Novel mononuclear η5-pentamethylcyclopentadienyl complexes of platinum group metals bearing pyrazolylpyridazine ligands: Syntheses and spectral studies

Article abstract of DOI:10.1016/j.ica.2010.03.052

Condensation of 3,6-dichloropyridazine with 3,5-dimethylpyrazole in 1:1 ratio yielded one side substituted pyrazolylpyridazine ligand 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine (L) while condensation of 3,6-dichloropyridazine with substituted pyrazoles in 1:2 ratio yielded both side substituted pyrazolylpyridazine ligands such as 3,6-bis(pyrazolyl)pyridazine (L1), 3,6-bis(3-methylpyrazolyl)pyridazine (L2) and 3,6-bis(3,5- dimethylpyrazolyl)pyridazine (L3). A new series of cationic mononuclear complexes of the type [(η⁵-Cp)M_a(L)(PPh₃)]PF₆, [(η⁵-Cp)M_b(L)Cl]PF₆, [(η⁵-Cp)Ru(L′)(PPh₃)]PF₆and [(η⁵-Cp)M_b(L′)Cl]⁺(where M_a= Ru, Os; M_b= Rh, Ir and L′ = L1, L2, L3) bearing pyrazolylpyridazine and η⁵-cyclopentadienyl ligands are reported. The complexes have been completely characterized by spectral studies. The molecular structures of representative complexes have been determined by single crystal X-ray crystallography.

Full text of DOI:10.1016/j.ica.2010.03.052

Inorganica Chimica Acta 363 (2010) 2287–2295
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Novel mononuclear
g
5-pentamethylcyclopentadienyl complexes of platinum
group metals bearing pyrazolylpyridazine ligands: Syntheses and spectral studies
Gajendra Gupta a, Kota Thirumala Prasad a, Anna Venkateswara Rao a, Steven J. Geib b, Babulal Das c,
Kollipara Mohan Rao a,
*
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Department of Chemistry, University of Pittsburgh, PA 15260, USA
c Department of Chemistry, Indian Institute of Technology, Guwahati, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2009
Received in revised form 15 March 2010
Accepted 22 March 2010
Available online 1 April 2010
Condensation of 3,6-dichloropyridazine with 3,5-dimethylpyrazole in 1:1 ratio yielded one side substi-
tuted pyrazolylpyridazine ligand 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine (L) while condensation
of 3,6-dichloropyridazine with substituted pyrazoles in 1:2 ratio yielded both side substituted pyra-
zolylpyridazine ligands such as 3,6-bis(pyrazolyl)pyridazine (L1), 3,6-bis(3-methylpyrazolyl)pyridazine
(L2) and 3,6-bis(3,5-dimethylpyrazolyl)pyridazine (L3). A new series of cationic mononuclear complexes
of the type [(
g
5-Cp)Ma(L)(PPh3)]PF6, [(
g
5-Cpꢀ)Mb(L)Cl]PF6, [(g5-Cpꢀ)Ru(L0)(PPh3)]PF6 and [(
g
5-Cpꢀ)-
Keywords:
Pentamethylcyclopentadienyl
Ruthenium
Osmium
Mb(L0)Cl]+ (where Ma = Ru, Os; Mb = Rh, Ir and L0 = L1, L2, L3) bearing pyrazolylpyridazine and
g
5-cyclo-
pentadienyl ligands are reported. The complexes have been completely characterized by spectral studies.
The molecular structures of representative complexes have been determined by single crystal X-ray
crystallography.
Rhodium
Ó 2010 Elsevier B.V. All rights reserved.
Iridium and pyrazolylpyridazine ligands
1. Introduction
scribed a series of arene ruthenium complexes of these ligands
which have exhibited interesting chemistry. In continuation of
Mononuclear complexes of platinum group metals containing
nitrogen based ligands have received considerable attention owing
to their photochemical properties [1–9], catalytic activities [10–
19], electrochemical behavior [20–26], as well as in the develop-
ment of new biological active agents [27–33]. In particular, the
chemistry of cyclopentadienyl and pentamethylcyclopentadienyl
ruthenium, osmium, rhodium and iridium complexes is the family
of an area of active research [34,35] due to their high reactivity and
catalytic activities [36–42]. These properties have prompted wide
spread interest regarding both the synthetic and the mechanistic
features of cyclopentadienyl and pentamethylcyclopentadienyl
complexes for a large number of transition metals. The chemistry
our studies here we describe the syntheses of 18 mononuclear
cyclopentadienyl and pentamethylcyclopentadienyl Ru, Os, Rh
and Ir complexes bearing substituted pyrazolylpyridazine ligands.
All these pyrazolylpyridazine complexes are interesting in their
own right from a synthetic, structural and electrochemical point
of view. However, attempts to make dinuclear complexes with
these metals have not been successful. The reason could be the
large size of the pentamethylcyclopentadienyl and triphenylphos-
phine ligands. These complexes are fully characterized by IR, NMR
and mass spectrometry. The molecular structures of some of the
representative complexes are described as well. The following pyr-
azolylpyridazine ligands were used in this study.
of [(
g
5-Cp)RuCl(PPh3)2], [(
g
5-Cpꢀ)RuCl(PPh3)2] or [(
g
5-Cp)-
OsBr(PPh3)2] is characterized by facile displacement of either chlo-
ride or one or both triphenylphosphine ligands depending on the
solvent and reaction conditions [43–47]. The reactivity of these
pyrazolylpyridazine ligands with different metals has also been re-
ported [48]. However, no reports are available for cyclopentadienyl
and pentamethylcyclopentadienyl platinum group metals (Ru, Os,
Rh and Ir) in connectivity with these ligands. Recently [49] we de-
CH3
Cl
N
N
N
N
H3C
L 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine
* Corresponding author.
E-mail address: mohanrao59@gmail.com (K.M. Rao).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.03.052

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2.1. Single crystal X-ray structures analyses
R'
N
R'
Crystals suitable for X-ray diffraction study for compound 2, 10
and 11 were grown by slow diffusion of petroleum ether into ace-
tone solution of the said complexes while crystals of compound 7
were grown by slow diffusion of hexane into chloroform solution
of complex 7. The intensity data of all these crystals were collected
using a Bruker SMART APEX-II CCD diffractometer, equipped with a
N
N
N
N
N
R
R
fine focus 1.75 kW sealed tube Mo Ka radiation (a = 0.71073 Å) at
273(3) K, with increasing (width of 0.3° per frame) at a scan
x
R=R'=H,
L1 (3,6-Bis(pyrazolyl)pyridazine)
speed of 3 s/frame. The SMART software was used for data acquisi-
tion. Data integration and reduction were undertaken with SAINT
and XPREP software. Multi-scan empirical absorption corrections
were applied to the data using the program SADABS. Structures were
solved by direct methods using SHELXS-97 [57] and refined with full-
matrix least squares on F2 using SHELXL-97 [58]. All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were lo-
cated from the difference Fourier maps and refined. Structural
illustrations have been drawn with ORTEP-3 for Windows. The OR-
TEP presentations of the representative complexes are shown in
Figs. 4–7 respectively. The data collection parameters and bond
lengths and angles are presented in Tables 1 and 2.
