Study of novel η5-cyclopentadienyl and η6-arene platinum group metal complexes containing a N4-type ligand and their structural characterization

Article abstract of DOI:10.1016/j.poly.2008.12.050

The mononuclear η⁵-cyclopentadienyl complexes [(η⁵-C₅H₅)Ru(PPh₃)₂Cl], [(η⁵-C₅H₅)Os(PPh₃)₂Br] and pentamethylcyclopentadienyl complex [

Full text of DOI:10.1016/j.poly.2008.12.050

Polyhedron 28 (2009) 844–850
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Study of novel
g g
5-cyclopentadienyl and 6-arene platinum group metal
complexes containing a N4-type ligand and their structural characterization
Gajendra Gupta a, Glenn P.A. Yap b, Bruno Therrien c, Kollipara Mohan Rao a,
*
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Brown Laboratory, Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
c Service Analytique Facultaire, Université de Neuchâtel, Case Postale 158, CH-2009, Neuchâtel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
The mononuclear
pentamethylcyclopentadienyl complex [(
tetradentate N,N0-chelating ligand 3,5-bis(2-pyridyl)pyrazole (bpp-H) and 1 eq. of NH4PF6 in methanol
to afford the mononuclear complexes [(
5-C5H5)Ru(PPh3)(bpp-H)]PF6 ([1]PF6), [( 5-C5H5)Os(PPh3)(bpp-
H)]PF6 ([2]PF6) and [(
5-C5Me5)Ru(PPh3)(bpp-H)]PF6 ([3]PF6), respectively. The dinuclear 5-pentam-
ethylcyclopentadienyl complexes [( -Cl)Cl]2 and [( -Cl)Cl]2 as well as the
5-C5Me5)Rh( 5-C5Me5)Ir(
dinuclear -Cl)Cl]2 and [( -Cl)Cl]2
6-arene ruthenium complexes [( 6-C6H6)Ru( 6-p-iPrC6H4Me)Ru(
react with 2 eq. of bpp-H in the presence of NH4PF6 or NH4BF4 to afford the corresponding mononuclear
complexes [(
5-C5Me5)Rh(bpp-H)Cl]PF6 ([4]PF6), [( 5-C5Me5)Ir(bpp-H)Cl]PF6 ([5]PF6), [( 6-C6H6)-
Ru(bpp-H)Cl]BF4 ([6]BF4) and [(
6-p-iPrC6H4Me)Ru(bpp-H)Cl]BF4 ([7]BF4). However, in the presence
of 1 eq. of bpp-H and NH4BF4 the reaction with the same
6-arene ruthenium complexes affords the
dinuclear salts [(
6-C6H6)2Ru2(bpp)Cl2]BF4 ([8]BF4) and [( 6-p-iPrC6H4Me)2Ru2(bpp)Cl2]BF4 ([9]BF4),
g
5-cyclopentadienyl complexes [(
g g
5-C5H5)Ru(PPh3)2Cl], [( 5-C5H5)Os(PPh3)2Br] and
g
5-C5Me5)Ru(PPh3)2Cl] react in the presence of 1 eq. of the
Received 4 November 2008
Accepted 18 December 2008
Available online 3 February 2009
g
g
g
g
Keywords:
Arene
Cyclopentadienyl
Ruthenium
Rhodium
g
l
g
l
g
g
l
g
l
g
g
g
g
Iridium
3,5-Bis(2-pyridyl)pyrazole
g
g
g
respectively. These compounds have been characterized by IR, NMR and mass spectrometry, as well
as by elemental analysis. The molecular structures of [1]PF6, [5]PF6 and [8]BF4 have been established
by single crystal X-ray diffraction studies and some representative complexes have been studied by
UV–vis spectroscopy.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
occurrence of isomers by the synthetic assembly of mononuclear
building blocks is a major problem in the design of supramolecular
systems.
Half-sandwich complexes have proved to be extremely useful in
Within the large family of
g
5- and
g
6-cyclichydrocarbon metal
complexes, piano–stool complexes of ruthenium are undeniably
the most studied class of complexes. They have found applications
in catalysis, supramolecular assemblies and molecular devices, and
have shown antiviral, antibiotic and anticancer activities. These
three-legged piano–stool complexes possess a pseudo-octahedral
geometry at the metal center, the arene ligand occupying three
coordinating sites (the seat) with three other ligands (the legs).
Therefore, the octahedral geometry can be viewed as pseudo-tetra-
hedral, thus limiting the number of possible isomers.
Transition metal complexes containing polypyridyl ligands are
associated with interesting photochemical and electrochemical
properties [1–8], and they are used as catalysts [9,10], multi-elec-
tron storage systems [11–13], in the design of new materials
[14–17] and as molecular devices [18–22]. Complexes with these
ligands are also potential DNA intercalators with an ability to inhi-
bit nucleic acid synthesis [23]. Recently, metal polypyridyl com-
plexes have been widely used as building blocks [24–27]. The
stoichiometric and catalytic asymmetric syntheses, and therefore,
have attracted lot of attention [28–31]. In addition, the four coor-
dinated, pseudo-tetrahedral geometry makes them particularly
suitable for investigation of the stereochemistry of reactions at
the metal center [32]. Many studies of cyclopentadienyl and arene
ruthenium(II) complexes with bidentate ligands have shown that
substitution reactions occur predominantly with retention of the
configuration at the metal center [33]. A few studies have been car-
ried out on pentamethylcyclopentadienyl rhodium(III) and irid-
ium(III) complexes with polypyridyl ligands [34]. The reactivity
of ruthenium(II), osmium(II), rhodium(III) and iridium(III) with
various polypyridyl ligands has been reported [35–37].
