Cyclometalated ruthenium chloro and nitrosyl complexes

Article abstract of DOI:10.1021/ic020451f

The novel cyclometalated RU(III) complex, [Ru(η²-phpy)(trpy)Cl][PF₆]·toluene 1, and the {Ru-NO}⁶ complex, [Ru-(η2-phpy)(trpy)NO][PF₆]₂ 2, where trpy is 2,2′: 6′,2″-terpyridine and phpy is 2-phenylpyridine, have been prepared and characterized by elemental analysis, IR, ¹H NMR, and electronic absorption spectroscopies, cyclic voltammetry, and crystallography. The crystal structure of 1 showed the chloride ion trans to the σ-bonding phenyl group of phpy and is an unusual example of a stable paramagnetic cyclometalated complex. The crystal structure of 2 shows the nitrosyl ligand trans to the σ-bonding phenyl group of phpy. The significant distortion of the normally linear Ru-NO bond angle (167.1(4)°) can be largely ascribed to the strong σ-donor properties of the phenyl group.

Full text of DOI:10.1021/ic020451f

Inorg. Chem. 2002, 41, 6521−6526
Cyclometalated Ruthenium Chloro and Nitrosyl Complexes
,‡
Hassan Hadadzadeh,† Maria C. DeRosa,‡ Glenn P. A. Yap,§ Ali R. Rezvani,| and Robert J. Crutchley*
Chemistry Department, Shahid Beheshti UniVersity, P.O. Box 19395, Tehran, Iran,
Ottawa-Carleton Chemistry Institute, Carleton UniVersity, 1125 Colonel By DriVe,
Ottawa, Ontario, Canada K1S 5B6, and UniVersity of Ottawa, Ottawa,
Ontario, Canada, K1N 6N5
Received February 4, 2002
The novel cyclometalated Ru(III) complex, [Ru(η2-phpy)(trpy)Cl][PF ]‚toluene 1, and the {Ru-NO}6 complex, [Ru-
6
(η2-phpy)(trpy)NO][PF ] 2, where trpy is 2,2′: 6′,2′′-terpyridine and phpy is 2-phenylpyridine, have been prepared
6 2
and characterized by elemental analysis, IR, 1H NMR, and electronic absorption spectroscopies, cyclic voltammetry,
and crystallography. The crystal structure of 1 showed the chloride ion trans to the σ-bonding phenyl group of
phpy and is an unusual example of a stable paramagnetic cyclometalated complex. The crystal structure of 2
shows the nitrosyl ligand trans to the σ-bonding phenyl group of phpy. The significant distortion of the normally
linear Ru−NO bond angle (167.1(4)°) can be largely ascribed to the strong σ-donor properties of the phenyl group.
Introduction
potential application to solar energy and sensor devices.2 In
the course of preparing cyclometalated precursor complexes
to our mixed-valence systems, it became apparent that the
chemistry of these cyclometalated complexes was sufficiently
unique to warrant further investigation.
Cyclometalated complexes of ruthenium are usually six
coordinate with ruthenium in the 2+ oxidation state, and
they therefore obey the 18-electron rule.3 Indeed, a literature
search of ruthenium cyclometalated complexes revealed only
Our research into mixed-valence complexes1 has led us
to cyclometalated complexes because of a desire to reduce
the charge of the complex cation and dramatically perturb
the stability of metal orbitals. One of the most commonly
used ligands, which can form cyclometalated complexes, is
2-phenylpyridine (phpyH). Under suitable conditions, this
ligand will deprotonate and will bind to a metal ion as a
bidentate anion ligand (phpy-),
(2) (a) Bruce, D.; Richter, M. M. Anal. Chem. 2002, 74, 1340-1342. (b)
Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E. Appl. Phys.
Lett. 2000, 77, 904-906. (c) Lee, C.-L.; Lee, K. B.; Kim, J.-J. Appl.
Phys. Lett. 2000, 77, 2280-2082. (d) Colombo, M. G.; Brunhold, T.
C.; Riedener, T.; Gu¨del, H. U.; Fo¨rtsch, M.; Bu¨rgi, H.-B. Inorg. Chem.