R=CH3, R'=H, L2 (3,6-Bis(3-methylpyrazolyl)pyridazine)
R=R'=CH3,
L3 (3,6-Bis(3,5-dimethylpyrazolyl)pyridazine )
Ligands used in this study
2. Experimental
All solvents were dried and distilled prior to use. Pyrazole; 3-
methylpyrazole; 3,5-dimethylpyrazole and 3,6-dichloropyridazine
(Aldrich) were purchased and used as received. The ligands were
prepared by following a literature procedure [48]. The precursor
2.1.1. Syntheses and characterization of [(
A mixture of [(
5-Cp)Ru(PPh3)2Cl] (100 mg, 0.137 mmol), L
g
5-Cp)Ru(L)(PPh3)]PF6 (1)
g
complexes [(
Cp)OsBr(PPh3)2], [(
g
5-Cp)RuCl(PPh3)2], [(
g
5-Cpꢀ)RuCl(PPh3)2], [(g5
-
(29 mg, 0.137 mmol) and two equivalents of NH4PF6 in dry meth-
anol (30 ml) was refluxed under dry nitrogen for 12 h. The solvent
was removed under vacuum, the residue obtained was dissolved in
dichloromethane (10 ml) and the solution was filtered to remove
ammonium halide. The orange solution was concentrated to
2 ml, and upon addition of hexane the reddish-brown complex
precipitated, which was separated and dried under vacuum.
Yield: 73 mg, 67.9%. Elemental Anal. Calc. for C32H29ClF6N4P2Ru:
C, 49.13; H, 3.76; N, 7.14. Found: C, 49.29; H, 3.91; N, 6.98%. 1H
g
5-Cpꢀ)RhCl(
l-Cl)]2 and [(
g
5-Cpꢀ)IrCl(
l-Cl)]2
were prepared following literature methods [50–56]. NMR spectra
were recorded on Bruker AMX – 400 MHz spectrometer. Elemental
analyses of the complexes were performed on a Perkin–Elmer 2400
CHN/S analyzer. All the complexes have given satisfactory C, H and
N analysis. Infrared spectra were recorded as KBr pellets on a Per-
kin–Elmer 983 spectrophotometer. Mass spectra were obtained
from Waters ZQ-4000 mass spectrometer by ESI method.
Fig. 1. 1H NMR spectrum of complex [( 5-Cp)Ru(L2)(PPh3)]PF6 (5) in CDCl3.
g

G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
2289
Fig. 2. 1H NMR spectrum of complex [(
g
5-Cpꢀ)Ir(L3)Cl]PF6 (15) in CDCl3.
Fig. 3. UV–Vis absorption spectra of mononuclear complexes 2, 5, 6, 7, 8, 10, 11, 14
and 15 in acetonitrile at 298 K.
Fig. 4. Molecular structure of complex 2 with 50% probability thermal ellipsoids.
Hydrogen atoms and PF6 anion are omitted for clarity.
NMR (400 MHz, CDCl3): d = 8.05 (d, 1H), 7.86 (d, 1H), 6.41 (d, 1H),
7.516–7.124 (m, 15H, PPh3), 2.20 (s, 3H, CH3); ESI-MS (m/z): 679.4
[MꢁPF6]+, 418.4 [MꢁPF6ꢁPPh3]. 31P {1H} NMR (CDCl3, d): 50.10 (s,
PPh3).
2.1.3. Syntheses and characterization of [(
g
5-Cpꢀ)Ir(L)Cl]PF6 (3)
A
mixture of [(
g
5-Cpꢀ)Ir(
l-Cl)Cl]2 (50 mg, 0.062 mmol), L
(26 mg, 0.124 mmol) and two equivalents of NH4PF6 in dry meth-
anol (15 ml) was refluxed under dry nitrogen for 12 h. The solvent
was removed under vacuum, the residue was dissolved in dichloro-
methane (10 ml) and the solution was filtered to remove ammo-
nium chloride. The orange solution was concentrated to 2 ml,
and upon addition of diethylether the orange–yellow complex pre-
cipitated, which was separated by filtration, washed with diethyl-
ether and dried under vacuum.
2.1.2. Syntheses and characterization of [(
g
5-Cpꢀ)Rh(L)Cl]PF6 (2)
A
mixture of [(
g
5-Cpꢀ)Rh(
l-Cl)Cl]2 (50 mg, 0.08 mmol), L
(34 mg, 0.16 mmol) and two equivalents of NH4PF6 in dry metha-
nol (15 ml) was stirred at room temperature for around 6 h. The
yellow compound formed was filtered, washed with methanol
and diethylether and dried under vacuum.
Yield: 62 mg, 69.04%. Elemental Anal. Calc. for C19H24Cl2F6N4PIr:
C, 31.87; H, 3.41; N, 7.80. Found: C, 31.99; H, 3.55; N, 7.69%. 1H
NMR (400 MHz, CDCl3): d = 8.12 (d, 1H), 7.98 (d, 1H), 6.63 (s,
1H), 2.68 (s, 6H, CH3), 1.79 (s, 15H, Cpꢀ); ESI-MS (m/z): 571
[MꢁPF6], 534.6 [MꢁPF6ꢁCl]+.
Yield: 75 mg, 74.03%. Elemental Anal. Calc. for C19H24Cl2-
F6N4PRh: C, 36.40; H, 3.88; N, 8.95. Found: C, 36.53; H, 3.99; N,
8.79%. 1H NMR (400 MHz, CDCl3): d = 8.45 (d, 1H), 8.24 (d, 1H),
6.55 (s, 1H), 2.72 (s, 6H, CH3) 1.86 (s, 15H, Cpꢀ); ESI-MS (m/z):
481.8 [MꢁPF6], 445.4 [MꢁPF6ꢁCl]+.

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G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
2.1.4. Syntheses and characterization of complexes 4–6
A mixture of [(
5-Cp)Ru(PPh3)2Cl] (100 mg, 0.137 mmol), corre-
g
sponding ligand (0.137 mmol) and two equivalents of NH4PF6 in
dry methanol (15 ml) was refluxed under dry nitrogen for 12 h.
The solvent was removed under vacuum, the residue was dissolved
in dichloromethane (10 ml) and the solution was filtered to re-
move ammonium halide. The orange solution was concentrated
to 2 ml, and upon addition of hexane the reddish-brown complex
precipitated, which was separated and dried under vacuum.
2.1.4.1. [(g
5-Cp)Ru(L1)(PPh3)]PF6 (4). Yield: 65 mg, 60.1%. Elemental
Anal. Calc. for C33H28F6N6P2Ru: C, 50.47; H, 3.61; N, 10.68. Found:
C, 50.58; H, 3.77; N, 10.57%. 1H NMR (400 MHz, CDCl3): d = 8.822
(d, 1H), 8.765 (d, 1H), 8.649 (d, 1H), 8.543 (d, 1H), 8.304 (d, 1H),
8.092 (d, 1H), 7.634–7.262 (m, 15H, PPh3), 7.006 (t, 1H), 6.716 (t,
1H), 4.785 (s, 5H, Cp); ESI-MS (m/z): 641.21 [MꢁPF6]+, 379.21
[MꢁPF6ꢁPPh3].
