiated by a high energy (330 nm)
19,20
dπ(Ru) f π*(NO) transitions (vide infra).
However,
over the years, our group and others have identified several
ligand characteristics that increase the efficiency of NO release
1
6,17
from the resulting ruthenium nitrosyls.
For example, the
-
use of charged ligands like Cl compared to neutral ligands
like H O or pyridine accelerates the release of NO in
2
21
22
[
(salen)Ru(NO) (Cl)] and [(Me bpb)Ru(NO)(Cl)]. The
2
use of strong σ-donating anionic donors such as carbox-
amido-N or phenolato-O has been shown to enhance the
phenolato-O donors, namely, 1,2-bis(pyridine-2-carboxamido)-
16
29
photolability in these ruthenium nitrosyls. Indeed, results
of theoretical studies indicate that the metal-to-ligand charge
transfer (MLCT) transitions observed in the electronic ab-
benzene (H bpb), 1-(2-hydroxybenzamido)-2-(2-pyridine-
2
30,31
carboxamido)benzene (H hypyb),
benzamido)- benzene (H hybeb) , respectively (Figure 1).
and 1,2-bis(2-hydroxy-
3
31
4
sorption spectra of [(salen)Ru(NO)(Cl)] and [((OMe) bQb)-
Herein we report the syntheses, structures, spectroscopic
properties, and NO photolability of (NEt ) [(hybeb)-
2
Ru(NO)(Cl)] are not purely dπ(Ru) f π*(NO) in character
but mixed transitions which include some (phenoxo) f
π*(NO) and (carboxamide) f π*(NO) character, respec-
4
2
Ru(NO)(OEt)] (1), (PPh )[(hypyb)Ru(NO)(OEt)] (2), and
4
[(bpb)Ru(NO)(OEt)] (3). In addition, we report the results of
DFT and TDDFT calculations which provide insights into
the electronic transition(s) associated with NO photolability
in these ruthenium nitrosyls.
2
3,24
tively.
It is therefore evident that the photolability of
6
designed {RuNO} nitrosyls can be modulated by careful
choice of ligand(s).
Scrutiny of the known photosensitive {RuNO} nitrosyls
reveals that apart from NH , most of the nitrosyls contain
pyridine-N, phenolato-O,
6
25
Experimental Section
3
21,27
26
22,28
and carboxamido-N
do-
Materials. All chemicals were purchased from Aldrich Che-
mical Co. and used without further purification except for the
acetylsalicyloyl chloride and quinaldic acid which were pur-
chased from Acros Organics. The solvents were dried by stan-
dard techniques and distilled prior to use.
nors around the metal center. However, there are a limited
n
(
18) The {M-NO} notation used in this paper is that of Feltham and
Enemark. See: Enemark, J. H.; Feltham, R. D. Coord. Chem. Rev. 1974, 13,
39–406.
19) Groelsky, S. I.; da Silva, S. C.; Lever, A. B. P.; Franco, D. W. Inorg.
Chim. Acta 2000, 30, 689–708.
20) Tfouni, E.; Krieger, M.; McGarvey, B. R.; Franco, D. W. Coord.
Chem. Rev. 2003, 236, 57–69.
21) Works, C. F.; Jocher, C. J.; Bart, G. D.; Bu, X.; Ford, P. C. Inorg.
Chem. 2002, 41, 3728–3739.
22) Patra, A. K.; Rose, M. J.; Murphy, K. M.; Olmstead, M. M.;
Mascharak, P. K. Inorg. Chem. 2004, 43, 4487–4495.
23) Sizova, O. V.; Ivanova, N. V.; Sizov, V. V.; Nikol’skii, A. B. Russ. J.
Syntheses of Ligands. The ligand 1,2-bis(pyridine-2-carbox-
amido)benzene (H bpb) was synthesized by following literature
3
(
2
2
7
procedure.
(H
4
amido)benzene (H hypyb) were synthesized by methods that
Both 1,2-bis(2-hydroxyben-zamido)benzene
hybeb) and 1-(2-hydroxybenzamido)-2-(2-pyridinecarbox-
(
3
(
28,29
were modified compared to their original procedures.
1,2-bis(2-hydroxybenzamido)benzene (H hybeb). To a solu-
(
4
tion containing 500 mg (4.6 mmol) of phenylenediamine in 5 mL
of dioxane was slowly added 1.83 g (9.3 mmol) of neat acetyl-
salicyloyl chloride. The mixture was allowed to stir for 20 h at
room temperature at which point, 1 mL of conc HCl was slowly
added to the solution. The pink solution was stirred for an
additional 20 h, followed by addition of 40 mL of water resulting
in a white precipitate. The product was filtered, washed several
times with water and MeCN to remove impurities, and dried in
vacuo. Yield: 1.29 g (80%). Selected IR frequencies (KBr disk,
(
Gen. Chem. 2004, 74, 481–485.
(
(
24) Rose, M. J.; Mascharak, P. K. Inorg. Chem. 2009, 48, 6904–6917.
25) (a) Carlos, R. M.; Cardoso, D. R.; Castellano, E. E.; Osti, R. Z.;
Camargo, A. J.; Macedo, L. G.; Franco, D. W. J. Am. Chem. Soc. 2004, 126,
546–2555. (b) Lang, D. R.; Davis, J. A.; Lopes, L. G. F.; Ferro, A. A.;
2
Vasconcellos, L. C. G.; Franco, D. W.; Tfouni, E.; Wieraszko, A.; Clarke, M. J.
Inorg. Chem. 2000, 39, 2294–3000. (c) da, S. S.; Borges, S.; Davanzo, C. U.;
Castellano, E. E.; Z-Schpector, J.; Silva, S. C.; Franco, D. W. Inorg. Chem. 1998,
3
7, 2670–2677. (d) Allen, A. D.; Bottomley, F.; Harris, R. D.; Reinslau, V. P.;
Senoff, C. V. Inorg. Synth. 1970, 12, 2–11.
26) (a) Patra, A. K.; Olmstead, M. M; Mascharak, P. K. Inorg. Chem.
003, 42, 7363–7365. (b) Ko, P.; Chen, T.; Zhu, J.; Cheng, K.; Peng, S.; Che, C.