1994, 33, 545-550. (e) Dedeian, K.; Djurovich, P. I.; Garces, F. O.;
Carlson, G.; Watts, R. J. Inorg. Chem. 1991, 30, 1685-1687. (f) Craig,
C. A.; Watts, R. J. Inorg. Chem. 1989, 28, 309-313. (g) Garces, F.
O.; King, K. A.; Watts, R. J. Inorg. Chem. 1988, 27, 3464-3471.
(3) (a) Brissard, M.; Gruselle, M.; Male´zieux, B.; Thouvenot, R.; Guyard-
Duhayon, C.; Convert, O. Eur. J. Inorg. Chem. 2001, 1745-1751.
(b) Barigelletti, F.; Ventura, B.; Collin, J. P.; Kayhanian, R.; Garvina,
P.; Sauvage, J. P. Eur. J. Inorg. Chem. 2000, 113-119. (c) Bennett,
M. A.; Clark, A. M.; Contel, M.; Rickard, C. E. F.; Roper, W. R.;
Wright, L. J. J. Organomet. Chem. 2000, 601, 299-304. (d) Clark,
A. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J. Organometallics
1999, 18, 2813-2820. (e) Guari, Y.; Sabo-Etienne, S.; Chaudret, B.
J. Am. Chem. Soc. 1998, 120, 4228-4229. (f) Coudret, C.; Fraysse,
S.; Launay, J.-P. Chem. Commun. 1998, 663-664. (g) Mul, W. P.;
Elsevier: C. J.; Vuurman, M. A.; Smeets, W. J. J.; Spek, A. L.; De
Boer, J. L. J. Organomet. Chem. 1997, 532, 89-100. (h) Collin, J.-
P.; Kayhanian, R.; Sauvage, J.-P.; Calogero, G.; Barigelletti, F.; De
Cian, A.; Fischer, J. Chem. Commun. 1997, 775-776. (i) Aneetha,
H.; Rao, C. R. K.; Rao, K. M.; Zacharias, P. S.; Feng, X.; Mak, T. C.
W.; Srinivas, B.; Chiang, M. Y. J. Chem Soc., Dalton Trans. 1997,
1697-1704.
Cyclometalated complexes have gained great interest because
of their photophysical and photochemical properties and their
* Author to whom correspondence should be addressed. E-mail: rcrutch@
ccs.carleton.ca.
† Shahid Beheshti University.
‡ Carleton University.
§ niversity of Ottawa.
| Sistan & Baluchestan University.
(1) (a) Evans, C. E. B.; Naklicki, M. L.; Rezvani, A. R.; White, C. A.;
Kondratiev, V. V.; Crutchley, R. J. J. Am. Chem. Soc. 1998, 120,
13096-13103. (b) Mosher, P. J.; Yap, G. P. A.; Crutchley, R. J. Inorg.
Chem. 2001, 40, 1189-1195.
10.1021/ic020451f CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/07/2002
Inorganic Chemistry, Vol. 41, No. 24, 2002 6521

Hadadzadeh et al.
roughly 1 × 2 cm with a path length of 0.2 mm, was fitted with a
silver/silver chloride reference electrode, and used ITO (indium-
tin oxide) coated glass for the working and counter electrodes.
Elemental analyses were performed by Canadian Microanalytical
Services.
one example of a cyclometalated mononuclear Ru(III)
complex4 and family of dinuclear complexes,5 both incor-
porating the tridentate dianion ligand,
Materials. All reagents and solvents used were reagent grade
or better. Nitrosonium tetrafluoroborate was purchased from
Aldrich, and [Ru(trpy)Cl3] was synthesized according to literature
procedures.10 ITO glass plates were purchased from Delta-
Technologies.
and its derivatives. For both studies,4,5 the assigned oxidation
state of ruthenium was supported by EPR spectroscopy and
elemental analysis. In this study, we report the facile
synthesis of a paramagnetic Ru(III) cyclometalated complex,
[Ru(η2-phpy)(trpy)Cl][PF6]‚toluene 1, where trpy is 2,2′:
6′,2′′-terpyridine, and the characterization of 1 by crystal-
lography, elemental analysis, IR and UV-vis spectroscopies,
and cyclic voltammetry.