31P {1H} NMR (CDCl3, d): 49.70 (s, PPh3).
Fig. 5. Molecular structure of complex 7 with 50% probability thermal ellipsoids.
Hydrogen atoms and PF6 anion are omitted for clarity.
2.1.4.2. [(g
5-Cp)Ru(L2)(PPh3)]PF6 (5). Yield: 67 mg, 59.8%. Elemental
Anal. Calc. for C35H32F6N6P2Ru: C, 51.67; H, 3.97; N, 10.31. Found: C,
51.79; H, 4.09; N, 10.19%. 1H NMR (400 MHz, CDCl3): d = 8.478 (d,
1H), 8.311 (d, 1H), 8.129 (d, 1H), 7.817 (d, 1H), 7.428–7.062 (m,
15H, PPh3), 6.499 (dd, 2H), 4.773 (s, 5H, Cp), 2.620 (s, 3H, CH3),
2.404 (s, 3H, CH3); ESI-MS (m/z): 669.3 [MꢁPF6]+, 406.3
[MꢁPF6ꢁPPh3].
31P {1H} NMR (CDCl3, d): 49.90 (s, PPh3).
2.1.4.3. [(g
5-Cp)Ru(L3)(PPh3)]PF6 (6). Yield: 68 mg, 58.6%. Elemental
Anal. Calc. for C37H36F6N6P2Ru: C, 52.82; H, 4.33; N, 9.96. Found: C,
52.96; H, 4.47; N, 10.07%. 1H NMR (400 MHz, CDCl3): d = 8.554 (d,
1H), 7.721 (d, 1H), 7.563–7.208 (m, 15H, PPh3), 6.294 (s, 2H), 4.761
(s, 5H, Cp), 2.741 (s, 6H, CH3), 2.618 (s, 6H, CH3); ESI-MS (m/z):
697.2 [MꢁPF6]+, 434.2 [MꢁPF6ꢁPPh3].
31P {1H} NMR (CDCl3, d): 50.09 (s, PPh3).
2.1.5. Syntheses and characterization of complexes 7–9
A mixture of [(
g
5-Cpꢀ)Ru(PPh3)2Cl] (100 mg, 0.125 mmol), cor-
responding ligand (0.125 mmol) and two equivalents of NH4PF6 in
dry methanol (15 ml) was refluxed under dry nitrogen for 12 h
producing a color change in solution from yellow to orange. The
solvent was removed under vacuum, the residue was dissolved
in dichloromethane (10 ml) and the solution was filtered to re-
move ammonium halide. The orange solution was concentrated
to 2 ml, and upon addition of excess hexane the reddish-brown
complex precipitated, which was separated and dried under
vacuum.
Fig. 6. Molecular structure of complex 10 with 50% probability thermal ellipsoids.
Hydrogen atoms and BF4 anion are omitted for clarity.
2.1.5.1. [(
g
5-Cpꢀ)Ru(L1)(PPh3)]PF6 (7). Yield: 65 mg, 60.4%. Elemen-
tal Anal. Calc. for C38H38F6N6P2Ru: C, 53.35; H, 4.49; N, 9.80. Found:
C, 53.43; H, 4.41; N, 9.89%. 1H NMR (400 MHz, CDCl3): d = 9.081 (d,
1H), 8.763 (d, 1H), 8.550 (d, 1H), 8.202 (d, 1H), 8.015 (d, 1H), 7.838
(d, 1H), 7.464–7.218 (m, 15H, PPh3),7.006 (t, 1H), 6.821 (t, 1H),
1.855 (s, 15H, Cpꢀ); ESI-MS (m/z): 710.2 [MꢁPF6]: 448.2
[MꢁPF6ꢁPPh3].
31P {1H} NMR (CDCl3, d): 50.29 (s, PPh3).
2.1.5.2. [(
g
5-Cpꢀ)Ru(L2)PPh3)]PF6 (8). Yield: 67 mg, 60.3%. Elemen-
tal Anal. Calc. for C40H42F6N6P2Ru: C, 54.37; H, 4.81; N, 9.50. Found:
C, 54.49; H, 4.90; N, 9.41%. 1H NMR (400 MHz, CDCl3): d = 8.461 (d,
1H), 8.610 (d, 1H), 8.166 (d, 1H), 7.743 (d, 1H), 7.377–7.111 (m,
15H, PPh3), 6.543 (d, 1H), 6.354 (d, 1H), 2.459 (s, 3H, CH3), 2.408
(s, 3H, CH3), 1.586 (s, 15H, Cpꢀ); ESI-MS (m/z): 738.2 [MꢁPF6]:
476.2 [MꢁPF6ꢁPPh3]. 31P {1H} NMR (CDCl3, d): 50.41 (s, PPh3).
Fig. 7. Molecular structure of complex 11 with 50% probability thermal ellipsoids.
Hydrogen atoms and ClO4 anion are omitted for clarity.

G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
2291
Table 1
Crystallographic and structure refinement parameters for complexes 2, 7, 10 and 11.
Compound
2
7
10
11
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C19H24Cl2F6N4PRh
627.20
296(2)
0.71073
orthorhombic
Pca2(1)
C38H38F6N6P2Ru
855.75
203(2)
0.71073
monoclinic
P2(1)/n
C20H23BClF4N6Rh
572.61
296(2)
0.71073
monoclinic
P21/c
C22H27Cl2N6O4Rh
629.31
296(2)
0.71073
monoclinic
P21/c
Unit cell dimensions
a (Å)
b (Å)
14.2891(3)
10.1246(3)
17.0868(4)
11.843(4)
19.694(7)
16.668(6)
103.547(10)
3779(2)
12.4751(3)
11.8730(3)
15.3094(4)
91.8840(10)
2266.35(10)
4, 1.678
11.1784(17)
7.7033(11)
32.731(5)
95.392(11)
2806.1(7)
4, 1.490
c (Å)
b (°)
Volume (A3)
Z, Dcalc (mg/m3)
Absorption coefficient
2471.97(11)
4, 1.685
1.032
4, 1.504
1.451
0.925
0.840
(mmꢁ1
F (0 0 0)
)
1256
1488
1152
1280
Crystal size (mm)
h Range for data
collection (°)
0.40 ꢂ 0.25 ꢂ 0.12
0.22 ꢂ 0.13 ꢂ 0.04
0.50 ꢂ 0.30 ꢂ 0.18
0.25 ꢂ 0.15 ꢂ 0.10
2.01–28.51
2.21–28.21
1.63–28.74
1.25–28.76
Index ranges
ꢁ18 ꢃ h ꢃ 18, ꢁ13 ꢃ k ꢃ 12,
ꢁ21 ꢃ l ꢃ 20
ꢁ14 ꢃ h ꢃ 14, ꢁ23 ꢃ k ꢃ 23,
ꢁ19 ꢃ l ꢃ 19
ꢁ16 ꢃ h ꢃ 16, ꢁ15 ꢃ k ꢃ 15,
ꢁ20 ꢃ l ꢃ 20
ꢁ15 ꢃ h ꢃ 14, ꢁ17 < 10 = k ꢃ 10,
ꢁ44 ꢃ l ꢃ 44
Reflections collected/
25 506/5618 (0.0662)
29 788/6659 (0.2384)
25 492/5622 (0.0251)
43 864/7274 (0.1384)
unique (Rint
)
Goodness-of-fit (GOF) on 0.971
0.821
1.043
1.023
F2
Table 2
Selected bond lengths and angles for complexes 2, 7, 10 and 11.