-1
cm ): 3281 (νNH, w), 3049 (w), 1640 (νCdO, m), 1591 (m), 1533
1
vs), 1496 (s), 1313 (m), 1223 (m), 751 (s). H NMR (500 MHz,
(
(
2
J. Chem. Soc., Dalton Trans. 1995, 1, 215–2219. (c) Pipes, D. W.; Meyer, T. J.
Inorg. Chem. 1984, 23, 2466–2472.
(29) Barnes, D. J.; Chapman, R. L.; Vagg, R. S.; Watton, E. C. J. Chem.
Eng. Data 1978, 23, 349–350.
(
27) (a) Leung, W.; Chan, E. Y. Y.; Chow, E. K. F.; Williams, I. D.; Peng,
S. J. Chem. Soc., Dalton Trans. 1996, 15, 1229–1236. (b) Odenkirk, W.;
Rheingold, A. L.; Bosnich, B. J. Am. Chem. Soc. 1992, 114, 6392–6398.
(30) Keramidas, A. D.; Papaioannou, A. B.; Vlahos, A.; Kabanos, T. A.;
Bonas, G.; Makriyannis, A.; Rapropoulou; Terzis, A. Inorg. Chem. 1996, 35,
357–367.
(
28) (a) Rose, M. J.; Patra, A. K.; Alcid, E. A.; Olmstead, M. M.;
Mascharak, P. K. Inorg. Chem. 2007, 46, 2328–2338. (b) Rose, M. J.;
Olmstead, M. M.; Mascharak, P. K. Polyhedron 2007, 26, 4713–4718.
(31) Hanson, G. R.; Kabanos, T. A.; Keramidas, A. D.; Mentzafos, D;
Terzis, A. Inorg. Chem. 1992, 31, 2587–2594.

Article
CD
Inorganic Chemistry, Vol. 49, No. 4, 2010 1489
(
3
)
2
SO, δ from TMS): 11.74 (s, 2H), 10.42 (s, 2H), 8.01 (d, 2H),
and washed several times with diethyl ether and dried in vacuo.
8.81 (t, 2H), 7.42 (t, 2H), 7.28 (dd, 2H), 6.96 (t, 4H).
57 5 6
Yield: 52 mg (25%). Anal. Calcd. for C38H N O Ru: C 58.44; H
N-(2-Nitrophenyl)pyridine-2-carboxamide) (Hpycan). Abatchof
.00 g (8 mmol) of picolinic acid was weighed out into a 50 mL
7.36; N 8.97; found: C 58.29; H 7.15; N 8.60. Selected IR
frequencies (KBr disk, cm ): 2982 (w), 1783 (νNO, s), 1594
-
1
1
round-bottom flask, and 10 mL of thionyl chloride was added. The
resulting solution changed from white to green. It was then heated
to reflux for 3 h when the color of the solution changed to a
burgundy red. Next, the excess solvent was removed, and the
resulting red solid was triturated 3 times with dichloromethane.
The solid was then dissolved in 100 mL of tetrahydrofuran (THF)
and added dropwise to a solution containing 1.76 g (16 mmol) of
triethylamine and 1.21 g (8 mmol) of 2-nitroaniline also in 100 mL
of THF. The solution was stirred for 20 h, and the resulting
(νCdO, s), 1558 (s), 1526 (m), 1465 (vs), 1438 (vs), 1347 (vs), 1259
1
(m), 1034 (νCO, w), 761 (m). H NMR (500 MHz, (CD
3 2
) SO, δ
from TMS): 9.08 (dd, 2H, J = 6 and 4 Hz), 8.12 (d, 2H, J = 8 Hz),
7.01 (t, 2H, J = 8 Hz), 6.77 (d, 2H, J = 8 Hz), 6.69 (dd, 2H, J = 6
and 4 Hz), 6.44 (t, 2H, J = 8 Hz), 3.37 (q, 2H, J = 7 Hz), 3.17 (q,
12H, J = 7 Hz), 1.13 (t, 18H, J = 7 Hz), 0.48 (t, 3H, J = 7 Hz).
-
1
-1
Electronic absorption spectrum, λmax, nm (ε, M cm ) in
EtOH: 320 (23 270) and in MeCN: 325 (25 000).
4
(PPh )[(hypyb)Ru(NO)(OEt)] (2). Abatchof100mg(0.3mmol)
NEt
3
HCl was filtered off using a Celite pad. The filtrate was
of H hypyb was dissolved in 5 mL of ethanol and mixed with a
3
3
condensed to half the original volume and cooled to -20 °C causing
the product to precipitate. The filtered product was washed 3 times
each with cold ethanol and diethyl ether and dried in vacuo. Yield: 1.7
solution containing 29 mg (1.2 mmol) of NaH in 5 mL ethanol to
generate a light yellow solution. To this solution, 71 mg (0.3 mmol)
of RuNOCl dissolved in 5 mL of ethanol was added dropwise, and
3
-
1
g (80%). Selected IR Frequencies (KBr disk, cm ): 3276 (νNH, m),
690 (νCdO, s), 1606 (s), 1580 (s), 1497 (vs), 1446 (s), 1423 (s), 1341
the mixture was heated to reflux for 5 h. The resulting dark red
brown solution was then treated with 135 mg (0.4 mmol) of PPh Cl.
1
4
1
(
s), 1271 (s), 1148 (m), 787 (m), 743 (s), 686 (m). H NMR (500
MHz, CDCl , δ from TMS): 12.78 (s, 1 H), 9.06 (d, 1H), 8,76 (d,
H), 8.30 (t, 2H), 7.95 (t, 1H), 7.74 (t, 1H), 7.54 (dd, 1H), 7.24 (t, 1H).
N-(2-Aminophenyl)pyridine-2-carboxamide (Hpyca). A solu-
Subsequently, the solvent was removed and replaced with MeCN to
filter off solid NaCl. About 5 mL of diethyl ether was added, and the
solution was cooled to -20 °C. The mixture was filtered after 24 h to
remove a small quantity of an impurity. The filtrate, upon further
cooling, afforded the desired product as an orange powder. The
product was filtered and washed several times with diethyl ether and
dried in vacuo. Yield: 120 mg (45%). Anal. Calcd. for C H N O
3
1
tion of 5.00 g (20.6 mmol) of Hpycan and 30 wt % of hydro-
genation catalyst (10% Pd on activated carbon) was prepared in
1
50 mL of acetone. Dihydrogen was admitted to the reaction
45
37
4 5-
vessel, and the mixture was stirred for 16 h under 45 atmos
pressure of dihydrogen. The reaction product was then sepa-
rated from the catalyst by filtration using a Celite pad, and the
filtrate was evaporated to dryness to yield an yellow-brown oil.
