Mononuclear complexes of platinum group metals containing η6- And η5cyclic II-perimeter hydrocarbon and pyridylpyrazolyl derivatives: Syntheses and structural studies

Article abstract of DOI:10.1002/zaac.200900475

Piano-stool-shaped platinum group metal compounds, stable in the solid state and in solution, which are based on 2-(5-pheny1-1H-pyrazol-3-yl)pyridine (L) with the formulas [(η⁶-arene)Ru(L)C1]PR₆{arene= C₆H₆ (1),p-cymene (2), and C₆Me₆, (3)}, [(η⁶-C₅Me₅)M(L)C1]PF₆ {M = Rh (4), Ir (5)}, and [(η⁵-C₅H₅) Ru(TPPh₃)(L)]PF₆ (6), [(η⁵-C ₅.H₅)Os(PPh₃)(L)]PF₆ (7), [(η⁵-C₅Me₅)Ru(PPh₃)(L)]PF ₆ (8), and [(η⁵-C₉H₇)Ru(PPh ₃)-(L)]PF₆ (9) were prepared by a general, method, and characterized by NMR and IR spectroscopy and mass spectrometry. The molecular structures of compounds 4 and 5 were established by single-crystal X-ray diffraction. In each compound the metal is connected to N1 and N11 in a k ² manner.

Full text of DOI:10.1002/zaac.200900475

ARTICLE
DOI: 10.1002/zaac.200900475
Mononuclear Complexes of Platinum Group Metals Containing η6- and η5-
Cyclic П-Perimeter Hydrocarbon and Pyridylpyrazolyl Derivatives:
Syntheses and Structural Studies
Gajendra Gupta,[a] Chong Zheng,[b] Peng Wang,[c] and Kollipara Mohan Rao*[a]
Keywords: Phenylpyrazolylpyridines; Ruthenium; Rhodium; Iridium; Osmium
Abstract. Piano-stool-shaped platinum group metal compounds, stable in (L)]PF6 (9) were prepared by a general method and characterized by
the solid state and in solution, which are based on 2-(5-phenyl-1H-pyra- NMR and IR spectroscopy and mass spectrometry. The molecular struc-
zol-3-yl)pyridine (L) with the formulas [(η6-arene)Ru(L)Cl]PF6 {arene = tures of compounds 4 and 5 were established by single-crystal X-ray
C6H6 (1), p-cymene (2), and C6Me6, (3)}, [(η6-C5Me5)M(L)Cl]PF6 {M = diffraction. In each compound the metal is connected to N1 and N11 in
Rh (4), Ir (5)}, and [(η5-C5H5)Ru(PPh3)(L)]PF6 (6), [(η5-C5H5)Os(PPh3)- a k2 manner.
(L)]PF6 (7), [(η5-C5Me5)Ru(PPh3)(L)]PF6 (8), and [(η5-C9H7)Ru(PPh3)-
carried out on η5- and η6-transition metal complexes; com-
1. Introduction
pounds containing phenylpyrazolylpyridine ligands of the type
Mononuclear compounds of platinum group metals contain-
ing nitrogen based ligands received considerable attention be-
cause of their photochemical properties [1–9], their catalytic
activities [10–19], and their electrochemical behavior [20–26],
as well as in the development of new biological active agents
[27–33]. In particular, η6-arene metal complexes emerged as
versatile intermediates in organic synthesis; they contain three
labile coordination sites, whereas another three coordination
sites are occupied by a rigid arene ring [34, 35]. They have
found application in catalysis, supramolecular assemblies, and
in molecular devices. Additionally, η6-arene metal complexes
showed antiviral, antibiotic, and anticancer activities. Half-
sandwich complexes attracted attention because they proved to
be extremely useful in stoichiometric and catalytic asymmetric
syntheses [36–39]. The tetracoordinate, pseudo-tetrahedral ar-
rangement makes them particularly suitable for investigation
of the stereochemistry of reactions at the metal atom [40]. In
recent years, we carried out reactions of η5- and η6- cyclic
П-perimeter hydrocarbon metal complexes with a variety of
nitrogen-based ligands [41–48] including various polypyridyl
ligands. Ruthenium compounds with these types of ligands
have the capacity to function as catalysts for the oxidation of
water to dioxygen [49, 50]. Although extensive studies were
shown below have not been investigated yet.