Nitrosyl complexes have gained a deserved recognition
as important models for nitrogen oxide regulation in biology.6
Recent reviews7 of the coordination chemistry of the nitrosyl
ligand speak to the importance of this research, and so it
was decided to attempt the synthesis of a nitrosyl complex
using 1. The result, [Ru(η2-phpy)(trpy)NO][PF6]2 2, was
prepared in nonaqueous solution and in high yields. Complex
2 was characterized by crystallography, elemental analysis,
IR, 1H NMR and UV-vis spectroscopies, and cyclic volta-
mmetry. Spectroelectrochemical studies of 1 and 2 were also
performed.
Preparation of [Ru(η2-phpy)(trpy)Cl][PF6]‚toluene, 1. [Ru-
(trpy)Cl3] (0.441 g, 1 mmol) and 2-phenylpyridine (0.155 g, 1
mmol) were dissolved in 20 mL of DMF and refluxed for 4 h,
after which TlPF6 (0.70 g, 2 mmol) was added and the solution
refluxed for a further 1 h. The solution was cooled to -20 °C
overnight and then filtered through Celite to remove the fine white
TlCl precipitate. Diethyl ether (600 mL) was then added to the
filtrate, precipitating the crude product, which was filtered off and
then was purified by chromatography (grade III alumina, weakly
acidic, 40 × 3 cm column). Elution with 1:2 acetonitrile/toluene
yielded a purple band, which was not identified, followed by the
green band of the target complex. The latter band was collected,
evaporated to dryness, and then recrystallized by slow evaporation
of a 3:1 acetonitrile/toluene solution of the complex. Yield: 0.39
g (51%). Anal. Calcd for [Ru(η2-phpy)(trpy)Cl][PF6]‚toluene
(C33H27N4F6PClRu): C, 52.08; H, 3.58; N, 7.36. Found: C, 51.88;
H, 3.67; N, 7.53.
Preparation of [Ru(η2- phpy)(trpy)NO][PF6]2, 2. A mixture
of 1 (0.669 g, 1 mmol) and TlPF6 (0.349 g, 1 mmol) was placed in
100 mL of acetonitrile and stirred at reflux for 1 h. The solution
was chilled to -20 °C and filtered through Celite to remove the
white TlCl precipitate. To the filtrate was then added nitrosonium
tetrafluoroborate (0.14 g,1.2 mmol), and the resulting solution was
stirred with slight heating (34-45 °C) for 5 h. The solution was
evaporated, and the crude light brown solid recrystallized by the
diffusion of diethyl ether into an acetonitrile solution of the complex.
Yield: 0.65 g, (80%). Anal. Calcd for [Ru(η2-phpy)(trpy)NO][PF6]2
(C26H19N5OF12P2Ru): C, 38.63; H, 2.37; N, 8.66. Found: C, 38.90;
Experimental Section
Equipment. UV-vis spectroscopy was performed on a CARY
5 UV-vis-NIR spectrophotometer. IR spectra were taken with a
BOMEM Michelson-100 FT-IR spectrophotometer (KBr disks). 1H
NMR data from acetonitrile-d3 solutions were obtained by using a
Bruker AMX-400 spectrometer. Cyclic voltammetry was performed
using a BAS CV-27 voltammograph and plotted on a BAS XY
recorder. The sample cell consisted of a double-walled glass crucible
with an inner volume of ∼15 mL which was fitted with a Teflon
lid incorporating a three-electrode system and argon bubbler. The
cell temperature was maintained at (25.0 ( 0.1) °C by means of a
HAAKE D8 recirculating bath. BAS 2013 Pt electrodes (1.6 mm
diameter) were used as the working and counter electrodes. A silver
wire functioned as a pseudo-reference electrode. Acetonitrile
(MeCN) was dried over P2O5 and vacuum distilled. Tetrabutylam-
monium hexafluorophosphate (TBAH), purchased from Aldrich,
was twice recrystallized from 1:1 ethanol/water and vacuum-dried
at 110 °C. Ferrocene (E° ) 0.665 V versus NHE) was used as an
internal reference.8 An OTTLE cell was used to perform the
spectroelectrochemistry.9 The cell had interior dimensions of
1
H, 2.45; N, 8.82. IR ν(NO): 1858 cm-1. H NMR (400 MHz):
9.06 (1H, doublet), 8.75 (3H, multiplet), 8.60 (2H, doublet), 8.33
(4H, multiplet), 7.98 (3H, multiplet), 7.79 (1H, triplet), 7.57 (2H,
triplet), 7.17 (1H, triplet), 6.88 (1H, triplet), 5.79 (1H, doublet) ppm.
