Syntheses and characterization of η5-cyclopentadienyl and η5-indenyl ruthenium(II) complexes of arylazoimidazoles: The molecular structure of the complex [(η5-C5H 5)Ru(PPh3)(C6H5-NN-C 3H3N2)]+

Article abstract of DOI:10.1016/j.jorganchem.2005.04.042

The complex [(η⁵-C₅H₅)Ru(PPh ₃)₂Cl] (1) reacts with several arylazoimidazole (RaaiR′) ligands, viz., 2-(phenylazo)imidazole (Phai-H), 1-methyl-2-(phenylazo)imidazole (Phai-Me), 1-ethyl-2-(phenylazo)imidazole (Phai-Et), 2-(tolylazo)imidazole (Tai-H), 1-methyl-2-(tolylazo)imidazole (Tai-Me) and 1-ethyl-2-(tolylazo)imidazole (Tai-Et), gave complexes of the type [(η⁵-C₅H₅)Ru(PPh₃)(RaaiR′) ]⁺ {where R, R′ = H (2), R = H, R′ = CH₃ (3), R = H, R′ = C₂H₅ (4), R = CH₃, R′ = H (5), R, R′ = CH₃ (6), R = CH₃, R′ = C ₂H₅ (7)}. The complex [(η⁵-C ₉H₇)Ru(PPh₃)₂(CH₃CN)] ⁺ (8) undergoes reactions with a series of N,N-donor azo ligands in methanol yielding complexes of the type [(η⁵-C₉H ₇) Ru(PPh₃)(RaaiR′)]⁺ {where R, R′ = H (9), R = H, R′ = CH₃ (10), R = CH₃, R′ = H (11), R = CH₃, R′ = C₂H₅ (12)}, respectively. These complexes were characterized by FT IR and FT NMR spectroscopy as well as by analytical data. The molecular structure of the complex [(η⁵-C₅H₅)Ru(PPh ₃)(C₆H₅-NN-C₃H₃N ₂)]⁺ (2) was established by single crystal X-ray diffraction study.

Full text of DOI:10.1016/j.jorganchem.2005.04.042

Journal of Organometallic Chemistry 690 (2005) 3465–3473
www.elsevier.com/locate/jorganchem
Syntheses and characterization of g5-cyclopentadienyl
and g5-indenyl ruthenium(II) complexes of arylazoimidazoles:
The molecular structure of the complex
[(g5-C5H5)Ru(PPh3)(C6H5–N@N–C3H3N2)]+
a
Padavattan Govindaswamy , Chittaranjan Sinha , Mohan Rao Kollipara
b
a,
*
a
Department of Chemistry, North-Eastern Hill University, Shillong 793 022, India
b
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
Received 26 February 2005; revised 26 April 2005; accepted 26 April 2005
Available online 15 June 2005
Abstract
The complex [(g5-C5H5)Ru(PPh3)2Cl] (1) reacts with several arylazoimidazole (RaaiR0) ligands, viz., 2-(phenylazo)imidazole
(Phai-H), 1-methyl-2-(phenylazo)imidazole (Phai-Me), 1-ethyl-2-(phenylazo)imidazole (Phai-Et), 2-(tolylazo)imidazole (Tai-H),
1-methyl-2-(tolylazo)imidazole (Tai-Me) and 1-ethyl-2-(tolylazo)imidazole (Tai-Et), gave complexes of the type [(g5-
C5H5)Ru(PPh3)(RaaiR0)]+ {where R, R0 = H (2), R = H, R0 = CH3 (3), R = H, R0 = C2H5 (4), R = CH3, R0 = H (5), R, R0 = CH3
(6), R = CH3, R0 = C2H5 (7)}. The complex [(g5-C9H7)Ru(PPh3)2(CH3CN)]+ (8) undergoes reactions with a series of N,N-donor azo
ligands in methanol yielding complexes of the type [(g5-C9H7) Ru(PPh3)(RaaiR0)]+ {where R, R0 = H (9), R = H, R0 = CH3 (10),
R = CH3, R0 = H (11), R = CH3, R0 = C2H5 (12)}, respectively. These complexes were characterized by FT IR and FT NMR spec-
troscopy as well as by analytical data. The molecular structure of the complex [(g5-C5H5)Ru(PPh3)(C6H5–N@N–C3H3N2)]+ (2) was
established by single crystal X-ray diffraction study.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cyclopentadienyl; Indenyl; Arylazoimidazole ligands; Ruthenium complexes
1. Introduction
The major work has grown around N,N-chelating pyri-
dine bases and related species [2–11]. The number of het-
eroatoms, the ring size, and the substituents in the
heterocyclic ring significantly modify the p-acidity and
regulate the physical and chemical properties of the
compounds [12].
