Synthesis of benzene ruthenium triazolato complexes by [3+2] cycloaddition reactions of activated alkynes and fumaronitrile to benzene ruthenium azido complexes

Article abstract of DOI:10.1016/j.ica.2007.05.063

The dinuclear complex [(η⁶-C₆H₆)Ru(μ-N₃)Cl]₂ (1) is obtained by the reaction of [(η⁶-C₆H₆)RuCl₂]₂ with sodium azide in ethanol. The benzene ruthe

Full text of DOI:10.1016/j.ica.2007.05.063

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Inorganica Chimica Acta 361 (2008) 3294–3300
www.elsevier.com/locate/ica
Synthesis of benzene ruthenium triazolato complexes by
[3+2] cycloaddition reactions of activated alkynes and fumaronitrile
to benzene ruthenium azido complexes
a
b
a,
*
Khenglawt Pachhunga , Bruno Therrien , Mohan Rao Kollipara
a
Department of Chemistry, North-Eastern Hill University, Shillong 793 022, India
Institute of Chemistry, University of Neuchatel, Case Postale 158, CH-2009, Neuchatel, Switzerland
b
Received 5 May 2007; accepted 14 May 2007
Available online 3 July 2007
This communication is dedicated to Professor Robert J. Angelici.
Abstract
The dinuclear complex [(g6-C6H6)Ru(l-N3)Cl]2 (1) is obtained by the reaction of [(g6-C6H6)RuCl2]2 with sodium azide in ethanol.
The benzene ruthenium b-diketonato complexes of the general formula [(g6-C6H6)Ru(L\L)Cl] {L\L = O,O0-acac (2); O,O0-bzac (3);
O,O0-dbzm (4)} are obtained in methanol by the reaction of [(g6-C6H6)RuCl2]2 with the corresponding b-diketonates. These complexes
further react with sodium azide in ethanol to yield complexes of the type [(g6-C6H6)Ru(L\L)N3] [L\L = O,O0-acac (5); L\L = O,O0-
bzac (6); L\L = O,O0-dbzm (7)]. The complexes 5–7 are obtained as well by treating 1 with sodium salts of b-diketonates. These neutral
benzene ruthenium azido complexes undergo [3+2] dipolar cycloaddition reaction with activated alkynes (MeO2CC„CCO2Me,
EtO2CC„CCO2Et) or fumaronitrile (NCHC@CHCN) to yield the corresponding benzene ruthenium triazolato complexes; [(g6-
C6H6)Ru(O,O0-acac){N3C2(CO2Me)2}] (8), [(g6-C6H6)Ru(O,O0-acac){N3C2(CO2Et)2}] (9), [(g6-C6H6)Ru(O,O0-acac){N3C2HCN}]
(10), [(g6-C6H6)Ru(O,O0-bzac){N3C2HCN}] (11) and [(g6-C6H6)Ru(O,O0-dbzm){N3C2HCN}] (12). These complexes are fully charac-
terized on the basis of microanalyses, FT-IR and FT-NMR spectroscopy. The molecular structure of [(g6-C6H6)Ru(O,O0-acac){N3C2-
(CO2C2H5)2}] (9) is confirmed by single crystal X-ray diffraction study.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Azide ligand; Ruthenium; Acetylacetonate; Benzoylacetonate; Diphenylbenzoylmethane
1. Introduction
of chloro bridged dimeric arene ruthenium complexes with
Lewis bases and a variety of ligands have been reported.
Azide chemistry has attracted the attention of many chem-
ists, as these compounds play an important role in organic
chemistry [6]. The 1,3-dipolar cycloaddition reactions
between substituted acetylenes and azides is a very impor-
tant reaction and the most efficient route to synthesize
1,2,2-triazoles. Among the various 1,3-dipolar cycloaddi-
tion reactions, organic azides have been particularly
important for synthesizing heterocyclic compounds [7]. Simi-
larly coordinated azides in metal complexes can also
undergo cycloaddition reaction [8]. We have recently repor-
ted the triazolato complexes [(g6-p-cymene)Ru(L\L){N3-
C2(CO2R)2}] and [(g5-indenyl)Ru(L\L){N3C2(CO2R)2}]
Arene ruthenium compounds belong to a well-estab-
lished family of robust metal–organic molecules that have
played an important role in the development of organome-
tallic chemistry [1]. Our interest in such systems arises due
their catalytic potential in a wide range of organic reactions
[2] and very promising anticancer activity [3]. The arene
ruthenium halide compounds obtained by Winkhaus and
Singer [4] are key starting materials for the formation of a
wide range of neutral and cationic derivatives [5]. Reaction
*
Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 2550486.