Herein we describe the syntheses of nine mononuclear η5-
and η6-cyclic П-perimeter hydrocarbon platinum group metal
compounds bearing the ligand phenylpyrazolylpyridine. Our
main goal in choosing this phenyl-substituted ligand was to
synthesize a series of mononuclear and dinuclear compounds
by activating the carbon atom of the phenyl ring. But attempts
to prepare a dimetallic derivative through the addition of a
second organometallic anion by activation of the carbon atom
were unsuccessful and we ended up with a series of mononu-
clear compounds only with metal bound to two nitrogen atoms
(N1 and N11) of the ligand. All these compounds were fully
characterized by IR and NMR spectroscopy, and mass spec-
trometry. Molecular structures of the two representative com-
pounds are also presented in this paper.
* Prof. Dr. K. M. Rao
2. Experimental Section
E-Mail: mohanrao59@gmail.com
[a] Department of Chemistry
North Eastern Hill University
Shillong 793 022, India
All solvents were dried and distilled prior to use. The ligand L was syn-
thesized by following a literature method [51]. The precursor complexes
[(η6-arene)Ru(μ-Cl)Cl]2 (arene = C6H6, C10H14, and C6Me6), [(η6-
C5Me5)M(μ-Cl)Cl]2 (M = Rh, Ir) [52–55], [(η5-C5H5)Ru(PPh3)2Cl], [(η5-
C5H5)Os(PPh3)2Br], [(η5-C5Me5)Ru(PPh3)2Cl], and [(η5-C9H7)Ru-
(PPh3)2Cl] were prepared by following the literature methods [56–61].
NMR spectra were recorded with a Bruker AMX 400 MHz spectrometer.
[b] Department of Chemistry and Biochemistry
Northern Illinois University
De Kalb, Illinois, USA
[c] Department of Chemistry
McMaster University
Hamilton, Ontario, L8S 4M1, Canada
758
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 636, 758–764

Mononuclear Complexes of Platinum Group Metals
Infrared spectra were recorded as KBr pellets with a Perkin–Elmer 983 SADABS. Structures were solved by direct methods using SHELXS-
spectrophotometer. Mass spectra were obtained with a ZQ mass spectrom- 97 [62] and refined with full-matrix least-squares on F2 using
eter by the ESI method.
SHELXL-97 [63]. All non-hydrogen atoms were refined anisotropi-
cally. The hydrogen atoms were located from the difference Fourier
maps and refined. Structural illustrations have been drawn with OR-
TEP-3 [64] for Windows. The ORTEP presentations of the representa-
tive compounds are shown in Figure 1 and Figure 2 respectively. The
data collection parameters and bond lengths and angles are presented
in Table 1 and Table 2.
2.1. Single-Crystal X-ray Structures Analyses
Crystals of compound 4 were grown from acetone/hexane as small red
plates. Crystals of compound 5 were grown by slow evaporation of a
methanol solution of the respective compound as deep red blocks. The
crystallizations were carried out at room temperature. The intensity
data of 4 and 5 were collected with a Bruker SMART APEX-II CCD
diffractometer, equipped with a fine focus 1.75 kW sealed tube Mo-
Kα radiation (α = 0.71073 Å) at 273(3) K, with increasing ω (width of
0.3° per frame) at a scan speed of 3 s per frame. The SMART software
was used for data acquisition. Data integration and reduction were
undertaken with the SAINT and XPREP software. Multi-scan empiri-
cal absorption corrections were applied to the data using the program
CCDC-749569 (4) and CCDC-749570 (5) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/data_request/cif, by E-Mail: data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax:
+44-1223-336033.
2.2. Syntheses
[(η6-C6H6)Ru(L)Cl]PF6 (1): A mixture of [(η6-C6H6)Ru(μ-Cl)Cl]2
(100 mg, 0.2 mmol), 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L)
(90 mg, 0.4 mmol), and two equivalents of NH4PF6 was stirred in dry
methanol (30 mL) for 4 h at room temperature. The brown compound
that formed was filtered, washed with ethanol and diethyl ether and
dried in vacuo. Yield 90 mg, 77 %. C20H17ClN3PF6Ru: calcd. C 41.34;
H 2.97; N 7.25 %; found: C 41.45; H 3.07; N 7.14 %. IR (KBr):
1
ν = 3436 (νN–H); 1625 (νC=C); 1457 (νC=N); 846 (νP–F) cm–1. H NMR
˜
(400 MHz, CD3CN): δ = 9.341 (d, J = 5.6 Hz, 1 H), 8.132 (dt, J =
8.4 Hz, 3 H), 8.00 (dd, J = 8 Hz, 2 H), 7.882 (d, J = 7.2 Hz, 2 H),
7.600–7.530 (m, 1 H), 7.321 (s, 1 H), 6.079 (s, 6 H, C6H6). ESI-MS
(m/z): 436.1 [M – PF6], 400.2[M – PF6 – Cl].