The oil was dissolved in dichloromethane, and hexane was
slowly added under vigorous magnetic stirring until a slight
precipitate formed. This solution was refrigerated overnight to
allow more yellow product to precipitate. The precipitate was
filtered, washed with hexane, and dried in vacuo. Yield: 3.95 g
PRu: C 63.90; H 4.41; N 6.62; found: C 63.85; H 4.31; N 6.55.
-
1
Selected IR Frequencies (KBr disk, cm ): 3052(w), 1793 (νNO, vs),
625 (νCdO, vs), 1593 (νCdO, vs), 1557 (vs), 1534 (s), 1462 (vs), 1436
vs), 1342 (vs), 1108 (vs), 1042 (νCO, m), 756 (vs), 723 (vs), 688 (s),
1
(
5
1
26 (vs). H NMR (500 MHz, CDCl , δ from TMS): 9.06 (d, 1H,
3
J = 8 Hz), 8.77 (d, 1H, J = 8 Hz), 8.60 (d, 1H, J = 8 Hz), 8.28
(
7
7
6
t, 1H, J = 8 Hz), 8.15 (d, 1H, J = 8 Hz), 8.11 (d, 1H, J = 8 Hz),
.96 (t, 4H, J = 8 Hz), 7.82 (m, 9H), 7.73 (dd, 8H, J = 1 and 8 Hz),
.05 (t, 1H, J=8Hz),6.86(d,1H,J= 8 Hz), 6.81 (t, 2H, J=8Hz),
.46 (t, 1H, J=8Hz),3.42(q,2H,J= 7 Hz), 0.38 (t, 3H, J=7Hz).
-
1
(90%). Selected IR Frequencies (KBr disk, cm ): 3387 (νNH, m),
3
(
314 (νNH, m), 1667 (νCdO, s), 1629 (νCdO, m), 1588 (m), 1527
vs), 1453 (m), 1431 (m), 1315 (m), 761 (s), 696 (m), 970 (m). H
-1
-1
Electronic absorption spectrum, λmax, nm (ε, M cm ) in EtOH:
15 (10 700) and in MeCN: 315 (9 250).
Ru(bpb)(NO)(OEt)] (3). A slurry of 100 mg (0.3 mmol) of
H bpb in 10 mL of ethanol was deprotonated via addition of
1
3
NMR (500 MHz, CDCl , δ from TMS): 10.89 (s, 1 H), 8.64
3
[
(
(
d, 1H), 8.31 (d, 1H), 7.92 (t, 1H), 7.50 (d, 2H), 7.10 (t, 1H), 6.87
t, 2H), 3.89 (s, 2 H).
2
2
solution containing 74 mg (0.31 mmol) of RuNOCl in 10 mL of
3 mg (0.9 mmol) of NaH dissolved in 5 mL of ethanol. A
1-(2-Hydroxybenzamido)-2-(2-pyridinecarboxamido)benzene
H hypyb). A batch of 460 mg (2.4 mmol) of neat acetylsalicyloyl
3
(
3
ethanol was added to the flask containing the deprotonated
ligand. The resulting dark orange solution was heated at reflux
temperature for 10 h. The solution was then cooled to -20 °C to
precipitate impurities and filtration. The filtrate was then con-
centrated, and 5 mL of diethyl ether was added. Upon cooling,
the target complex precipitated out as an orange solid which was
filtered, washed several times with diethyl ether, and dried in
chloride was slowly added to a solution containing 500 mg
2.4 mmol) of Hpyca dissolved in 5 mL of dioxane. After the
(
mixture was stirred for 20 h at room temperature, 1 mL of conc
HCl was slowly added to the solution. The orange solution was
stirred for 20 h followed by addition of 40 mL of water added
dropwise to the stirred solution. The resulting white precipitate
was filtered, washed several times with water, and dried in
vacuo. Yield: 800 mg (75%). Selected IR frequencies (KBr disk,
vacuo. Yield: 62 mg (40%). Anal. Calcd. for C20
4
17 5 4
H N O Ru: C
8.78; H 3.48; N 14.22; found: C 48.75; H 3.41; N 14.18. Selected
-
1
-1
cm ): 3252 (νNH, m), 3058 (w), 1665 (νCdO, s), 1641 (νCdO, s),
593 (s), 1544 (vs), 1518 (vs), 1491 (s), 1339 (m), 1227 (m), 751
IR Frequencies (KBr disk, cm ): 2923(w), 1838 (νNO, s), 1632
(νCdO, vs), 1595 (s), 1472 (s), 1356 (s), 1286 (m), 1047 (νCO, m),
782 (w), 752 (m), 683 (w), 502 (w). H NMR (500 MHz,
1
(
1
vs), 692 (m). H NMR (500 MHz, (CD
1
3
)
2
SO, δ from TMS):
1
1.58 (s, 1H), 10.55 (s, 1H), 10.46 (s, 1H), 8.59 (d, 1H), 8.14
(CD ) SO, δ from TMS): 9.34 (d, 2H, J = 6 Hz), 8.54 (dd,
3
2
(
(
d, 1H), 8.04 (t, 1H), 7.99 (d, 1H), 7.86 (d, 1H), 7.69 (d, 1H), 7.64
t, 1H), 7.42 (t, 1H), 7.29 (dt, 2H), 6.96 (t, 2H).
2H, J = 6 and 4 Hz), 8.38 (t, 2H, J= 8 Hz), 8.19 (d, 2H, J = 8Hz),
7.93 (t, 2H, J = 6 Hz), 7.08 (dd, 2H, J = 6 and 4 Hz), 3.34 (q, 2H,
J = 7 Hz), 0.30 (t, 3H, J = 7 Hz). Electronic absorption
4 2
Syntheses of Complexes. (NEt ) [(hybeb)Ru(NO)(OEt)] (1).
