Synthesis, characterization and molecular structure of the [(η6-C6Me6)Ru(μ-N3) (N3)]2 complex and its reactions with some monodentate ligands

Article abstract of DOI:10.1016/j.jorganchem.2004.06.034

The reaction of complex [(η⁶-C₆Me₆) Ru(μ-Cl)Cl]₂ (1) with sodium azide yielded complexes of the composition [(η⁶-C₆Me₆) Ru(μ-N₃)(N₃)]₂ (2) and [(η⁶-C₆Me₆)Ru(μ-N₃) (Cl)]₂ (3), depending upon the reaction conditions. Complex 3 with excess of sodium azide in ethanol yielded complex 2 . Complexes 2 and 3 undergo substitution reactions with monodentate ligands such as PPh₃, PMe₂Ph and AsPh₃ to yield monomeric complexes. The structure of complex 2 was determined by X-ray crystallography. All these complexes were characterized by micro analytical data and by FT-IR and FT-NMR spectroscopy. Complex 2 crystallizes in the monoclinic space group P2_1n with a = 8.5370(11) A?, b = 16.192(2) A?, c = 10.4535(13) A? and β = 110.877(2)°.

Full text of DOI:10.1016/j.jorganchem.2004.06.034

Journal of Organometallic Chemistry 689 (2004) 3108–3112
www.elsevier.com/locate/jorganchem
Note
Synthesis, characterization and molecular structure of the
[(g6-C6Me6)Ru(l-N3)(N3)]2 complex and its reactions with
some monodentate ligands
a
P. Govindaswamy , Hemant P. Yennawar , Mohan Rao Kollipara
b
a,
*
a
Department of Chemistry, North-Eastern Hill University, Shillong 793 022, India
b
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, PA 16802, USA
Received 12 April 2004; accepted 7 June 2004
Available online 30 July 2004
Abstract
The reaction of complex [(g6-C6Me6)Ru(l-Cl)Cl]2 (1) with sodium azide yielded complexes of the composition [(g6-C6Me6)Ru(l-
N3)(N3)]2 (2) and [(g6-C6Me6)Ru(l-N3)(Cl)]2 (3), depending upon the reaction conditions. Complex 3 with excess of sodium azide in
ethanol yielded complex 2. Complexes 2 and 3 undergo substitution reactions with monodentate ligands such as PPh3, PMe2Ph and
AsPh3 to yield monomeric complexes. The structure of complex 2 was determined by X-ray crystallography. All these complexes
were characterized by micro analytical data and by FT-IR and FT-NMR spectroscopy. Complex 2 crystallizes in the monoclinic
˚
˚
˚
space group P21/n with a=8.5370(11) A, b=16.192(2) A, c=10.4535(13) A and b=110.877(2)°.
Ó 2004 Published by Elsevier B.V.
Keywords: Hexamethylbenzene; Azide; Ruthenium
1. Introduction
arene–ruthenium complexes, which exhibit antibiotic,
antiviral [3] and catalytic activities [4]. The arene–ruthe-
nium(II) complexes having labile chloride groups under-
go exchange reactions with bromide and iodide to form
bromo and iodo compounds [5]. No reports are available
on the reactivity studies of these complexes with azide
groups. Recently, the azide complexes have become very
important due to the synthesis of triazoles and tetrazoles
from these compounds [6]. In continuation of our work,
we report here the title compound and its reactions with
mono substituted ligands. The molecular structure of the
complex 2 is reported as well.
During the last few years, arene–ruthenium(II) com-
plexes have been an area of immense attraction due to
their similarity in reactivity with cyclopentadienyl ruthe-
nium(II) half-sandwich complexes. Arene–ruthenium(II)
complexes undergo a variety of substitution reactions
with various ligands to yield neutral as well as cationic
complexes [1]. We had earlier carried out a few reactions
of these dimers with Schiff bases and pyrazoles to yield
cationic Schiff base compounds and amidine complexes
as well as bis disubstituted pyrazole complexes [2]. Re-
cently, a lot of interest has been generated in these
complexes due to the synthesis of water-soluble
2. Experimental
2.1. General considerations
*
Corresponding author. Tel.: +91-364-272-2620; fax: +91-364-255-
0076.
E-mail addresses: mrkollipara@yahoo.com, kmrao@nehu.ac.in
(M. Rao Kollipara).
All solvents were dried and distilled by standard
methods. Triphenylphosphine, PPhMe2 and AsPh3 were
0022-328X/$ - see front matter Ó 2004 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2004.06.034

