Hydrazine nitrosation of a metal-bound nitric oxide: Structural evidence for the formation of an ammine complex

Article abstract of DOI:10.1021/ic060096j

Hydrazine nitrosation of [Ru(NO)(py^siS₄)] Br·THF (1) (py^siS₄^2- = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)-pyridine^2-) in methanol/DMF led to the formation of mononuclear ammine complex [Ru(NH ₃)(py^siS₄)] (2) and N₂O, whereas the reaction performed in THF/CH₂Cl₂/toluene afforded thioether-bridged dinuclear ammine complex [(NH₃)-Ru(μ-py ^siS₄)Ru(py^siS₄)] (3). Compound 2 dimerizes in solution at room temperature to form 3 and is regenerated upon treatment of 3 with NH₃. A plausible mechanism for the hydrazine nitrosation of 1 has been proposed. The reaction of 1 with NH₃ or N₃^- does not lead to a nucleophilic attack at the NO ⁺ ligand but to a deprotonation that yields neutral nitrosyl complex [Ru(NO){py^siS₄(H⁺)}] (4), which is supported by density functional theory calculations.

Full text of DOI:10.1021/ic060096j

Inorg. Chem. 2006, 45, 4661−4667
Hydrazine Nitrosation of a Metal-Bound Nitric Oxide: Structural
Evidence for the Formation of an Ammine Complex
Raju Prakash,*,†,§ Andreas W. Gotz, Frank W. Heinemann,† Andreas Gorling, and Dieter Sellmann†,‡
1 1
Institut fu¨r Anorganische Chemie, UniVersita¨t Erlangen-Nu¨rnberg, Egerlandstrasse 1,
D-91058 Erlangen, Germany, and Lehrstuhl fu¨r Theoretische Chemie,
UniVersita¨t Erlangen-Nu¨rnberg, Egerlandstrasse 3, D-91058 Erlangen, Germany
Received January 18, 2006
2
-
Hydrazine nitrosation of [Ru(NO)(pysiS4)]Br
‚
THF (1) (pysiS4
) 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)-
pyridine2-) in methanol/DMF led to the formation of mononuclear ammine complex [Ru(NH3)(pysiS4)] (2) and N2O,
whereas the reaction performed in THF/CH2Cl2/toluene afforded thioether-bridged dinuclear ammine complex [(NH3)-
Ru(µ
-pysiS4)Ru(pysiS4)] (3). Compound 2 dimerizes in solution at room temperature to form 3 and is regenerated
upon treatment of 3 with NH3. A plausible mechanism for the hydrazine nitrosation of 1 has been proposed. The
-
reaction of 1 with NH3 or N3 does not lead to a nucleophilic attack at the NO+ ligand but to a deprotonation that
yields neutral nitrosyl complex [Ru(NO)
{
pysiS4(H+)
}] (4), which is supported by density functional theory calculations.
Introduction
depending on the reaction conditions.5 The reaction between
nitrous acid and hydrazine in aqueous solution is known to
The electrophilic reaction of nitrogen monoxide (NO) at
the transition-metal centers of designed complexes is cur-
rently a topic of great significance, particularly because of
their fundamental chemical interest in relation to various
important biological and environmental processes.1,2 The
transition metal nitrosyl complexes generally possess an
electronically delocalized [M-N-O] moiety, with the N
atom being the site for the nucleophilic addition.3 The
nucleophilic reaction of hydrazine with NO+ to undergo
nitrosation has been well thought out in the in vitro studies
of dissimilatory nitrite reductases.4 The reactivity of hydra-
zine toward simple compounds as well as metal complexes
is of much interest even at the mechanistic level, because it
acts as a one-, two-, or four-equivalent reducing agent
be a normal N-nitrosation.6 Stedman proposed two parallel
routes for the decomposition of the N-nitrosohydrazine
intermediate:6a,b the first route led to the formation of HN3
and H2O, which is analogous to the well-established mech-
anism of the diazotization of aromatic amines in moderately
concentrated mineral acid solutions,6c and obtained a 100%
yield of HN3 at high acidities; the second route led to the
formation of NH3 and N2O exclusively at low acidities.
(2) (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. (c) Wasser, I. M.; de Vries, S.; Moe¨nne-Loccoz, P.;
Schro¨der, I.; Karlin, K. D. Chem. ReV. 2002, 102, 1201-1234. (d)
Lopez, J. P.; Heinemann, F. W.; Prakash, R.; Hess, B. A.; Horner,
O.; Jeandey, C.; Oddou, J.-L.; Latour, J.-M.; Grohmann, A. Chem.s
Eur. J. 2002, 8, 5709-5722. (e) Clarke, M. J. Coord. Chem. ReV.
2003, 236, 209-233. (f) McCleverty, J. A. Chem. Rev. 2004, 104,
403-418. (g) Afshar, R. K.; Patra, A. K.; Olmstead, M. M.;
Mascharak, P. K. Inorg. Chem. 2004, 43, 5736-5743. (h) Bo¨ttcher,
H.-C.; Graf, M.; Mereiter, K.; Kirchner, K. Organometallics 2004,
23, 1269-1273. (i) Roncaroli, F.; van Eldik, R.; Olabe, J. A. Inorg.
Chem. 2005, 44, 2781-2790. (j) Sauaia, M. G.; de Lima, R. G.;
Tedesco, A. C.; da Silva, R. S. Inorg. Chem. 2005, 44, 9946-9951.
(3) Bottomley, F.; Grein, F. J. Chem. Soc., Dalton Trans. 1980, 1359-
1367.
(4) (a) Kim, C. H.; Hollocher, T. C. J. Biol. Chem. 1984, 259, 2092-
2099. (b) Averill, B. A. Chem. ReV. 1996, 96, 2951-2964.
(5) Stanbury, D. M. Prog. Inorg. Chem. 1998, 47, 511-561.
(6) (a) Perrot, J. R.; Stedman, G.; Uysal, N. J. Chem. Soc., Dalton Trans.