-
1
-1
A slurry containing 100 mg (0.3 mmol) of H hybeb and 200 mg (1.2
4
mmol) NEt Cl in 15 mL of ethanol was treated with 35 mg (1.4
4
mmol) of NaH under dinitrogen. The solution was then filtered to
remove NaCl, producing a clear tan solution of the deprotonated
ligand. Subsequently, 68 mg (0.3 mmol) of RuNOCl dissolved in
spectrum, λmax, nm (ε, M cm ) in EtOH: 380 (7680) and in
MeCN: 380 (9800).
1
Physical Measurements. The H NMR spectra were recorded
at 298 K on a Varian Inova 500 MHz instrument. A Perkin-
Elmer Spectrum-One FT-IR spectrometer was used to monitor
the IR spectra of the complexes. The electronic absorption
spectra were obtained with a scanning Cary 50 spectrophot-
ometer (Varian Associates). Release of NO in aqueous solution
upon illumination was monitored by using the inNO Nitric
Oxide Monitoring System (Innovative Instruments, Inc.) fitted
with the ami-NO 2008 electrode. The NO amperograms were
3
1
0 mL of degassed ethanol was added to the reaction flask under
dinitrogen via cannula generating an orange brown solution. The
solution was heated under refluxing condition for 24 h and then
cooled to room temperature. The solution was concentrated and
cooled to -20 °C. Upon addition of 5 mL of diethyl ether to the
cold solution, an orange solid precipitated. The solid was filtered

1
490 Inorganic Chemistry, Vol. 49, No. 4, 2010
Fry et al.
Table 1. Summary of Crystal Data, Intensity Collection and Refinement Parameters for (NEt
4
)
1.5(Na)0.5[(hybeb)Ru(NO)(OEt)] EtOH(1 EtOH),
3
3
(
PPh4)[(hypyb)Ru(OEt)] MeCN(2 MeCN), and [(bpb)Ru(OEt)](3)
3
3
1
2
3
empirical formula
formula weight
crystal color
crystal size (mm )
temperature(K)
˚
wavelength(A)
C
72
H
105
1545.78
N
9
NaO14Ru
2
C
47
H
40
N
5
O
5
PRu
C
20 17
H
492.46
N
5
O
4
Ru
886.89
red blocks
dark orange needles
0.81 ꢀ 0.76 ꢀ 0.34
150(2)
0.71073
monoclinic
red-orange blocks
0.07 ꢀ 0.05 ꢀ 0.03
150(2)
0.71073
orthorhombic
Pnma
15.6611(17)
13.0504(14)
9.1589(10)
90
90
90
1871.9(4)
4
1.747
0.878
1.050
3
0.40 ꢀ 0.16 ꢀ 0.10
150(2)
0.71073
triclinic
P1
crystal system
space group
1
P2 /n
˚
a (A)
11.827(2)
18.817(4)
33.222(7)
90
96.74(3)
90
7342(3)
4
1.398
0.486
1.028
9.9537(14)
12.5967(17)
17.043(2)
86.677(2)
73.852(2)
86.616(2)
2047.1(5)
2
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
3
d
cal (g/cm )
1.439
0.476
1.043
-
1
μ (mm
GOF on F
)
a
2
final R indices
I > 2σ(I)]
R indices
R
1
= 0.0434
wR = 0.1183
= 0.0628
wR = 0.1077
R
1
= 0.0400
wR = 0.1018
= 0.0483
R
1
= 0.0213
wR = 0.0513
2
R = 0.0261
[
2
2
2
b
R
1
R
1
c
All data
2
wR
2
= 0.1073
wR
2
= 0.0536
P
P
P
P
a
2
o
2 2
1/2
)] (N
b
= number of variables). R
c
|. wR
2
GOF = [ w(F
2 2 1/2
) ]
- F
c
) /(N
o
- N
v
o
= number of observations, N
v
1
=
||F
o
| - |F
c
||/ |F
o
2
= [ w(F
o
-
P
2 2
) / w(F
F
c
o
.
˚
Table 2. Selected Bond Distances (A) and Angles (deg) of 1, 2, and 3 along with the Optimized DFT Bond Distances and Bond Angles for Comparison
complex 1 complex 2 complex 3
X-ray X-ray X-ray
DFT
DFT
DFT
Bond Distances
Ru-N3
N3-O5
Ru-N1
Ru-N2
Ru-O1
Ru-O4
Ru-O6
1.733(3)
1.174(4)
2.019(3)
2.024(3)
2.028(3)
2.028(3)
1.976(3)
1.726
1.173
2.043
2.029
2.034
2.058
1.978
Ru-N4
N4-O4
Ru-N1
Ru-N2
Ru-O1
Ru-N3
Ru-O5
1.738(2)
1.161(3)
2.019(2)
1.985(2)
2.024(2)
2.107(2)
1.973(2)
1.732
1.166
2.008
2.002
2.029
2.127
1.975
Ru-N5
N5-O3
Ru-N1
Ru-N2
Ru-N3
Ru-N4
Ru-O4
1.742(2)
1.153(2)
1.986(1)
1.986(1)
2.130(1)
2.130(1)
1.967(2)
1.742
1.159
1.988
1.985
2.166
2.144
1.956
Bond Angles
Ru-N3-O5
N3-Ru-O6
N1-Ru-N2
O1-Ru-O4
N1-Ru-O1
N2-Ru-O4
170.5(3)
177.0(1)
83.0(1)
82.8(1)
96.3(1)
97.0(1)
170.2
177.0
83.2
84.8
95.3
96.2
Ru-N4-O4
N4-Ru-O5
N1-Ru-N2
O1-Ru-N3
N1-Ru-O1
N2-Ru-N3
177.6(2)
177.8(1)
83.4(1)
97.4(1)
96.8(1)
81.3(1)
176.6
177.5
83.3
97.0
97.6
80.7
Ru-N5-O3
N5-Ru-O4
N1-Ru-N2
N3-Ru-N4
N1-Ru-N3
N2-Ru-N4
176.1(2)
175.9(1)
83.8(1)
114.9(1)
80.3(1)
80.3(1)
177.0
175.1
84.1
114.3
80.0
80.6
recorded using stirred solutions contained in open vials. X-band
electron paramagnetic resonance (EPR) spectra were obtained
with a Bruker ELEXSYS 500 spectrometer at 125 K.