E-mail address: mohanrao59@hotmail.com (M.R. Kollipara).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.05.063

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 3294–3300
3295
(L\L = b-diketonates, dppe, dppm) from the reaction of
[(g6-p-cymene)Ru(l-N3)Cl]2 and [(g5-indenyl)Ru(L\L)-
(N3)], respectively, with various substituted acetylenes [9].
However, to the best of our knowledge, there is no report
in the literature on structurally characterized benzene ruthe-
nium triazolato complexes. Our continuing interest in
chloro bridged dimeric arene ruthenium involves the substi-
tution of chloride with azide group and the synthesis of the
corresponding azido complexes. We had already reported
that complete substitution of chloride by azido groups in
the p-cymene ruthenium dimer is not achieved, whereas in
the case of the hexamethylbenzene ruthenium dimer, the
complete chloride substitution reaction is successfully
carried out [10]. Keeping this in mind, the reaction of sodium
azide with benzene ruthenium dimer is studied in this
work. The substitution of all the chlorides in benzene ruthe-
nium dimer with azide was incomplete as observed for the
p-cymene analogue. This work presents a comparison
between the 1,3–dipolar cycloaddition reactions of p-cym-
ene ruthenium dimer and benzene ruthenium dimer in
relation to azide bonding and activated acetylene groups.
The benzene ruthenium triazolato complexes thus generated
were characterized on the basis of microanalyses and spec-
troscopic data. The molecular structure of the representative
complex 9 was established by single crystal X-ray structure
analysis.
ethanol (20 ml) was stirred at room temperature for 5 h; a
yellow colored compound was precipitated. The precipitate
was filtered and washed with methanol (3 · 10 ml) and then
dried in vacuo. The additional complex was isolated by
concentration of the filtrate and washing with methanol
(3 · 10 ml), and then dried in vacuum to give a yellow pow-
dered compound.
Yield: 50.5 mg, 48.3%. IR (KBr, cmꢀ1): 2044 (mN3), 1639
1
(mC@C). H NMR (CDCl3, d): 5.81 (s, 6H, C6H6).
2.2. Preparation of [(g6-C6H6)Ru(L\L)Cl][L\L = O,O0-
acac (2), O,O0-bzac (3), O,O00-dbzm (4)]
2.2.1. General method of preparation of these complexes
A mixture of [{(g6-C6H6)RuCl2}]2 (0.1 g, 0.20 mmol)
and the L\L sodium salt (0.06 g, 0.40 mmol) in dry
methanol (20 ml) was stirred at room temperature for
3 h. The color of the solution turns a brick-red and the
reaction mixture is evaporated to dryness under reduced
pressure. The solid residue is dissolved in dichlorometh-
ane and filtered to remove NaCl. The solution is concen-
trated to ca. 5 ml and addition of hexane precipitates an
orange powdered solid which is filtered and dried under
vacuum.
Complex [(g6-C6H6)Ru(O,O0-acac)Cl] (2): Yield:
35 mg, 51.0%. IR (KBr, cmꢀ1): 1570, 1533 (mC@O+C@C).
1H NMR (CDCl3, d): 2.35 (s, 6H, CH3), 5.72 (s, 1H, cH),
5.81 (s, 6H, C6H6).
2. Experimental
Complex [(g6-C6H6)Ru(O,O0-bzac)Cl] (3): Yield:
37 mg, 46.3%. IR (KBr, cmꢀ1): 1520, 1447 (mC@O+C@C).
1H NMR (CDCl3, d): 2.14 (s, 3H, CH3), 5.68 (s, 1H, cH),
5.80 (s, 6H, C6H6), 7.32-7.61 (m, 5H, Ph).