1976, 2058-2064. (b) Doherty, A. M. M.; Howes, K. R.; Stedman,
G.; Naji, M. Q. J. Chem. Soc., Dalton Trans. 1995, 3103-3107. (c)
Challis, B. C.; Ridd, J. H. J. Chem. Soc. 1962, 5208.
* To whom correspondence should be addressed. E-mail: raju.prakash@
chemie.uni-erlangen.de.
† Institut fu¨r Anorganische Chemie.
§ Current address: Institut fu¨r Organische Chemie, Universita¨t Erlangen-
Nu¨rnberg, Henkestrasse 42, D-91054 Erlangen, Germany.
Lehrstuhl fu¨r Theoretische Chemie.
‡ Deceased: May 6, 2003.
(1) (a) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford
University Press: New York, 1992. (b) Stamler, J. S.; Singel, D. J.;
Loscalzo, J. Science 1992, 258, 1989-1902. (c) Snyder, S. H. Science
1992, 257, 494-496. (d) Feelisch, M.; Stamler, J. S. In Methods in
Nitric Oxide Research; Feelisch, M., Stamler, J. S., Eds.; Wiley:
Chichester, U.K., 1996, and references therein. (e) Nitric Oxide,
Principles and Actions; Lancaster, J., Jr., Ed.; Academic Press: New
York, 1996.
10.1021/ic060096j CCC: $33.50
Published on Web 05/10/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 12, 2006 4661

Prakash et al.
techniques. Reactions with hydrazine were carried out in the dark
using a Schlenk tube (volume ) 100 mL) fitted with a gastight
rubber septum, unless stated otherwise. Solvents were dried under
dinitrogen from appropriate drying agents and distilled prior to use.
The hydrazine (1 M solution in THF) was purchased from Aldrich
Chemicals Co. and used as received. Compound 1 was synthesized
as described in our earlier communication.11 Physical measurements
were performed with the following instruments: IR (KBr disks or
CaF2 cuvettes with solvent bands were compensated), Perkin-Elmer
983, 1620 FT-IR, and 16PC FT-IR. NMR: JEOL JNM-GX 270,
JEOL JNM-EX 270, or Lambda LA 400 with the residual signals
of the deuterated solvent used as an internal reference. Chemical
shifts are quoted in the parts per million scale (downfield shifts
are positive). Elemental analysis: Carlo Erba EA 1106 or 1108
analyzer. Mass spectra: JEOL MSTATION 700 spectrometer. Gas
chromatography/mass spectrometry: Thermo Finnigan MAT 95 XP
gas chromatograph/mass spectrometer coupled to a high sensitive
split/splitless injector. A separate helium supply was regulated by
a mass flow controller. The gas samples were taken from the
Schlenk tube before the addition of hydrazine as well as at the end
of the reaction by means of a 250 µL gastight syringe. The entire
contents of the syringe were injected into the 20 µL loop in order
to enhance sample-to-sample reproducibility, and the analysis was
repeated three times. The gas separations were accomplished with
a fused silica capillary (30 mm × 0.25 mm; 0.25 µm film thickness)
column OPTIMA-5 (inner diameter 0.25 µm). The helium gas flow
rate was 0.7 mL/min, and the temperature at the injector, interface,
and column was kept at 50 °C. The separated gases were analyzed
consecutively by positive ion electron impact (EI) mass spectra
mode. Cyclic voltammetry: EG&G Princeton Applied Research
(PAR) model 264A potentiostat coupled with a conventional three-
electrode cell-assembly consisting of a glassy carbon working
electrode, a platinum wire reference electrode, and a platinum rod
There are some reports available on the reaction of
hydrazine with transition metal nitrosyls.7-10 However, they
show different reaction modes depending on the metal as
well as coligand environment, which lead to the formation
of different products. To date, only one report describes the
nucleophilic reaction of hydrazine with metal-bound NO+
([Fe(CN)5(NO)]2-) in aqueous solution to yield ammonia and
nitrous oxide exclusively, according to Stedman’s second
route.7d On the other hand, the reactivity of ruthenium
nitrosyls with hydrazine reported so far in the literature
yielded predominantly metal-bound azide and H2O.8 The
reaction of [Ru(NO)(NH3)5]3+ with hydrazine gave N2O and
N2, but no ammonia was found.9 It has been reported recently
that sulfur-rich ruthenium complex [Ru(NO)(Et2NpyS4)]Br
2-
(Et2NpyS4 ) 2,6-bis(2-sulfanylphenylthiomethyl)-4-di-
ethylaminopyridine2-) interacts with an excess of hydrazine
to form [Ru(N2H4)(EtNpyS4)].10a Later, it was confirmed by
IR spectroscopy that the hydrazine complex is formed via
the intermediate azide complex by ligand exchange.10b
In our previous work, we have synthesized a ruthenium
2-
nitrosyl complex, [Ru(NO)(pysiS4)]Br‚THF (1) (pysiS4
)
2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)-
pyridine2-), that contains two sterically bulky SiPh3 groups
ortho to the thiolate donors.11 This {Ru-NO}6 nitrosyl
(according to the notation of Enemark and Feltham12) is
photolabile in methanol and releases NO under visible light
irradiation to form [Ru(Br)(pysiS4)]. Treatment of the bromo
derivative with NO in methanol generates 1, without any
side reaction. In the course of a more-detailed study on the
reactivity of 1 toward various nucleophiles, we report herein
the nitrosation reaction of 1 with hydrazine in different
nonaqueous solvents to form nitrous oxide and [Ru(NH3)-
(pysiS4)] (2). The latter complex dimerizes in solution to
afford a very stable thioether-bridged dinuclear ammine
complex [(NH3)Ru(µ-pysiS4)Ru(pysiS4)] (3). We furthermore
describe the reactivity of 1 with ammonia and azide in
various organic solvents that results in deprotonation product
[Ru(NH3){pysiS4(H+)}] (4).