2.1.6.2. [(
g
5-Cpꢀ)Rh(L2)Cl]ClO4 (11). Yield: 72 mg, 72.7%. Elemental
Anal. Calc. for C22H27Cl2N6O4Rh: C, 43.10; H, 4.45; N, 13.70. Found:
C, 43.02; H, 4.56; N, 13.61%. 1H NMR (400 MHz, CDCl3): d = 8.651
(d, 1H), 8.418 (d, 1H), 8.302 (d, 1H), 8.136 (d, 1H), 6.672 (d, 1H),
6.432 (d, 1H), 2.693 (s, 3H, CH3), 2.408 (s, 3H, CH3), 1.809 (s,
15H, Cpꢀ); ESI-MS (m/z): 513.75 [MꢁClO4], 477.2 [MꢁClO4ꢁCl]+.
2
7
10
11
Distances (Å)
N(1)–M(1)
N(3)–M(1)
N(3)–N(4)
N(5)–N(6)
Cl(1)–M(1)
M(1)–CNT(1)
2.105(3)
2.109(3)
1.387(4)
2.072(7)
2.098(6)
1.351(8)
1.363(8)
2.104(2)
2.105(2)
1.342(3)
1.361(3)
2.3957(7)
1.776
2.127(2)
2.115(6)
1.349(8)
1.381(9)
2.408(2)
1.788
2.1.6.3. [(
g
5-Cpꢀ)Rh(L3)Cl]PF6 (12). Yield: 77 mg, 69.6%. Elemental
2.386(10)
1.785
1.840
Anal. Calc. for C24H31ClF6N6PRh: C, 40.98; H, 4.56; N, 12.22. Found:
C, 41.07; H, 4.67; N, 12.31%. 1H NMR (400 MHz, CDCl3): d = 8.160
(d, 1H), 8.696 (d, 1H), 7.909 (d, 1H), 6.394 (s, 2H), 2.745 (s, 6H,
CH3), 2.622 (s, 6H, CH3), 2.176 (s, 15H, Cpꢀ). ESI-MS (m/z): 533.97
[MꢁPF6], 504.52 [MꢁPF6ꢁCl].
Angles (°)
N(4)–N(3)–M(1)
N(2)–N(1)–M(1)
N(3)–M(1)–N(1)
N(1)–M(1)–Cl(1)
N(3)–M(1)–Cl(1)
114.2(2)
120.4(2)
74.40(11)
88.10(8)
88.70(8)
121.7(5)
115.0(5)
75.4(2)
121.28(16)
113.58(16)
75.25(8)
85.32(7)
84.97(6)
121.4(5)
113.6(5)
75.0(3)
86.0(2)
87.07(18)
2.1.7. Syntheses and characterization of complexes 13–15
A mixture of [(
g
5-Cpꢀ)Ir(
l-Cl)Cl]2 (50 mg, 0.062 mmol), corre-
sponding ligand (0.124 mmol) and two equivalents of NH4PF6 in
dry methanol (15 ml) was refluxed under dry nitrogen for 12 h.
The solvent was removed under vacuum, the residue was dissolved
in dichloromethane (10 ml) and the solution was filtered to re-
move ammonium chloride. The orange solution was concentrated
to 2 ml, and upon addition of diethylether the orange–yellow com-
plex precipitated, which was separated by filtration, washed with
diethylether and dried under vacuum.
2.1.5.3. [(
g
5-Cpꢀ)Ru(L3)PPh3)]PF6 (9). Yield: 70 mg, 61.1%. Elemen-
tal Anal. Calc. for C42H46F6N6P2Ru: C, 55.34; H, 5.10; N, 9.20. Found:
C, 55.41; H, 5.02; N, 9.11%. 1H NMR (400 MHz, CDCl3): d = 8.736 (d,
1H), 7.928 (d, 1H), 7.431–7.107 (m, 15H, PPh3), 6.432 (s, 2H), 2.938
(s, 6H, CH3), 2.714 (s, 6H, CH3), 1.632 (s, 15H, Cpꢀ); ESI-MS (m/z):
766.2 [MꢁPF6]: 504.2 [MꢁPF6ꢁPPh3].
31P {1H} NMR (CDCl3, d): 50.37 (s, PPh3).
5-Cpꢀ)Ir(L1)Cl]PF6 (13). Yield: 62 mg, 65.9%. Elemental
2.1.6. Syntheses and characterization of complexes 10–12
2.1.7.1. [(
g
A mixture of [(
g
5-Cpꢀ)Rh(
l-Cl)Cl]2 (50 mg, 0.08 mmol), corre-
Anal. Calc. for C20H23ClF6N6IrP: C, 33.37; H, 3.24; N, 11.65. Found:
C, 33.49; H, 3.38; N, 11.76%. 1H NMR (400 MHz, CDCl3): d = 9.180
(d, 1H), 9.066 (d, 1H), 8.778 (d, 1H), 8.556 (d, 1H), 8.206 (d, 1H),
7.936 (d, 1H), 7.012 (t, 1H), 6.720 (t, 1H), 1.873 (s, 15H, Cpꢀ);
ESI-MS (m/z): 575.01 [MꢁPF6], 539.56 [MꢁPF6ꢁCl].
sponding ligand (0.16 mmol) and two equivalents of counter ion
in dry methanol (15 ml) was stirred at room temperature for
around 6 h. The yellow compound formed was filtered, washed
with methanol and diethylether and dried under vacuum.
2.1.6.1. [(
g
5-Cpꢀ)Rh(L1)Cl]BF4 (10). Yield: 70 mg, 75.7%. Elemental
2.1.7.2. [(
g
5-Cpꢀ)Ir(L2)Cl]PF6 (14). Yield: 60 mg, 63.8%. Elemental
Anal. Calc. for C20H23BClF4N6Rh: C, 41.97; H, 4.07; N, 14.66. Found:
C, 42.08; H, 4.19; N, 14.57%. 1H NMR (400 MHz, CDCl3): d = 8.754
(d, 1H), 8.696 (d, 1H), 8.549 (d, 1H), 8.444 (d, 1H), 8.204 (d, 1H),
8.082 (d, 1H), 6.922 (t, 1H), 6.656 (t, 1H), 1.861 (s, 15H, Cpꢀ);
ESI-MS (m/z): 485.55 [MꢁBF4], 449.2 [MꢁBF4ꢁCl]+.