Caution: Reactions with azide salts and their complexes
should be perform with extreme care.
All solvents were dried in appropriate drying agents and
distilled prior to use [11]. Dimethylacetylenedicarboxylate
(Aldrich), diethylacetylenedicarboxylate (Across), fumaro-
nitrile (Aldrich) and RuCl3 Æ 3H2O (Arora Matthey Lim-
ited) were used as received. NMR spectra were recorded
on an AMX-400 MHz spectrometer at 400.13 (1H), or
100.61 MHz (13C) with SiMe4 as internal reference and
coupling constants are given in Hz. The starting material
[(g6-C6H6)RuCl2]2 was synthesized according to the litera-
ture procedure [12]. Sodium salts of acetylacetone, benzoy-
lacetone and diphenylmethane were prepared by treating
the appropriate b-diketonates with NaOH in ethanol
(Chart 1).
Complex [(g6-C6H6)Ru(O,O0-dbzm)Cl] (4): Yield:
34 mg, 38.7%. IR (KBr, cmꢀ1): 1533, 1525 (mC@O+C@C).
1H NMR (CDCl3, d): 5.75 (s, 1H, cH), 6.04 (s, 6H,
C6H6), 7.32–7.59 (m, 10H, Ph).
2.3. Preparation of [(g6-C6H6)Ru(L\L)N3]
[(L\L = O,O0-acac (5), O,O0-bzac (6), O,O00-dbzm (7)]
2.3.1. Two routes were used to prepare these complexes
Route (a): A mixture of [(g6-C6H6)Ru(L\L)Cl] (0.1 g,
0.29 mmol) and NaN3 (0.06 g, 0.73 mmol) in ethanol
(20 ml) was stirred at room temperature for 8 h. The mix-
ture solution turned a brick-red color. The reaction mix-
ture was evaporated to dryness under reduced pressure;
the solid residue was dissolved in dichloromethane and fil-
tered to remove NaCl. The filtrate on evaporation at room
temperature afforded orange-yellow powder complexes 5–
7, which were separated and dried under vacuum.
2.1. Preparation of [(g6-C6H6)Ru(l-N3)Cl]2 (1)
A mixture of the starting complex [{(g6-C6H6)RuCl2}]2
(0.1 g, 0.20 mmol) and sodium azide (0.03 g, 0.50 mmol) in
Route (b): The above complexes 5–7 can also be synthe-
sized by the reaction of azide dimer [{(g6-C6H6)Ru(l-
N3)Cl}2] (1) (0.1 g, 0.20 mmol) and the appropriate sodium
salts of b-diketonates (0.07 g, 0.48 mmol) in ethanol
(20 ml). The mixture was stirred at room temperature for
7 h. The solvent was evaporated off under reduced pres-
sure. The residue was dissolved in dichloromethane (5 ml)
Me
Me Me
Ph Ph
Ph
O
O-Na+
O
O-Na+
O
O-Na+
Na[acac]
Na[bzac]
Na[dbzm]
Chart 1. L\L ligands used in this study.

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K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 3294–3300
and filtered to remove sodium chloride. The filtrate upon
concentration to a minimum volume ca. 5 ml and addition
of excess hexane gave the orange-yellow complexes 5–7,
which were separated and dried under vacuum.
2.6. Preparation of complexes
[(g6-C6H6)Ru(L\L){N3C2HCN}] L\L = O,O0-acac (10);
O,O0-bzac (11); O,O0-dbzm (12)
(Caution: This complex should be handled with extreme
care and usage of spatula is avoided).
To a round-bottom flask charged with the azido com-
plex 5 (0.1 g, 0.31 mmol) was added fumaronitrile (0.05 g,
0.63 mmol) and 20 ml of dichloromethane–methanol mix-
ture. The solution was stirred at room temperature for
24 h. The solvent was reduced to ca. 5 ml and an excess
of n-pentane added to give a chocolate color precipitate.
The powder compound was collected and washed with n-
pentane (3 · 10 ml) and dried under vacuum.