counter electrode. Measurements were made with ca. 1 × 10-3
M
solutions of the complexes in CH2Cl2, using 0.1 M tetrabutylam-
monium hexafluorophosphate as a supporting electrolyte. Ferrocene
was used as an internal standard {E1/2(Fc/Fc+) ) +410 mV vs NHE
(normal hydrogen electrode);13 scan speeds: 10-200 mV s-1: T
) 20 °C. The reversibility and the number of electrons involved in
the redox processes were evaluated on the basis of their (∆E and
Ep- Ep/2) similarity to ferrocene in the cyclic voltammograms,
whereas the diffusion-controlled property of the voltammograms
was determined according to the literature method.14
Experimental Section
[Ru(NH3)(pysiS4)] (2). Method 1: To a violet solution of 1 (450
mg, 0.38 mmol) in methanol (20 mL) was injected N2H4 (1 M
solution in THF, 0.4 mL, 0.4 mmol) through a syringe. The solution
was stirred for 25 min at room temperature. During the course of
time, orange-red microcrystals were precipitated. The microcrystals
were filtered, washed with methanol (20 mL) and then diethyl ether
(10 mL), and dried in vacuo. Yield: 295 mg (76%). Anal. Calcd
for 2 (C55H46N2RuS4Si2): C, 64.73; H, 4.54; N, 2.75; S, 12.57.
Found: C, 64.67; H, 4.59; N, 2.81; S, 12.49. 1H NMR (269.7 MHz,
CD2Cl2): δ 7.61 (d, 3JH-H ) 7.1 Hz, 2 H, C5H3N), 7.43-7.10 (m,
31 H, C5H3N/C6H5/C6H3), 6.90-6.68 (m, 6 H, C6H5/C6H3), 4.08
Materials and Methods. All reactions and manipulations were
performed under a dinitrogen atmosphere using standard Schlenk
(7) (a) Sellmann, D.; Shaban, S. Y.; Heinemann, F. W. Eur. J. Inorg.
Chem. 2004, 4591-4601. (b) Shaban, S. Y. Ph.D. Dissertation,
University of Erlangen-Nu¨rnberg, Erlangen, Germany, 2005.
(8) (a) Katz, N. E.; Olabe, J. A.; Aymonino, P. J. J. Inorg. Nucl. Chem.
1977, 39, 910-912. (b) Katho`, AÄ .; Beck, M. T. Inorg. Chim. Acta
1988, 154, 99-102. (c) Sellmann, D.; Seubert, B.; Moll, M.; Knoch,
F. Angew. Chem., Int. Ed. 1988, 27, 1164-1165. (d) Chevalier, A.
A.; Gentil, L. A.; Amorebieta, V. A.; Gutierrez, M. M.; Olabe, J. A.
J. Am. Chem. Soc. 2000, 122, 11238-11239. (e) Gutierrez, M. M.;
Amorebieta, V. A.; Estiu, G. L.; Olabe, J. A. J. Am. Chem. Soc. 2002,
124, 10307-10319.
(9) (a) Douglas, P. G.; Feltham, R. D.; Metzger, H. G. J. Chem. Soc.,
Chem. Commun. 1970, 889-890. (b) Douglas, P. G.; Feltham, R. D.;
Metzer, H. G. J. Am. Chem. Soc. 1971, 93, 84-90. (c) Bottomley, F.;
Kiremire, E. M. R. J. Chem. Soc., Dalton Trans. 1977, 1125-1131.
(10) (a) Bottomley, F.; Crawford, J. R. J. Chem. Soc., Chem. Commun.
1971, 200-201. (b) Bottomley, F.; Crawford, J. R. J. Am. Chem. Soc.
1972, 94, 9092-9095.
2
2
(d, JH-H ) 15.3 Hz, 2 H, CH2), 3.75 (d, JH-H ) 15.3 Hz, 2 H,
CH2), 1.38 (s, 3 H, NH3). 13C NMR (100.4 MHz, CD2Cl2): δ 166.1,
159.4, 138.5, 136.6, 136.4, 135.8, 134.3, 132.7, 130.2, 128.9, 127.7,
120.3, 120.1 (C5H3N/C6H3/C6H5), 56.7 (CH2). IR (KBr): ν˜ 3356,
(13) (a) Koepp, H. M.; Wendt, H.; Strehlow, H. Z. Elektrochem. 1960, 64,
483-491. (b) Gagne´, R. R.; Koval, C. A.; Lisinsky, G. C. Inorg. Chem.
1980, 19, 2854-2855. (c) Gritzner, G.; Kuta, J. Pure Appl. Chem.
1984, 56, 461-466.
(14) Bard, A. J.; Faulkner, L. R. Electrochemical Methods, Fundamentals
and Applications; Wiley: New York, 1980.
(11) Prakash, R.; Czaja, A. U.; Heinemann, F. W.; Sellmann, D. J. Am.
Chem. Soc. 2005, 127, 13758-13759.
(12) Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV. 1974, 13, 339-
406.
4662 Inorganic Chemistry, Vol. 45, No. 12, 2006

Hydrazine Nitrosation of a Metal-Bound Nitric Oxide
3271, 3185, 3094 cm-1 ν(NH3). MS (FD, THF) m/z (%): 1020
(100) [M]+, 1003 (30) [M - NH3], 925 (40) [M - NH3 - C6H5]+.
Method 2: To a solution of 1 (450 mg, 0.38 mmol) in methanol
(20 mL) was injected N2H4 (1 M solution in THF, 0.8 mL, 0.8
mmol). After the solution was stirred for 10 min at room
temperature, orange-red microcrystals precipitated. Yield: 322 mg
(83%).
Method 3: To a solution of 1 (225 mg, 0.19 mmol) in methanol
(20 mL) was added N2H4 (1 M solution in THF, 4.0 mL, 4.0 mmol).
Instantaneously, microcrystalline 2 precipitated. Yield: 180 mg
(94%).
Method 4: 1 (450 mg, 0.38 mmol) in DMF (20 mL), N2H4
(1 M solution in THF, 0.4 mL, 0.4 mmol); reaction time, 30 min;
orange-red microcrystalline 2. Yield: 275 mg (71%).