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3108–3112
3109
purchased from Merck and used as supplied. The dimer
[(g6-C6Me6)RuCl2]2 (1) was prepared by a literature
method [7]. Infrared spectra were recorded as KBr pel-
lets using a Perkin–Elmer model 983 spectrophotometer.
1H and 31P{1H} NMR spectra were recorded on a Bru-
ker-ACF-300 (300 MHz) and referenced to tetrameth-
ylsilane and H3PO4 (85%), respectively, at the
Regional Sophisticated Instrumentation Centre (RSIC),
NEHU, Shillong, India.
(s, 18H, HMB), 7.41–7.55 (m, 15H, Ph). 31P{1H} NMR
(CDCl3, d): 34.66. Elemental analysis (%) for
C30H33RuN6P: Calc. C, 59.10; H, 5.45; N, 13.78. Found:
C, 59.36; H, 5.14; N, 13.92%.
Compound 4b (Yield 36 mg, 42.85%) IR (KBr pellets,
1
cmÀ1): 2037s (terminal mN3). H NMR (CDCl3, d): 1.66
(s, 6H, CH3), 1.89 (s, 18H, HMB), 7.47–7.69 (m, 5H,
Ph). 31P{1H} NMR (CDCl3, d): 29.33. Elemental analy-
sis (%) for C20H29RuN6P: Calc. C, 49.43; H, 6.02; N,
17.31. Found: C, 49.36; H, 5.86; N, 17.92%.
Compound 4c (Yield 45 mg, 40.18%) IR (KBr pellets,
cmÀ1): 2027s. 1H NMR (CDCl3, d): 1.86 (s, 18H, HMB),
7.31–7.72 (m, 15H, Ph). Anal. Calc . (%) for C30H33Ru-
N6As: C, 55.13; H, 5.09; N, 12.85. Found: C, 55.28; H,
5.35; N, 12.45%.
2.2. Synthesis of [(g6-C6Me6)Ru(l-N3)(N3)]2 (2)
A mixture of [(g6-C6Me6)RuCl2]2 (100 mg, 0.149
mmol) and excess sodium azide (60 mg, 0.897 mmol)
was stirred in dry ethanol (25 ml) for 4 h, whereby
the orange-coloured product was separated out. The
compound was filtered and washed with diethylether
and dried under vacuum (Yield 95 mg, 92%). IR
(KBr pellets, cmÀ1): 2064s (l-mN3), 2024s (terminal
2.6.
{L=PPh3 (5a), PMe2Ph (5b), AsPh3 (5c)}
Synthesis
of
[(g6-C6Me6)Ru(N3)(Cl)(L)]
m
N3).1H NMR (CDCl3, d): 2.06 (s, 36H, HMB). Ele-
These complexes were synthesized using the same
procedure given above, except that complex 3 (60 mg,
0.088 mmol) was used as the starting material instead
of complex 2.
mental analysis (%) for C24H36Ru2N12: Calc. C,
33.87; H, 5.90; N, 27.43. Found: C, 33.32; H, 6.21;
N, 27.33%.
Compound 5a (Yield 41 mg, 38.67%) IR (KBr pellets,
1
2.3. Synthesis of [(g6-C6Me6)Ru(l-N3)(Cl)]2 (3)
cmÀ1): 2037s (terminal mN3). H NMR (CDCl3, d): 1.82
(s, 18H, HMB), 6.94–7.56 (m, 15H, Ph). 31P{1H} NMR
(CDCl3, d): 33.68. Elemental analysis (%) for
C30H33RuN3ClP: Calc. C, 59.74; H, 5.51; N, 6.96.
Found: C, 59.39; H, 5.87; N, 7.06%.
A mixture of complex 1 (100 mg, 0.149 mmol) and
twofold sodium azide (18 mg, 0.288 mmol) was stirred
in dry acetone (20 ml) for 10 h, whereby the orange-
red coloured product was separated out. The compound
was filtered and washed with diethylether and dried un-
der vacuum (Yield 87 mg, 85%). IR (KBr pellets, cmÀ1):
2057s (l-mN3). 1H NMR (CDCl3, d): 2.09 (s, 36H,
HMB). Elemental analysis (%) for C24H36Ru2N6Cl2:
Calc. C, 42.29; H, 5.32; N, 12.32. Found: C, 42.38; H,
5.09; N, 12.44%.
Compound 5b (Yield 37 mg, 44.04%) IR (KBr pellets,
1
cmÀ1): 2037s (terminal mN3). H NMR (CDCl3, d): 1.54
(s, 6H, CH3), 1.76 (s, 18H, HMB), 7.43–7.51 (m, 5H,
Ph). 31P{1H} NMR (CDCl3, d): 30.43. Elemental analy-
sis (%) for C20H29RuN3ClP: Calc. C, 50.15; H, 6.10; N,
8.77. Found: C, 49.12; H, 5.86; N, 8.43%.
Compound 5c (Yield 46 mg, 41.07%) IR (KBr pellets,
1
cmÀ1): 2037s (terminal mN3). H NMR (CDCl3, d): 1.78
2.4. Synthesis of complex 2 (second method)
(s, 18H, HMB), 6.91–7.65 (m, 15H, Ph). Elemental anal-
ysis (%) for C30H33RuN3ClAs: Calc. C, 55.68; H, 5.14;
N, 6.49. Found: C, 55.37; H, 4.97; N, 6.62%.
A mixture of complex 3 (100 mg, 0.146 mmol) and ex-
cess of sodium azide (38 mg, 0.587 mmol) was stirred in
dry ethanol (20 ml) for 2 h, whereby the orange-col-
oured product was separated out. The compound was
filtered and washed with diethylether and dried under
vacuum (Yield 86 mg, 84.31%).
3. X-ray crystallography
Diffusing hexane into dichloromethane solution of
complex 2 grew suitable crystals. A suitable crystal of
complex 2 was mounted on a Bruker SMART APEX
CCD area detector system equipped with a graphite
monochromator and a Mo Ka fine-focus sealed tube
2.5. Synthesis of [(g6-C6Me6)Ru(N3)2(L)] {L=PPh3
(4a), PMe2Ph (4b) AsPh3 (4c)}
A mixture of complex 2 (60 mg, 0.086 mmol) and lig-
and L (0.173 mmol) was stirred in dry acetone (10 ml)
for 12 h, whereby the orange-coloured product was sep-
arated out. The compound was filtered and washed with
diethylether and dried under vacuum.
˚
(k=0.71071 A) with w range 0–200° at increment of
˚
1.0–2.3° and DmaxÀDmin =12.45À0.81 A. The structure
was solved by direct methods using the program SHEL-
XS-97 [8]. The refinement and all further calculations
were carried out using SHELXL-97 [9]. The hydrogen at-
oms have been included in calculated positions and
Compound 4a (Yield 45 mg, 42.77%) IR (KBr pellets,
1
cmÀ1): 2030s (terminal mN3). H NMR (CDCl3, d): 1.88