Additional refinement details are contained in the CIF
files (Supporting Information). Instrument parameters, cry-
stal data, and data collection parameters for all the comp-
lexes are summarized in Table 1. Selected bond distances
and bond angles for 1 EtOH, 2 MeCN, and 3 are listed in
X-ray Crystallography. Vapor diffusion of diethyl ether into a
solution of 1 in acetone afforded orange crystalline needles
suitable for X-ray studies. The structure revealed that the crystal
3
3
Table 2.
Photolysis Experiments. The quantum yield (φ) values were
obtained using a UV-transilluminator (UVP-TM-36, λ =
max
þ
included one Na ion per two anions leading to a composition
(
NEt4)1.5Na0.5[(hybeb)Ru(NO)(OEt)]. Red orange crystals
2
2
of 2, suitable for diffraction study, were obtained via vapor
diffusion of diethyl ether into a solution of 2 in MeCN while
vapor diffusion of pentane into a solution of 3 in THF afforded
orange crystals used for the structural studies. Diffraction
data for 1 EtOH, 2 MeCN, and 3 were collected at 150 K on
302 nm; intensity, 7 mW/cm ) and IL 410 Illuminator (175 W/cm )
equipped with a high energy light filter (380 nm cutoff).
Standard ferrioxalate actinometry was used to determine the
quantum yield values at 300 nm (φ300) and 400 nm (φ400). Samples
of 1, 2, and 3 were prepared in MeCN and placed in 4 ꢀ 10 mm
quartz cuvettes, 1 cm away from the light source. All solutions
were prepared to ensure sufficient absorbance (>90%) at the
irradiation wavelength, and changes in electronic spectrum at
600, 700, and 800 nm for 1-3, respectively (<10% photolysis),
were used to determine the extent of NO photorelease.
3
3
a Bruker APEX-II instrument using monochromated Mo KR
˚
radiation (λ = 0.71073 A). All diffraction data were corrected
for absorption and calculations were performed using the
SHELXTL (1995-99) software package (Bruker Analytical
X-ray Systems Inc.) for structure solution and refinement.

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1491
Figure 2. Anionic tetradentate dicarboxamido-N ligands with either
pyridine- or quinoline-N donors.
Figure 3. Thermal ellipsoid (probability level 50%) plot of [(hybeb)-
Ru(OEt)] (anion of 1) with select atom-labeling. H atoms are omitted
for the sake of clarity.
DFT and TDDFT Calculations. DFT calculations were car-
ried out using the double-ζ basis set 6-311G* for all atoms
except Ru, for which the quasi-relativistic Stuttgart-Dresden
effective core potential (ECP) was implemented. Calculations
2-
3
2
particularly under the basic conditions of the synthetic
procedures. This is not surprising since we have synthe-
were carried out with the aid of the program PC-GAMESS
using the hybrid functional PBE0. For TDDFT calculations,
solvent (EtOH) effects were added using the Polarized Con-
sized [(Me
(OH)] in moist MeCN in the presence of a base like
bpb)Ru(NO)(OH)] and [(Me bQb)Ru(NO)-
2
2
3
3
tinuum Model (PCM). The X-ray coordinates of 1, 2, and 3
were used as a starting point for each geometry optimization and
molecular orbital (MO) energy level analysis. MOs were visua-
1
4
aniline. Clearly, presence of a protic solvent and a base
give rise to the HO- or EtO-bound nitrosyls in this type of
reaction. Search of the literature also reveals that ruthenium
3
4
lized in MacMolPlt for analysis. Graphical representations of
TDDFT data were created by the ChemCraft Software.
3
5
nitrosyls such as trans-[Ru(OEt)(2mqn) NO] (H2mqn =
2
3
6
2-methyl-8-quinolinol) and trans-(NO, OC H ), cis-(Cl,
OC H )-[RuCl-(OC H )(NO)(terpy)]PF (terpy = 2,2 :
2 5
Results and Discussion
0
2
00
5
2
5
6
0
37
Synthesis. During the past few years, we have synthe-
sized a series of {RuNO} nitrosyls derived from anionic
6 ,2 -terpyridine) have also been synthesized in EtOH
under basic conditions. It is apparent that in such reac-
tions, Cl ions are better leaving groups, and the Ru-NO
6
-
tetradentate ligands that include carboxamido-N donors
along with pyridine- or quinoline-N donors such as
moiety prefers O-donors (trans to NO). For example,
when [(bpb)Ru(NO)(Cl)] is heated to reflux in EtOH in
the presence of triethylamine (as base), one obtains the
2-
2-
2-
14,22
[
These nitrosyls were uniformly synthesized by the reac-
Me bpb] , [Me bQb] , or [(OMe) bQb] (Figure 2).
2 2 2
-
tion of RuCl with the deprotonated (with NaH) ligands
3
EtO bound product and NEt Cl.
4
in N,N-dimethylformamide (DMF) followed by the addition
of NO(g). However, as we included both carboxamido-N
and phenolato-O donors in the ligand frame (as in
Structures. (NEt ) (Na) [(hybeb)Ru(NO)(OEt)] EtOH.
4
1.5
0.5
3
The structure of the anion of 1 is shown in Figure 3 and
selected structural parameters are listed in Table 2. The
ruthenium center of 1 resides in a slightly distorted
octahedral geometry with one of the phenolato moieties
4
-
3-
[
hybeb] and [hypyb] ), surprisingly, this method did
not afford the desired nitrosyls. After several attempts, it
became evident to us that both the choice of solvent and
the starting metal source required change. We soon
discovered that the desired products could be obtained
with RuNOCl as the starting metal salt and EtOH as
3
solvent (use of RuNOCl in DMF also did not afford any
3
4
-
slightly raised above the rest of the [hybeb] ligand frame
in the equatorial plane. A similar distortion is seen in
ruthenium nitrosyls containing [salophen] type ligands.
2-
16
˚
The average Ru-Namide bond distance (2.022 A) of 1 is
22
˚
longer than that found for [(bpb)Ru(NO)(Cl)] (1.983 A),
presumably because of the increase in charge in the equatorial
product with these two ligands). One interesting outcome
of using EtOH (instead of DMF) as the solvent was the
isolation of the final products as the ethanolate (-OEt)
plane of the ligand frame. Similarly, the average Ru-
˚
bond distance (2.028 A) is slightly longer than that
O
phenoxo
2
-
t
t
˚
noted for [( Bu salophen)Ru(NO)(Cl)] (2.022 A, Bu salo-
2 2
bound species, namely, [(hybeb)Ru(NO)(OEt)] (1) and
[(hypyb)Ru(NO)(OEt)] (2). In both cases, no chloride-
bound nitrosyl was obtained. It is important to note that
-
0
phen = N,N -1,2-phenylenediaminebis(3-tert-butylsalicyli-
2
1
deneiminato) dianion) which contains neutral imine-N
donors in place of the charged carboxamido-N donors.