Method 5: 1 (450 mg, 0.38 mmol) in DMF (20 mL), N2H4
(1 M solution in THF, 0.8 mL, 0.8 mmol); reaction time, 10 min;
orange-red microcrystalline 2. Yield: 300 mg (78%).
solution was stirred for about 1h at 20 °C. Grey-brown micro-
crystalline 4 precipitated. Yield: 215 mg (82%).
Protonation of 4 with HBF4 to [Ru(NO)(pysiS4)]BF4 {[1+]BF4-}.
To a solution of 4 (200 mg 0.19 mmol) in CH2Cl2 was added an
equimolar amount of HBF4 (54% solution in Et2O) at -20 °C. The
solution was allowed to attain to room temperature. The dark-violet
microcrystals formed were collected, washed with CH2Cl2 (10 mL),
1
and dried in vacuo. IR (KBr): ν˜ 1859 cm-1 ν(NO). H and 13C
NMR: similar to that reported for 1.11
X-ray Structure Analysis. A suitable single crystal was embed-
ded in protective perfluoro polyether oil. Data were collected at T
) 100 K on a Bruker-Nonius KappaCCD diffractometer using Mo
KR radiation (λ ) 0.71073 Å) and a graphite monochromator. A
semiempirical absorption correction based on multiple scans
(SADABS15) was performed. The structure was solved by direct
methods; full-matrix least-squares refinement was carried out on
F2 using SHELXTL NT 6.12. All non-hydrogen atoms were refined
anisotropically. The H-atoms were geometrically positioned, with
isotropic displacement parameters being 1.5 U(eq) of their corre-
sponding C or N carrier atom. The unit cell of 3 contains approx-
imately 1.83 CH2Cl2 and 2.17 Et2O molecules. These solvent mole-
cules were heavily disordered and, in part, they shared crystal-
lographic sites. The remaining significant residual electron density
maxima were all located close to the disordered solvent. Selected
Method 6: To a solution of 1 (225 mg, 0.19 mmol) in DMF (20
mL) was added N2H4 (1 M solution in THF, 4.0 mL, 4.0 mmol).
Rapidly, microcrystals of 2 precipitated. Yield: 165 mg (86%).
[(NH3)Ru(µ-pysiS4)Ru(pysiS4)] (3). Method 1: To a violet
suspension of 1 (450 mg, 0.38 mmol) in THF (25 mL) was rapidly
injected N2H4 (1 M solution in THF, 0.8 mL, 0.8 mmol) through
a syringe. The mixture was continuously stirred for 4 h at room
temperature, after which a blood-red solution developed. The solu-
tion was then filtered through a cannula, and the filtrate was con-
centrated (about 2 mL) under reduced pressure. The resulting gel
was treated with diethyl ether (20 mL) to afford a dark-red powder.
Yield: 217 mg (76%). Single crystals suitable for X-ray analysis
were obtained after 10 days by the slow diffusion of Et2O into a
CH2Cl2 solution of 2. Anal. Calcd for 3 (C110H89N3Ru2S8Si4): C,
65.28; H, 4.43; N, 2.08; S, 12.67. Found: C, 65.22; H, 4.40; N,
crystallographic data for 3:
C120.52H114.38Cl3.65N3O2.17Ru2S8Si4,
crystal size 0.25 × 0.23 × 0.15 mm3, monoclinic, space group
P21/n, a ) 17.336(1) Å, b ) 37.357(6) Å, c ) 17.580(3) Å, â )
106.221(6)°, V ) 10932(3) Å3, Z ) 4, Fcalcd ) 1.422 g cm-3, µ )
0.616 mm-1, (6.7° < 2θ < 52.8°), Tmin/max ) 0.935/1.000, 90 032
measured reflections, 21 101 unique reflections, 15 814 observed
reflections [I > 2σ(I)], 1373 parameters, R1 ) 0.0547 [I > 2σ(I)],
wR2 ) 0.1272 (all data).
1
2.03; S, 12.58. H NMR (269.7 MHz, CD2Cl2): δ 7.72-6.79 (m,
Density Functional Theory (DFT) Calculations. All DFT
calculations were performed with the program package Turbomole
5.7,16 employing the BP86 exchange-correlation functional17 and
a triple-ú valence-polarized Gaussian basis set.18 A 28-electron
effective core potential (ECP), which accounts for the most-
important relativistic effects, was used for ruthenium.19 The
resolution of identity (RI) technique20 was employed to accelerate
the calculations. The natural population analysis (NPA)21 was done
with Gaussian03,22 employing the Kohn-Sham molecular orbitals
obtained from the Turbomole calculations. The program gOpen-
mol23 was used for the visualization of the structures. All structures
were fully optimized and characterized as minima on the potential
energy hypersurface by means of a vibrational analysis. Accurately
converged self-consistent field (SCF) results (a termination threshold
of at least 1 × 10-8 a.u. for the total energy) were used to guarantee
2
78 H, C5H3N/C6H5/C6H3), 4.14 (d, JH-H ) 15.6 Hz, 2 H, CH2),
2
2
3.95 (d, JH-H ) 15.4 Hz, 2 H, CH2), 3.76 (d, JH-H ) 15.6 Hz,
2
2 H, CH2), 3.68 (d, JH-H ) 15.4 Hz, 2 H, CH2), 1.41 (s, 3 H,
NH3). 13C{1H} NMR (100.4 MHz, CD2Cl2): δ 160-115 (many
overlapping signals for C5H3N/C6H5/C6H3), 57.4, 57.0, 56.2, 55.7
(CH2). IR (KBr): ν˜ 3365, 3278, 3189, 3095 cm-1 ν(NH3). MS
(FD, THF) m/z (%): 2024 (100) [M]+, 2006 (30) [M - NH3]+,
1020 (40) [M - Ru(pysiS4)]+.
Method 2: 1 (450 mg, 0.4 mmol) in CH2Cl2 (25 mL) and N2H4
(1 M solution in THF, 0.8 mL, 0.8 mmol); reaction time, 5 h; further
workup, as above; dark-red powder 3. Yield: 210 mg (74%).