In this paper, we report a series of
nium, osmium,
5-pentamethylcyclopentadienyl ruthenium, rho-
dium and iridium and
6-arene ruthenium complexes with a
g
5-cyclopentadienyl ruthe-
g
g
tetradentate N,N0-donor ligand, viz. 3,5-bis(2-pyridyl)pyrazole
(bpp-H) (see below). The 3,5-bis(2-pyridyl)pyrazole (bpp-H) ruthe-
nium metal complexes are associated with being an extremely
interesting water oxidation catalyst [38,39]. This ligand can act as
* Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 255 0486.
E-mail address: mohanrao59@hotmail.com (K. Mohan Rao).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.12.050

G. Gupta et al. / Polyhedron 28 (2009) 844–850
845
a bidentate as well as tetradentate ligand depending on the ratio of
metal-to-ligand used. The molecular structures of representative
compounds are reported as well.
into a dichloromethane solution of [1]PF6, and [5]PF6, respectively.
Whereas in the case of compound [8]BF4, crystals were grown by
slow diffusion of wet diethylether into an acetonitrile solution of
[8]BF4. A bright red crystal of [1]PF6 ꢀ H2O and a pale green crystal
of [5]PF6 were mounted on a Stoe-Image Plate Diffraction System
equipped with a / circle goniometer, using Mo Ka graphite mono-
chromated radiation (k = 0.71073 Å) with the / range 0–200°,
increment of 1.2°, Dmax ꢁ Dmin = 12.45–0.81 Å. Whereas a crystal
of [8]BF4 ꢀ H2O was mounted on a Bruker Apex CCD diffractometer
in the full reciprocal sphere equipped with a CCD detector, X-ray
N
N
N
N
H
intensity data were collected with Mo Ka graphite monochromated
radiation at 120 (2) K, with a 0.3° scan mode and 10 s per frame.
x
Ligand used in this study
The intensity data were corrected for Lorenz and polarization
effects. The structures were solved by direct methods using the
program SHELXS-97 [51]. Refinement and all further calculations
were carried out using SHELXL-97 [52]. The H-atoms were included
in calculated positions and were treated as riding atoms using
the SHELXL default parameters. The non-H atoms were refined aniso-
tropically, using weighted full-matrix least-squares on F2. The data
collection parameters and bond lengths and angles are presented
in Tables 1 and 2, respectively.
2. Experimental
2.1. Physical measurements
Elemental analyses were 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. The 1H NMR spectra were recorded on a Bruker ACF-400
(400 MHz) spectrometer in CDCl3 solvent with TMS as the internal
reference. All chemicals used were of reagent grade. All reactions
were carried out in distilled and dried solvents. Ruthenium trichlo-
ride trihydrate, iridium trichloride, rhodium trichloride and os-
mium tetraoxide (OsO4) were purchased from Arora Matthey Ltd.
The 3,5-bis(2-pyridyl)pyrazole (bpp-H) was prepared by following
2.3. Preparation of [(g
5-C5H5)M(bpp-H)(PPh3)]PF6 {M = Ru [1]PF6,
Os [2]PF6}
A mixture of [(g
5-C5H5)M(PPh3)2X] {M = Ru, X = Cl and M = Os,
X = Br} (100 mg, 0.11 mmol), 3,5-bis(2-pyridyl)pyrazole (bpp-H)
(50 mg, 0.22 mmol) and NH4PF6 (36 mg, 0.22 mmol) in dry metha-
nol (15 ml) were refluxed under dry nitrogen for 8 h until the color
of the solution changed from pale yellow to orange. The solvent
was removed under vacuum, the residue was dissolved in dichloro-
methane (10 ml) and the solution was filtered to remove ammo-
nium halide. The orange solution was concentrated to 5 ml, and
upon addition of diethylether the orange–yellow complex precipi-
tated, which was separated and dried under vacuum.
a literature procedure [40,41]. The precursor complexes [(g5
C5H5)Ru(PPh3)2Cl] [33,42,43], [(
5-C5H5)Os(PPh3)2Br] [44,45],
[( -Cl)Cl]2, [(
5-C5Me5)Ir( 5-C5Me5)Rh( -Cl)Cl]2 [46], [(g5
C5Me5)Ru(PPh3)2Cl] [47], [( -Cl)Cl]2 and [(
6-C6H6)Ru( 6-p-
iPrC6H4Me)Ru(
-Cl)Cl]2 [48–50], were prepared by following the
-
g
g
l
g
l
l
-
g
g
l
reported literature methods.
Complex [(g
5-C5H5)Ru(bpp-H)(PPh3)]PF6 [1]PF6: Yield: 75 mg,
2.2. Single-crystal X-ray structure analyses
68.4%. Elemental Anal. Calc. for C36H30N4P2F6Ru: C, 54.3; H, 3.7;
N, 7.1. Found: C, 54.87; H, 4.13; N, 7.94%. IR (KBr pellets, cmꢁ1):
Crystals suitable for X-ray diffraction studies for compounds
[1]PF6 and [5]PF6 were grown by slow diffusion of wet diethylether
3429 (
m
N–H); 1460 (
m
C@N); 850 (
m
P–F). 1H NMR (CDCl3, d): 9.31 (d,
Table 1
Crystallographic and structure refinement parameters for complexes [1]PF6 ꢀ H2O, [5]PF6 and [8]BF4 ꢀ H2O.