In 1, the bound NO molecule is trans to the EtO ligand
2
the reaction of [bpb] with RuNOCl in EtOH also
-
3
-
afforded [(bpb)Ru(NO)(OEt)] (3) in good yield while
the reaction of RuCl with [bpb] in DMF followed by
addition of NO(g) afforded [(bpb)Ru(NO)(Cl)] in our
2
-
˚
3
and the Ru-NO distance (1.733 A) as well as the Ru-NO
bond angle (170.5°) are as expected for this type of
2
0
6
previous work. It is thus evident that in ethanol, the
ethanolate-bound nitrosyls are the predominant products
{Ru-NO} nitrosyls. Finally, the Ru-OEt bond dis-
tance (1.976 A) of 1 is longer than that observed for other
ruthenium nitrosyls containing an EtO ligand trans to
˚
-
3
NO, such as trans-[Ru(OEt)(2mqn) NO] (1.928 A) and
6
˚
(
32) Nemukhin, A. V.; Grigorenko, B. L.; Granovsky, A. A. Moscow
2
Univ. Chem. Bull 2004, 45, 75.
(
(
33) Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 1981, 55, 117–120.
34) Waller, M. P.; Braun, H.; Hojdis, N.; B u€ hl, M. J. Chem. Theory
(36) Wang, H.; Hagihara, T.; Ikezawa, H.; Tomizawa, H.; Miki, E. Inorg.
Chim. Acta 2000, 299, 80–90.
(37) Nagao, H.; Enomoto, K.; Wakabayashi, Y.; Komiya, G.; Hirano, T.;
Oi, T. Inorg. Chem. 2007, 46, 1431–1439.
Comput. 2007, 3, 2234–2242.
35) Zhurko, G. A. ChemCraft Software, Version 1.6; (http://www.
chemcraftprog.com).
(

1
492 Inorganic Chemistry, Vol. 49, No. 4, 2010
Fry et al.
Figure 4. Thermal ellipsoid (probability level 50%) plot of [(hypyb)-
Ru(OEt)] (anionof 2) with select atom-labeling. H atoms are omitted for
the sake of clarity.
Figure 6. Electronic absorption spectra of 1 (dashed line), 2 (solid line),
3
-
(dotted line) in EtOH.
˚
(1.986 A) and
equatorial plane (Table 2). The Ru-N
amide
˚
Ru-Npy (2.130 A) bond distances of 3 are very similar to
those of [(bpb)Ru(NO)(Cl)] (1.990 and 2.131 A re-
˚
2
2
spectively). The presence of pyridine-N donors versus
phenolato-O donors does not appear to have any signifi-
cant effect on the Ru-NO (1.742 A) and Ru-OEt (1.967
A) bond distances of 3 compared to those observed in 1
and 2.
˚
˚
Spectroscopic Properties. The carbonyl stretching fre-
-
1
quency (νCdO) of the free ligands H hybeb (1640 cm ),
4
-
1
H hypyb (1641 and 1665 cm ), H bpb (1676 cm ) all
-1
3
2
shift to lower energy upon formation of complexes 1
(
-
1
1594 cm ), 2 (1625 and 1593 cm ), and 3 (1632 cm ),
-1
-1
respectively (Figure S1-S3, Supporting Information). As
the charge on the deprotonated ligand decreases from
[
Figure 5. Thermal ellipsoid (probability level 50%) plot of [(bpb)-
Ru(NO)(OEt] (3) with select atom-labeling. H atoms are omitted for
the sake of clarity.
4
hybeb] to [hypyb] to [bpb] , the corresponding
-
3-
2-
ruthenium nitrosyls display NO stretching frequencies
(νNO) of increasing energy (1, νNO = 1783; 2 νNO = 1793;
3, νNO = 1838). This trend suggests an increase in metal
to (NO)π* pi-backbonding as the overall charge of the
complex increases.
trans-(NO, OC H ), cis-(Cl, OC H )-[RuCl-(OC H )-
(
(PPh )[(hypyb)Ru(NO)(OEt)] (2). The structure of the
4
anion of 2 is shown in Figure 4, and selected structural
2
5
2
5
2
5
3
7
˚
NO)(terpy)]PF (1.943 A).
6
parameters are listed in Table 2. The deprotonated
[
All three complexes are diamagnetic (as expected for
3
hypyb] ligand is bound to the ruthenium center in the
-
6
{Ru-NO} nitrosyls) and display narrow-width peaks in
1
their H NMR spectra in (CD ) SO (Figure S4, Support-
equatorial plane, and the phenolato moiety is slightly out
of the plane compared to the rest of ligand resulting in a
slightly distorted octahedral geometry. The Ru-Ophenoxo
3
2
ing Information). The symmetry of 1 and 3 is confirmed
by the overlap of H NMR peaks of equivalent aryl
protons. Conversely, the spectrum of complex 2, which
1
˚
and Ru-Namide bond distances (2.024 and 2.019 A re-
3
-
spectively) on the right side of the ligand frame (as shown
in Figure 4) are similar to those noted in complex 1.
contains the asymmetric ligand [hypyb] , displays in-
dividual aryl proton peaks corresponding to the pheno-
late and pyridine moieties.
˚
Similarly, the Ru-Namide bond distance (1.985 A) next to
the pyridine moiety (on the left side of the ligand in
The electronic absorption spectra of 1, 2, and 3 in EtOH
are shown in Figure 6. Complex 1 exhibits an absorption
band at 320 nm with the highest extinction coefficient
value of the three complexes. Two smaller absorption
bands at 315 and 420 nm are observed in the spectrum of 2
while 3 displays an absorption band at 380 nm, similar to
Figure 4) is comparable to that noted for complex 3
˚
˚
(
is shorter than the same bond distance in complex 3 (avg
1.986 A). However, the Ru-Npy distance of 2 (2.107 A)
˚
value 2.130 A). This difference could arise from distortions
-
caused by the asymmetry of the ligand frame in 2. The EtO
ligand is bound trans to NO in the axial positions. The
2
2
the spectrum of [(bpb)Ru(NO)(Cl)]. A more in depth
discussion of the electronic transitions responsible for the
absorption bands observed in these spectra is included in
the DFT and TDDFT section below.