Method 3: 1 (450 mg, 0.4 mmol) in toluene (25 mL) and N2H4
(1 M solution in THF, 0.8 mL, 0.8 mmol); reaction time, 12 h;
further workup, as above; dark-red powder 3. Yield: 180 mg (63%).
[Ru(NO){pysiS4(H+)}] (4). Method 1: A solution of 1 (300 mg,
0.25 mmol) in MeOH (20 mL) was stirred under an ammonia
atmosphere for about 10 min at 20 °C. During this time, gray-
brown microcrystals were precipitated. The microcrystals were
filtered, washed with MeOH (25 mL), and dried in vacuo. Yield:
235 mg (90%). Anal. Calcd for 4 (C55H42N2ORuS4Si2): C, 63.98;
H, 4.10; N, 2.71; S, 12.42. Found: C, 63.89; H, 4.01; N, 2.74; S,
(15) SADABS 2.06; Bruker AXS, Inc.: Madison, WI, 2002.
(16) (a) Ahlrichs, R.; Ba¨r, M.; Ha¨ser, M.; Horn, H.; Ko¨lmel, C. Chem.
Phys. Lett. 1989, 162, 165-169. (b) For the current version, see http://
www.turbomole.com.
(17) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100. (b) Perdew, J.
P. Phys. ReV. B 1986, 33, 8822-8824.
(18) Scha¨fer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829-
5835.
1
12.36. IR (KBr): ν˜ 1826 cm-1 ν(NO). H NMR (269.7 MHz,
(19) Andrae, D.; Ha¨ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123-141.
[D8]THF): δ 7.50-6.80 (m, 39 H, C5H3N/C6H3/C6H5), 4.76 (d,
2
2JH-H ) 15.7 Hz, 1H, CH2), 4.66 (s, 1H, CH), 3.98 (d, JH-H
)
(20) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor. Chem.
Acc. 1997, 97, 119-124.
15.6 Hz, 1H, CH2). 13C{1H} NMR (100.4 MHz, [D8]THF): δ 158-
121 (26 signals, C5H3N/C6H3/C6H5), 53.4 (CH2), 51.0 (CH). MS
(FD, THF) m/z (%): 1033 (100) [M]+, 1002 (45) [M - NO]+,
925 (65) [M - NO - C6H5]+.
(21) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735-746.
(22) Frisch, M. J.; et al. Gaussian 03, revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
(23) (a) Laaksonen, L. J. Mol. Graphics Modell. 1992, 10, 33-34. (b)
Bergman, D. L.; Laaksonen, L.; Laaksonen, A. J. Mol. Graphics
Modell. 1997, 15, 310-306.
Method 2: To a solution of 1 (300 mg 0.25 mmol) in MeOH
(25 mL) was added NaN3 (25 mg, 0.38 mmol), and the resulting
Inorganic Chemistry, Vol. 45, No. 12, 2006 4663

Prakash et al.
Scheme 1
satisfactory accuracy in the force constant calculations. The
symmetry was constrained to C2 for complex cation [1]+.
Results and Discussion
The reaction of 1 with hydrazine was carried out with
various ratios (1-50) of hydrazine at room temperature. The
addition of an equimolar ratio of hydrazine to a violet
solution of 1 in methanol caused a change in color to dark-
red followed by a gas evolution (Scheme 1). When the
solution was stirred for about 25 min, red microcrystalline
[Ru(NH3)(pysiS4)] (2) precipitated in good yield (76%). The
reaction was monitored by solution IR spectroscopy (Figure
1). Upon addition of hydrazine, the original NO band of 1
at 1872 cm-1 disappeared gradually and a new weak band
at 2223 cm-1 appeared. The new band is consistent with the
formation of N2O,24 and the evolved N2O gas was further
confirmed by GC/MS analysis (Figures 1S and 2S, Support-
ing Information). Because of the highly air-sensitive nature
of the complexes and the complicated experimental setup,
it was not possible to determine the accurate quantity of N2O
produced (in the gas phase as well as in solution) during the
reaction. Nevertheless, because of the amount of 1 and
hydrazine used to the amount of 2 produced, the stoichiom-
etry of the reaction can be recognized as 1:1:1. When the
ratio of hydrazine was doubled, the NO band of 1 vanished
within 10 min and the ammonia complex was isolated in
83% yield. With excess hydrazine concentrations (20-50
times), the reaction was very rapid and microcrystals of 2
formed instantaneously. Analogous experiments performed
in DMF afforded identical results. But in none of these
reactions was the formation of hydrazine complex observed.
Moreover, the IR spectra (Figure 1) did not show any
new band in the regions between 2200 and 1900 cm-1 or
1700-1600 cm-1, which suggests that no azide (either free
or in coordinated form) or one-electron reduced (19-val-
ence-electron) neutral nitrosyl complex [Ru(NO)(pysiS4)]0
({Ru-NO}7) was produced during the reaction. On the other
hand, the cyclic voltammogram of 111 suggested that the
species {Ru-NO}7 exists in solution at approximately 0.0
V vs NHE. However, attempts to generate the species by
chemical as well as electrochemical methods remained un-
Figure 1. IR spectroscopic monitoring of the reaction between an
equimolar ratio of 1 and hydrazine in methanol at 20 °C. Complex 1 without
(black) and with hydrazine after 6 min (magenta), 12 min (blue), 18 min
(green), and 25 min (red).
suggests that the reactivity of NO+ depends largely on the
metal as well as on the coligand environment, which
influences the electron density of the nitrosyl ligand.
Complex 2 is soluble in THF, CH2Cl2, CHCl3, and toluene.
The IR (KBr) spectrum of 2 displays sharp bands at 3356,
3271, 3185, and 3094 cm-1 assignable to ν(ΝΗ) of the NH3
ligand, which is characteristic for thiolate-ruthenium-
1
ammine complexes.26 The well-resolved H and 13C NMR
spectra of 2 indicate its ground-state spin is zero. The
observed resonances (see Experimental Section) are typical
for the C2 symmetric [Ru(pysiS4)] fragment.11 The cyclic
voltammogram of 2 exhibits a reversible one-electron wave
at E1/2 ) 0.255 V vs NHE, which is assigned to the RuII/III
redox couple (Figure 3S, Supporting Information). The
couple is reversible on the basis of its similarity to ferrocene
in the cyclic voltammogram. The peak current increases
linearly with the square root of the scan speeds, indicating
that the redox reaction is a diffusion-controlled process.