[1]PF6
[5]PF6 ꢀ H2O
[8]BF4 ꢀ H2O
Chemical formula
Formula weight
C36H30F6N4P2Ru
795.65
C23H27ClF6IrN4OP
748.11
C25H23BCl2F4N4ORu2
755.32
Crystal system
Space group
Crystal color and shape
monoclinic
P21/n (no. 14)
green block
0.32 ꢂ 0.20 ꢂ 0.20
13.663(1)
14.426(1)
17.172(1)
104.284(8)
3280.1(4)
4
monoclinic
Pc (no. 7)
red block
0.25 ꢂ 0.24 ꢂ 0.21
8.760(1)
13.903(2)
13.706(2)
129.18(1)
1293.8(3)
2
monoclinic
P21/c (no. 14)
orange plate
0.22 ꢂ 0.13 ꢂ 0.04
14.229(7)
11.265(6)
16.008(8)
95.750(5)
2553(2)
Crystal size
a (Å)
b (Å)
c (Å)
b (o)
V (Å3)
Z
4
T (K)
173(2)
1.611
0.644
2.09 < h < 26.00
6310
173(2)
1.920
5.393
2.41 < h < 26.02
4670
120(2)
1.965
1.451
2.21 < h < 28.21
5885
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
Scan range (o)
Unique reflections
Reflections used [I > 2
Rint
r
(I)]
5334
0.0542
3109
0.1067
5452
0.0230
Flack parameter
ꢁ0.06(3)
Final R indices [I > 2
R indices (all data)
Goodness-of-fit
r
(I)]ꢃ
0.0324, wR2 0.0854
0.0414, wR2 0.0940
1.008
0.662, ꢁ1.640
0.0715, wR2 0.1780
0.0942, wR2 0.1872
0.932
0.0252, wR2 0.0622
0.0282, wR2 0.0647
1.026
0.758, ꢁ0.415
Max., min.
D
q
/e (Åꢁ3
)
4.068, ꢁ4.524
ꢃ
2
Structures were refined on F02: wR2 = [
R
[w(F0 ꢁ Fc2)2]/
R R
w(F02)2]1/2, where wꢁ1 = [ (F02) + (aP)2 + bP] and P = [max(F02,0) + 2Fc2]/3.

846
G. Gupta et al. / Polyhedron 28 (2009) 844–850
Table 2
dichloromethane (5 ml), and the solution filtered to remove
ammonium chloride. The pale green solution was concentrated
to 2 ml, when addition of excess hexane gave the orange–yellow
complex, which was separated and dried under vacuum.
Selected bond lengths and angles for complexes [1]PF6, [5]PF6 ꢀ H2O and [8]BF4 ꢀ H2O.
Distances (Å)
[1]PF6
[5]PF6 ꢀ H2O
[8]BF4 ꢀ H2O
N(1)–M(1)
N(2)–M(1)
Cl(1)–M(1)
N(2)–N(3)
M(1)–CNT(1)
N(3)–M(2)
N(4)–M(2)
Cl(2)–M(2)
M(2)–CNT(2)
2.188(2)
2.085(2)
2.07(8)
2.01(5)
2.398(17)
1.37(8)
1.786
2.103(2)
2.096(2)
2.403(13)
1.350(3)
1.685
2.090(2)
2.090(2)
2.4339(14)
1.681
Complex [4]PF6: Yield: 70 mg, 76%. Elemental Anal. Calc. for
C23H25N4PClF6Rh: C, 37.8; H, 3.4; N, 7.7. Found: C, 38.0; H, 3.9; N,
7.0%. IR (KBr pellets, cmꢁ1): 3426 (
mN–H); 1612 (mC@N); 850 (mP–F).
1.342(3)
1.830
1H NMR (CDCl3, d): 11.80 (s, 1H); 8.9 (d, 1H); 8.6 (d, 1H); 8.2 (td,
1H); 8.0 (s,1H); 7.5 (t, 2H); 7.4 (t, 1H); 7.2 (t, 2H); 1.48 (s, 15H).
ESI-MS (m/z): 494.2 [MꢁPF6], 459.2 [MꢁPF6ꢁCl]. UV–vis [(CH3CN;
kmax, nm (e
, Mꢁ1 cmꢁ1)]: 308 (26000).
Complex [5]PF6: Yield: 68 mg, 74.1%. Elemental Anal. Calc. for
Angles (°)
N(3)–N(2)–M(1)
N(2)–M(1)–N(1)
N(2)–M(1)–Cl(1)
N(1)–M(1)–Cl(1)
N(2)–N(3)–M(2)
N(3)–M(2)–N(4)
N(4)–M(2)–Cl(2)
N(3)–Ru(2)–Cl(2)
135.60(15)
75.75(8)
135(4)
77(2)
83.1(15)
87.9(15)
135.49(14)
76.63(8)
87.4
C23H25N4ClPF6Ir: C, 43.1; H, 3.9; N, 8.7. Found: C, 43.6; H, 4.2; N,
8.0%. IR (KBr pellets, cmꢁ1): 3429 (
mN–H); 1613 (mC@N); 850 (mP–F).
1H NMR (CDCl3, d): 11.86 (s,1H); 8.75 (d,1H); 8.58 (d, 1H); 8.45
(td, 1H); 8.24 (s, 1H); 7.5 (t, 2H); 7.4 (t, 2H); 7.2 (t, 1H); 1.45 (s,
15H). ESI-MS (m/z): 583.2 [MꢁPF6], 548.2 [MꢁPF6ꢁCl].