Anal. Calc. for C22H27ClF6N6IrP: C, 35.33; H, 3.65; N, 11.21. Found:
C, 35.40; H, 3.79; N, 11.16%. 1H NMR (400 MHz, CDCl3): d = 8.596
(d, 1H), 8.505 (d, 1H), 8.472 (d, 1H), 8.338 (d, 1H), 8.050 (d, 1H),
6.822 (d, 1H), 2.706 (s, 3H, CH3), 2.378(s, 3H, CH3), 2.136 (s, 15H,
Cpꢀ); ESI-MS (m/z): 603.05 [MꢁPF6], 567.60 [MꢁPF6ꢁCl].

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G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
2.1.7.3. [(
g
5-Cpꢀ)Ir(L3)Cl]PF6 (15). Yield: 66 mg, 67.7%. Elemental
Cl
+
Anal. Calc. for C24H31ClF6N6IrP: C, 37.15; H, 4.04; N, 10.81. Found:
C, 37.27; H, 4.16; N, 10.72%. 1H NMR (400 MHz, CDCl3): d = 8.273
(d, 1H), 7.918 (d, 1H), 6.444 (s, 2H), 2.855 (s, 6H, CH3), 2.675 (s,
6H, CH3), 1.739 (s, 15H, Cpꢀ); ESI-MS (m/z): 631.11 [MꢁPF6],
595.65 [MꢁPF6ꢁCl].
N
N
N
N
N
N
N
Ru
Cl
N
Rh
Cl
Ph3P
(i)
M
e
(1)
O
H
2.1.8. Syntheses and characterization of complexes 16–18
mixture of [(g
5-Cp)Os(PPh3)2CH3CN]BF4 (100 mg, 0.110
(2)
A
mmol), corresponding ligand (0.110 mmol) and one equivalent of
NH4BF4 in dry methanol (35 ml) was refluxed under dry nitrogen
for 12 h whereby the colorless suspension gradually changed to
dark red solution. The solvent was removed under vacuum, the res-
idue was dissolved in acetone (2 ml) and upon addition of excess
hexane the reddish-brown complex precipitated, which was sepa-
rated and dried under vacuum.
Cl
N
N
N
N
(iii)
MeOH
+
2.1.8.1. [(g
5-Cp)Os(L1)(PPh3)]BF4 (16). Yield: 60 mg, 67.9%. Elemen-
N
Cl
N
N
N
tal Anal. Calc. for C33H28BF4N6OsP: C, 48.54; H, 3.47; N, 10.27.
Found: C, 48.60; H, 3.55; N, 10.15%. 1H NMR (400 MHz, CDCl3):
d = 8.722 (d, 1H), 8.745 (d, 1H), 8.608 (d, 1H), 8.516 (d, 1H),
8.330 (d, 1H), 8.106 (d, 1H), 7.324–7.232 (m, 15H, PPh3), 7.018 (t,
1H), 6.626 (t, 1H), 4.758 (s, 5H, Cp); ESI-MS (m/z): 730.2 [MꢁBF4]+,
468.2 [MꢁBF4ꢁPPh3].
Ir
Cl
(3)
(i) = [{( η5-Cp)RuCl(PPh3)2}]
2.1.8.2. [(g
5-Cp)Os(L2)(PPh3)]BF4 (17). Yield: 56 mg, 60.6%. Elemen-
(ii) = [{( η5-Cp*)RhCl( μ−Cl)}2]
tal Anal. Calc. for C35H32BF4N6OsP: C, 49.78; H, 3.84; N, 9.93. Found:
C, 49.87; H, 3.73; N, 10.01%. 1H NMR (400 MHz, CDCl3): d = 8.518
(d, 1H), 8.432 (d, 1H), 8.339 (d, 1H), 7.987 (d, 1H), 7.408–7.162
(m, 15H, PPh3), 6.529 (dd, 2H), 4.753 (s, 5H, Cp), 2.618 (s, 3H,
CH3), 2.420 (s, 3H, CH3); ESI-MS (m/z): 758.2 [MꢁBF4]+, 496.3
[MꢁBF4ꢁPPh3].
(iii) = [{( η5-Cp*)IrCl( μ−Cl)}2]
Scheme 1.
kind known in the literature. The tautomerized products were sup-
ported by 1H NMR and 13C NMR as well as single crystal structure.
But surprisingly, here in this work, although we used the same pyr-
azolylpyridazine ligands, we did not observe any tautomerized
product with the pentamethylcyclopentadienyl complexes of Ru,
Os, Rh and Ir metals.
2.1.8.3. [(g
5-Cp)Os(L3)(PPh3)]BF4 (18). Yield: 59 mg, 61.8%. Elemen-
tal Anal. Calc. for C37H36BF4N6OsP: C, 50.94; H, 4.15; N, 9.62. Found:
C, 51.05; H, 4.27; N, 9.69%. 1H NMR (400 MHz, CDCl3): d = 8.632 (d,
1H), 7.921 (d, 1H), 7.363–7.204 (m, 15H, PPh3), 6.334 (s, 2H), 4.765
(s, 5H, Cp), 2.731 (s, 6H, CH3), 2.642 (s, 6H, CH3). ESI-MS (m/z):
786.3 [MꢁBF4]+, 524.3 [MꢁPF6ꢁPPh3].
The infrared spectra of these complexes exhibit a strong mC@N
band in the range of 1543–1583 cmꢁ1 and mC@C in the range of
1437–1450 cmꢁ1 which are the characteristic bands of the ligands.
Besides these, for the complexes 1–9 and 12–15, a strong band in
the range of 841–844 cmꢁ1 is observed due to the stretching fre-
quency of mP–F band of the counter ions of these complexes.
Whereas, the complex 10 displays a strong band at 1098 cmꢁ1
which is due to the stretching frequency of the perchlorate ion
[59] and complexes 11, 16–18 exhibit a strong band at around
1082–1084 cmꢁ1 corresponding to the stretching frequency of
the mB-F band of the counter ions of these complexes. The m/z val-
ues of all these complexes and their stable ion peaks, as given in
the experimental section, are in good agreement with the theoret-
ical values, in its ZQ mass spectra. ESI mass spectra of the com-
plexes also displayed prominent peaks corresponding to the
molecular ion fragment. Complexes 1, 4–9 and 16–18 displayed
the loss of the coordinated triphenylphosphine in the first step,
whereas 2, 3 and 10–15 displayed the loss of the chloride ions. In
these complexes, the metal to cyclopentadiene and pentamethyl-
cyclopentadiene bond is stronger and remains intact.
3. Results and discussion
The synthetic route for the mononuclear
g
5-cyclopentadienyl
and pentamethylcyclopentadienyl complexes of Ru, Os, Rh and Ir
are presented in Schemes 1 and 2, respectively. All these com-
plexes were obtained in good yield from the reaction of starting
precursors and pyrazolylpyridazine ligands in methanol. Attempts
to make dinuclear complexes by increasing the metal to ligand ra-
tio were unsuccessful. The reason could be the steric bulkiness of
the complex because of the presence of bulky triphenylphosphine
ligand and methyl groups of pentamethylcyclopentadienyl ligand.