Complex [(g6-C6H6)Ru(O,O0-acac)N3] (5): Yield:
42 mg, 41%. IR (KBr, cmꢀ1): 2026 (mN3); 1568, 1387
(mC@O + C@C). 1H NMR (CDCl3, d): 2.20 (s, 6H, CH3),
5.69 (s, 1H, cH), 5.81 (s, 6H, C6H6), 7.37–7.42 (m, Ph).
Complex [(g6-C6H6)Ru(O,O0-bzac)N3] (6): This com-
plex was prepared by following a similar method employed
in the preparation of [(g6-C6H6)Ru(O,O0-acac)N3] (5),
using Na(O,O0-bzac) Æ H2O instead of Na(O,O0-aca-
Complex [(g6-C6H6)Ru(O,O0-acac){N3C2HCN}] (10):
Yield: 50 mg, 43.14%. IR (KBr, cmꢀ1): 2236 (mC„N),
c) Æ H2O. Yield: 49 mg, 51%. IR (KBr, cmꢀ1): 2025 (mN ),
1580, 1520 (mC@N + mC@C). H NMR (CDCl3, d): 2.25 (s,
1
3
1
1553, 520 (mC@O + mC@C). H NMR (CDCl3, d): 2.02 (s,
6H, CH3), 5.59 (s, 1H, cH), 6.02 (s, 6H, C6H6); 6.82 (s,
1H, CH).
3H, CH3), 5.59 (s, 1H, cH), 5.91 (s, 6H, C6H6), 7.02–7.28
(m, 5H, Ph).
Complex [(g6-C6H6)Ru(O,O0-bzac){N3C2HCN}] (11):
Yield: 54 mg, 47.64%. Elemental Anal. (%), Calc. for
C19H16N4O2Ru: C, 52.66; H, 3.69; N, 12.93. Found: C,
52.03; H, 3.96; N, 13.15%. IR (KBr, cmꢀ1): 2234 (mC@N),
Complex [(g6-C6H6)Ru(O,O0-dbzm)N3] (7): This com-
plex was prepared by following the similar procedure as
described in the preparation of complex [(g6-
C6H6)Ru(O,O0-acac)N3] (5) using Na(O,O0-dbzm) Æ H2O
instead of Na(O,O0-acac) Æ H2O. Yield: 56 mg, 58%. IR
1
1572, 1520 (mC@N + mC@C). H NMR (CDCl3, d): 2.12 (s,
3H, (bzac–CH3), 5.75 (s, 1H, cH), 5.79 (s, 6H, C6H6);
6.86 (s, 1H, CH); 7.24–7.52 (m, 5H).
(KBr, cmꢀ1): 2022, 1646, 1573 (mN ), (mC@O, C@C). 1H
3
NMR (CDCl3, d): 5.47 (s, 1H, cH), 5.89 (s, 6H, C6H6),
7.30–7.62 (m, 10H, Ph).
Complex [(g6-C6H6)Ru(O,O0-dbzm){N3C2HCN}] (12):
Yield: 56 mg, 50.3%. IR (KBr, cmꢀ1): 2225 (mC„N), 1571,
1
1520 (mC@N + mC@C). H NMR (CDCl3, d): 5.81 (s, 1H,
2.4. Preparation of triazolato complex
[(g6-C6H6)Ru(O,O0-acac){N3C2(CO2CH3)2}] (8)
cH), 5.94 (s, 6H, C6H6), 6.83 (s, 1H, CH); 7.28–7.42 (m,
10H, Ph).
To a round-bottom flask charged with the corresponding
azido complex [(g6-C6H6)Ru(O,O0-acac)N3] (0.1 g, 0.31
mmol) was added a fivefold excess of dimethylacetylenedi-
carboxylate and CH2Cl2 (20 ml). The mixture was stirred
at room temperature for 14–15 h. The solution was evapo-
rated to ca. 5 ml. To this solution was added 30 ml of hex-
ane, whereby the compound was precipitated out as a
yellow solid. The solid compound was collected by filtration
and washed with 2 · 20 ml of hexane and dried under vac-
uum to gave the triazolato complexes [(g6-C6H6)Ru-
(L\L){N3C2(CO2CH3)2}]. Yield: 52 mg, 34%. IR (KBr,
cmꢀ1): 1437–1446 (mN@N), 1580, 1529 (mC@O+C@C). 1H
NMR (CDCl3, d): 1.91(s, 6H, acac–Me); 2.87 (s, 6H,
OCH3); 5.47 (s, 1H, acac-cH); 5.69 (s, 6H, C6H6).