Recently, the design of molecular architectures with
imidazole ligands has contributed to the understanding
of biomolecular interactions with metal ions in biology
and provides models for the active sites of metallopro-
teins [13–16]. Ruthenium–imidazole complexes are of
interest for their antitumor activities [16]. The molecule
bears the azoimine (–N@N–C@N–) functional group,
and is an efficient p-acid system for the stabilization of
Cyclopentadienyl ruthenium(II) complexes have been
mainly considered as useful model compounds and have
recently been successfully employed as catalysts in a ser-
ies of C-C bond forming reactions [1]. The chemistry of
ruthenium with unsaturated nitrogen ligands [2–11] has
been studied extensively in recent times, including the
study of photophysical and photochemical properties.
*
Corresponding author. Tel.: +91 364 272 2620; fax: +91 364
2550076.
E-mail addresses: kmrao@nehu.ac.in, mrkollipara@yahoo.com
(M.R. Kollipara).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.04.042

3466
P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
low oxidation state metal ions. The chemistry of this
functional group with platinum is also known in detail
[17–19]. We had previously reported half-sandwich com-
plexes of ruthenium with nitrogen-based ligands [20].
However, no reports are available on these half-
sandwich ruthenium complexes with azoimine ligands.
The complex [(g5-C9H7)Ru(PPh3)2Cl] differs from its
analogue [(g5-C5H5)Ru(PPh3)2Cl] in certain aspects
such as stability of the complex in solution. Reaction
of the complex [(g5-C9H7)Ru (PPh3)2Cl] with N-donor
bases in methanol yielded the complexes without the
indenyl group, resulting in simple coordination com-
pounds. However, insofar as our knowledge goes, the
chemistry of bidentate nitrogen-chelating indenyl-ruthe-
nium complexes remains relatively unexplored [21]. The
ligands used in the present study are shown in Chart 1.
Herein, we present the syntheses of arylazoimidazole
(RaaiR0) complexes of cyclopentadienyl-ruthenium(II)
and indenyl-ruthenium(II). The single crystal X-ray
structure analysis of the representative complex [(g5-
C5H5)Ru(PPh3)(C6H5–N@N–C3H3N2)]+ (2) is also
presented.
Ruthenium chloride trihydrate was purchased from
Arora Matthey Ltd., and used as received. The ligands
[17a,22] and the precursor complexes [23] were prepared
by the following literature methods.
2.2. Synthesis of [(g5-C5H5)Ru(PPh3)(L)]PF6 {L =
Phai-H (2), Phai-Me (3), Phai-Et (4), Tai-H (5),
Tai-Me (6), Tai-Et (7)}
The following general procedure was used for prepar-
ing these compounds:
A mixture of complex 1 (100 mg, 0.138 mmol), the ary-
lazo-imidazole (RaaiR0) ligand (0.165 mmol) and
NH4PF6 (0.207 mmol) was refluxed in methanol (30 ml)
under nitrogen atmosphere for 2 h. The yellow suspension
gradually turned light green in color. The solvent was re-
moved under reduced pressure. The light green solid was
dissolved in 10 ml of CH2Cl2 and filtered to remove
ammonium chloride. The filtrate was concentrated to 2
ml, whereupon addition of excess of hexane gave a green-
ish-brown precipitation. The greenish-brown colored
product was washed with hexane 2–3 times and dried un-
der vacuum. The product was dissolved in chloroform,
when layering with hexane gave the crystalline product.
2. Yield: 85 mg (83%). IR (KBr pellets, cmꢀ1): m(N–H)
3423 (s), m(N@N) 1447 (s), m(C@N) 1633 (s), m(P–F) 850 (s).
1H NMR (CDCl3, d): 4.83 (s, 5H, C5H5), 6.93–7.69
(m, 20H, Ph), 7.77 (d, 1H, JH–H = 7.68 Hz, imidazole),
7.95 (d, 1H, JH–H = 7.43 Hz, imidazole), 8.10 (b, 1H,
NH).
2. Experimental
2.1. Physical measurements
Elemental analysis was performed on a Perkin–Elmer-
2400 CHN/O analyzer. Infrared spectra were recorded
on a Perkin–Elmer-model 983 spectrophotometer with
the sample prepared as KBr pellets. Electronic spectra
were recorded on a Hitachi-300 spectrophotometer.
The 1H NMR and 13C {1H} NMR spectra were recorded
in CDCl3 solvent with tetramethylsilane as internal
standard and on Bruker AMX-400 (400 MHz) and
Bruker ACF-300 (300 MHz) spectrometers, the coupling
constants J being given in hertz. The 31P {1H} NMR
spectra was recorded in CDCl3 solvent and on a Bruker
AMX-400 (400 MHz), chemical shifts being recorded
relative to H3PO4 (85%).
13C {1H} NMR (CDCl3, d): 81.32 (C5H5), 121.35,
123.56, 124.96, 126.37, 126.92, 127.83, 130.06, 132.42
(Ph), 134.26, 135.52, 152.17 (imidazole).
31P {1H} NMR (CDCl3, d): 45.05 (s).
Elemental Anal. Calc. for C32H28N4P2F6Ru: C,
51.54; H, 3.78; N, 7.51. Found: C, 51.62; H, 3.39; N,
7.63%.