[(η6-p-iPrC6H4Me)Ru(L)Cl]PF6 (2): A mixture of [(η6-C10H14)Ru(μ-
Cl)Cl]2 (100 mg, 0.163 mmol), 2-(5-phenyl-1H-pyrazol-3-yl)pyridine
(L) (72 mg, 0.325 mmol), and two equivalents of NH4PF6 was stirred
in dry methanol (30 mL) for 4 h at room temperature. The yellow
compound that formed was filtered, washed with ethanol and diethyl
ether and dried in vacuo. Yield 87 mg, 84 %. C24H25ClN3PF6Ru:
calcd. C 45.23; H 3.99; N 6.63 %; found: C 45.33; H 3.84; N 6.48 %.
IR (KBr): ν = 3446 (νN–H); 1635 (νC=C); 1451 (νC=N); 849 (νP–F) cm–1.
˜
1H NMR (400 MHz, CDCl3): δ = 9.204 (d, J = 5.6 Hz, 1 H), 8.006
(t, J = 8.8 Hz, 2 H), 7.827 (t, J = 7.2 Hz, 1 H), 7.550- 7.491 (m, 1 H),
7.473 (d, J = 6.8 Hz, 2 H), 6.984 (s, 1 H), 6.341(d, J = 6 Hz, 2 H),
5.941(d, J = 6 Hz, 1 H, Arp–cy), 5.868 (d, J = 6 Hz, 1 H, Arp–cy), 5.769
(d, J = 6 Hz, 1 H, Arp–cy), 5.651(d, J = 6 Hz, 1 H, Arp–cy), 2.792 (sep,
1 H), 2.234 (s, 3 H), 1.055 (dd, J = 6.8 Hz, 6 H). ESI-MS (m/z): 492.1
[M – PF6], 456.3 [M – PF6 – Cl], 458.3 [M – PF6 – Cl]2+.
Figure 1. Molecular structure of compound 4 with 35 % probability
thermal ellipsoids. Hydrogen atoms and the BF4 ion are omitted for
clarity.
[(η6-C6Me6)Ru(L)Cl]PF6 (3): A mixture of [(η6-C6Me6)Ru(μ-Cl)Cl]2
(100 mg, 0.15 mmol), 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L)
(66 mg, 0.30 mmol), and two equivalents of NH4PF6 was stirred in
dry methanol (30 mL) for 4 h at room temperature. The solvent was
removed by using a rotary evaporator. The solid was dissolved in di-
chloromethane and afterwards filtered to remove ammonium chloride.
The solution was concentrated to 2 mL and excess of diethyl ether was
added for precipitation. The light brown colored product was sepa-
rated, washed with diethyl ether and dried in vacuo. Yield 84 mg,
84 %. C26H29ClN3PF6Ru: calcd. C 46.93; H 4.45; N 6.30 %; found: C
46.26; H 4.51; N 6.21 %. IR (KBr): ν = 3430 (νN–H); 1632 (νC=C);
˜
1452 (νC=N); 847 (νP–F)m cm–1. 1H NMR (400 MHz, CDCl3): δ =
9.432 (d, J = 6.8 Hz, 1 H), 8.332 (dt, J = 8 Hz, 3 H), 8.110 (dd, J =
7.2 Hz, 2 H), 7.972 (d, J = 7.6 Hz, 2 H), 7.720–7.610 (m, 1 H), 7.431
(s, 1 H), 2.188 (s, 18 H, C6Me6). ESI-MS (m/z): 448.1 [M – PF6], 413
[M – PF6 – Cl].
Figure 2. Molecular structure of compound 5 with 35 % probability
thermal ellipsoids. Hydrogen atoms and the perchlorate ion are omitted
for clarity.
Z. Anorg. Allg. Chem. 2010, 758–764
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
759

G. Gupta, C. Zheng, P. Wang, K. M. Rao
ARTICLE
Table 1. Crystallographic and structure refinement parameters for compounds 4 and 5.