˚
Ru-OEt and Ru-NO bond distances (1.973 and 1.738 A
respectively) of 2 are similar to those of 1 and the Ru-NO
bond angle (177.6°) is almost linear, as expected for a
6
{
Ru-NO} nitrosyl.
Photochemistry. Exposure of solutions of 1-3 to low
power UV light causes rapid release of NO (as evi-
denced by the responses of an NO-sensitive electrode).
Such NO photorelease (eq 1) also brings about notable
[(bpb)Ru(NO)(OEt)](3). The structure of 3 contains a
-fold symmetry (Figure 5) as reflected in the bond
2
distances and angles related to the bpb ligand in the
2
-

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1493
donor, in complex 1, lowers the quantum yield value
below that of 3. When exposed to lower energy light
(400 nm), only nitrosyls 2 and 3 (which contain lower
energy absorption bands at 420 and 380 nm, respectively)
are photoactive. The quantum yield values measured at
400 nm (φ400) for 2 (0.8%) and 3 (1.4%) reveal that both
are less efficient NO donors when they are exposed to low
energy light.
DFT and TDDFT Calculations. To elucidate how
changes in the ligand frame affect the absorption of
lower energy light leading to the photorelease of NO, we
have performed DFT and TDDFT calculations on 1, 2,
and 3. The lowest 20 calculated energy transitions are
shown as a bar graph in Figure 8a. The height of each
bar corresponds to the calculated oscillator strength of
each transition. Descriptions of all calculated transi-
tions can be found in the Supporting Information
Figure 7. Changes in the electronic absorption spectrum upon photo-
lysis of2 in MeCN following illuminationwithintervals ofUVlight. Inset:
NO amperogram of 2 in H O upon illumination with UV light for time
2
(
Table S4). The experimental electronic absorption
spectrum of each complex (solid lines) and the spectra
derived from the calculated data using Lorentzian
broadening (dashed lines) are also shown for compar-
periods as indicated.
changes in the electronic spectra of these nitrosyls. For
example, photolysis of 2 in MeCN under UV light
39
ison in Figure 8a. The relative intensities and wave-
lengths of the calculated data match very well with the
corresponding experimental data and thus support the
theoretical treatment.
The molecular orbital (MO) energy diagrams shown in
Figure 8b summarize the electronic configuration of
complexes 1, 2, and 3. The highest occupied molecular
orbitals (HOMO) of all three nitrosyls are predominately
derived from orbitals on the negatively charged dicarbox-
amido-Ns delocalized across the phenylenediamine por-
tion of each ligand (π(PDA)). There is significant overlap
2
(
λmax = 302 nm; intensity, 7 mW/cm ) produces pro-
minent changes in its absorption spectrum (Figure 7).
New absorption peaks at 700 and 490 nm are gene-
rated along with a clean isosbestic point at 355 nm.
As discussed before, the low energy transition at 700 nm
arises from a ligand to metal charge transfer (LMCT) band
hν
n -
n -
½ðLÞRuðNOÞðOEtÞꢁ
f
½ðLÞRuðMeCNÞðOEtÞꢁ þ NO ð1Þ
MeCN
of d (Ru)-π(NO) bonding orbitals (π(RuNO)) with the
π
arising from the negatively charged ligand to the Ru(III)
metal center of the photoproduct [(hypyb)Ru(MeCN)-
(
tion band at 540 nm and shoulder at 400 nm with an
isosbestic point at 375 nm (Figure S5, Supporting
Information) indicates clean release of NO upon illumi-
nation. Complex 3 also behaves similarly upon expo-
sure to UV light. The color of the orange solution
of 3 changes to blue-green, and new bands at 790 and
π(PDA) in the HOMO of 3 while the HOMO of 2 has only
slight overlap and 1 has none. The replacement of neutral
pyridine with charged phenolato donors raises the energy
of the HOMO of 2 (-5.28 eV) and further in 1 (-4.87 eV)
compared to that of 3 (-5.74 eV). However, only the
HOMO of 2 contains phenolato π-orbital (π(PhO)) char-
acter whereas the HOMO of 1 is purely π(PDA). The
corresponding π(PhO)/π(RuNO) MOs of 1 are the
HOMO-1 and HOMO-2.
-
38
OEt)] . In case of 1, the generation of a new absorp-
5
3
90 nm appear in addition to an isosbestic point at
20 nm (Figure S6, Supporting Information).
The photoproducts of 1, 2, and 3 all display strong EPR
The lowest unoccupied molecular orbitals (LUMO) of
all three nitrosyls contain d (Ru)-π*(NO) antibonding
π
character (π*(RuNO)). Franco and co-workers have
suggested that in ruthenium nitrosyls, MLCT transitions
into π*(NO) orbitals would lead to the formation of a
5
signals characteristic of low-spin, d Ru(III) metal cen-
ters. For example, the photoproduct of 3 exhibits its EPR
signals with g = 2.30, 2.18, and 1.91 in MeCN glass
0
formal Ru(III)-NO moiety. From this singlet excited
(
Figure S7, Supporting Information).
To study the effects of combining carboxamido-N and
phenolato-O donors on the efficiency of NO photolability
state, relatively efficient interconversion and intersystem
crossing to lower energy triplet excited states can occur.
Rapid solvation of such triplet species could be competi-
tive with other deactivation pathways and account for
6
in this type of {Ru-NO} nitrosyl, we have measured the
2
0,40
quantum yield values of 1, 2, and 3 under similar condi-
tions at both 300 and 400 nm. In MeCN, the quantum
yield values at 300 nm (φ300) for 1, 2, and 3 are 2.5%,
NO photolability.
triplet excited states of 1, 2, and 3 reveal elongated
Optimization of the lowest energy
˚
Ru-NO bond lengths (1.936, 1.937, and 1.926 A res-
pectively) compared to those observed in the calculated
˚
singlet states (1.726, 1.732, and 1.742 A respectively).