3110
P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3108–3112
3 exhibits the characteristic band for the bridging azide
groups at 2057 cmÀ1, indicating that no terminal azide
ligands are present. This was further confirmed by the
elemental analysis, which indicated only two azide
groups.
Cl
Cl
Ru
Ru
Cl
Cl
1:6
complex 1
1:2
NaN
NaN
3
3
EtOH
acetone
N
N
N
N
N
N
N
N
N
Cl
Excess
Ru
Ru
N
Ru
Ru
Cl
NaN
3
N
N
N
N
N
N
N
EtOH
N
complex 2
complex 3
Fig. 1. ORTEP diagram of the complex 2 with 50% probability
thermal ellipsoids.
The proton NMR spectrum of the complex 2 ex-
hibits a strong peak at 2.06 ppm for the hexamethyl-
benzene protons, whereas in the case of complex 3 the
signal is observed at 2.09 ppm. The molecular struc-
ture of complex 2 was determined by X-ray crystallog-
treated as per the ÔridingÕ model, using the SHELXL
default parameters. All non-H atoms were refined aniso-
tropically, using a weighted full matrix least-squares fit
on F2. An ORTEP [10,11] diagram of the molecule is
presented in Fig. 1.
raphy (Fig. 1). Complex
2
crystallizes in the
monoclinic space group P2(1)/n with centro-symmetry.
The geometry around the ruthenium atom in the com-
plex 2 is octahedral, where the hexamethylbenzene oc-
cupies three coordination positions. The compound
has a piano stool type structure, where the bond angle
N(1)–Ru(1)–N(4) around ruthenium is equal to
81.55(7)°, a little lower than for other reported com-
pounds. The bond distance between the centroid of
4. Results and discussion
˚
The chloro arene–ruthenium dimer 1, which reacted
with excess of sodium azide in ethanol gave the orange-
coloured tetra-azido complex 2 in 92% yield. When the
reaction was carried out with the complex 1 and sodi-
um azide in 1:2 molar ratio in acetone, the orange-
red di-azido complex 3 was obtained in 85% yield.
The similar reaction in the case of p-cymene dimer
[(g6-C10H14)Ru(l-Cl)Cl]2 invariably yielded only
bridged disubstituted azido complex [(g6-C10H14)-
Ru(l-N3)Cl]2 analogous to complex 3 [12a]. The com-
plex 3 with excess of sodium azide gave the complex
2. These complexes are stable in air and soluble in polar
solvents such as chloroform and dichloromethane, but
insoluble in non-polar solvents such as hexane and pen-
tane. The infrared spectrum of complex 2 shows two
characteristic bands – one in the region of terminal
azide ligands at 2024 cmÀ1and another in the region
of bridging azide ligands at 2064 cmÀ1 [13]. Complex
HMB and Ru is 1.663 A, while the Ru–N bond dis-
˚
tances are 2.1520(18) A for the Ru(1)–N(1) bond
˚
and 2.1090(18) A for the Ru(1)–N(4) bond, which
are within the limits of reported complexes [14]. The
terminal azide nitrogens have N–N bond distances
˚
of 1.188(3) A for the (N4)–(N5) bond and 1.159(3)
˚
A for the (N5)–(N6). N–N bond distances in the
bridging azide nitrogens are 1.209(2)
(N1)–(N2) bond and 1.144(3) A for the (N2)–(N3)
bond. In the case of terminal azide, the N(4)–N(5)
bond distance is slightly smaller than the bridging az-
ide N(1)–N(2), whereas N(5)–N(6) distance of terminal
azide is slightly longer than the bridging azide N(2)–
N(3) distances. However, these bond distances of the
bridging and terminal azide nitrogens are close to
other reported values [12].
˚
A
for the
˚
These dimers undergo bridge cleavage reactions with
a twofold excess of L [L=PPh3, PMe2Ph, AsPh3 (4,5)] in