Crystallography. Crystals of 1 were grown by the slow
evaporation of a 3:1 acetonitrile/toluene solution of the complex.
Diffusing diethyl ether into an acetonitrile solution of the complex
grew crystals of 2. For both complexes, the data were collected on
a 1K Siemens Smart CCD using Mo KR radiation (λ ) 0.71073
Å) at 203(2) K using an ω-scan technique and corrected for
absorptions using equivalent reflections.11 No symmetry higher than
triclinic was observed, and solution in the centric space group option
yielded chemically reasonable and computationally stable results
of refinement. The structure was solved by direct methods and
refined with full-matrix least-squares procedures. For 1, two half-
occupied molecules of toluene were found cocrystallized near the
inversion center in the asymmetric unit. These were refined with
phenyl groups idealized as rigid, flat hexagons. In addition, the
PF6 counterion in 1 was restrained to have similar cis F‚‚‚F
interatomic separations. Anisotropic refinement was performed on
all non-hydrogen atoms. All hydrogen atoms were calculated.
(4) Hariram, R.; Santra, B. K.; Lahiri, G. K. J. Organomet. Chem. 1997,
540, 155-163.
(5) Munshi, P.; Samanta, R.; Lahiri, G. K. J. Organomet. Chem. 1999,
586, 176-183.
(6) Wang, P. G.; Xian, M.; Tang, X.; Wu, X.; Wen, Z.; Cai, T.; Janczuk,
A. J. Chem. ReV. 2002, 102, 1091-1134.
(7) (a) Hayton, T. W.; Legzdins, P.; Sharp, W. B. Chem. ReV. 2002, 102,
935-991. (b) Ford, P. C.; Lorkovic, I. M. Chem. ReV. 2002, 102,
993-1017.
(8) Gennett, T.; Milner, D. F.; Weaver, M. J. J. Phys. Chem. 1985, 89,
2787-2794.
(9) (a) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. 1991,
317, 179-187. (b) Evans, C. E. B. Ph.D. Thesis, Carleton University,
1997.
(10) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg. Chem. 1980, 19,
1404-1407.
(11) Blessing, R. Acta Crystallogr. 1995, A51, 33-38.
6522 Inorganic Chemistry, Vol. 41, No. 24, 2002

Cyclometalated Ruthenium Chloro and Nitrosyl Complexes
Table 1. Crystal Data and Structure Refinement for Complexes
1 and 2
1
2
formula
fw
C33H27F6ClN4PRu
761.08
P1h
triclinic
2
1.636
11.165(3)
11.335(3)
13.447(4)
68.768(2)
78.303(3)
80.274(3)
1544.7(8)
203(2)
C26H19F12N5OP2Ru
808.47
P1h
triclinic
space group
cryst syst
Z′
Dc, g/cm3
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
1.864
8.9387(8)
10.4325(9)
16.7004(15)
77.6950(10)
88.7732(2)
71.3870(10)
1440.2(2)
203(2)
temp, K
GOF on F2
R1a
wR2b
1.038
0.0518
0.1075
1.063
0.0509
0.1494
Figure 1. ORTEP drawing of [Ru(η2-phpy)(trpy)Cl]PF6‚toluene 1. The
counterion and solvent of crystallization have been omitted for clarity.