The complexes 1 and 4–9 are reddish-brown in color whereas com-
plexes 2, 3 and 10–15 are yellow in color, while the complexes 16–
18 are of cream color. They are non-hygroscopic crystalline solids
soluble in common polar solvents and are very much stable in solid
state as well as in solution. Information about the complexes was
also obtained from ESI-MS spectrometry. The molecular structures
of 2, 7, 10 and 11 have been authenticated by single crystal X-ray
diffraction analyses.
1H NMR spectral data of the complexes, along with their assign-
ments, are well formulated in the experimental section. The NMR
spectra of the Cp and Cpꢀ derivatives, which have ligands L, L1,
L2 and L3 exhibit three resonances for L, eight resonances for L1,
six resonances for L2 and three resonances for L3 in the aromatic
region corresponding to the pyrazole and pyridazine protons
which are clearly assigned in the experimental section. Besides,
Recently, we have reported [49] a series of arene ruthenium
complexes using these pyrazolylpyridazine ligands, where we ob-
served that in the ligand L2, the starting 3-methyl-pyrazole was
tautomerized to 5-methylpyrazole and the existence of both these
isomers was also observed in the same reaction products. The for-
mation of both the tautomers in the same reaction is the first of its

G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
2293
+
R'
R'
R
+
N
R
N
N
R'
R
N
N
M
N
Cl
N
N
b
N
R'
N
N
N
M
M
e
a
H
O
O
H
e
PPh3
(i)
R
M
(ii)
R'
R'
N
Mb=Rh, L1=(10)
L2=(11)
Ma=Ru, L1=(4)
L2=(5)
N
N
N N
L3=(12)
N
R
R
L3=(6)
Mb=Ir, L1=(13)
L2=(14)
Ma=Os, L1=(16)
L2=(17)
(iii)
L3=(15)
L3=(18)
+
R'
R'
L1=(7)
L2=(8)
L3=(9)
N
N
N
N
N
N
R
R
Ru
Ph3P
(i) = [{(η5-Cp)MaCl(PPh3)2}]; Ma=Ru, Os
(ii) = [{(η5-Cp*)MbCl(μ−Cl)}2]; Mb=Rh, Ir
(iii) = [{(η5-Cp*)RuCl(PPh3)2}]
Scheme 2.
all the ligands other than L1 show singlet in the region d = 2.93–
2.20 ppm which corresponds to the methyl protons of the ligands.
1H NMR spectra of the complexes bearing L2 as ligand give very
informative NMR spectra with peaks spread over a quiet wide
range as compared to that of the free ligand. The metal complexes
of the ligand L2 (Fig. 1) show two signals, a singlet at around
d = 2.378–2.408 ppm and another singlet at around d = 2.459–
2.706 ppm as compared to that of the free ligand which gives only
one singlet at d = 2.377 ppm. The singlet at around 2.378–
2.408 ppm is arising from the methyl protons of free pyrazole ring
containing methyl group while the second singlet comes from the
methyl protons of the binded pyrazole ring. But we do not find
much variation with the methyl protons in case of the ligand L3
and its complexes. In the case of the free ligand L3, we observe
two signals, a singlet at around 2.418 ppm which is assigned to
the R0R0 protons and another singlet at 2.731 ppm which corre-
sponds to the RR protons. Likewise the complexes bearing this li-
gand also show two singlets at almost the same range. Apart
from the ligands signals, the methyl protons associated to the
Cpꢀ of the complexes 2, 3 and 10–15 (Fig. 2) displayed a downfield
shift, a singlet, in the range of 2.17–1.73 ppm as compared to that
in the precursor complexes which show at around 1.59 ppm. The
downfield shift in the position of the Cpꢀ protons and the methyl
protons of the complexes bearing ligand L2 might result from a
change in the electron density on the metal center due to chelation
of the ligands through two nitrogen atoms. These indicate that
there is a significant deshielding after substituting one chloride
with chelating N,N0-donor ligands. Further, the protons associated
in the range of 7.563–7.062 ppm corresponding to the phenyl pro-
tons of the triphenylphosphine group of these complexes.
The 31P {1H} NMR spectra of the complexes 1 and 4–9 exhibit a
single sharp resonance for triphenylphosphine in the range of
50.41 and 49.70 ppm, indicating the presence of triphenylphos-
phine group in these complexes whereas for the starting com-
plexes [(g g
5-C5Me5)Ru(PPh3)2Cl] and [( 5-C5H5)Ru(PPh3)2Cl] the
signals appear at 38.5 and 42.0 ppm, respectively, [52–55].
3.1. UV–Vis spectroscopy
UV–Vis spectra of the complexes 2, 5, 6, 7, 8, 10, 11, 14 and 15
were acquired in acetonitrile and spectral data are summarized in
Table 3. Electronic spectra of representative complexes are de-
picted in Fig. 3. The low spin d6 configuration of these dinuclear
complexes provides filled orbitals of proper symmetry at the Ru(II)
centers which can interact with the low lying pꢀ orbital of the li-
Table 3
UV–Vis absorption data of the representative complexes in acetonitrile at 298 K.
Complex
kmax/nm (
e
/10ꢁ4 Mꢁ1 cmꢁ1
)
2
5
6
7
232.8 (0.70)
224.9 (0.25)
231.7 (0.97)
226.6 (0.43)
225.7 (0.49)
231.7 (0.64)
232.5 (0.70)
244.4 (0.30)
264.8 (0.64)
260.7 (0.63)
289.5 (0.21)
287.9 (0.42)
283.2 (0.58)
289.5 (0.89)
290.4 (0.80)
298.3 (1.02)
300.3 (0.90)
286.6 (0.56)
383.9 (0.07)
374.9 (0.05)
364.0 (0.10)
417.0 (0.06)
428.0 (0.07)
393.0 (0.05)
393.9 (0.06)
368.6 (0.11)
366.9 (0.15)
8
10
11
14
15
with the
g
5-Cp ring in complexes 1, 4–9 (Fig. 1) and 16–18 reso-
nated at almost same the position as singlets, i.e., at around
ꢄ4.78 ppm. Beside this, the complexes also displayed a multiplet

2294
G. Gupta et al. / Inorganica Chimica Acta 363 (2010) 2287–2295
gands. One should therefore expect a band attributable to the me-
tal–ligand charge transfer (MLCT) t2g
pꢀ transition in their elec-
uted to the presence of large size and steric nature of the triphen-
ylphosphine group.