87.1
136.49(15)
76.83(8)
82.77(6)
87.43(5)
2.6. Preparation of [(
g
6-C6H6)Ru(bpp-H)Cl]BF4 [6]BF4
A mixture of [(
g
6-C6H6)Ru(
l-Cl)Cl]2 (50 mg, 0.1 mmol), 3,5-
1H); 8.55 (d, 1H); 8.06 (s, 1H); 7.8 (td, 1H); 7.75 (d, 2H); 7.62 (m,
2H); 7.45 (m, 2H); 4.75 (s, 5H, C5H5); 7.32–7.2 (m, 15H, PPh3).
31P {1H} NMR (CDCl3, d): 50.83 (s, PPh3). ESI-MS (m/z): 651.1
[MꢁPF6], 650.1 [MꢁPF6ꢁH], 389.0 [MꢁPF6ꢁPPh3]. UV–vis
bis(2-pyridyl)pyrazole (bpp-H) (88 mg, 0.395 mmol) and NH4BF4
(52 mg, 0.496 mmol) was stirred in dry methanol (15 ml) for 4 h
at room temperature. The solvent was rotary evaporated. The solid
was dissolved in dichloromethane and then filtered to remove
ammonium chloride. The solution was concentrated to 2 ml and
excess of diethylether was added for precipitation. The light brown
color product was separated out, washed with ether and dried in
vacuum. Yield: 70 mg, 67.3%. Elemental Anal. Calc. for
C19H16N4BClF4Ru: C, 42.75; H, 4.91; N, 10.50. Found: C, 42.6; H,
[(CH3CN; kmax, nm (
Complex [(
e
, Mꢁ1 cmꢁ1)]: 329 (24000).
g
5-C5H5)Os(bpp-H)(PPh3)]PF6 [2]PF6: Yield: 65 mg,
66.7%. Elemental Anal. Calc. for C36H30N4P2F6Os: C, 48.9; H, 3.4;
N, 6.3. Found: C, 49.2; H, 3.91; N, 6.87%. IR (KBr pellets, cmꢁ1):
3425 (mN–H); 1474 (mC@N); 850 (m
P–F). 1H NMR (CDCl3, d): 9.2 (d,
5.0; N, 10.41%. IR (KBr pellets, cmꢁ1): 3416 (
1082 (
B–F). 1H NMR (CDCl3, d): 9.2 (d, 1H), 8.79 (d, 1H), 8.65 (s,
mN–H); 1613 (mC@N);
1H); 8.55 (d, 1H); 8.45 (s, 1H); 7.81 (td, 1H); 7.78 (d, 1H); 7.7 (m,
2H); 7.38 (m, 1H); 6.9 (t, 2H); 4.69 (s, 5H, C5H5); 7.3–7.25 (m,
15H, PPh3). ESI-MS (m/z): 740.3 [MꢁPF6], 739.2 [MꢁPF6ꢁH],
478.3 [MꢁPF6ꢁPPh3].
m
1H), 7.98 (t, 2H), 7.84 (d, 2H), 7.45 (m, 2H), 7.38 (m, 1H), 6.25 (s,
6H). ESI-MS (m/z): 437 [MꢁBF4], 435.9 [MꢁBF4ꢁH]. UV–vis
[(CH3CN; kmax, nm (e
, Mꢁ1 cmꢁ1)]: 318 (14000).
2.4. Preparation of [(
g
5-C5Me5)Ru(bpp-H)(PPh3)]PF6 [3]PF6
2.7. Preparation of [(
g
6-p-iPrC6H4Me)Ru(bpp-H)Cl]BF4 [7]BF4
A mixture of [(
g
5-C5Me5)Ru(PPh3)2Cl] (100 mg, 0.125 mmol),
6-C10H14)Ru(
l
-Cl)Cl]2 (100 mg, 0.163 mmol),
3,5-bis(2-pyridyl)pyrazole (bpp-H) (56 mg, 0.25 mmol) and
NH4PF6 (40 mg, 0.25 mmol) in dry methanol (15 ml) were refluxed
under dry nitrogen for 12 h until the color of the solution changed
from pale yellow to orange. The solvent were removed in a rotary
evaporator under reduced pressure, the residue was dissolved in
dichloromethane (10 ml), and the solution filtered to remove
ammonium chloride. The orange solution was concentrated to
5 ml, when addition of excess hexane gave the orange–yellow
complex, which was separated and dried under vacuum. Yield:
70 mg, 64.3%. Elemental Anal. Calc. for C41H45N4P2F6Ru: C, 56.6;
H, 5.2; N, 6.4. Found: C, 57.0; H, 5.9; N, 6.8%. IR (KBr pellets,
A mixture of [(
g
3,5-bis(2-pyridyl) pyrazole (bpp-H) (144 mg, 0.65 mmol) and
NH4BF4 (85 mg, 0.81 mmol) was stirred in dry methanol (15 ml)
for 4 h at room temperature. The yellow compound which formed
was filtered, washed with ethanol and diethylether, and dried un-
der vacuum. Yield: 140 mg, 74%. Elemental Anal. Calc. for
C23H24N4BClF4Ru: C, 47.65; H, 4.17; N, 9.66. Found: C, 47.5; H,
4.1; N, 9.61%. IR (KBr pellets, cmꢁ1): 3416 (
1082 (
B–F). 1H NMR (CDCl3, d): 9.2 (d, 1H), 8.64 (d, 1H), 8.53 (d,
mN–H); 1613 (mC@N);
m
1H), 7.95 (t, 2H), 7.84 (d, 2H), 7.8 (m, 2H), 7.36 (t, 1H), 6.51 (d,
1H, Arp–cy), 6.1 (d, 1H, Arp–cy), 5.88 (d, 1H, Arp–cy), 5.78 (d, 1H, Arp–cy),
2.63 (sep, 1H), 2.32 (s, 3H), 1.03 (d, 6H). ESI-MS (m/z): 492.1
[MꢁBF4], 491.1 [MꢁBF4ꢁH], 457.1[MꢁBF4ꢁCl]. UV–vis [(CH3CN;
cmꢁ1): 3424( P–F). 1H NMR (CDCl3, d):
mN–H); 1613 (mC@N); 850 (m
11.92 (s,1H); 8.7 (d, 1H); 8.5 (s, 1H); 7.8 (td, 1H); 7.6 (d, 1H);
7.28 (t, 2H); 7.1 (m, 1H); 6.89 (t, 2H); 1.45 (s, 15H); 7.33–7.18
(m, 15H, PPh3). 31P {1H} NMR (CDCl3, d): 49.72 (s, PPh3). ESI-MS
kmax, nm (
2.8. Preparation of [(
A mixture of [(
e
, Mꢁ1 cmꢁ1)]: 430 (10000).