4
5
Emperical formula
C24H26BClF4N3Rh
581.65
C25H29Cl2IrN3O5
714.61
Formula weight
Temperature /K
293(2)
293(2)
Wavelength /Å
0.71073
0.71073
Monoclinic
P21/n
Crystal system
Triclinic
¯
Space group
P1
Unit cell dimensions
a /Å
10.5688(6)
13.0524(8)
b /Å
11.4582(7)
10.0571(9)
c /Å
11.4748(7)
20.7255(14)
90
α /°
116.3150(10)
94.7380(10)
94.3690(10)
1231.40(13)
2
β /°
100.251(5)
γ /°
90
Volume /A3
2677.2(3)
Z
4
Calculated density /Mg·m–3
Absorption coefficient /mm–1
F(000)
1.569
1.775
0.850
5.227
588
1404
Crystal size /mm
Θ range for data collection /°
Index ranges
0.20 × 0.10 × 0.02
1.95 to 25.00
–12 ≤ h ≤ 12
–13 ≤ k ≤ 13
–13 ≤ l ≤ 13
9432/4327, 0.0305
R1 = 0.0471, wR2 = 0.1049
R1 = 0.0657, wR2 = 0.1120
0.761 and –0.643
0.11 × 0.08 × 0.02
1.72 to 25.37
–14 ≤ h ≤ 14
–12 ≤ k ≤ 11
–24 ≤ l ≤ 24
22770/4556, 0.0609
R1 = 0.0272, wR2 = 0.0316
R1 = 0.0790, wR2 = 0.0358
0.704 and –0.890
Reflections collected / unique, Rint
Final R indices [I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole /e·Å–3
Table 2. Selected bond lengths and angles for compounds 4 and 5.
BF4 – Cl – H]. Compound (5): Yield 69 mg, 82 %. C24H26ClN3BF4Ir:
calcd. C 42.99; H 3.95; N 5.53 %; found: C 43.07; H 4.04; N 5.46 %.
4
5
IR (KBr): ν = 3460 (νN–H); 1634 (νC=C); 1453 (νC=N); 1099 (νCl–O
)
˜
1
cm–1. H NMR (400 MHz, CDCl3): δ = 8.778 (d, J = 5.6 Hz, 1 H),
8.137 (dt, J = 7.6 Hz, 2 H), 8.068 (d, J = 7.6 Hz, 2 H), 7.792 (dd, J =
6 Hz, 2 H), 7.681 (dt, J = 6.4 Hz, 1 H), 7.568–7.505 (m, 1 H), 7.383
(s, 1 H), 1.724 (s, 15 H, C5Me5). ESI-MS (m/z): 494.4 [M – BF4],
459.1 [M – BF4 – Cl].
N(1)–M(1)
2.139(9)
2.090(9)
1.378(14)
2.401(4)
1.773
75.8(4)
134.0(7)
85.5(3)
88.7(3)
2.125(3)
2.069(2)
1.373(3)
2.399(15)
1.791
75.49(9)
133.52(17)
86.11(9)
86.74(10)
N(11)–M(1)
N(10)–N(11)
Cl(1)–M(1)
M(1)–CNT(1)a)
N(1)–M(1)–N(11)
N(10)–N(11)–M(1)
N(1)–M(1)–Cl(1)
N(11)–M(1)–Cl(1)
[(η5-C5H5)M(L)(PPh3)]PF6 {M = Ru (6), Os (7)}: A mixture of [(η5-
C5H5)M(PPh3)2X] {M = Ru, X = Cl and M = Os, X = Br}
(0.137 mmol), 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L) (30 mg,
0.137 mmol), and one equivalent of NH4PF6 in dry methanol (30 mL)
was heated under reflux for 12 h until the color of the solution changed
from pale yellow to orange. The solvent was removed under vacuum,
a) CNT = Metal to centroid of Cp*.
[(η5-C5Me5)M(L)Cl]X {M = Rh, X = BF4 (4), Ir, X = ClO4 (5)}: A the residue was dissolved in dichloromethane (10 mL), and the solu-
mixture of [(η5-C5Me5)M(μ-Cl)Cl]2 (M = Rh, Ir) (0.16 mmol), 2-(5- tion was filtered to remove ammonium halide. The orange solution
phenyl-1H-pyrazol-3-yl)pyridine (L) (71 mg, 0.32 mmol), and two was concentrated to 5 mL. Afterwards, addition of ethyl ether gave a
equivalents of NH4BF4 (compound 4) and NaClO4 (compound 5) in orange-yellow precipitate, which was separated and dried in vacuo.