UV–Vis (CH2Cl2): kmax = 460, 371, 362 nm.
3. Yield: 77 mg (74%). IR (KBr pellets, cmꢀ1): m(N@N)
1437 (s), m(C@N) 1629 (s), m(P–F) 850 (s).
1H NMR (CDCl3, d): 3.74 (s, 3H, CH3), 4.89 (s, 5H,
C5H5), 7.00–7.44 (m, 20H, Ph), 7.75-7.79 (m, 2H,
imidazole).
2.1.1. Materials and methods
All chemicals used were of reagent grade. All reac-
tions were carried out in distilled and dried solvents.
13C {1H} NMR (CDCl3, d): 34.48 (CH3), 81.65
(C5H5), 123.47, 126.19, 128.58, 129.58, 130.24, 131.91,
132.89, 133.60 (Ph), 135.51, 157.75, 158.25 (imidazole).
31P {1H} NMR (CDCl3, d): 45.16 (s).
3
N
4
Elemental Anal. Calc. for C33H30N4P2F6Ru: C,
52.17; H, 3.97; N, 7.37. Found: C, 52.47; H, 4.02; N,
7.31%.
N
11
6
10
9
5
2
N
1
R
N
R'
UV–Vis (CH2Cl2): kmax = 581, 473, 378 nm.
4. Yield: 83 mg (78%). IR (KBr pellets, cmꢀ1): m(N@N)
1440 (s), m(C@N) 1626 (s), m(P–F) 850 (s).
8
7
R = H, CH
3
R' = H, CH , C H
2 5
3
1H NMR (CDCl3, d): 1.41 (t, 3H, JH–H = 7.32 Hz,
CH3), 4.15 (q, 2H, JH–H = 6.80 Hz, CH2), 4.89 (s, 5H,
Chart 1.

P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
3467
C5H5), 6.99–7.42 (m, 20H, Ph), 7.75 (d, 1H, JH–H = 7.48
Hz, imidazole), 7.83 (d, 1H, JH–H = 7.38 Hz, imidazole).
13C {1H} NMR (CDCl3, d): 15.45 (CH3), 43.32
(CH2), 81.72 (C5H5), 123.46, 124.31, 128.63, 129.58,
130.87, 131.35, 132.17, 132.89 (Ph), 133.70, 135.52,
157.69 (imidazole).
2.3. Synthesis of [(g5-C9H7)Ru(PPh3)(L)]BF4
{C9H7 = indenyl, L = Phai-H (9), Phai-Me (10), Tai-H
(11), Tai-Et (12)}
The following general procedure was used for prepar-
ing these compounds:
31P {1H} NMR (CDCl3, d): 45.06 (s).
A
mixture of the complex
8
[(g5-C9H7)Ru-
Elemental Anal. Calc. for C34H32N4P2F6Ru: C,
52.78; H, 4.17; N, 7.24. Found: C, 52.43; H, 4.26; N,
7.22%.
UV–Vis (CH2Cl2): kmax = 584, 474, 376 nm.
5. Yield: 85 mg (82%). IR (KBr pellets, cmꢀ1): m(N–H)
3409 (s), m(N@N) 1440 (s), m(C@N) 1600 (s), m(P–F) 850 (s).
1H NMR (CDCl3, d): 2.41 (s, 3H, CH3), 4.62 (s, 5H,
C5H5), 6.92–7.44 (m, 19H, Ph), 7.49 (s, 1H, NH), 7.65
(d, 1H, JH–H = 8.30 Hz, imidazole), 7.79 (d, 1H,
JH–H = 8.08 Hz, imidazole).
13C {1H} NMR (CDCl3, d): 31.60 (CH3), 80.94
(C5H5), 123.42, 128.26, 128.70, 129.22, 129.92, 130.97,
131.21, 132.67 (Ph), 133.36, 142.47, 155.31 (imidazole).
31P {1H} NMR (CDCl3, d): 45.25 (s).
(PPh3)2(CH3CN)]BF4 (100 mg, 0.115 mmol) and the
arylazoimidazole (RaaiR0) ligand (0.165 mmol) was
refluxed in methanol (30 ml) under nitrogen atmosphere
for 2 h. The yellow suspension gradually turned to brown
in color. The solvent was removed under the reduced
pressure. The brown solid was dissolved in dichlorometh-
ane and filtered. The filtrate was concentrated to 2 ml and
addition of excess of hexane gave a brown precipitation.
The brown colored product was washed with hexane
and diethyl ether and dried under vacuum. The brown
product was dissolved in chloroform, when layering with
hexane gave the crystalline product.
9. Yield: 74 mg (87%). IR (KBr pellets, cmꢀ1): m(N–H)
3436 (s), m(N@N) 1434 (s), m(C@N) 1633 (s), m(B-F) 1082 (s).