6-C6H6)2Ru2(bpp)Cl2]BF4 [8]BF4
(m/z): 722.3 [MꢁPF6], 460.3 [MꢁPF6ꢁPPh3]. UV–vis [(CH3CN; kmax
,
g
nm (
e
, Mꢁ1 cmꢁ1)]: 358 (17000).
g
6-C6H6)Ru(
l-Cl)Cl]2 (50 mg, 0.10 mmol), 3,5-
2.5. Preparation of [(g
5-C5Me5)M(bpp-H)Cl]PF6 {M = Rh [4]PF6,
Ir [5]PF6}
bis(2-pyridyl)pyrazole (bpp-H) (22 mg, 0.10 mmol) and NH4BF4
(51 mg, 0.49 mmol) was stirred in dry methanol (15 ml) for 4 h
at room temperature. The brown compound which formed was fil-
tered, washed with methanol and diethylether, and dried under
vacuum. Yield: 50 mg, 67.9%. Elemental Anal. Calc. for
C25H23N4BCl2F4ORu2: C, 39.75; H, 3.07; N, 7.42. Found: C, 39.6; H,
A
mixture of [(g l-Cl)Cl]2 (M = Rh, Ir) (Rh di-
5-C5Me5)M(
mer = 100 mg, 0.16 mmol and Ir dimer = 125 mg, 0.16 mmol), 3,5-
bis(2-pyridyl)pyrazole (bpp-H) (70 mg, 0.325 mmol) and NH4PF6
(50 mg, 0.325 mmol) in dry methanol (15 ml) were stirred at room
temperature for 6 h until the color of the solution changed from
pale yellow to pale green. The solvents were removed in a rotary
evaporator under reduced pressure, the residue was dissolved in
3.0; N, 7.38%. IR (KBr pellets, cmꢁ1): 3416 (
1082 (
B–F). 1H NMR (CDCl3, d): 8.91 (d, 1H), 8.5 (d, 1H), 8.35 (t,
mN–H); 1613 (mC@N);
m
2H), 8.12 (s, 1H), 7.92 (m, 2H), 7.7 (d, 1H), 7.55 (d, 1H), 6.35 (s,
6H), 6.1 (s, 6H). ESI-MS (m/z): 650.9 [MꢁBF4], 649.9 [MꢁBF4ꢁH].

G. Gupta et al. / Polyhedron 28 (2009) 844–850
847
UV–vis [(CH3CN; kmax, nm (
(3000).
e
, Mꢁ1 cmꢁ1)]: 328 (18000), 424
downfield
C5H5)Ru(PPh3)2Cl] and [(
shift
from
the
starting
complexes
[(g5
-
g
5-C5H5)Os(PPh3)2Br] [42,45]. The down-
field shift in the position of the cyclopentadienyl protons might re-
sult from a change in the electron density on the metal center due
to chelation of the 3,5-bis(2-pyridyl)pyrazole (bpp-H) ligand
through two nitrogen atoms. In addition to the other ligand peaks,
as mentioned in the Section 2, a multiplet in the range 7.3–
7.2 ppm, which corresponds to the phenyl protons of the triphen-
ylphosphine group of these complexes, is observed.