Moreover, in multisweep experiments under thin-layer
conditions, the redox wave revealed complete reversibility
over several cycles, suggesting that the Ru-NH3 bond is
intact during oxidation.
In the solid state under an N2 atmosphere at ambient
temperature, 2 is stable for a prolonged period of time;
however, in solution (THF, CH2Cl2, CHCl3, or toluene), it
dimerizes after 2 days and forms dinuclear ammine complex
3 (Scheme 2). Because the CH2 protons are good NMR
probes, the reaction could be monitored by 1H NMR
spectroscopy (Figure 2). The two doublet signals of the
diastereotopic protons of C2 symmetric 2 changed into four
doublets, which corresponds to the CH2 protons of C1
symmetric complex 3. When the solution of 3 is stirred under
successful. So far, only in the case of the related iron com-
2-
pound [Fe(NO)(pyS4)]+ {pyS4
) 2,6-bis(2-sulfanyl-
phenylthiomethyl)pyridine2-} ({Fe-NO}6) was such a one-
electron reduction achieved with hydrazine, and the resulting
{Fe-NO}7complex was isolated in the solid state.25 This
(24) For ν(N2O) in solution, see: (a) Gorga, J. C.; Hazzard, J. H.; Caughey,
W. S. Arch. Biochem. Biophys. 1985, 240, 734-746. (b) Hu, T. A.;
Chappell, E. L.; Sharpe, S. W. J. Chem. Phys. 1993, 98, 6162-6169.
(25) Sellmann, D.; Blum, N.; Heinemann, F. W. Chem.sEur. J. 2001, 7,
1874-1880.
(26) (a) Sellmann, D.; Prakash, R.; Heinemann, F. W. Eur. J. Inorg. Chem.
2004, 4291-4299. (b) Sellmann, D.; Hille, A.; Ro¨sler, A.; Heinemann,
F. W.; Moll, M.; Brehm, G.; Schneider, S.; Reiher, M.; Hess, B. A.;
Bauer, W. Chem.sEur. J. 2004, 10, 819-830. (c) Sellmann, D.; Hein,
K.; Heinemann, F. W. Eur. J. Inorg. Chem. 2004, 3136-3146.
4664 Inorganic Chemistry, Vol. 45, No. 12, 2006

Hydrazine Nitrosation of a Metal-Bound Nitric Oxide
Scheme 2
Table 1. Selected Bond Distances (Å) and Angles (deg) for
3‚1.83CH2Cl2‚2.17Et2O
Ru1-N1
Ru1-S11
Ru1-S12
Ru1-S13
Ru1-S14
Ru1-S23
Ru2-N2
Ru2-N3
Ru2-S21
Ru2-S22
Ru2-S23
Ru2-S24
2.064(3)
2.373(2)
2.323(1)
2.311(1)
2.399(2)
2.354(1)
2.030(3)
2.138(4)
2.360(2)
2.307(2)
2.315(2)
2.382(2)
N1-Ru1-S11
N1-Ru1-S23
S11-Ru1-S12
S11-Ru1-S14
S12-Ru1-S13
N2-Ru2-N3
N2-Ru2-S21
S21-Ru2-S22
S21-Ru2-S24
S22-Ru2-S23
Ru1-S23-Ru2
89.20(9)
177.30(9)
86.94(4)
174.12(4)
165.51(4)
175.1(2)
91.0(1)
86.84(4)
177.42(4)
166.26(4)
131.26(4)
Figure 2. 1H NMR spectroscopic monitoring of the conversion of 2 to 3
in CD2Cl2 under N2 at 20 °C. Only the region between δ ) 4 and δ ) 1
is shown. Time intervals are (a) 1, (b) 10, (c) 20, (d) 30, (e) 40, (f) 50, and
(g) 60 h.
In contrast to the observation made in MeOH/DMF, the
addition of hydrazine to a suspension of 1 in THF (or
CH2Cl2) did not cause any immediate color change or
solution formation. A clear red solution formed only when
the suspension was stirred for more than 4 h at room
temperature. In toluene, the reaction had to be prolonged
for 12 h to get the red solution. The IR spectrum of the
resulting solution in all cases displayed only a weak band at
2224 cm-1, indicating that the one-electron reduced neutral
nitrosyl complex or azide complex was not formed. Further
workup of this solution directly afforded dinuclear ammine
complex [(NH3)Ru(µ-pysiS4)Ru(pysiS4)] (3) in good yield
(Scheme 2).27 The IR (KBr) spectrum of 3 exhibits sharp
ν(NH3) bands at 3365, 3278, 3189, and 3095 cm-1, which
1
are slightly blue-shifted when compared to those of 2. H
and 13C NMR spectra of 3 suggest that the complex has C1
symmetry, which has also been confirmed by an X-ray
structure analysis. 3 exhibits two one-electron reversible (with
respect to the ferrocene couple) waves at E1/2 ) 0.228 and
0.780 V vs NHE (Figure 4S, Supporting Information). These
waves can be assigned to the two RuII/III redox couples of 3,
which show complete reversibility over several successive
cycles.
The molecular structure of 3 is depicted in Figure 3, and
selected distances and angles are given in Table 1. Complex
3 crystallizes in the monoclinic space group P21/n.28 Each
ruthenium (Ru1, Ru2) center exhibits a distorted octahedral
coordination geometry comprised of one nitrogen and four
sulfur donor atoms of the ligand pysiS42-. The sixth coor-
Figure 3. Top: Molecular structure of 3 (50% probability level ellipsoids;
H atoms and solvent molecules omitted). Bottom: SiPh3 phenyl groups of
the Ru2 fragment and the ligand unit, except core atoms around Ru1 are
omitted.
an ammonia atmosphere for about 6 h, the mononuclear
compound 2 is formed again. Consequently, several attempts
to grow single crystals of 2 suitable for X-ray analysis, even
in some cases under an atmosphere of ammonia, inevitably
yielded only crystals of dinuclear complex 3.