1H NMR (CDCl3, d): 4.93 (d, 2H, JH–H = 4.38 Hz,
UV–Vis (CH2Cl2): kmax = 566, 460, 401 nm.
Elemental Anal. Calc. for C33H30N4P2F6Ru: C,
52.17; H, 3.97; N, 7.37. Found: C, 52.53; H, 3.84; N
7.41%.
indenyl), 5.34 (t, 1H, indenyl), 6.65 (d, 2H, JH–H
=
8.36 Hz, Ph), 6.87–7.47 (m, 22H, Ph), 7.66 (d, 1H,
JH–H = 6.78 Hz, imidazole), 7.79 (b, 1H, NH), 7.85 (d,
1H, JH–H = 7.64 Hz, imidazole).
13C {1H} NMR (CDCl3, d): 64.55, 65.06, 88.97 (inde-
nyl), 123.29, 124.02, 124.74, 125.43, 127.66, 128.58,
129.21, 130.24, 130.98, 131.60 (Ph), 133.88, 135.31,
156.56 (imidazole).
31P {1H} NMR (CDCl3, d): 50.77 (s).
Elemental Anal. Calc. for C36H29N4PBF4Ru: C,
58.71; H, 3.97; N, 7.61. Found: C, 58.39; H, 3.86; N,
7.56%.
UV–Vis (CH2Cl2): kmax = 475, 391, 356, 292 nm.
10. Yield: 72 mg (83%). IR (KBr pellets, cmꢀ1):
m(N@N) 1440 (s), m(C@N) 1600 (s), m(B-F) 1082 (s).
1H NMR (CDCl3, d): 3.65 (s, 3H, CH3), 4.98 (d, 2H,
JH–H = 13.40 Hz, indenyl), 5.70 (t, 1H, indenyl), 6.54 (d,
2H, JH–H = 9.42 Hz, Ph), 6.81–7.48 (m, 22H, Ph), 7.83
(d, 1H, JH–H = 7.52 Hz, imidazole), 7.67 (d, 1H,
JH–H = 7.48 Hz, imidazole).
13C {1H} NMR (CDCl3, d): 31.06 (CH3), 62.43,
64.35, 87.68 (indenyl), 122.62, 123.36, 124.42, 125.03,
125.79, 127.34, 127.97, 129.21, 130.46, 132.24 (Ph),
134.05, 135.97, 153.27 (imidazole).
31P {1H} NMR (CDCl3, d): 50.86 (s).
Elemental Anal. Calc. for C37H31N4PBF4Ru: C,
59.21; H, 4.16; N, 7.47. Found: C, 59.57; H, 3.97; N,
7.16%.
UV–Vis (CH2Cl2): kmax = 489, 376, 289 nm.
11. Yield: 75 mg (87%). IR (KBr pellets, cmꢀ1): m(N–H)
3423 (s), m(N@N) 1440 (s), m(C@N) 1600 (s), m(BF) 1082 (s).
1H NMR (CDCl3, d): 2.45 (s, 3H, CH3), 4.94 (d, 2H,
indenyl), 5.31 (t, 1H, indenyl), 6.67 (d, 2H, JH–H = 8.62
6. Yield: 81 mg (76%). IR (KBr pellets, cmꢀ1): m(N@N)
1437 (s), m(C@N) 1629 (s), m(P–F) 849 (s).
1H NMR (CDCl3, d): 2.43 (s, 3H, CH3), 3.72 (s, 3H,
CH3), 4.87 (s, 5H, C5H5), 7.00–7.42 (m, 19H, Ph), 7.66–
7.78 (m, 2H, imidazole).
13C {1H} NMR (CDCl3, d): 21.27 (CH3), 34.45
(CH3), 81.42 (C5H5), 123.44, 125.93, 128.56, 129.34,
130.18, 130.89, 132.02, 133.62 (Ph), 135.46, 142.42,
155.84 (imidazole).
31P {1H} NMR (CDCl3, d): 45.31 (s).
Elemental Anal. Calc. for C34H32N4P2F6Ru: C,
52.78; H, 4.17; N, 7.24. Found: C, 52.37; H, 4.44; N,
7.35%.
UV–Vis (CH2Cl2): kmax = 580, 471, 386 nm.
7. Yield: 87 mg (81%). IR (KBr pellets, cmꢀ1): m(N@N)
1440 (s), m(C@N) 1633 (s), m(P–F) 850 (s).
1H NMR (CDCl3, d): 1.39 (t, 3H, JH–H = 5.24 Hz,
CH3), 2.43 (s, 3H, CH3), 4.09–4.14 (m, 2H, CH2), 4.87
(s, 5H, C5H5), 6.98 (d, 2H, JH–H = 8.64 Hz, Ph), 7.13
(d, 2H, JH–H = 8.40 Hz, Ph), 6.98–7.80 (m, 17H, Ph
and imidazole).
13C {1H} NMR (CDCl3, d): 22.67 (CH3), 29.69
(CH3), 54.34 (CH2), 81.53 (C5H5), 122.25, 123.40,
124.07, 128.58, 129.28, 130.14, 130.82, 131.91 (Ph),
132.88, 133.65, 135.41 (imidazole).