2.9. Preparation of [(
g
6-p-iPrC6H4Me)2Ru2(bpp)Cl2]BF4 [9]BF4
A mixture of [(
g
6-C10H14)Ru(
l-Cl)Cl]2 (100 mg, 0.163 mmol),
3,5-bis(2-pyridyl)pyrazole (bpp-H) (36 mg, 0.16 mmol) and NH4BF4
(85 mg, 0.81 mmol) was stirred in dry methanol (15 ml) for 4 h at
room temperature. The pale yellow compound which formed was
filtered, washed with methanol and diethylether, and dried under
vacuum. Yield: 95 mg, 68.44%. Elemental Anal . Calc. for
C33H37N4BCl2F4Ru2: C, 46.66; H, 4.39; N, 6.60. Found: C, 46.5; H,
The 3,5-bis(2-pyridyl)pyrazole (bpp-H) ligand reacts with the
pentamethylcyclopentadienyl ruthenium(II) complexes in the
presence of NH4PF6 in methanol, to yield the mononuclear cationic
4.4; N, 6.7%. IR (KBr pellets, cmꢁ1): 3416 (
1082 (
B–F). 1H NMR (CDCl3, d): 9.1 (s,1H); 8.8 (d, 1H); 8.77 (d,
mN–H); 1613 (
m
C@N);
complex [(g
5-C5Me5)Ru(PPh3)(bpp-H)]PF6 ([3]PF6) (Chart 1). The
m
complex is an orange crystalline solid, soluble in polar solvents
and air stable. The infrared spectrum displays a sharp band at
3424, 1613 and 850 cmꢁ1, corresponding to the stretching fre-
quencies of the N–H bond of the pyrazole ring, the C–N bond of
the pyridine ring and the P–F bond of the counter ion of the com-
plex. In addition to the proton peaks of the ligand, as mentioned in
the Section 2, the proton NMR spectrum also displays a singlet
peak at 1.45 ppm corresponding to the methyl protons of the
pentamethylcyclopentadienyl ring and a multiplet in the range
7.3–7.2 ppm which corresponds to the phenyl protons of the tri-
phenylphosphine group. The 31P {1H} NMR spectra of the complexes
[1]PF6 and [3]PF6 exhibit a single sharp resonance for triphenylphos-
phine at 50.8 and 49.7 ppm, respectively, whereas for the starting
1H); 8.37 (t, 1H); 7.95 (t, 2H); 7.93 (s, 1H); 7.68 (t, 1H); 6.46 (d,
1H); 6.09 (d, 1H, Arp–cy), 6.01 (d, 1H, Arp–cy), 5.99 (d, 2H, Arp–cy);
2.67 (sep, 1H), 2.17 (s, 3H), 1.04 (d, 6H). ESI-MS (m/z): 763 [MꢁBF4],
762.0 [MꢁBF4ꢁH]. UV–vis [(CH3CN; kmax, nm (
e
, Mꢁ1 cmꢁ1)]: 322
(19000), 425 (3000).
3. Results and discussion
The mononuclear
C5H5)Ru(PPh3)2Cl], [(
g
g
5-cyclic hydrocarbon complexes [(g5
5-C5H5)Os(PPh3)2Br] and [( 5-C5Me5)-
-
g
Ru(PPh3)2Cl] react with 3,5-bis(2pyridyl)pyrazole (bpp-H) in the
presence of ammonium hexafluorophosphate in methanol to form
the mononuclear cationic cyclopentadienyl ruthenium and
cyclopentadienyl osmium complexes having the general formula
complexes [(g g
5-C5H5)Ru(PPh3)2Cl] and [( 5-C5Me5)Ru(PPh3)2Cl]
the signals appear at 42.0 and 38.5 ppm, respectively [33,42,
43,47]. The structure of a representative complex, [1]PF6, was solved
by a single crystal X-ray diffraction study (Fig. 1).
[(
tamethylcyclopentadienyl ruthenium complex having the formula
[(
5-C5Me5)Ru(bpp-H)PPh3]+ ([3]PF6) (Chart 1). The complexes are
g
5-C5H5)M(bpp-H)PPh3]+ (M = Ru [1]PF6; M = Os [2]PF6) and pen-
g
orange–yellow, non-hygroscopic, air stable, crystalline solids. They
are soluble in polar solvents such as methanol, dichloromethane,
chloroform and acetone, but insoluble in hexane, petroleum ether
and diethylether.
3.2. Pentamethylcyclopentadienyl rhodium [4]PF6 and iridium
complexes [5]PF6
The dinuclear complexes [(g l-Cl)Cl]2 (M = Rh or Ir)
5-C5Me5)M(
undergo a bridge cleavage reaction with the N,N0-bidentate nitro-
gen base (bpp-H) ligand in methanol at room temperature, leading
to the formation of the chloride displaced complexes [4]PF6 and
[5]PF6, respectively (Scheme 1).
3.1. Cyclopentadienyl ruthenium [1]PF6 and osmium [2]PF6 complexes
The analytical data of these compounds are consistent with the
formulations (Chart 1). These complexes are formed by the reac-
tion of metal complexes with the bpp-H ligand, irrespective of
the metal-to-ligand ratio, yielding only mononuclear compounds.
Attempts to make dinuclear complexes by increasing the metal
complex ratio were unsuccessful, which might be due to the steric
bulkiness of the complex due to the presence of the triphenylphos-
phine group. The infrared spectra of the complexes [1]PF6 and
[2]PF6 exhibit a chelated N,N0-bidentate ligand with strong bands
at 3429, 3425, 1460 and 1474 cmꢁ1 corresponding to the stretch-
ing frequencies of the N–H bond of the pyrazole ring and the
C–N bond of the pyridine ring of the ligand. In addition, the infra-
red spectra contained a strong band at 850 cmꢁ1 due to the stretch-
ing frequency of the P–F bond of PF6 for both the complexes. The
proton NMR spectra of these complexes exhibit a singlet at 4.75
and 4.69 ppm for the cyclopentadienyl ring protons, indicating a
These complexes were isolated as their hexafluorophosphate
salts. Here also we were only able to isolate the mononuclear com-
plexes, despite the lack of triphenylphosphine groups. Change in
concentration and longer reaction times do not change the reaction
pathways. The orange–yellow complexes are air stable, soluble in
polar solvents but insoluble in hexane, petroleum ether and dieth-
ylether. Complex [4]PF6 exhibits a pale green color when dissolved
in solution. The infrared spectra of the complexes [4]PF6 and [5]PF6
exhibit for the chelated N,N0-bidentate ligand, strong bands at
3426, 1612, 3429 and 1613 cmꢁ1, corresponding to the stretching
frequencies of the C–N bond of the pyridine group and the N–H
bond of the pyrazole ring. In addition, the infrared spectra contain
a strong band at 850 cmꢁ1 due to the mP–F stretching frequency of
PF6. The proton NMR spectra of compounds [4]PF6 and [5]PF6 dis-
plays a singlet at 1.48 and 1.45 ppm, corresponding to the protons
+
+
+
Ru
N
Os
N
Ru
N
NH
N
NH
NH
N
N
N
N
N
Ph3P
Ph3P
Ph3P
1
2
3
Chart 1.