(27) The reaction between 1 and hydrazine (>20 equiv) in THF (CH2Cl2
or toluene) yielded a mixture that could not be separated even by
chromatography. However, crystallization of the mixture exclusively
yielded the crystals of 3.
(28) CCDC 255036 (3) contains supplementary crystallographic data for
this paper. These data can be obtained free of charge via www.
ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge CB21EZ, U.K.;
fax: (44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
This result prompted us to study the reaction in less-polar
(THF and CH2Cl2) as well as nonpolar (toluene) solvents.
Inorganic Chemistry, Vol. 45, No. 12, 2006 4665

Prakash et al.
Scheme 3
dination site of Ru2, trans to the pyridine N atom, is occupied
by the NH3 ligand. The thioether donor S23 of the Ru2 unit
bridges the Ru1 fragment. In this respect, complex 3 differs
distinctly from many of our common dinuclear complexes,
where two thiolate donors exclusively bridge two metal
centers.29 The thiolate and thioether donors occupy trans
position to each other. The distances around ruthenium,
including the Ru-NH3 bond, are in the range usually found
for the diamagnetic octahedral RuII-thiolate-thioether com-
plexes.26,29 The bridging Ru1-S23 bond length is distinctly
shorter than even the Ru-S (thiolate) distances; however, it
coincides with the value that is reported for known ruthe-
nium-thioether-bridged complexes.30 The Ru1-S23-Ru2
angle of 131.26(4)° may be due to steric effects caused by
the bulky SiPh3 groups.
proton from similar thiolate-thioether complexes.34 The 1H
NMR spectrum of 4 (see Experimental Section) indicated
that the deprotonation occurred at one of the bridging CH2
protons. It has already been proven that the bridging CH2
protons of 1 are more acidic, because of the electron-
withdrawing effect of the NO+ ligand, and undergo H+/D+
exchange with CD3OD.11 The cyclic voltammogram of 4
exhibits two one-electron reversible (with respect to the
ferrocene couple) waves at E1/2 ) 0.42 and -0.56 V vs NHE
for the redox couples of [4]-1/0 and [4]-1/-2, respectively.
This is in concurrence with 1,11 indicating that the 19-
valence-electron anionic species [Ru(NO){pysiS4(-H+)}]-
exists in solution at approximately -0.1 V. When the CV
of 4 is compared with that of 1, the half-wave potentials of
the corresponding peaks of 4 are shifted to more-negative
values. Protonation of 4 with HBF4 in CH2Cl2 at -20 °C
led to the regeneration of [1]+ with BF4 as counterion. These
Alternatively, electrochemical reductions of coordinated
nitrosyls to coordinated ammonia in aqueous solution have
been reported for a variety of polypyridyl complexes of both
ruthenium and osmium.31 The mechanism involves a series
of facile one-electron-transfer steps. Therefore, efforts have
been made to electrochemically convert 1 to 2. The cyclic
voltammogram of 1 exhibits the NO0/NO-1 reduction wave
at E1/2 ) -1.25 V vs NHE, which is irreversible. No other
redox wave was observed up to -1.8 V. Constant potential
coulometric reactions were carried out with 1 in the presence
of protons in CH2Cl2 at -1.05 V vs SCE.32 No ammonia or
ammine complex was formed, and the reaction yielded only
a brown solid that cannot yet be characterized. Thus, the
electrochemical reduction of the bound NO+ of 1 to NH3
seems to be impossible under this condition.
-
results obviously confirmed that both NH3 and N3 acted
simply as bases to deprotonate one of the highly acidic -CH2
protons rather than as nucleophiles.
To corroborate the experimental findings, DFT calculations
were carried out for [1]+ and its deprotonation product 4
(Table 1S and Figure 5S, Supporting Information). The
theoretical structure determination (geometry optimization)
yielded bond distances and bond angles in very good
agreement with the X-ray structure determination of [1]+
(Table 1S, Supporting Information), which underlines the
reliability of the calculations. The deprotonation at one of
the bridging CH2 groups is accompanied by distinct structural
changes in the framework of the pySiS4 ligand (see the
Supporting Information) and a slight elongation of the NO
bond length. A natural population analysis did not reveal
any significant differences in the natural atomic charges of
individual atoms between [1]+ and 4. The charge is rather
uniformly distributed over the pySiS4 ligand; deprotonation
simply frees up more electron density for a better back-
bonding to the NO ligand, which is reflected by a reduction
of the natural charge of the NO ligand by 0.08e. The
calculation of the harmonic force fields for [1]+ and 4
resulted in a red-shift of 34 cm-1 for the ν(NO) band upon
deprotonation. This is in perfect agreement with the experi-
mentally observed value of 32 cm-1 and thus proves the
Unlike in the reaction with hydrazine, 1 reacts readily with
other N-donor nucleophiles such as ammonia and azide in
methanol at 20 °C to exclusively give the neutral nitrosyl
complex [Ru(NO){pysiS4(-H+)}] (4) in very high yields
(Scheme 3).33 This finding precludes the formation of 2 and
3 from 1 and ammonia as an intermediary decomposition
product of hydrazine. The IR (KBr) spectrum of 4 exhibits
a sharp ν(NO) band at 1826 cm-1. When compared to 1,
the NO band of 4 is red-shifted by 32 cm-1. This is in good
agreement with the values that are reported for the loss of a
(29) (a) Sellmann, D.; Prakash, R.; Heinemann, F. W.; Moll, M.; Klimow-
icz, M. Angew. Chem., Int. Ed. 2004, 43, 1877-1880. (b) Sellmann,
D.; Sutter, J. Prog. Inorg. Chem. 2003, 52, 585-681.