?
tronic spectra. The electronic spectra of these complexes display a
medium intensity bands in the UV–Vis region. The lowest energy
absorption bands in the electronic spectra of these complexes in
the visible region ꢄ428–364 nm have been tentatively assigned
Acknowledgements
K.M. Rao gratefully acknowledges financial support from the
Department of Science and Technology, New Delhi, through the Re-
search Grant No. SR/S1/IC-11/2004. G.G. is thankful for financial
support from University Grant Commissions, New Delhi.
on the basis of their intensity and position to t2g
?
pꢀ MLCT tran-
sitions. The bands on the high energy side at ꢄ300.3–224.9 nm for
the complexes 2, 5, 6, 7, 8, 10, 11, 14 and 15, have been assigned to
ligand-centered
p ?
pꢀ/n ? pꢀ transitions. In general, these com-
plexes follow the normal trend observed in the electronic spectra
Appendix A. Supplementary material
of the nitrogen-bonded metal complexes, which display a ligand-
based
p ?
pꢀ transition for pyrazolylpyridazine ligand in the UV
CCDC 738547, 727093, 727091 and 727092 contain the supple-
mentary crystallographic data for 2, 7, 10, 11. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supple-
mentary data associated with this article can be found, in the on-
line version, at doi:10.1016/j.ica.2010.03.052.
region and metal–ligand charge transfer transitions in the visible
region.
3.2. Molecular structures
Molecular structures of 2, 7, 10 and 11 have been determined
crystallographically. The complexes crystallize in Pca2 (1), P21/c
(1), P21/c (2) and P21/n (10) space groups. Details about data collec-
tion, refinement and structure solution are recorded in Table 1, and
selected bond lengths and angles are presented in Table 2. Crystal
structures of 2, 7, 10 and 11 with atom-numbering schemes are
shown in Figs. 4–7. In complexes 2, 10 and 11, the metal is bonded
with the major coordinating sites N1 and N3 in a k2 manner, one
chloro group, and the pentamethylcyclopentadienyl (Cpꢀ) ring in
References
[1] G. Di Marco, A. Bartolotta, V. Ricevuto, S. Campagna, G. Denti, L. Sabatino, G. De
Rosa, Inorg. Chem. 30 (1991) 270.
[2] V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 96 (1996)
759.
[3] J.F. Endicott, H.B. Schlegel, Md.J. Uddin, D.S. Seniveratne, Coord. Chem. Rev. 229
(2002) 95.
[4] W.R. Browne, R. Hage, J.G. Vos, Coord. Chem. Rev. 250 (2006) 1653.
[5] M.T. Indelli, C. Chiorboli, F. Scandola, Top. Curr. Chem. 80 (2007) 215.
[6] M. Yanagida, J. Chem. Soc., Dalton Trans. 16 (2000) 2817.
[7] Y. Wang, W. Perez, G.Y. Zheng, D.P. Rillema, Inorg. Chem. 37 (1998) 2051.
[8] A.C. Lees, B. Evrard, T.E. Keyes, J.G. Vos, C.J. Kleverlaan, M. Alebbi, C.A. Bignozzi,
Eur. J. Inorg. Chem. 12 (1999) 2309.
[9] C.J. Kleverlaan, M.T. Indelli, C.A. Bignozzi, L. Pavanin, F. Scandola, G.M.
Hasselman, G.J. Meyer, J. Am. Chem. Soc. 122 (2000) 2840.
[10] T. Ohta, S. Nakahara, Y. Shigemura, K. Hattori, I. Furukawa, Appl. Organomet.
Chem. 15 (2001) 699.
[11] S. Ogo, K. Uehara, T. Abura, Y. Watanabe, S. Fukuzumi, Organometallics 23
(2004) 304.
[12] C.A. Sandoval, T. Ohkuma, N. Utsumi, K. Tsutsumi, K. Murata, R. Noyori, Chem.
Asian J. 1–2 (2006) 102. and reference cited therein.
[13] R. Noyori, S. Hashigushi, Acc. Chem. Res. 30 (1997) 97. and reference cited
therein.
[14] E.P. Kündig, A. Quattropani, M. Inage, A. Ripa, C. Dupre, A.F.J. Cunningham, B.
Bourdin, Pure Appl. Chem. 68 (1996) 97.
a
g
5 manner. Similarly, Ru1 in 7 is also coordinated through pyra-
zole nitrogen N1, pyridazine nitrogen N3 in a k2 manner, one phos-
phorus P1 of PPh3, and the pentamethylcyclopentadienyl (Cpꢀ) ring
in a g5 manner. Typical piano-stool geometry about the metal in
all these complexes is maintained. The Cpꢀ ring in 2, 10 and 11
is planar with an average Rh-C distance of 2.155 Å and the Rh cen-
ter is displaced by 1.785 Å, 1.776 Å and 1.788 Å from the centroid
of the Cpꢀ ring, which are comparable to the distances in other rho-
dium pentamethylcyclopentadienyl complexes. The C–C bond
lengths within the Cpꢀ ring and C–Me distances are normal. Rh–
N and Rh–Cl bond lengths are consistent with the values reported
in the literature [60–63]. The Cpꢀ ring in complex 7 is also planer,
the average Ru–C distance is 2.203 Å, and the Ru to centroid bond
distance is 1.840 Å, which is comparable to the distances reported
in other ruthenium pentamethylcyclopentadienyl complexes [64–
66]. The Ru–P and Ru–Cl distances are normal and consistent with
the values reported in other related complexes [64–66]. The che-
lating N–Rh–N bite for the coordination of the pyrazole nitrogen
and the pyridazine nitrogen of the ligand in the complexes 2, 10
and 11 are 74.40°, 75.25° and 75.0°, while in the case of the com-
plex 7 the N–Ru–N angle is 75.4° which is comparable to other re-
ported [64–66] similar ruthenium complexes. The N(4)–N(3)–M(1)
angles in complexes 7, 10 and 11 are close to each other and are in
the range of around ꢄ121.28–121.70°, whreas in complex 2 the
N(4)–N(3)–M(1) angle is much lower than that in the other above
mentioned complexes.The N–Rh–Cl angles in complexes 2, 10 and
11 are normal [63].
[15] J.W. Faller, M.R. Mazzieri, J.T. Nguyen, J. Parr, M. Tokunaga, Pure Appl. Chem.
66 (1994) 1463.
[16] S.G. Davies, Pure Appl. Chem. 60 (1988) 13.
[17] C.A. Goss, H.D. Abruna, Inorg. Chem. 24 (1985) 4263.
[18] F. Hanasaka, K.-I. Fujita, R. Yamaguchi, Organometallics 24 (2005) 3422.
[19] M.S. El-Shahawi, A.F. Shoair, Spectrochim. Acta, A 60 (2004) 121.
[20] J.-P. Sauvage, J.-P. Collin, J.-C. Chambron, S. Guillerez, C. Coudret, V. Balzani, F.
Barigelletti, L. De Cola, L. Flamigni, Chem. Rev. 94 (1994) 993.
[21] Z. Shirin, R. Mukherjee, J.F. Richardson, R.M. Buchanan, J. Chem. Soc., Dalton
Trans. (1994) 465.
[22] W. Kaim, R. Reinhardt, J. Fiedler, Angew. Chem., Int. Ed. Engl. 36 (1997) 2493.
[23] S. Chellamma, M. Lieberman, Inorg. Chem. 40 (2001) 3177.
[24] T.J. Meyer, M.H.V. Huynh, Inorg. Chem. 42 (2003) 8140.
[25] M. Newell, J.A. Thomas, J. Chem. Soc., Dalton Trans. (2006) 705.
[26] H. Nakajima, H. Nagao, K. Tanaka, J. Chem. Soc., Dalton Trans. (1996) 1405.