6
.7%, and 5.1% respectively. The addition of one phe-
nolato-O donor in 2 slightly increases its quantum yield
above that of 3 which contains no phenolato-O donors.
Interestingly, the addition of a second phenolato-O
In addition, the Ru-N-O bond angles (170°, 177°, and
(39) Nazeeruddin, M. K.; De Angelis, F.; Fantacci, S.; Selloni, A.;
(
38) (a) Bordini, J.; Hughes, D. L.; Da Motta Neto, J. D.; da Cunha, J. C.
Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.; Gr €a tzel, M. J. Am. Chem. Soc.
Inorg. Chem. 2002, 41, 5410–5416. (b) Sellmann, D.; H €a uβinger, D.; Gottschalk-
Gaudig, T.; Heinemann, F. W. Z. Naturforsch. 2000, 55b, 723–729.
2005, 127, 16835–16847.
(40) Greene, S. N.; Richards, G. J. Inorg. Chem. 2004, 43, 7030–7041.

1
494 Inorganic Chemistry, Vol. 49, No. 4, 2010
Fry et al.
Figure 8. (a) TDDFT calculated energy transitions and oscillator strengths (shown as vertical lines, red = major low energy transition), experimental
solid lines) andcalculated (dashedlines) electronic absorptionspectra. (b) CalculatedHOMO/LUMO energy diagram ofcomplexes1 (left), 2 (middle), and
(right). The most prominent MOs involved in the lowest energy transitions (labeled in red) and their diagrams are shown. Other orbitals involved in
TDDFT calculated transitions are labeled in black.
(
3
1
77° in the singlet state for 1, 2, and 3, respectively)
to that of complex 1 (-1.17 eV, LUMOþ1), which con-
tains no pyridine donors. The most prominent low energy
transition of 2 (420 nm) and 3 (380 nm) both start in
their respective HOMOs. However, the higher energy
π(RuNO)/π(OPh) orbitals of 1 (HOMO-1 and -2) are
not involved in any of the predicted transitions. Instead,
the lowest energy transition of complex 1 (334 nm) starts in
the HOMO-4 which contains ethanolate oxygen nonbond-
ing p-orbital character (p(OEt)) in addition to π(PDA).
Overall the addition of phenolato-O donors raises the
energy of the highest occupied MOs while addition of
pyridine donors lowers the energy of the lowest unoccu-
pied MOs. Thus complex 2 which contains both pheno-
lato and pyridine donors has the lowest energy transition
from an occupied orbital with phenolato character into
an orbital with pyridine character. In addition, complex 1
which has all charged (electron-donating) donors and no
electron-accepting groups exhibits only high energy tran-
sitions. Thus, it becomes apparent that the correct mix of
electron-accepting and electron-donating groups in the
decrease to 139°, 140°, and 138° in the triplet state.
þ
These changes in geometry agree with a Ru(II)-NO to
0
Ru(III)-NO transformation which would decrease
the amount of π-back bonding and cause bending of the
Ru-N-O bond which is characteristic of an Ru(III)-
NO moiety.
0
41
Diagrams of the orbitals involved the lowest energy
transitions of appreciable oscillator strength for each
complex are shown in Figure 8b at their corresponding
energy levels (in red). All three transitions start from
orbitals with some π(PDA) character and end in orbitals
with π*(RuNO) antibonding character. However, consid-
erable mixing of the π*(RuNO) with pyridine based
orbitals (π(py)) is seen for 2 (-1.50 eV, LUMOþ2) and
3
(-1.80 eV, LUMOþ3). Interestingly, this mixing has
lowered the energy of these π*(RuNO) orbitals compared
(
41) Karidi, K.; Garoufis, A.; Tsipis, A.; Hadjiliadis, N.; den Dulk, H.;
Reedijk, J. Dalton Trans. 2005, 1176–1187.

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1495
ligand frame promotes the absorption of lower energy
light (and comcomitant NO photolability) in this type of
ruthenium nitrosyls derived from designed ligands.
observed in the electronic absorption spectra of 1-3. The
lowest energy transitions are from MOs with (electron-
donating) phenolato and carboxamido character into orbi-
tals with (electron-accepting) pyridine mixed with π*(RuNO)
antibonding character.
Summary and Conclusions
The following are the summary and conclusions of the
present work.
Acknowledgment. Financial support from the NSF
Grant CHE-0553405 is gratefully acknowledged. M.K.
and C.N. were supported by REU-NSF (SURF, CHE-
(
1) Three ruthenium nitrosyls, namely, (NEt ) [(hybeb)-
4 2
Ru(NO)(OEt)] (1), (PPh )[(hypyb)Ru(NO)(OEt)] (2), and
4
0552641) and NIH MARC (GM 007910-29) grant, res-
[(bpb)Ru(NO)(OEt)] (3), have been synthesized and structu-
pectively. We thank Dr. Allen Oliver for help in crystallo-
graphic work. The diffraction facility at UCSC is sup-
ported by the NSF Major Research Instrumentation
rally characterized by X-ray crystallography. 1 and 2 are the
first examples of {RuNO} nitrosyls containing both pheno-
lato-O and carboxamido-N atom donors.
6
(MRI) program under Grant CHE-0521569.
(
2) All three nirosyls are diamagnetic and exhibitν inthe
NO
1
-
range 1780-1840 cm . They release NO upon exposure to
UV light of low power (7 mW) with concomitant production
Supporting Information Available: FTIR spectra (Figure S1,
S2, and S3), H NMR spectra (Figure S4), changes in the
1
of EPR active low-spin Ru(III) photoproducts of the type
n-
electronic absorption spectrum upon photolysis of 1 and 3
(
[
(L)Ru(solv)(OEt)] .
Figure S5 and S6), EPR spectrum of the photoproduct of 3 in
(
3) The quantum yield values at 300 nm of the three
nitrosyls follow the trend 2 > 3 > 1 and 3 > 2 at 400 nm.
4) Results of DFT and TDDFT calculations indicate that
the ligand orbitals are critically involved in the transitions
MeCN (Figure S7), tables of DFT parameters for 1-3 (Table
S1-S7), and X-ray crystallographic data (in CIF format) for
complexes 1-3. This material is available free of charge via the
Internet at http://pubs.acs.org.
(