Selected bond lengths (Å) and bond angles (deg): Ru-N(3), 1.971(4); Ru-
N(4), 2.060(4); Ru-N(2), 2.076(3); Ru-C(11), 2.024(4); Ru-N(1), 2.091-
(4); Ru-Cl, 2.4431(13); N(3)-Ru-C(11), 95.43(16); N(3)-Ru-N(4),
79.70(15); C(11)-Ru-N(4), 90.93(15); N(3)-Ru-N(2), 79.05(14); C(11)-
Ru-N(2), 86.23(15); N(4)-Ru-N(2), 158.19(15); N(3)-Ru-N(1), 174.54-
(14); C(11)-Ru-N(1), 79.77(16); N(4)-Ru-N(1); 97.68(14); N(2)-Ru-
N(1), 103.07(14); N(3)-Ru-Cl, 90.64(10); C(11)-Ru-Cl, 171.43(13);
N(4)-Ru-Cl, 96.11(10); N(2)-Ru-Cl, 89.00(10); N(1)-Ru-Cl, 94.41-
(10).
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2
.
Scattering factors are contained in the SHELXTL 5.1 program
library.
Results and Discussion
The synthetic strategy to prepare complex 1 was based
on a modification of the procedure used to prepare [Ru(bpy)2-
(η2-phpy)]+.12 The latter complex was prepared by the
reaction of stoichiometric amounts of [Ru(bpy)2Cl2], phe-
nylpyridine, and silver(I) tetrafluoroborate in refluxing
dichloromethane, without the addition of base to deprotonate
2-phenylpyridine. In this study, a similar reaction between
the Ru(III) complex, [Ru(trpy)Cl3], 2-phenylpyridine, and
thallium hexafluorophosphate in refluxing dimethylforma-
mide (eq 1), gave 1 in 51% final yield. Refluxing dimeth-
Cyclic voltammetry was performed on an acetonitrile
solution of 1 with 0.1 M TBAH supporting electrolyte. Three
couples were observed at +0.46, -1.32, and -1.61 V vs
NHE that we assigned to the Ru(III/II) reduction couple and
two terpyridine reduction couples, respectively. Terpyridine’s
π* orbitals are expected to be more stable compared to
anionic phenylpyridine and should be reduced first.1b The
cyclic voltammogram of the Ru(III/II) couple possessed
equivalent anodic and cathodic waves whose separation (60
mV) was independent of scan rate (100-450 mV/s). Figure
2 shows the spectroelectrochemistry associated with this Ru-
(III/II) couple. In Figure 2, complex 1 shows low-energy
bands in the visible region that, due to their intensity, are
likely phenyl to Ru(III) ligand-to-metal charge transfer
transitions, pπ f dπ. Upon reduction to Ru(II) (Figure 2),
these bands are replaced by a number of dπ f pπ* metal-
to-ligand charge transfer transitions derived from the π*
orbitals of terpyridine. Regeneration of 1 occurred with
greater than 95% recovery of the original spectrum.
[Ru(trpy)Cl3] + 2TlPF6 + Hphpy f
[Ru(phpy)(trpy)Cl]+ + 2TlClV + 2PF6- + H+ (1)
ylformamide was thought necessary to overcome the greater
inertness of Ru(III) toward substitution reactions. Elemental
analysis of 1 was entirely consistent with its proposed
stoichiometry, and attempts to determine its 1H NMR
spectrum showed that the complex was paramagnetic,
supporting a Ru(III) oxidation state. An unambiguous
determination of the stoichiometry of 1 was made by
crystallography.
For 1, crystal structure data can be found in Table 1 and
an ORTEP is shown in Figure 1 together with selected bond
lengths and bond angles. The crystal structure shows
terpyridine, phenylpyridine, and chloride ligands coordinated
to a Ru(III) ion in which the σ-bonded phenyl group of
phenylpyridine is trans to the chloride ligand. Ru-nitrogen
and Ru-carbon bond lengths of 1 are significantly shorter
than those of complex 2 (discussed below), whose metal ion
oxidation state is formally Ru(II). The contracted coordina-
tion sphere of 1 compared to 2 is therefore a consequence
of the oxidation state of the central metal ion.