dry methanol (30 mL) was stirred at room temperature for 6 h until Compound (6): Yield 74 mg, 68 %. Elemental Anal (%)
the color of the solution changed to dark yellow. The solvent was C37H31N3P2F6Ru: calcd. C 55.94; H 3.97; N 5.27 %; found: C 56.19;
removed by using a rotary evaporator under reduced pressure. The H 4.08; N 5.18 %. IR (KBr): ν = 3430 (νN–H); 1628 (νC=C); 1450
˜
1
residue was dissolved in dichloromethane (5 mL), and the solution (νC=N); 849 (νP–F) cm–1. H NMR (400 MHz, CDCl3): δ = 9.006 (d,
was filtered to remove ammonium chloride. The light red solution was J = 5.2 Hz, 1 H), 8.614 (d, J = 4.4 Hz, 2 H), 8.009 (d, J = 7.2 Hz, 2
concentrated to 2 mL; addition of excess hexane gave the orange-yel- H), 7.939 (t, J = 8 Hz, 2 H), 7.672 (t, J = 7.6 Hz, 1 H), 7.591–7.523
low complex, which was separated and dried in vacuo. Compound
(m, 1 H), 7.333–7.022 (m, 15 H, PPh3), 7.189 (s, 1 H), 4.723 (s, 5 H,
(4): Yield 80 mg, 85 %. C24H26ClN3BF4Rh: calcd. C 49.58; H 4.57; C5H5). 31P{1H} NMR (CDCl3): δ = 50.82 (s, PPh3). ESI-MS (m/z):
N 7.24 %; found: C 49.67; H 4.63; N 7.13 %. IR (KBr): ν = 3438 583.6 [M – PF6], 548.2 [M – PF6 – Cl]. Compound (7): Yield 75 mg,
˜
(νN–H); 1628 (νC=C); 1450 (νC=N); 1088 (νB–F) cm–1. 1H NMR 69 %. Elemental Anal (%) C35H30N6P2F6Os: calcd. C 50.31; H 3.55;
(400 MHz, CDCl3): δ = 8.708 (d, J = 5.6 Hz, 1 H), 8.062 (t, J = N 4.72 %; found: C 50.42; H 3.63; N 4.66 %. IR (KBr): ν = 3448
7.6 Hz, 1 H), 7.973 (d, J = 7.6 Hz, 2 H), 7.713(d, J = 7.2 Hz, 2 H), (νN–H); 1629 (νC=C); 1451 (νC=N); 844 (νP–F
˜
)
cm–1. 1H NMR
7.587 (t, J = 6.8 Hz, 2 H), 7.474–7.403 (m, 1 H), 7.194 (s, 1 H), 1.688 (400 MHz, CDCl3): δ = 12.882 (s, NH, 1 H), 9.130 (d, J = 5.6 Hz, 1
(s, 15 H, C5Me5). ESI-MS (m/z): 459.2 [M – BF4 – Cl], 458.3 [M – H), 8.622 (d, J = 7.2 Hz, 2 H), 7.804 (d, J = 7.2 Hz, 2 H), 7.720
760
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 758–764

Mononuclear Complexes of Platinum Group Metals
(t, J = 8 Hz, 3 H), 7.573–7.498 (m, 1 H), 7.387–7.018 (m, 15 H, PPh3),
6.560 (s, 1 H), 4.658 (s, 5 H, C5H5). 31P{1H} NMR (CDCl3): δ = –
0.254 (s, PPh3). ESI-MS (m/z): 740.5 [M – PF6], 738.3 [M – PF6 –
2H], 737.3 [M – PF6 – 3H].
[(η5-C5Me5)Ru(L)(PPh3)]PF6
(8):
A
mixture
of
[(η5-
C5Me5)Ru(PPh3)2Cl] (100 mg, 0.125 mmol), 2-(5-phenyl-1H-pyrazol-
3-yl)pyridine (L) (37.7 mg, 0.125 mmol), and one equivalent of
NH4PF6 in dry methanol (30 mL) was heated under reflux for 12 h
until the color of the solution changed from pale yellow to orange.
The solvent was removed by using a rotary evaporator under reduced
pressure. The residue was dissolved in dichloromethane (10 mL), and
the solution was filtered to remove ammonium chloride. The orange
solution was concentrated to 5 mL. Addition of excess hexane gave
the orange-yellow compound, which was separated and dried in vacuo.
Yield 72 mg, 66 %. Elemental Anal (%) C42H41N3P2F6Ru: calcd. C
58.36; H 4.80; N 4.89 %; found: C 58.43; H 4.91; N 4.76 %. IR (KBr):
˜
Scheme 1.