31P {1H} NMR (CDCl3, d): 45.20 (s).
Elemental Anal. Calc. for C35H35N4P2F6Ru: C,
53.30; H, 4.47; N, 7.10. Found: C, 53.42; H, 4.07; N,
6.96%.
UV–Vis (CH2Cl2): kmax = 571, 469, 378 nm.

3468
P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
Table 1
Crystal data and structure refinement parameters for complex
2[PF6]CHCl3
Hz, Ph), 6.86–7.43 (m, 21H, Ph), 7.66 (d, 1H, JH–H
4.36 Hz, imidazole), 7.78 (d, 1H, JH–H = 8.08 Hz,
imidazole), 7.80 (b, 1H, NH).
=
13C {1H} NMR (CDCl3, d): 22.15 (CH3), 63.87,
65.26, 88.38 (indenyl), 121.06, 123.52, 124.48, 125.07,
125.72, 126.93, 128.31, 129.43, 130.04, 131.23 (Ph),
133.52, 134.62, 147.83 (imidazole).
Formula
C33H29Cl3F6N4P2Ru
Mr
864.96
T (K)
373 (2)
0.71073
Triclinic
˚
Wavelength (A)
Crystal system
Space group
31P {1H} NMR (CDCl3, d): 50.79 (s).
ꢀ
P1
Elemental Anal. Calc. for C37H32N4PBF4Ru: C,
59.13; H, 4.29; N, 7.45. Found: C, 59.33; H, 4.26; N,
7.31%.
Unit cell dimensions
˚
a (A)
˚
8.9496(8)
b (A)
˚
c (A)
11.7707(11)
16.6002(16)
79.832(2)
UV–Vis (CH2Cl2): kmax = 472, 397, 389 nm.
12. Yield: 82 mg (92%). IR (KBr pellets, cmꢀ1):
m(N@N) 1440 (s), m(C@N) 1626 (s), m(B-F) 1082 (s).
1H NMR (CDCl3, d): 1.29 (t, 3H, JH–H = 4.68 Hz,
CH3), 2.46 (s, 3H, CH3), 4.03 (q, 2H, JH–H = 7.46 Hz,
CH2), 4.94 (d, 2H, JH–H = 4.14 Hz, indenyl), 5.69 (t,
1H, indenyl), 6.59 (d, 2H, JH–H = 8.35 Hz, Ph), 7.14
(d, 2H, JH–H = 8.39 Hz, Ph), 6.79–7.41 (m, 19H, Ph),
7.67 (d, 1H, JH–H = 4.69 Hz, imidazole), 7.77 (d, 1H,
JH–H = 8.42 Hz, imidazole).
a (°)
b (°)
c (°)
82.355(2)
82.0680(10)
1694.2 (3)
4
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
1.696
0.859
l (Mo Ka) (mmꢀ1
F(000)
)
868
2.31 to 28.30
11073
h (°)
Reflections collected
Independent reflections
Completeness to h
Data/restraints/parameters
Goodness-of-fit on F2
R1 (I > 2r(I)), wR2
7974 [R(int) = 0.0159]
28.30 to 94.8
7974/0/443
1.025
13C {1H} NMR (CDCl3, d): 15.37 (CH3), 21.38
(CH3), 43.00 (CH2), 64.57, 65.99, 88.96 (indenyl),
123.01, 123.74, 124.49, 126.14, 127.38, 128.59, 128.97,
129.63, 130.79, 132.47 (Ph), 133.20, 133.81, 142.59
(imidazole).
0.0405, 0.0976
0.0460, 0.1007
+1.322 and ꢀ0.888
R1, R2 (all data)
Largest difference peak and hole (e A
ꢀ3
˚
)
31P {1H} NMR (CDCl3, d): 51.07 (s).
Elemental Anal. Calc. for C39H36N4PBF4Ru: C,
60.08; H, 4.65; N, 7.18. Found: C, 60.15; H, 4.42; N,
7.21%.
as per the ‘‘riding’’ model. Fig. 2 displays the ORTEP [28]
representations of the molecule. Refinement converged
at final R1 values of 0.0405 (for observed data F) for
compound 2.
UV–Vis (CH2Cl2): kmax = 484, 399, 292 nm.
3. Structure analysis and refinement
4. Results and discussion
X-ray quality crystals of the complex 2[PF6] were
grown by slow diffusion of hexane into chloroform solu-
tion. The green crystal of complex 2[PF6] was mounted
on a Bruker Apex CCD diffractometer in a full recipro-
cal sphere equipped with a CCD detector and used for
data collection. X-ray intensity data were collected with
graphite monochromated Mo Ka radiation at 373 (2) K,
with 0.3° x scan mode and 10 s per frame. The intensity
data were corrected for Lorentz and polarization effects.