Ruthenium nitrosyl complexes have been previously
prepared13-15 by the acid decomposition of the corresponding
nitro complex in aqueous solution,
RuII - NO2 + 2H+ f {Ru(NO)}6 + H2O
(2)
To prepare 2 in nonaqueous solution, nitrosonium tetrafluo-
roborate was added to an acetonitrile solution of the complex
(eqs 3-5). Nitrosonium oxide is a powerful oxidant (1.52
(13) Callahan, R. W.; Meyer, T. J. Inorg. Chem. 1977, 16, 574-581.
(14) Pipes, D. W.; Meyer, T. J. Inorg. Chem. 1984, 23, 2466-2472.
(15) Dovletoglou, A.; Adeyemi, S. A.; Meyer, T. J. Inorg. Chem. 1996,
35, 4120-4127.
(12) Constable, E. C.; Holmes, J. M. J. Organomet. Chem. 1986, 301, 203-
208.
Inorganic Chemistry, Vol. 41, No. 24, 2002 6523

Hadadzadeh et al.
Figure 3. ORTEP drawing of [Ru(η2-phpy)(trpy)NO][PF6]2 2. The
counterions have been omitted for clarity. Selected bond lengths (Å) and
bond angles (deg): Ru-N(1), 2.111(4); Ru-N(4), 2.108(3); Ru-N(2),
2.101(3); Ru-N(3), 1.991(4); Ru-C(11), 2.096(4); Ru-N(5), 1.826(4);
N(5)-O(1), 1.139(5); N(5)-Ru-C(11), 170.30(16); N(5)-Ru-N(3), 100.79-
(15); N(3)-Ru-C(11), 88.31(15); N(5)-Ru-N(2), 97.13(15); N(3)-Ru-
N(2), 79.60(14); C(11)-Ru-N(2), 87.76(14); N(5)-Ru-N(4), 91.59(15);
N(3)-Ru-N(4), 79.12(14); C(11)-Ru-N(4), 86.78(14); N(5)-Ru-N(1),
92.62(15); N(2)-Ru-N(4), 158.17(14); C(11)-Ru-N(1), 78.41(15); N(2)-
Ru-N(1), 97.35(13); N(4)-Ru-N(1), 102.21(13); O(1)-N(5)-Ru, 167.1-
(4).
Figure 2. Spectroelectrochemical reduction of 1, 0.1 M TBAH electrolyte
in acetonitrile. Potential change from +0.6 to -0.3 V vs silver/silver chloride
reference electrode.
V vs NHE),16 and it seems probable, on the basis of the yield
of 2 (80%), that the concentration of reducing impurities in
acetonitrile generated sufficient nitrogen oxide to nearly
quantitatively react with the Ru(III)-solvato complex.
mode of the nitrosyl ligand.19 As the phenyl group of the
phpy ligand is also expected to be trans to the nitrosyl in 2,
it was therefore of interest to determine the crystal structure
of 2.
[Ru(phpy)(trpy)Cl]+ + Tl+ + CH3CN f
[Ru(phpy)(trpy)(CH3CN)]2+ + TlClV (3)
Crystal structure data for 2 can be found in Table 1, and
an ORTEP drawing is shown in Figure 3, together with
selected bond lengths and bond angles. The crystal structure
shows that the phenyl group is trans to the nitrosyl ligand.
The Ru-nitrosyl bond length (Ru-N(5)) is 1.826(4) Å and
is significantly shorter than the other Ru-N bonds. In
addition, the NO bond length of 1.139(5) Å shows the triple-
bond character of the nitrosyl ligand. These facts are
consistent with a π acceptor NO+ ligand. On the other hand,
the Ru-NO bond angle (O(1)-N(5)-Ru) is 167.1(4)° and
outside the normal range of linear ruthenium nitrosyl bonds
(170-180°).19 As mentioned above, crystal structures of
ruthenium and iron octaethylporphyrinato dianion {M(NO)}6
complexes in which the nitrosyl ligand is trans to a strong
σ-donating phenyl ligand showed unexpected metal-nitrosyl
bending (154.9(3)° and 157.4(2)°, respectively).19 Density
functional based calculations reproduced these structural
distortions, and the authors suggest that a bent metal-nitrosyl
bond is intrinsic to species of the type [(por)M(NO)X] where
X is a strong σ donor ligand and por is a porphyrin.19 While
the same degree of bending is not seen in 2 despite having
a phenyl ligand trans to the nitrosyl, this is probably related
to the charge and electron-donating ability of the auxiliary
ligands. Porphyrins are dianion tetradentate ligands and are
expected to donate significantly greater electron density to
the metal ion compared to the four neutral pyridine moieties
in 2.