1
ν = 3434 (νN–H); 1626 (νC=C); 1445 (νC=N); 847 (νP–F) cm–1. H NMR
(400 MHz, CDCl3): δ = 8.807 (d, J = 5.6 Hz, 1 H), 8.693 (d, J =
7.2 Hz, 2 H), 7.862 (t, J = 7.6 Hz, 1 H), 7.815 (t, J = 7.6 Hz, 2 H),
7.576–7.454 (m, 1 H), 7.371–7.263 (m, 15 H, PPh3), 7.002 (d, J =
10.8 Hz, 2 H), 6.583 (s, 1 H), 2.071 (s, 15 H, C5Me5). 31P{1H} NMR
(CDCl3): δ = 50.430 (s, PPh3). ESI-MS (m/z): 719.3[M – PF6], 457.3
[M – PF6 – PPh3].
The infrared spectra of compounds 1–3 exhibit the signals
of the chelating N,N'-bidentate ligand as broad bands at 3436,
3446, 3430, 1625, 1635, 1632, 1457, 1451, and 1452 cm–1,
which correspond to the stretching frequencies of the N–H
bond of pyrazole ring, and of the C=C and C=N bonds of the
pyridine ring of the ligand, respectively. In addition, the IR
spectra of all these compounds display a strong band at about
[(η5-C9H7)Ru(L)(PPh3)]PF6
(9):
A
mixture
of
[(η5-
C9H7)Ru(PPh3)2Cl] (100 mg, 0.128 mmol), 2-(5-phenyl-1H-pyrazol-
3-yl)pyridine (L) (38.4 mg, 0.128 mmol), and one equivalent of
NH4PF6 in dry methanol (30 mL) was heated under reflux for 8 h until 846 cm–1 corresponding to the stretching frequency of the P–
1
the color of the solution changed from pale yellow to dark red. The
solvent was removed under vacuum. The residue was dissolved in di-
chloromethane (10 mL), and the solution was filtered to remove am-
monium chloride. The red solution was concentrated to 5 mL. After-
wards, addition of ethyl ether gave the orange-red precipitate, which
was separated and dried in vacuo. Yield 77 mg, 61 %. Elemental Anal
C41H33N3P2F6Ru: calcd. C 58.33; H 3.97; N 4.00 %; found: C 58.42;
F bond of the counterion of these compounds. The H NMR
spectrum of the free ligand shows seven different sets of sig-
1
nals in the aromatic region. In the H NMR spectra of com-
plexes with the ligand L, the signals are spread over a wide
range compared to the spectrum of the free ligand. Compounds
1 and 3 show a doublet signal at around 9.204 and 9.341 ppm,
which corresponds to the pyridyl proton adjacent to the nitro-
gen atom (i.e., H6), whereas in the case of the free ligand, the
same proton comes in the up-field region at around 8.601 ppm.
H 4.08; N 3.89 %. IR (KBr): ν = 3432 (νN–H); 1630 (νC=C); 1453
˜
1
(νC=N); 847 (νP–F) cm–1. H NMR (400MHz, CDCl3): δ = 11.924 (s,
NH, 1 H), 9.296 (d, J = 5.2 Hz, 1 H), 8.453 (d, J = 7.2 Hz, 2 H),
7.720 (d, J = 7.6 Hz, 2 H), 7.575 (t, J = 8 Hz, 2 H), 7.480 (t, J = The free ligand also shows two doublet signals in the range of
7.2 Hz, 1 H), 7.389–7.027 (m, 23 H), 6.433 (s, 1 H), 4.859 (d, J =
8 Hz, 1 H), 4.320 (t, J = 2.4 Hz, 1 H), 3.507 (dd, J = 7.2 Hz, 1 H).
31P{1H} NMR (CDCl3): δ = 59.441 (s, PPh3). ESI-MS (m/z): 20.5
[M – PF6], 718.4 [M – PF6 – 2H], 458.2 [M – PF6 – PPh3].
7.800–7.704 ppm, two triplet signals at around 7.426–
7.261 ppm, and a multiplet and a singlet signal corresponding
to the protons of the pyridyl and phenyl group of the ligand.