Absorption correction was done using the SAINT pro-
gram [24]. A summary of the crystal data, data collec-
tion parameters and convergence results is compiled in
Table 1. An empirical absorption correction was made
by modeling a transmission surface by spherical har-
monics, employing equivalent reflections with I > 2r(I)
(program SADABS) [25]. The structure was solved by di-
rect methods [26]. All the non-hydrogen atoms were re-
fined anisotropically using the full-matrix least-squares
technique on F2 using the SHELXL 97 software [27]. All
the hydrogen atoms were found from difference Fourier
synthesis after four cycles of an isotropic refinement and
1-Methyl-2-(arylazo)imidazole (aai-Me), 1-ethyl-2-
(arylazo)imidazole (aai-Et) and 2-(arylazo)imidazole
(aaiH) were synthesized by coupling the aryldiazonium
ions with imidazole in aqueous sodium carbonate solu-
tion (pH 7) and purified by the reported method [22].
The alkylation was carried out by adding alkyl halide
in dry THF solution to the corresponding 2-(arylazo)
imidazole in the presence of sodium hydride [29].
The cyclopentadienyl and indenyl complexes such as
[CpRu(PPh3)2Cl] (1) and [(indenyl)Ru(PPh3)2(MeCN)]+
(8) reacted with arylazoimidazoles (RaaiR0) in the
presence of ammonium salts in methanol to form the
mononuclear cationic cyclo-pentadienyl and indenyl
ruthenium complexes having the general formula
[Cp0Ru(PPh3)(RaaiR0)]+ (Cp0 = cyclopentadienyl, inde-
nyl) (Scheme 1). The cationic complexes 2–7 are brown-
ish-green, while the complexes 9–12 are brown in color.
These complexes are non-hygroscopic, air-stable, shiny
crystalline solids. They are sparingly soluble in methanol
and benzene; soluble in dichloromethane, chloroform,

P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
3469
Scheme 1.
acetone, acetonitrile, and insoluble in hexane, petroleum
ether and diethyl ether.
around 155 ppm may be due to the azoimine (C@N) car-
bon of the ligand. The spectra also show resonance in
the range of 122.25–142.42 ppm for the aromatic car-
bons and carbons of imidazole C–H group. The 31P
{1H} NMR of the complexes display a singlet at around
45 ppm due to the triphenylphosphine moiety as com-
pared to 42 ppm observed in the neutral precursor com-
plex [CpRu(PPh3)2Cl]. This downfield shift relative to
the complex 1 indicates the cationic nature of these com-
plexes. In all these complexes, 31P nuclei exhibit a down-
field shift as compared with those in the complex 1. The
31P nuclei of the counter ion PFꢀ6 appear as a septet
around 145 (ppm) in the above complexes.
4.1. Cyclopentadienyl-ruthenium complexes
The analytical data of these complexes are consistent
with our formulations. The infrared spectra of the com-
plexes 2–7 exhibit a chelated azoimine group as strong
bands at 1437–1447 cmꢀ1 and 1626–1633 cmꢀ1 corre-
sponding to m(N@N) and m(C@N), respectively [19,20]. In
addition, the IR spectra contain a strong band at 850
cmꢀ1 due to the mP–F of the PF6 group. The proton
NMR spectra of these complexes (2–7) exhibit a singlet
at 4.62–4.89 ppm for the cyclopentadienyl ring protons,
indicating a downfield shift from the starting complex 1.
Downfield shift in the position of the cyclopentadienyl
protons might result from a change in electron density
on the metal center due to chelation of the arylazo-imid-
azole ligand through its nitrogen atoms. The N–methyl
(N–Me) protons of the complexes 3 and 6 appear as
singlets at 3.74 and 3.72 ppm, respectively. The N–meth-
ylene (N–CH2–) protons of the complexes 4 and 7 ap-
pear as triplets at 1.41 ppm (JH–H = 7.32 Hz) and 1.39
ppm (JH–H = 5.24 Hz), respectively. The imidazole 4H
and 5H protons appear at 7.78–7.95 and 7.65–7.77
ppm, respectively. All these complexes show a multiplet
in the range of 6.98–7.80 ppm due to the phenyl protons
of the triphenylphosphine moiety and the aryl group of
the azoimine ligands.
4.2. Indenyl-ruthenium complexes
The reaction of the complex 8 with ligands RaaiR0
in methanol yielded brown colored and air-stable cat-
ionic azoimine complexes of the type 9–12 (Scheme 1)
by substitution of one of the triphenylphosphine and
acetonitrile ligands. The IR spectra of these complexes
show a strong band in the range of 3436 and 3426
cmꢀ1 due to the m(N–H) mode for complexes 9 and
11. In addition, the IR spectra contain strong bands
at ꢁ1440 and ꢁ1600 cmꢀ1, corresponding to the
m(N@N) and m(C@N) modes of the azoimine ligands
[30], and a strong band 1082 cmꢀ1 due to the m(B–F)
mode of the BF4 group.