NO+ + e- f NO•
(4)
[Ru(phpy)(trpy)(CH3CN)]2+ + NO• f
[Ru(phpy)(trpy)(NO)]2+ + CH3CN (5)
Another possible route to 2 is the ligand substitution reaction
of the Ru(II) solvato complex with NO+, but this seems less
likely as it would require that the ruthenium(III) solvato
complex be reduced before NO+.17
1
For 2’s H NMR spectrum (see Experimental Section),
only 10 chemical shifts out of the expected 14 were observed,
but, as indicated by integration, this was clearly due to the
overlap of chemical shifts. The elemental analysis is in
agreement with the proposed stoichiometry, which, because
there are six π electrons between metal and the nitrosyl
ligand, identifies 2 as a {Ru(NO)}6 system.18 For the majority
of ruthenium nitrosyl complexes, the nitrosyl ligand is
formally NO+ and its coordination to the metal ion is
linear.13-15,19 However, crystal structures of iron and ruthe-
nium porphyrin {M-NO}6 systems, in which a phenyl group
was trans to a nitrosyl ligand, showed a bent coordination
(16) Rathore, R.; Lindeman, S. V.; Kochi, J. K. J. Am. Chem. Soc. 1997,
119, 9393-9404. NO+/0 ) 1.28 V vs SCE.
(17) Mukaida, M.; Sato, Y.; Kato, H.; Mori, M.; Ooyama, O.; Nagao, H.;
Howell, F. S. Bull. Chem. Soc. Jpn. 2000, 73, 85-95. The
[Ru(phpy)(trpy)(CH3CN)]2+/+ couple can be estimated from that of
[Ru(bpy)2(CH3CN)Cl]2+/+ ) 0.48 V vs Ag|AgNO3 or 0.68 V vs NHE.
(18) (a) Feltham, R. D.; Enemark, J. H. Top. Stereochem. 1981, 12, 155-
215. (b) Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV. 1974, 13,
339-406.
(19) Richter-Addo, G. B.; Wheeler, R. A.; Hixson, A.; Chen, L.; Khan,
M. A.; Ellison, M. K.; Schulz, C. E.; Scheidt, W. R. J. Am. Chem.
Soc. 2001, 123, 6314-6326.
6524 Inorganic Chemistry, Vol. 41, No. 24, 2002

Cyclometalated Ruthenium Chloro and Nitrosyl Complexes
Figure 4. Irreversible spectroelectrochemical reduction of 2, 0.1 M TBAH
electrolyte in acetonitrile. Potential change from +0.6 to -0.6 V vs silver/
silver chloride reference electrode.
Figure 5. Plot of {Ru(NO)}6/7 couples in acetonitrile versus ν(NO). Data
points: 2, [Ru(η2-phpy)(trpy)(NO)]2+, and from refs 13-15, (a) cis-[Ru-
(trpy)(acetylacetonate)NO]2+ in CH2Cl2, (b) trans-[Ru(bpy)2(NO)Cl]2+, (c)
cis-[Ru(bpy)2(NO)N3]2+, (d) cis-[Ru(bpy)2(NO)Cl]2+, (e) cis-[Ru(bpy)2-
(NO)NO2]2+, (f) cis-[Ru(bpy)2(NO)NH3]3+, (g) [Ru(trpy)(bpy)NO]3+, (h)
cis-[Ru(bpy)2(NO)pyridine]3+, (i) cis-[Ru(bpy)2(NO)(CH3CN)]3+. Best fit
linear equation: ν(NO) ) 126{Ru(NO)}6/7 + 1870, R2 ) 0.91.