Compound 1 exhibits a doubly triplet instead of two triplet
signals corresponding to the pyridyl protons of the ligand,
which is shifted downfield compared to the free ligand. In ad-
1
3. Results and Discussion
dition to all these peaks, the H NMR spectrum of compound
1 also shows a singlet signal at around 6.079 ppm, which cor-
responds to the six protons of the benzene ring, whereas com-
3.1. Arene Ruthenium Compounds 1–3
The dinuclear arene ruthenium complexes [(η6-arene)Ru(μ- pound 3 exhibits a singlet signal at around 2.188 ppm corre-
Cl)Cl]2 (arene = C6H6, p-cymene, and C6Me6) react with the sponding to the eighteen protons of the hexamethylbenzene
N,N'-based ligand (L) in methanol to produce the mononuclear ring. Compound 2 exhibits an unusual pattern of resonances
cationic compounds 1, 2, and 3 (Scheme 1). Compound 1 is for the p-cymene ligand. For instance, the methyl protons of
brown, whereas compounds 2 and 3 are yellow. The com- the isopropyl group display a doubly doublet at ca. 1.055 ppm
pounds are non-hygroscopic and stable in air as well as in instead of the doublet found in the starting precursor. The aro-
solution. They are sparingly soluble in polar solvents like di- matic protons of the p-cymene ligand for these compounds
chloromethane, chloroform, acetone, and acetonitrile but are also display four doublets at ca. 5.941–5.651 ppm, instead of
insoluble in non-polar solvents like hexane, diethyl ether, and two doublet signals found in the starting precursor. This pattern
petroleum ether. All compounds were isolated as their hexaflu- is due to the diastereotopic nature of the methyl protons of the
orophosphate salts.
isopropyl group and the aromatic protons of the p-cymene li-
gand. It may also be attributed to the behavior of the ruthenium
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761

G. Gupta, C. Zheng, P. Wang, K. M. Rao
ARTICLE
atom which is stereogenic when coordinated with four differ- pound 5 also displays two triplet signals corresponding to the
ent ligand atoms [65]. In other words, it is obvious that the pyridyl protons at around 8.1 and 7.6 ppm, whereas the spec-
different signals are entirely due to the chiral nature of the trum of the free ligand shows two triplet signals at around 7.4
metal [66, 67] (Scheme 1).
and 7.3 ppm. Besides these signals, the other ligand signals
are mentioned in the Experimental Section. The 1H NMR spec-
tra of these compounds also display a singlet signal at
1.688 ppm for compound 4 and at 1.724 ppm for compound 5
respectively, which corresponds to the protons of the pentam-
ethylcyclopentadienyl group. The molecular structures of com-
pounds 4 and 5 were solved by single-crystal X-ray crystallog-
raphy and the structures are presented in Figure 1 and
Figure 2.
3.2. Pentamethylcyclopentadienyl Rhodium and Iridium
Compounds 4 and 5
The dinuclear complexes [(η5-C5Me5)M(μ-Cl)Cl]2 (M = Rh
or Ir) undergo a bridge cleavage reaction with the N,N'-biden-
tate nitrogen base ligand (L) in methanol at room temperature,
which leads to the formation of chloride-substituted com-
pounds 4 and 5, respectively (Scheme 2).
3.3. Cyclopentadienyl Ruthenium and Osmium Compounds
6–9
The analytical data of these compounds are in agreement
with the formulations given in Scheme 3. These mononuclear
compounds are formed by the reaction of metal complexes
with the ligand L. All complexes are isolated as their hexafluo-
rophosphate salt. The infrared spectra of the complexes exhibit
the signals of the chelating N,N'-bidentate ligand as broad
bands between 3430 and 3448 cm–1, 1626 and 1630 cm–1 and
between 1445 and 1453 cm–1 as mentioned in the Experimen-
tal Section, which correspond to the stretching frequencies of
the N–H bond of the pyrazole ring and of the C=C and C–N
Scheme 2.
Compound 4 was isolated as its tetrafluoroborate salt, bonds of the pyridine ring of the ligand, respectively. In addi-
whereas compound 5 was isolated as perchlorate salt. Both tion, the infrared spectra of these compounds also exhibit a
compounds are orange-yellow in color and are stable in the strong band between 844 cm–1 and 849 cm–1due to the stretch-
solid state as well as in solution. They are soluble in polar ing frequency of the P–F bond of the counterion. The 1H spec-
solvents but insoluble in non-polar solvents like hexane, petro- tra of compounds 6 and 7 each exhibit a singlet signal at 4.723
leum ether, and diethyl ether. The infrared spectra of both com- and 4.658 ppm for the cyclopentadienyl ring protons, which
pounds exhibit the signal of the chelating N,N'-bidentate ligand indicates a downfield shift from the starting complexes [(η5-
as broad bands at 3438, 3460, 1628, 1634, 1450, and C5H5)Ru(PPh3)2Cl] and [(η5-C5H5)Os(PPh3)2Cl] [69, 59]. The
1453 cm–1, which correspond to the stretching frequencies of downfield shift in the position of the cyclopentadienyl protons
the N–H bond of the pyrazole ring and of the C=C and C–N might result from a change in the electron density on the metal
bonds of the pyridine ring of the ligand respectively. The IR atom due to chelation of the ligand L through two nitrogen
spectrum of compound 4 also exhibits a strong band at atoms. In addition to the other ligand signals, as mentioned
1088 cm–1 due to the stretching frequency of the B–F bond of in the Experimental Section, a multiplet in the range 7.387–
its counterion. However, in the case of compound 5, a strong 7.018 ppm, which corresponds to the phenyl protons of the
signal at 1099 cm–1 is observed due to the perchlorate ion [68]. triphenylphosphine group of these compounds, is observed.