The 1H NMR spectra of the complexes 9–12 display a
doublet at around 4.95 ppm and a triplet at 5.34–5.70
ppm for the cyclopentadienyl ring protons of the indenyl
group. The CH group of imidazole appears as a doublet
The 13C {1H} NMR spectrum of the complexes (2–7)
contain resonances for the cyclopentadienyl ring car-
bons at around 81 ppm. The resonance observed at

3470
P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
in the range of 7.64–7.83 ppm. The NH protons of the
complexes 9 and 11 exhibit a strong peak at ꢁ8.0
ppm. All these complexes also show multiplets in the
range of 6.54–7.48 ppm due to the phenyl protons of
the triphenylphosphine moiety, the arene ring of the
indenyl group and the aryl group of the azoimine li-
gands. The 13C {1H} NMR spectrum also exhibits
appropriate signals. The carbon attached to nitrogen
(N1, see Chart 1) in the ligand (in the case of complexes
10 and 12) exhibits signals around 31 and 43 ppm for the
N–methyl and N–CH2 groups, respectively. The methyl
carbon of the N-ethyl group (N–CH2–CH3) of complex
12 exhibits a signal at 15.37 ppm. The cyclopentadienyl
carbons of indenyl group appear around 62–89 ppm,
while the imidazole carbons appear in the range between
133 and 156 ppm. The carbons of arene group are thus
similar to those in other similar reported compounds
[30]. The 31P spectra of these complexes exhibit sharp
resonance in the range of 50.77–51.07 ppm due to the
triphenylphosphine moiety as compared to 46.5 ppm
observed in the neutral complex [(g5-C9H7)Ru-
(PPh3)2Cl] [23b]. This downfield chemical shift indicates
the cationic nature of these complexes following substi-
tution of one chloride ion and one triphenylphosphine
unit by the ligands.
electron donating group (H, CH3, and C2H5) in the
imidazole nitrogen of the azoimine ligand should
increase the energy of transition causing a red shift
in the MLCT maxima [31], while an electron with-
drawing group should decrease the transition energy.
The electronic spectra of cyclopentadienyl-ruthe-
nium(II) azoimine complexes (2–7) with the formula-
tions [(g5-C5H5)Ru(PPh3)(RaaiR0)]+ displayed very
weak bands at 560–584 nm, a medium absorption
band at ꢁ460 nm and a very strong absorption band
at ꢁ360 nm (Fig. 1). The band at 460 nm has been
assigned to a MLCT transition [t2g {Ru(II) ! p*
(azoimine)}]. The kmax values of this band is consistent
with those of the azoimine ligand bound to the
complexes of ruthenium(II) [32].
The free ligand itself shows intraligand charge-trans-
fer transitions (n–p*, p–p*) of high intensity (e ꢁ 104–
105 Mꢀ1 cmꢀ1) at <400 nm. The transitions at ꢁ380
nm and below are thus not considered further. Other
two transitions at longer wavelength region (460–480
and 560–580 nm) differ in their intensities. The first tran-
sition (460–480 nm) is of moderate intensity and has
been assigned to the MLCT band (dp(Ru) ! p* (azoi-
mine)) in the complexes [17] or else from the hybrid
orbitals composed of dp(Ru) and p (Cp/indenyl) to the
p* (azoimine) orbital of the ligand. The weak transition
at 560–580 nm may originate from a singlet–triplet tran-
sition, particularly that allowed by the strong spin–orbit
coupling in ruthenium [33], Because of better delocaliza-
tion in the indenyl ring the CT bands are shifted to longer
wavelength compared to cyclopentadienyl complexes.
Electronic spectra of indenyl complexes (9–12) dis-
play bands in the region 475–489, ꢁ395 and ꢁ350 nm.
The broad medium intensity bands centering around
480 nm are assigned to MLCT bands arising from drift
4.3. Electronic spectra
The interaction of the filled dp (t2g) orbitals on
ruthenium(II) with low lying p* orbitals on the azoi-
mine ligands should provide a metal-to-ligand charge
transfer (MLCT) transition (t2g–p*) in the electronic
spectra of these complexes [5,8,17], where the transi-
tion energy of these bands varies with the nature of
the ligands acting as p-acceptors. The presence of an
Fig. 1. Electronic spectra have taken in dichloromethane. Key: 1, represents complex [(g5-C5H5)Ru(PPh3)(Phai-H)]+ (3); 2, represents complex [(g5-
C5H5)Ru(PPh3)(Tai-Me)]+ (6); 3, represents complex [(g5-C5H5)Ru(PPh3)(Phai-Et)]+ (4) and 4, represents complex [(g5-C9H7)Ru(PPh3)(Phai-Me)]+
(10).

P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
3471
Table 2
of electron density from the filled Ru(II) ! dp(t2g) orbi-
5
˚
tals to the low lying p* orbitals of the RaaiR0 ligand.
The position of this band is consistent with those in
other metal–azo complexes [34]. The band around 350
nm is assigned to an MLCT transition [Ru(II) ! d*
on the cyclopentadienyl ring].