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3108–3112
3111
acetone, giving the mononuclear complexes 4a, 4b, 4c,
5a, 5b and 5c.
ruthenium l-azido dimer [(g6-C10H14)Ru(l-N3)Cl]2 irre-
spective of sodium azide concentration [12a], whereas
the latter gives both disubstituted l-azido and tetrazido
substituted complexes. These complexes can undergo a
variety of substitution reactions with monodentate and
bidentate ligands to yield monomeric compounds as well
as bridged dimeric compounds. This work is currently
under progress.
Complex 2
+
L
N
N
Ru
N
N
acetone
N
N
L
L =PPh , PMe Ph, AsPh
3
2
3
Acknowledgement
Complex 4
H.P.Y. acknowledges NSF grant CHE-0131112 for
the purchase of the diffractometer.
Complex 3
+
L
Appendix A. Supplementary material
N
N
N
Ru
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre (CCDC), CCDC No. 235560 for complex 2. Cop-
ies of this information may be obtained free of charge
from the director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2004.06.034.
acetone
Cl
L
L = PPh3, PMe Ph, AsPh3
2
complex 5
The infrared spectra of these complexes show a
strong band in the range of 2037–2026 cmÀ1 due to
the terminal azide group [15] along with strong bands
due to the phenyl groups of the phosphine ligands.
The 1H NMR spectra of these complexes exhibit a
strong peak for hexamethylbenzene at 1.88 ppm for
complex 4a, 1.89 ppm for complex 4b and 1.86 ppm
for complex 4c [16], respectively. The aromatic protons
of the ligands L appear as multiplets at around 6.91–
7.69 ppm for these complexes. The 31P{1H} NMR spec-
tra of these complexes exhibit a singlet at around 29.33–
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