Table 1
Crystal data and experimental details for [(g6-C6H6)Ru(O,O0-acac)-
{N3C2(CO2C2H5)2}] (9)
Chemical formula
Formula weight
Crystal system
C19H24N3O6Ru
491.48
monoclinic
P21/c (no. 14)
red block
0.42 · 0.22 · 0.10
11.265(2)
7.2910(10)
24.976(5)
98.36(3)
Space group
Crystal colour and shape
Crystal size
˚
a (A)
˚
b (A)
˚
c (A)
b (o)
3
˚
V (A )
2029.6(6)
4
173(2)
Z
2.5. Preparation of triazolato complexes
[(g6-C6H6)Ru(O,O0-acac){N3C2(CO2C2H5)2}] (9)
T (K)
Dcalc (g cmꢀ3
)
1.608
l (mmꢀ1
)
0.813
The complex is prepared by following the same proce-
dure for the preparation of [(g6-C6H6)Ru(O,O0-acac){N3-
C2(CO2CH3)2}] (8), where diethylacetylenedicarboxylate
is used instead of dimethylacetylenedicarboxylate. Yield:
55 mg, 39%. IR (KBr, cmꢀ1): 1437–1446 (mN@N), 1533
(mC@O+C@C). 1H NMR (CDCl3, d): 1.92 (s, 6H, (acac–
Me), 2.35 (q, 6H, {OCH2(CH3)2}, 2.62 (t, 6H, CH2(CH3)2);
3.65 (q, 4H, (–CH2 of OCH2 (CH3)2); 5.85 (s, 1H, (acac-
cH), 5.94 (s, 6H, C6H6).
Scan range (ꢁ)
2.28 < h < 25.97
3941
2772
Unique reflections
Reflections used [I > 2r(I)]
Rint
Final R indices [I > 2r(I)]*
R indices (all data)
Goodness-of-fit
0.0481
0.0364, wR2 = 0.0894
0.0574, wR2 = 0.0951
1.038
ꢀ3
˚
Maximum, minimum Dq/e (A
)
0.794, ꢀ0.549
2
2 1=2
*
Structures were refined on F 2o : wR2 ¼ ½R½wðF o2 ꢀ F c2Þ ꢁ=RwðF 2oÞ ꢁ
;
2
where wꢀ1 ¼ ½RðF o2Þ þ ðaPÞ þ bPꢁ and P ¼ ½maxðF o2; 0Þ þ 2F 2c ꢁ=3.

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 3294–3300
3297
Fig. 1. ORTEP diagram of 9 with labeling scheme at 50% probability level
˚
and H atoms being omitted for clarity. Selected bond distances (A) and
angles (ꢁ): C(2)–C(3) 1.386(6), C(3)–C(4) 1.388(6), N(1)–N(2) 1.331(4),
N(1)–N(3) 1.343(4), N(1)–Ru(1) 2.078(3), O(2)–Ru(1) 2.063(3), O(1)–
Ru(1) 2.062(3), N(2)–N(1)–N(3) 112.8(3), N(2)–N(1)–Ru(1) 125.1(2),
N(3)–N(1)–Ru(1) 122.2(2), C(2)–O(1)–Ru(1) 124.4(2), C(4)–O(2)–Ru(1)
124.6(2), O(1)–Ru(1)–O(2) 88.21(10), O(1)–Ru(1)–N(1) 83.95(12), O(2)–
Ru(1)–N(1) 83.27(12).
Scheme 1. Reaction pathways.
a strong adsorption peak at 2044 cmꢀ1 which corresponds
to the stretching frequency of the bridging mN group and
3
compares well with analogous compounds [10]. The 1H
NMR spectrum shows a singlet peak at 5.86 ppm corre-
sponding to the protons of the benzene ligand. However,
attempts to substitute all the chlorides in the starting ben-
zene dimer with azide group was incomplete, possibly due
to less electron density on the ruthenium metal atom in
comparison to hexamethylbenzene ruthenium dimer
where we reported the substitution of all the chlorides
with azide group [10].