[27] Y.K. Yan, M. Melchart, A. Hebtemariam, P.J. Sadler, Chem. Commun. (2005)
4764.
[28] W.H. Ang, P.J. Dyson, Eur. J. Inorg. Chem. (2006) 4003.
[29] M. Auzias, B. Therrien, G. Süss-Fink, P. Štepnicka, W.H. Ang, P.J. Dyson, Inorg.
Chem. 47 (2008) 578.
ˇ
ˇ
[30] A.F.A. Peacock, A. Habtemariam, R. Fernandez, V. Walland, F.P.A. Fabbiani, S.
Parsons, R.E. Aird, D.I. Jodrell, P.J. Sadler, J. Am. Chem. Soc. 128 (2006) 1739.
[31] A. Habtemariam, M. Melchart, R. Fernandez, S. Parsons, I.D.H. Oswald, A.
Parkin, F.P.A. Fabbiani, J.E. Davidson, A. Dawson, R.E. Aird, D.I. Jodrell, P.J.
Sadler, J. Med. Chem. 49 (2006) 6858.
4. Conclusion
[32] M. Melchart, A. Habtemariam, O. Novakova, S.A. Moggach, F.P.A. Fabbiani, S.
Parsons, V. Brabec, P.J. Sadler, Inorg. Chem. 46 (2007) 8950.
[33] C. Scolaro, A. Bergamo, L. Brescacin, R. Delfino, M. Cocchietto, G. Laurenczy, T.J.
Geldbach, G. Sava, P.J. Dyson, J. Med. Chem. 48 (2005) 4161.
[34] W. Baratta, E. Herdtweck, W.A. Hermann, P. Rigo, J. Schwarz, Organometallics
21 (2002) 2101.
[35] M.A. Bennett, K. Khan, E. Wenger, in: G. Wilkinson, F.G.A. Stone, E.W. Abel
(Eds.), Comprehensive Organometallic Chemistry II, second ed., vol. 7, Elsevier,
Oxford, 1995. Chapter 8 and references cited therein.
In summary, a series of new mononuclear platinum group metal
complexes 1–18 have been synthesized using pyrazolylpyridazine
ligands in good yield, which are remarkably stable in air as well as
in solution. In all these complexes, the metal is bonded with the
major coordinating sites N1 and N3, whereas an effort to make
binuclear complexes or to put another metal at the other binding
sites, i.e., N4 and N6, was not fruitful. The reason could be attrib-

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2295
[36] S.G. Davies, J.P. McNally, J. Smallridge, Adv. Organomet. Chem. 30 (1991) 1.
[37] B.M. Trost, J.A. Marting, R.J. Kulawiec, A.F. Indolese, J. Am. Chem. Soc. 115
(1993) 10402.
[38] P. Pertici, V. Ballantini, P. Salvadori, M.A. Bennett, Organometallics 14 (1995)
2565.
[39] D.L. Davies, J. Fawcett, R. Krefczyk, D.R. Russell, J. Organomet. Chem. 545–546
(1997) 581.
[52] M.I. Bruce, N.J. Windsor, Aust. J. Chem. 30 (1977) 1601.
[53] P.W. Wanandi, T.D. Tilley, Organometallics 16 (1997) 4299.
[54] M.I. Bruce, P.J. Low, B.W. Skelton, E.R.T. Tiekink, A. Werth, A.H. White, Aust. J.
Chem. 48 (1995) 1887.
[55] M.I. Bruce, B.C. Hall, N.N. Zaitseva, B.W. Skelton, A.H. White, J. Chem. Soc.,
Dalton Trans. (1998) 1793.
[56] L.A. Oro, M.A. Ciriano, M. Campo, C. Foces-Foces, F.H. Cano, J. Organomet.
Chem. 289 (1995) 117.
[57] G.M. Sheldrick, Acta Crystallogr., Sect. A46 (1990) 467.
[58] G.M. Sheldrick, SHELXL-97, University of Göttingen, Göttingen, Germany.,
1999.
[59] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fifth ed., Wiley-Inter Science, New York, 1997. p. 273, Part B.
[40] B.M. Trost, M.U. Frederiksen, M.T. Rudd, Angew. Chem., Int. Ed. Eng. 44 (2005)
6630. and references cited therein.
[41] W. Baratta, A.D. Zotto, P. Rigo, Chem. Commun. (1997) 2163.
[42] A.D. Zotto, W. Baratta, G. Verardo, P. Rigo, Eur. J. Org. Chem. (2000) 2795.
[43] T. Blackmore, M.I. Bruce, F.G.A. Stone, J. Chem. Soc. A (1971) 2376.
[44] G.S. Ashby, M.I. Bruce, I.B. Tomkins, R.C. Wallis, Aust. J. Chem. 32 (1979) 1003.
[45] S.G. Davies, S.J. Simpson, H. Felkin, T. Fillebeen-Khan, Organometallics 2 (1983)
539.
ˇ
ˇ
ˇ
[60] P. Govindaswamy, J. Canivet, B. Therrien, G. Süss-Fink, P. Štepnicka, Jiri Ludvik,
J. Organomet. Chem. 692 (2007) 3664.
ˇ
ˇ
ˇ
[46] S.G. Davies, S.J. Simpson, H. Felkin, T. Fillebeen-Khan, F. Tadjand, O. Watts, J.
Chem. Soc., Chem. Commun. (1981) 341.
[61] P. Govindaswamy, B. Therrien, G. Süss-Fink, P. Štepnicka, Jiri Ludvik, J.
Organomet. Chem. 692 (2007) 1661.
[47] M.I. Bruce, S.F. Wong, B.W. Skelton, A.H. White, J. Chem. Soc., Dalton Trans.
(1981) 1398.
[62] C. Tejel, M.A. Ciriano, S. Jimenez, V. Passarelli, J.A. Lopez, Inorg. Chem. 47
(2008) 10220.
[48] L.K. Thompson, T.C. Woon, David B. Murphy, Eric J. Gabe, Florence L. Lee, Y. Le,
Inorg. Chem. 24 (1985) 4719.
[63] C. Scheeren, F. Maasarani, A. Hijazi, J.P. Djukic, M. Pfeffer, Organometallics 26
(2007) 3336.
[49] G. Gupta, K.T. Prasad, B. Das, G.P.A. Yap, K. Mohan Rao, J. Organomet. Chem.
694 (2009) 2618.
[64] K.S. Singh, Y.A. Mozharivskyj, P.J. Carroll, K. Mohan Rao, J. Organomet. Chem.
689 (2004) 1249.
[50] J.W. Kang, K. Moseley, P.M. Maitlis, J. Am. Chem. Soc. 91 (1969) 5970.
[51] C. White, A. Yates, P.M. Maitlis, Inorg. Synth. 29 (1992) 228.
[65] K.S. Singh, P.J. Carroll, K. Mohan Rao, Polyhedron 24 (2005) 391.
[66] G. Gupta, G.P.A. Yap, B. Therrien, K. Mohan Rao, Polyhedron 28 (2009) 844.