(30) (a) Shin, R. Y. C.; Ng, S. Y.; Tan, G. K.; Koh, L. L.; Khoo, S. B.;
Goh, L. Y.; Webster, R. D. Organometallics 2004, 23, 547-558. (b)
Grapperhaus, G. A.; Poturovic, S.; Mashuta, M. S. Inorg. Chem. 2002,
41, 4309-4311.
(31) (a) Armor, J. N.; Hofmann, M. Z. Inorg. Chem. 1975, 14, 444-446.
(b) Murphy, W. R., Jr.; Takeuchi, K. J.; Meyer, T. J. J. Am. Chem.
Soc. 1982, 104, 5817-5819. (c) Murphy, W. R., Jr.; Takeuchi, K. J.;
Barley, M. H.; Meyer, T. J. Inorg. Chem. 1986, 25, 1041-1053.
(32) Constant potential coulometric reductions were performed in a gastight
coulometric cell with a Pt working electrode, a platinum wire counter
and a SCE reference electrode. [Complex] ) 1 mM; [H+] ) 3-10
mM; [NBu4PF6] ) 0.1 M; CH2Cl2 ) 50 mL. Applied potential )
-1.05 V vs SCE; SCE ) +234 V with respect to NHE.14 In all
experiments, the pink suspension of 1 was changed to brown 30-60
min after consuming coulombs nearly equivalent to 2-3 electrons.
Gas samples taken before and after the electrolysis were analyzed for
NH3.
-
formation of 4 upon reaction of [1]+ with NH3 or N3 .
The reaction of 1 with hydrazine is interesting because of
the formation of N2O as one of the products, which is not a
common product of hydrazine oxidation.6 In addition, 2
cannot be obtained directly from the reaction between 1 and
NH3. Thus, it is obvious that complex 1 underwent nitrosation
(33) Only complex 4 is formed, regardless of solvents (polar or nonpolar)
and concentrations of the nucleophilies used. The HN3 showed a sharp
IR band at 2131 cm-1 in methanol.
(34) Sellmann, D.; Utz, J.; Blum, N.; Heinemann, F. W. Coord. Chem.
ReV. 1999, 190-192, 607-627.
4666 Inorganic Chemistry, Vol. 45, No. 12, 2006

Hydrazine Nitrosation of a Metal-Bound Nitric Oxide
Scheme 4
bond. The one-electron reduced neutral nitrosyl complex
[Ru(NO)(pysiS4)]0 ({Ru-NO}7) is not detected during this
reaction, which suggests that the bound NO+ underwent two-
electron reduction to form N2O. To our knowledge, 1 seems
to be the first ruthenium nitrosyl complex to yield nitrous
oxide and ammonia upon hydrazine nitrosation, according
to Stedman’s prediction in nonacidic medium.6
Conclusion
In this paper, we have described the nitrosation reaction
of [Ru(NO)(pysiS4)]Br‚THF (1) with hydrazine in various
nonaqueous solvents. The reaction carried out in polar
solvents such as methanol and DMF afforded mononuclear
[Ru(NH3)(pysiS4)] (2) and N2O, whereas in less polar solvents
such as THF, CH2Cl2 and toluene dinuclear [(NH3)Ru-
(µ-pysiS4)Ru(pysiS4)] (3) formed in high yield. The X-ray
structure analysis indicated that in complex 3, the two
[Ru(pysiS4)] fragments are bridged by a thioether donor.
Complex 2 dimerizes in solution to give 3, and the reverse
reaction was achieved by treatment of 3 with NH3. On the
ith hydrazine to form 2 and N2O. The plausible mechanism
for the hydrazine nitrosation is given in Scheme 4, which is
similar to the one that was proposed earlier.7d It involves
the initial nucleophilic addition of N2H4 on the nitrosyl
nitrogen of 1 to form a labile adduct A, which rapidly
deprotonates at the bond-forming nitrogen of hydrazine (B).
The stoichiometry requires the second proton to migrate to
the remote N-atom of hydrazine, followed by the cleavage
of the N-N bond in the hydrazine-derived moiety, resulting
in [Ru(N2O)(pysiS4)] (C) and NH3. Subsequent release of
the N2O from C leads to the formation of an unstable five-
coordinate fragment [Ru(pysiS4)] (D). Because of the steric
effect of the SiPh3 groups in the vicinity of the thiolate
donors, a dimerization of the fragment D through thiolate
bridges is not favorable. In the final step, the NH3 is
coordinated into the vacant site of D to give 2.
The different modes of NO+ reactivity of Fe, Ru, and Os
complexes toward hydrazine may directly be related to the
metal and coligand environment, which influences the
electron density of the nitrosyl ligand through σ-π interac-
tions.35 After the removal of two protons from the coordi-
nated N atom of the hydrazine, most rutheniumnitrosyls
facilitate the proton loss from the terminal nitrogen atom of
hydrazine and the subsequent removal of water, leading to
azide complexes. Whereas the reactivity of complex 1 closely
resembles the iron nitrosyl complex [Fe(NO)(CN)5]2-,7d the
protons in the terminal nitrogen atom are retained and
ammonia is released after a heterolytic cleavage of the N-N
-
contrary, reaction of 1 with NH3 as well as N3 merely
yielded the neutral nitrosyl complex [Ru(NO){pysiS4(-H+)}]
(4). A plausible mechanism for the hydrazine nitrosation of
1 has been proposed. The reactivity of 1 toward hydrazine
differs remarkably from other rutheniumnitrosyls, which
might be due to the fine-tuning effect of the thioether-
thiolate donors of the chelate ligand. Efforts are currently
underway to explore the reactivity features of 1 with various
other nucleophiles.
Acknowledgment. We gratefully acknowledge the finan-
cial support provided by the Deutsche Forschungsgemein-
schaft (SFB-583) and Fonds der Chemischen Industrie.
Supporting Information Available: GC/MS spectra, cyclic
voltammograms, additional results from the DFT calculations,
complete list of authors in ref 22, crystallographic data for 3 in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
(35) Callahan, R. W.; Meyer, T. J. Inorg. Chem. 1977, 16, 574-581.
IC060096J
Inorganic Chemistry, Vol. 45, No. 12, 2006 4667