2.7. Single-crystal X-ray structures analysis
A crystal suitable for X-ray diffraction study for com-
pound 9 was grown by slow diffusion of diethylether into
a dichloromethane solution of the complex. The orange red-
dish crystal of compound 9 was mounted on a Stoe Image
Plate Diffraction system equipped with a / circle goniome-
˚
ter, with / range 0–200ꢁ, Dmax ꢀ Dmin = 12.45–0.81 A. X-
ray intensity data were collected with Mo-Ka graphite
˚
monochromated radiation (k = 0.71073 A) at 173 (2) K,
3.2. Syntheses of benzene ruthenium b-diketonato complexes
having increment of 1.0ꢁ and 3 min per frame. The intensity
data were corrected for Lorenz and polarization effects. The
structure was solved by direct methods using the program
SHELXS-97 [13]. Refinement and all further calculations were
carried out using SHELXL-97 [14]. The H-atoms were
included in calculated positions and treated as riding atoms
using the SHELXL default parameters. The non-H atoms were
refined anisotropically, using weighted full-matrix least-
square on F2. Crystallographic details are summarized in
Table 1. Fig. 1 was drawn with ORTEP32 [15].
Reaction of [(g6-C6H6)RuCl2)2] with sodium salt of the
appropriate b-diketonate in dry methanol for 5 h results in
orange colored complexes of the general formula [(g6-
C6H6)Ru(L\L)Cl] [L\L = O,O0-acac (2); O,O0-bzac (3);
O,O0-dbzm (4)] (Scheme 1). The infrared spectrum of these
complexes shows strong bands within the range of 1570–
1447 cmꢀ1 corresponding to the stretching frequency of
1
C@O and C@C groups. The H NMR spectra of these
complexes (2–4) shows a characteristic singlet resonance
within the range of 5.80–6.04 ppm assignable to the pro-
tons of the benzene ligand. Singlet peaks observed within
the range of 2.14–2.35 ppm and 5.68–5.72 ppm are
assigned to the –CH3 group and to the c-H proton of the
b-diketonate ligand, respectively. Phenyl protons of b-
diketonate ligand show characteristic multiplet resonance
at the aromatic region.
3. Results and discussion
3.1. Syntheses of benzene ruthenium azide dimer complex
Reaction of [(g6-C6H6)RuCl2)2] with an excess of
sodium azide in ethanol after stirring for 5 h affords a yel-
low colored complex [{(g6-C6H6)Ru(l-N3)Cl}2] (1).
Safety measure should be taken while handling the solid
in dry condition, scratching with a spatula should be
avoided since it can explode. The formation of this com-
pound can be readily confirmed from the appearance of
3.3. Syntheses of benzene ruthenium azido complexes
Treatment of complexes 2–4 with sodium azide forms
the corresponding azido complexes: [(g6-C6H6)Ru(L\L)N3]

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K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 3294–3300
[L\L = O,O0-acac (5); O,O0-bzac (6); O,O0-dbzm (7)]
(Scheme 1). The formation of these complexes is readily
confirmed by the observation of a sharp absorption peak
in the range 2020–2035 cmꢀ1 which is characteristic to ter-
minal azido group [10]. Accordingly, complexes 5–7 can
also be prepared by reacting the azido dimer [{(g6-
C6H6)Ru(l-N3)Cl)}2] (1) with sodium salts of b-diketo-
nates in methanol at room temperature (Scheme 1). The
formation of azido complexes is confirmed by the disap-
pearance of the bridging azide stretching frequency at
2044 cmꢀ1 and the appearance of a new band at 2020–
2035 cmꢀ1 corresponding to stretching frequencies of
Scheme 2. Reaction of carboxylates with ruthenium azide complex 5.
terminal mN . The IR spectra also showed a pair of strong
3
to medium absorption bands in the range 1571–1520
cmꢀ1 which is assigned to m(C@O) + m(C@C) stretching fre-
quencies of b-diketonate ligands [16].