Cyclic voltammetry was performed on an acetonitrile
solution of 2 with 0.1 M TBAH supporting electrolyte. In
contrast to 1, the voltammogram of 2 showed significant
irreversibility of the reduction couples. A couple at -0.03
V vs NHE was assigned to the {Ru(NO)}6/7 reduction and
based on previous studies14,15 is likely nitrosyl localized. This
couple’s cyclic voltammogram showed the cathodic wave
to be considerably larger than the anodic wave, suggesting
that a rearrangement or chemical reaction follows reduction.
The electronic absorption spectra associated with this ir-
reversible reduction are seen in Figure 4. Two new absorp-
tions centered at 415 and 481 nm are likely dπ* metal-to-
ligand charge transfer transitions of Ru(II) to the π* orbitals
of terpyridine (by analogy compare Figure 4 to the reduction
of 1, Figure 2). The oxidation of this reduction product did
not reproduce the original spectrum of 2, and so a new
complex has formed. If this oxidized complex was reduced,
the same absorption spectrum seen upon reduction of 2 was
obtained (Figure 4). A recent study of the final degradation
products of ruthenium nitrosyl complexes of the general
formula cis-[Ru(bpy)2X(NO)]n+ {Ru(NO)}7 in acetonitrile
showed a significant dependence of products upon the nature
of the ligand X.17 For the complex, cis-[Ru(bpy)2Cl(NO)]+
only two products were identified: the starting material cis-
[Ru(bpy)2Cl(NO)]2+ and the solvolysis product, cis-[Ru-
(bpy)2Cl(CH3CN)]+. By analogy to this result, we suggest
that the final absorption spectrum of the reduction product
of 2 in Figure 4 is likely [Ru(η2-phpy)(trpy)(CH3CN)]+ (eq
6). The oxidation of this complex (eq 7) was reversible.
Linear plots of the {Ru(NO)}6/7 couple versus ν(NO) have
appeared in the literature14,15 with the rationalization that if
the initial reduction of a nitrosyl complex is associated with
the NO+/0 couple, it should be very sensitive to the energy
of the lowest unoccupied molecular orbital (LUMO) of NO+,
which will vary depending on the ability of the metal ion to
π-donate to the π acceptor NO+. Figure 5 shows this plot
together with a data point derived from 2 and the linear least-
squares best-fit equation of all the data. Inclusion of 2 has
almost doubled the range of the linear correlation in Figure
5, but there is still a need for further data to establish this
relationship throughout the entire range.
Conclusions
Two novel cyclometalated ruthenium complexes have been
synthesized and structurally characterized. Complex 1 rep-
resents an unusual example of a paramagnetic organometallic
complex possessing a Ru(III) central ion. This complex
showed good reversibility upon reduction as evidenced by
spectroelectrochemical studies. The crystal structure of the
{Ru(NO)}6 complex, 2, showed a σ-donating phenyl group
trans to the nitrosyl ligand and significant deviation of the
Ru-NO bond angle (167.1(4)°) from linearity. This degree
of bending is not as much as that seen for ruthenium and
iron octaethylporphyrinato dianion {M(NO)}6 complexes in
which the nitrosyl ligand is trans to a strong σ-donating
phenyl ligand (M-NO angle ) 154.9(3)° and 157.4(2)°,
respectively) and is likely a consequence of the greater
electron density donated by the porphyrin ligand to ruthe-
nium. Complex 2 is suggested to be an intermediate case
between linear and bent coordination modes for ruthenium
nitrosyl complexes.
[Ru(phpy)(trpy)(NO)]2+ + e - f
[Ru(phpy)(trpy)(CH3CN)]+ + NO• (6)
[Ru(phpy)(trpy)(CH3CN)]+ S
[Ru(phpy)(trpy)(CH3CN)]2+ + e- (7)
Inorganic Chemistry, Vol. 41, No. 24, 2002 6525

Hadadzadeh et al.
Supporting Information Available: Two X-ray crystallo-
graphic files, in CIF format, for 1 and 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the Natural Sci-
ences and Engineering Research Council (NSERC) of
Canada for financial support. M.C.D. wishes to acknowledge
the support of a graduate scholarship from NSERC. H.H.
thanks the Ministry of Science, Research and Technology
of Iran for a graduate student scholarship.
IC020451F
6526 Inorganic Chemistry, Vol. 41, No. 24, 2002