848
G. Gupta et al. / Polyhedron 28 (2009) 844–850
R
R
+
Ru
Cl
Ru
N
bpp-H
Cl
Cl
½
NH
N
Cl
N
Cl
NH4BF4
Ru
R
R
6:
7:
=
=
R
Scheme 2.
and [7]BF4 are brown in color in solution, while they are yellow,
non-hygroscopic, air stable solids. The complexes [8]BF4 and
[9]BF4 are also yellow, non-hygroscopic, air stable solids, but they
are sparingly soluble in polar solvents like dichloromethane, chlo-
roform, acetone and acetonitrile, and are insoluble in non-polar
solvents like hexane, diethylether and petroleum ether.
Fig. 1. ORTEP diagram with the labeling scheme for [(Cp)Ru(bpp-H)(PPh3)]+ ([1]PF6),
at the 50% probability level, the PF6 anion is omitted for clarity.
These complexes display strong bands at 3416 and 1613 cmꢁ1
corresponding to the stretching frequencies of the N–H bond of
the pyrazole ring and the C–N bond of the pyridine ring. In addi-
tion, the IR spectra of all these complexes contain a strong band
at 1082 cmꢁ1 due to the stretching frequency of the B–F bond of
the counter ion of these complexes. In complex [6]BF4, in addition
to the proton peaks of the ligand, the NMR spectra also displays a
singlet at around 6.25 ppm which corresponds to the six protons of
the benzene ring. Whereas in the case of the dinuclear complex
[8]BF4, in addition to the ligand peaks, the spectra displays two sin-
glet in the range of 6.3–6.1 ppm which corresponds to the protons
of the two benzene rings. The formation of these compounds is also
confirmed by ESI-MS spectrometry. The presence of peaks at m/z =
651.1, 740.3, 722.3, 658.5, 748.2, 437.2, 650.9, 492.1 and 763,
which coincides with the molecular mass of the cationic complexes
[1]PF6 to [9]BF4, also confirms the formation of these compounds.
An interesting point to make here is when the starting dimers
+
M
M
Cl
NH
bpp-H
N
Cl
N
Cl
½
Cl
Cl
N
NH4PF6
M
M = Rh, 4; Ir, 5
Scheme 1.
of the pentamethylcyclopentadienyl group. The molecular struc-
ture of the complex [5]PF6 was solved by single crystal X-ray crys-
tallography and the structure is presented in Fig. 2.
[(g
6-arene)RuCl2]2 (arene = benzene, p-cymene and hexamethyl-
3.3. Mononuclear arene ruthenium complexes [6]BF4 and [7]BF4 and
dinuclear complexes [8]BF4 and [9]BF4
benzene) are treated with terpyridine in methanol, rapid displace-
ment of the arene group with terpyridine takes place to form a
ruthenium terpyridine complex. In contrast, when [8]BF4 or
[9]BF4 is treated with terpyridine, the reaction does not occur,
i.e., the direct displacement of the arene group by terpyridine is
not possible [53,54]. This could be due to the following reasons:
(i) The formation of a mononuclear complex, as a solvated cationic
The dinuclear arene ruthenium complexes [(g
6-arene)RuCl2]2
(arene = benzene and p-cymene) react with the N,N0-based ligand
(bpp-H) in methanol to produce the mononuclear cationic com-
plexes [6]BF4 and [7]BF4 (Scheme 2) and the dinuclear cationic
complexes [8]BF4 and [9]BF4 (Scheme 3). The complexes [6]BF4
complex in the case of [(g
6-arene)RuCl2]2, is not possible in the
case of [8]BF4 or [9]BF4. (ii) In these complexes the arene binds
to the metal with fac-coordination, it is difficult then to replace this
with mer-coordinating ligands such as terpyridine due to the fro-
zen free rotation of ligands, unlike in the starting dimers. These
complexes are prepared by different methods [38,39]. The dinucle-
ar structure of representative complex [8]BF4 was further con-
firmed by its molecular structure determination from a single
crystal X-ray study (Fig. 3).
4. UV–vis spectroscopy
The UV–vis spectra of the representative complexes [1]PF6,
[3]PF6, [4]PF6, [6]BF4, [7]BF4, [8]BF4 and [9]BF4 were acquired in
acetonitrile, and spectral data are summarized in the Section 2.
Mononuclear complexes [1]PF6, [3]PF6, [4]PF6 and [6]BF4 displayed
an intense transition in the UV region. The high energy absorption
bands in the electronic spectra of [1]PF6, [3]PF6, [4]PF6 and [6]BF4
in the UV region at ꢄ308–358 nm and have been assigned to li-
diagram with the labeling scheme for [(g
5-C5Me5)Ir(bpp-H)Cl]+
gand-centered
of [7]BF4, it shows a low energy absorption band in the visible
p ?
pꢃ/n ? pꢃ transitions [55], whereas in the case
Fig. 2.
([5]PF6 ꢀOHRT2EOP), at the 50% probability level, the PF6 anion is omitted for clarity.