(CO2C2H5)2}] where a terminal nitrogen of the triazolato
group bonds to the metal [9]. In the case of benzene
ruthenium triazolato complexes, the ruthenium metal
binds with the middle nitrogen atom, which is a (N1)-
bound isomer (Fig. 1), as confirmed from the single
crystal X-ray analysis of complex 9 (see Fig. 1). The bond
formation of ethoxy substituted complexes of p-cymene
ruthenium and benzene ruthenium indicates that steric
factors play an important role. The bulkier organic frag-
ment of p-cymene ruthenium could cause steric hindrance
for the incoming diethylacetylenedicarboxylate ligand
which leads to bond formation with the terminal nitrogen.
In the case of the benzene derivative 6, the organic frag-
ment does not encountered steric hindrance for the
incoming ligands which results in metal bonding to the
middle nitrogen (N1). Similarly, indenyl ruthenium bis(tri-
phenylphosphine) azido complexes did not yield the tria-
zolato complexes due to steric factor [9]. Study of the
molecular models of the linkage isomer indicates that this
congestion would be totally relieved in the isomer involv-
ing the middle nitrogen atom (N2) bonding. It should be
noted that the triazole anion may be coordinated to a
metal either through the N(1) atom or the N(2) atom
[17]. Evidence obtained to date indicates that both the
N(1) and N(2)-bonded products may be formed simulta-
neously [18]. In our study, the ethoxy substituted complex
exclusively produces the isomer with the metal bonded to
the middle nitrogen atom (N1).
It has been reported that the initial formation of the
N(1)-bonded complex via azide attack on the coordinated
nitrile carbon of the pentamethylamine cobalt complexes
is followed by slow isomerization to the N(2)-bonded com-
plex [19]. In case of complexes 5 and 6, our efforts to pre-
pare the corresponding triazole complexes were
unsuccessful. This may be due to lower electron density
on the metal center (i) no methyl groups on aromatic ring
and (ii) the substituents on the b-diketonate ligand, viz.,
phenyl and methyl in (O,O0-bzac) and phenyl and phenyl
in (O,O0-dbzm). At the same time, solubility problems
are also encountered throughout the whole reaction pro-
cess. The complexes 8 and 9 are soluble in chlorinated sol-
vents but insoluble in non-polar solvents and stable in air.
The complexes 1–7 are partially soluble in methanol,
The 1H NMR spectra of these complexes exhibit a char-
acteristic peaks in the range 5.80–6.00 ppm which corre-
sponding to the protons of the benzene ligand. A singlet
peak observed at 2.70–2.85 ppm is assigned to the methyl
group of the b-diketonate ligand. In 4, 5, 7 and 8 multiplets
are observed in the aromatic region corresponding to the
protons of the phenyl groups of the chelating ligands. A
singlet at 5.60–5.78 ppm may be attributed to the c-H pro-
ton of the b-diketonate ligands.
3.4. Reaction of benzene ruthenium azido complexes with
dimethylacetylenedicarboxylate and
diethylacetylenedicarboxylate
Treatment of complex [(g6-C6H6)Ru(O,O0-acac)N3] (5)
with a fivefold excess of a substituted acetylenes viz.,
dimethylacetylenedicarboxylate (MeO2CC”CCO2Me) and
diethylacetylenedicarboxylate (EtO2CC”CCO2Et) in dichlo-
romethane or acetone and stirring at room temperature
for 14–15 h affords the yellow-colored benzene ruthenium
triazolato complexes in low yield: [(g6-C6H6)Ru(O,O0-acac)-
{N3C2(CO2CH3)2}] (8) and [(g6-C6H6)Ru(O,O0-acac){N3-
C2(CO2C2H5)2}] (9), respectively (Scheme 2).
The formation of the yellow triazolato complexes 8 and
9 is confirmed by observing the disappearance of the azido
stretching frequency and appearance of a carbonyl (mC@O
)
stretch at 1580 cmꢀ1 for complex 8 and 1533 cmꢀ1 for com-
plex 9. Apart from mC@O, the IR spectra show medium
bands in the region 1580–1437 cmꢀ1 due to (mC@C) and
(mN@N), respectively.