Selected bond lengths (A) and bond angles (°) for [(g -C5H5)-
Ru(PPh3)(C6H5–N@N–C3H3N2)]PF6 Æ CHCl3 (2)
˚
Bond lengths (A)
Ru(1)–C(25)
Ru(1)–C(28)
Ru(1)–N(4)
N(1)–C(30)
P(1)–C(7)
2.189(3)
2.223(3)
2.047(2)
1.337(3)
1.833(3)
2.21
Ru(1)–Ca
5. Molecular structure
Ru(1)–C(26)
Ru(1)–C(29)
Ru(1)–P(1)
N(1)–C(32)
P(1)–C(1)
2.206(3)
2.212(3)
2.3291(7)
1.375(3)
1.828(3)
2.220(3)
2.051(2)
1.307(3)
1.436(3)
1.834(3)
A summary of the single-crystal X-ray structure anal-
ysis is shown in Table 1. The ORTEP drawing of the com-
pound 2 is shown in Fig. 2, with selected bond lengths
and bond angles given in Table 2. The geometry around
the ruthenium atom in the complex is octahedral, where
the cyclopentadienyl ligand occupies three coordination
positions.
Ru(1)–C(27)
Ru(1)–N(1)
N(4)–N(3)
N(4)–C(19)
P(1)–C(13)
The complex crystallizes in the triclinic space group
5
Bond angles (°)
P(1)–Ru(1)–N(1)
N(1)–Ru(1)–N(4)
P(1)–Ru(1)–N(4)
ꢀ
P1. The structure of the compound [(g -C5H5)Ru-
94.06(7)
74.99(10)
91.16(6)
(PPh3)(C6H5–N@N–C3H3N2)]PF6 Æ CHCl3 (2) consists
of a ruthenium atom g5-coordinated to a cyclopen-
tadienyl molecule, to the two nitrogen atoms of the
Phaai-H group, and to a triphenylphosphine ligand
through the P atom, leading to a ꢀthree-legged piano
stoolꢁ type structure. The Phaai-H moiety acts as a che-
lating ligand to the ruthenium center in this complex.
a
Ruthenium to average distance of Cp.
N(1) and N(1)–Ru(1)–P(1) are 91.16(6)°, 74.99(10)°
and 94.06(7)°, respectively, indicating a piano stool type
of structure around the ruthenium center. The N@N
bond distance N(3)–N(4) is 1.307(3) A, which is longer
˚
than the value for the free ligand (1.250 (1) A) [37]. This
˚
˚
The two Ru–N distances 2.051(2) and 2.047(2) A are
slightly different, as found in related structures involving
˚
phosphine complexes (2.177(2) A) [20d,21b,35]. The
˚
average Ru–C (cyclopentadienyl) distance is 2.21 A.
˚
The Ru–P bond distance of 2.3291(7) A is similar to
refers to significant charge delocalization from the metal
d-orbital, namely, the dp(Ru) ! p*(azo) transition in
the coordinated Phaai-H.
those in ruthenium–phosphorus complexes reported ear-
lier [19c,d,36]. The cyclopentadienyl ring is nearly planar
and shows C–C bond distances that appear to be nor-
mal. The bond angles N(4)–Ru(1)–P(1), N(4)–Ru(1)–
6. Concluding remarks
We have prepared new g5-cyclopentadienyl and
g5-indenyl ruthenium(II) complexes containing arylazo-
imidazole (RaaiR0) ligands. The complex [(g5-C5H5)-
Ru(PPh3)2Cl] with arylazoimidazole (RaaiR0) in the
presence of methanol gave complexes of the type
[(g5-C5H5)Ru(PPh3)(RaaiR0)]+. The indenyl-ruthenium
chloro complex [(g5-C9H7)Ru (PPh3)2Cl] with arylazo-
imidazole ligands in the presence of methanol under
refluxing conditions gave rise to a product without the
organic fragment, while the indenyl-ruthenium acetoni-
trile complex [(g5-C9H7)Ru(PPh3)(NCCH3)]+ under
similar conditions gave rise to complexes of the type
[(g5-C9H7)Ru(PPh3)(RaaiR0)]+ due to the labile nature
of the acetonitrile group.
Acknowledgments
K.M.R. and P. G. thank Professor R. H. Duncan
Lyngdoh for his help in preparing the manuscript, and
the Sophisticated Instruments Facility (SIF), Indian
Fig. 2. ORTEP drawing of compound 2. Hydrogen atoms, PF6 and
CHCl3 omitted for clarity.

3472
P. Govindaswamy et al. / Journal of Organometallic Chemistry 690 (2005) 3465–3473
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of Chemistry, Indian Institute of Technology, Kanpur
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Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre (CCDC), CCDC No. 263827 for complex 2.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK, fax: +44 1223 336 033,
e-mail: deposit@ccdc.cam.ac.uk or on the web www:
http://www.ccdc.cam.ac.uk. Supplementary data associ-
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