G. Gupta et al. / Polyhedron 28 (2009) 844–850
849
R
+
R
R
Ru
Cl
Ru Cl
bpp-H
Ru
Cl
Cl
N
N
Cl
N
Cl
NH4BF4
N
Ru
R
R
R
8:
9:
=
=
Scheme 3.
Fig. 4. UV–Visible spectra of the complexes [1]PF6, [3]PF6, [4]PF6, [6]BF4, [7]BF4,
[8]BF4 and [9]BF4 in acetonitrile at 298 K.
to N3 and N4 in a five-membered ring chelating fashion involving
nitrogen atoms of the pyridine and the pyrazolyl moiety, respec-
tively. The aromatic ring occupies three coordinate sites in these
complexes to complete the octahedral geometry around the metal
center. The molecular structures of complexes [1]PF6, [5]PF6 and
[8]BF4 are shown in Figs. 1–3, respectively. Selected bond lengths
and angles are presented in Table 2.
The distances between the iridium atom and the centroid of the
g
5-C5Me5 ring is 1.786 Å in complex [5]PF6, whereas the distance
g
5-C5H5 ring
Fig. 3.
diagram with the labeling scheme for [(g
6-C6H6)2Ru2(bpp)Cl2]+
betwen the ruthenium atom and the centroid of the
is 1.830 Å in complex [1]PF6. These bond distances are comparable
to those in the related complex cations [(
5-C5Me5)IrCl(C5H4 N-2-
CH@N–C6H4–p–X)]+, where X = NO2 and Cl [56] and [Ru(g5
C5H5)(PPh3)(
2-paa)]+ and [Ru( 5-C5H5)( 1-dppm)( 2-paa)]+ [57].
([8]BF4 ꢀOHRT2EOP), at the 50% probability level, the water and BF4 anion are omitted
for clarity.
g
-
j
g
j
j
region at ꢄ430 nm which can be assigned to a MLCT transition. The
dinuclear complexes [8]BF4 and [9]BF4 exhibited similar trends,
with an additional band at ꢄ425 nm that can be assigned to
Whereas in the complex [8]BF4, the distances between the metal
and the centeriod of the arene rings are 1.685 and 1.681 Å, which
are in accordance with the values reported in other related com-
plexes [58].
the MLCT band due to a d
p
M-arene ? pꢃ
transition [55], and
bpp
they exhibit significant red shifts. In general, these complexes
follow the normal trends observed in the electronic spectra of
nitrogen bonded metal complexes, which display ligand based
All these complexes crystallize in monoclinic space groups. The
complexes [5]PF6 and [8]BF4 crystallize with a molecule of water
per asymmetric unit. The M–N distance in complex [5]PF6 appears
to be significantly shorter than the M–N distances in complexes
[1]PF6 and [8]BF4. There are no significant differences in the C–C
bond lengths in the pentamethylcyclopentadienyl ring, all being
p
?
pꢃ/n ? pꢃ transitions in the UV region and metal-to-ligand
charge transfer transitions in the visible region. The electronic
spectra of these complexes are shown in Fig. 4.
about 1.337 Å and pointing to uniform
p-electron delocalization
5. Molecular structures
in the ring. Furthermore, the five-membered ring is planar as evi-
dent in the nearly equal bond distances between metal atom and
the ring carbons. The Ir–Cl bond distance is 2.398 Å, which is close
to that in related iridium and rhodium complexes with two-coordi-
nated chelating N,N0-based ligands [56]. An interesting structural
feature of the homodinuclear complex [8]BF4 is the presence of
an orientational disorder for the location of the benzene ring
C14–C19 (occupancy factor of 75). The ring C14–C19 is the major
contribution of the disordered system, whereas the corresponding
minor contribution is the orientational disorder ring C26–C31
(occupancy factor of 25) (not shown in Fig. 3). The refined site dis-
tribution of C14–19 to C26–31 is 75/25. The Ru(1)ꢀ ꢀ ꢀCl(1)
2.403(13) Å and Ru(2)ꢀ ꢀ ꢀCl(2) 2.4339(14) Å bond lengths are com-
parable to mononuclear complexes. However, the bond length of
Ru(2)ꢀ ꢀ ꢀCl(2) is much longer than the other metal to chloride
Ru(1)ꢀ ꢀ ꢀCl(1) distance despite there being no significant change in
their environments.
The molecular structures of [(g
5-C5H5)Ru(bpp-H)PPh3]PF6
([1]PF6) [(
g
5-C5Me5)Ir(bpp-H)Cl]PF6 ꢀ H2O ([5]PF6) and [(g6
-
C6H6)2Ru2(bpp)Cl2]BF4ꢀH2O ([8]BF4) have been established by
single-crystal X-ray analysis of their hexafluorophosphate and
tetrafluoroborate salts. The complexes show a typical piano–stool
geometry with the metal center coordinated by the cyclopentadi-
enyl or arene ligand, a terminal chloride in complexes [5]PF6 and
[8]BF4, triphenylphosphine in complex [1]PF6 and the chelating
bpp-H ligand. The metal atom is in an octahedral arrangement
with two cis-nitrogen atoms of the bpp-H ligand acting as a biden-
tate chelating ligand through the neighboring pyridyl and pyrazolyl
nitrogen atoms. In this study, the mononuclear complexes [1]PF6
and [5]PF6 were found to be coordinated to N1 and N2, and the
dinuclear complex [8]BF4 was found to have the first metal center
coordinated to N1 and N2 and the second metal center coordinated

850
G. Gupta et al. / Polyhedron 28 (2009) 844–850
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Acknowledgements
K.M. Rao greatly acknowledges the Department of Science and
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Appendix A. Supplementary data
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