1
The H NMR spectra of complexes 8 and 9 show a sin-
glet resonance at 5.80–6.00 ppm corresponding to the pro-
tons of the benzene ligand. A singlet peak observed
around 2.14–2.35 ppm is assigned to the methylene
protons of the b-diketonate ligand. The protons of the
methoxy group of the triazole ring appear as singlet at
1
1.91–2.21 ppm. In the case of 9, the H NMR spectrum
exhibits a quartet at 3.65 ppm and a triplet at 2.35 ppm
due to the methylene and methyl protons of the ethyl
groups. We had recently reported the p-cymene ruthenium
triazolato complex [(g6-p-cymene)Ru(O,O0-bzac){N3C2-

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 3294–3300
3299
dichloromethane, acetone and acetonitrile, but insoluble in
non-polar solvents. Solubility problem with starting com-
pounds have been faced throughout this study, which
results in low yields.
In addition, the aromatic protons of the benzene ligand
give a signal at 5.92 ppm. In principle, cycloaddition of
fumaronitrile to coordinated azide can take place through
the C„N or the C@C bond.
The molecular structure of the complex [(g6-
C6H6)Ru(O,O0-acac){N3C2(CO2C2H5)2}] (9) is presented
in Fig. 1 and selected bond lengths and angles are given
as well. The complex shows typical piano-stool geometry
with the metal center being coordinated by a benzene
ligand, a chelating b-diketonate and triazolate ligands.
The Ru(1)–O(1) and Ru(1)–O(2) bond distances [2.062(3)
and 2.063(3)] of the acetylacetato complex are similar to
reported Ru–O bond lengths of other ruthenium b-diketo-
nate systems [3b,9,20]. The Ru(1)–N(1) bond distance
4. Conclusions
The syntheses of benzene ruthenium azido complexes of
b-diketonates are described. These complexes undergo
[3+2] cycloaddition reaction with substituted alkynes or
fumaronitrile leading to the formation of substituted tria-
zolato complexes. The cycloaddition of diethylacetylenedi-
carboxylate produces triazolato complexes with the middle
nitrogen atom of the triazole group bonded to the metal. In
the case of the p-cymene ruthenium triazolato analogue,
the same reaction produces terminal nitrogen-bonded tri-
azalato complexes.
6
˚
[2.078(3)] A in complex 9 is comparable to those in [(g -
p-cymene)Ru(O,O0-acac){N3C2(CO2C2H5)2}] [9a] and
other ruthenium triazolato complexes [21]. The N–N bond
˚
distances of the triazole ring are 1.331(4) and 1.343(4) A
which is comparable to reported triazolato N–N bond
lengths [9a,21]. The O(1)–Ru(1)–O(2) [88.21(10)] bond
angles of the complex are also comparable to other related
systems [3b,9,20].
Acknowledgements
K.M.R thanks Dr. B. Therrien (University of Neucha-
tel) for his help to solve the molecular structure. K.M.R
also greatly acknowledges the Department of Science and
Technology, New Delhi (sanction order No. SR/S1/IC-11/
3.5. Reaction of ruthenium azido complexes with
fumaronitrile
´
´
2004) for financial support. We also thank Mıriam Perez,
`
Servei RMN Universitat Autonoma de Barcelona 08193
The reaction of azido complexes 5–7 with an excess of
fumaronitrile at room temperature for 24 h affords the
chocolate-colored triazolato complexes 10–12 (Scheme 3).
The complexes are readily soluble in polar solvents like
dichloromethane, chloroform, acetone and methanol but
insoluble in non-polar solvents. The formation of the tria-
zolato complexes is readily confirmed by the absence of the
starting azide stretching frequency and the appearance of a
strong peak in the range of 2225–2236 cmꢀ1 which corre-
sponds to the stretching frequency of the C„N group of
the coordinated triazolato ligands.
Bellaterra, Barcelona for providing the NMR facility. We
also thank Professor R. H. Duncan Lyngdoh for his help
in preparing the manuscript.
Appendix A. Supplementary material
CCDC 644831 contains the supplementary crystallo-
graphic data for 9. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2007.05.063.
The 1H NMR spectrum of the complexes shows charac-
teristic singlet resonance at 6.86 ppm assignable to the CH
proton of the triazolato group. A singlet in the region 5.59–
5.81 ppm is attributed to the c-H proton of the b-diketo-
nate group.
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