Compounds 4 and 5 also show a slight downfield shift in the
The ligand 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L) reacts
1H NMR spectrum compared to that of the free ligand. It with pentamethylcyclopentadienyl ruthenium(II) complexes
shows a doublet signal at around 8.7 ppm corresponding to the in the presence of NH4PF6 in methanol, to yield the mononu-
proton next to the nitrogen atom of the pyridyl group of the clear cationic compound [(η5-C5Me5)Ru(PPh3)(L)]PF6, (8)
ligand (i.e., H6) whereas in the case of the free ligand, the (Scheme 3) This orange crystalline solid is soluble in polar
same proton comes at around 8.6 ppm. The spectrum of com- solvents and air stable. The infrared spectrum of complex 8
Scheme 3.
762
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Mononuclear Complexes of Platinum Group Metals
displays a sharp signal at 847 cm–1 corresponding to the similar to the distances in other rhodium and iridium pentam-
stretching frequency of the P–F bond of the counterion in addi- ethylcyclopentadienyl compounds. The Rh–N and Rh–Cl bond
1
tion to the bands due to ligand. The H NMR spectrum also lengths are in agreement with the values reported in the litera-
displays a singlet signal at 2.071 ppm corresponding to the ture [65, 70–72]. The C–C bond lengths within the Cp* ring
methyl protons of the pentamethylcyclopentadienyl ring and a and C–Me distances are in the normal range. The B–F and
multiplet signal in the range 7.371–7.263 ppm, which corre- Cl–O bond lengths are in agreement with the values reported
sponds to the phenyl protons of triphenylphosphine. Com- previously [41, 43].
pound 9 exhibits three characteristic sets of signals for the pro-
tons of the indenyl group. The protons of the
5. Conclusions
triphenylphosphine ligand exhibit a multiplet signal at 7.389–
1
A series of new η5-and η6- cyclic П-perimeter hydrocarbon
metal compounds with the ligand 2-(5-phenyl-1H-pyrazol-3-
yl)pyridine (L), which are remarkably stable in the solid state
and in solution were synthesized in good yield. Our main goal
to synthesize dimetallic compounds by incorporating a second
metal coordinating through the third nitrogen atom and activat-
ing the carbon atom of the phenyl group of ligand L was not
successful.
7.027 ppm. If the H NMR spectra of all these compounds are
observed carefully, it is obvious that the spectra of all com-
pounds containing ruthenium display the ligand peak shifted
downfield compared to that of the rhodium, iridium, and os-
mium compounds. The 31P{1H} NMR spectra of compounds
6, 8, and 9 exhibit a single sharp signal for triphenylphosphine
at 59.441–49.625 ppm respectively, whereas in the starting
precursors the signals appear in the upfield region. In the case
of compound 7, the 31P{1H} NMR spectrum display a sharp
singlet signal at –0.254 ppm as compared to the starting com-
plex which shows a signal at –6.29 ppm.
Acknowledgement
The m/z values of all compounds and their stable ion peaks
obtained from the ZQ mass spectra, as listed in the Experimen-
tal Section, are in good agreement with the theoretically ex-
pected values. The ESI mass spectra also displayed prominent
peaks corresponding to the molecular ion fragments. All halo-
genated compounds displayed a prominent peak corresponding
to the loss of the chloride ion from the molecular ion peak, but
the loss of arene or Cp or Cp* group is not observed, which
indicates that the stronger bond of the metal ions to these
groups remains intact. Similarly, in some of the compounds
containing the triphenylphosphine ligand, the loss of the tri-
phenylphosphine group from the molecular ion peak is obvi-
ous, which is also given in the Experimental Section.
K. M. Rao gratefully acknowledges financial support from the Depart-
ment of Science and Technology, New Delhi, through the Research
grant No. SR/S1/IC-11/2004. G. G. is also thankful for financial sup-
port from University Grant Commissions, New Delhi. The authors also
acknowledge the reviewers for their helpful suggestions.
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Received: October 2, 2009
Published Online: January 14, 2010
764
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Z. Anorg. Allg. Chem. 2010, 758–764