Reactivity studies of cyclopentadienyl bis(triphenylphosphine)ruthenium(II) complex towards some polypyridyl ligands

Article abstract of DOI:10.1016/j.poly.2004.01.002

The reaction of [CpRu(PPh₃)₂Cl] (1) (Cp=η⁵-C₅H₅) with excess of some potentially bridging ligands viz. 2,3-bis(α-pyridyl)pyrazine (bpp), 2,3-bis(α-pyridyl)quinoxaline (bpq), 1,3,5-tris(pyridyl)-2,4,6-

Full text of DOI:10.1016/j.poly.2004.01.002

Polyhedron 23 (2004) 1069–1073
www.elsevier.com/locate/poly
Reactivity studies of cyclopentadienyl
bis(triphenylphosphine)ruthenium(II) complex
towards some polypyridyl ligands
a
R. Lalrempuia , P. Govindaswamy , Yurij A. Mozharivskyj , Mohan Rao Kollipara
a
b
a,
*
a
Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b
Ames Laboratory, Iowa State University of Science and Technology, Ames, Iowa, IA 50011, USA
Received 5 December 2003; accepted 7 January 2004
Abstract
The reaction of [CpRu(PPh3)2Cl] (1) (Cp ¼ g5-C5H5) with excess of some potentially bridging ligands viz. 2,3-bis(a-pyr-
idyl)pyrazine (bpp), 2,3-bis(a-pyridyl)quinoxaline (bpq), 1,3,5-tris(pyridyl)-2,4,6-triazine (tptz) and 2,3,5,6-tetrakis(pyridyl)pyrazine
(tppz) yielded cationic mononuclear complexes of the type [CpRu(PPh3)(bpp)]þ (2), [CpRu(PPh3)(bpq)]þ (3), [CpRu(PPh3)(tptz)]þ
(4) and [CpRu(PPh3)(tppz)]þ (5), respectively. These complexes have been isolated as hexafluorophosphate salts. They were
characterized by FT-IR, 1H NMR and 31P {1H} NMR spectroscopy. The molecular structures of representative complexes 3 and 5
have been solved by single crystal X-ray crystallography.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Ruthenium; Cyclopentadienyl; 2,3-Bis(a-pyridyl)pyrazine; 1,3,5-Tris(pyridyl)-2,4,6-triazine; 2,3,5,6-Tetrakis(pyridyl)pyrazine
1. Introduction
bridge complex [(g6-p-cymene)RuCl2]2 to give two
products of the formula [(g6-p-cymene)RuCl(L)]þ and
[{(g6-p-cymene)RuCl}2(L)]2þ [1] and the ligands
L ¼ tppz, tptz and py-terpy displaced arene moiety as
well as chloride ligands to form dicationic complexes of
the formula [LRuL0]2þ. However, py-terpy can also acts
as a monodentate ligand binding the metal with nitrogen
of the pendant 4-pyridyl group to form [(g6-p-cym-
ene)RuCl2(py-terpy)] when the reaction medium is di-
ethylether [10]. In the present case, we do not
observe the formation of dimeric complexes that could
be due to the presence of sterically demanding bulky
triphenylphosphine.
As part of our investigation of the complexes of
areneruthenium(II) [1], cyclopentadienylruthenium(II)
[2], osmium(II) [3] and indenylruthenium(II) [4] with a
variety of nitrogen-based ligands, we here report on
complexes of cyclopentadienylruthenium(II) system
with some potentially bridging polypyridyl ligands. The
current interest in complexes of polypyridyl ligands,
2,20-bipyridine, 1,10-phenanthroline, 2,20:60,200-terpyri-
dine, etc., is associated with the extremely interesting
electrochemical, photophysical and photoelectrochemi-
cal properties that they exhibit [5–8]. Complexes with
these ligands are also DNA intercalators, showing an
ability to inhibit nucleic acid synthesis in vivo [9]. The
recent report on the reactivity studies of arene ruthe-
nium(II) with the ligands (Scheme 1) showed that the
ligands L ¼ bpp and bpq cleanly cleaved the halide
2. Experimental
The solvents were purified and dried by standard
methods and all reactions were carried out under dry
nitrogen atmosphere. Infrared spectra were recorded as
KBr pellets using on a Perkin–Elmer Model 983 spec-
trophotometer. 1H and 13C {1H} NMR spectra were
recorded on a Bruker ACF 300, spectrometer and
* Corresponding author. Tel.: +91-364-272-2620; fax: +91-364-255-
0076.
E-mail addresses: kmrao@nehu.ac.in, mrkollipara@yahoo.com
(M.R. Kollipara).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.01.002

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R. Lalrempuia et al. / Polyhedron 23 (2004) 1069–1073
1H, J ¼ 8:1 Hz), 8.01–7.86 (m, 3H), 7.79 (t, 1H, J ¼ 6:8
Hz), 7.60 (t, 1H, J ¼ 6:9 Hz), 6.39–7.71 (m, 9H), 7.09 (t,
1H, J ¼ 9:9 Hz), 6.90 (m, 7H), 6.76 (d, 1H, 8.4), 5.04 (s,
5H).
31P {1H} NMR (d, CDCl3): 52.66 (s), )143(sept).
Anal. Calc. for C41H32N4RuP2F6: C, 57.41; H, 3.73;
N, 6.52. Found: C, 57.56; H, 3.82; N, 6.44%.
UV–Vis (CH2Cl2, 10ꢀ3 M): kmax ¼ 486 nm.
2.1.3. [CpRu(PPh3)(tptz)]PF6 (4PF6)
1H NMR (d, CD3CN): 9.30 (d, 1H, J ¼ 5:2 Hz), 8.91
(d, 1H, J ¼ 4:2 Hz), 8.68 (d, 1H, J ¼ 7:9 Hz), 8.64 (d,
1H, J ¼ 8 Hz), 8.39 (d, 1H, J ¼ 4:8 Hz), 8.03–7.84 (m,
3H), 7.56–7.46 (m, 4H), 8.36–6.96 (m, 17H), 4.53 (s, 5H,
Cp).
Scheme 1. Ligands used in this work.
31P {1H} NMR (d, CDCl3): 48.98 (s), )143 (sept).
Anal. Calc. for C41H32N6RuP2F6: C, 55.60; H, 3.64;
N, 9.49. Found: C, 55.83; H, 3.72; N, 9.63%.
UV–Vis (CH2Cl2, 10ꢀ3 M): kmax ¼ 477 nm.
referenced to external tetramethylsilane. 31P {1H} NMR
chemical shifts are reported relative to H3PO4 (85%).
Elemental analyses were performed by RSIC, Shillong.
The ligands 2,3-bis(a-pyridyl)pyrazine (bpp), 2,3-
bis(a-pyridyl)quinoxaline (bpq), 2,3,5,6-tetrakis(pyr-
idyl)pyrazine (tppz) [11] and py-terpy [12] and
[CpRu(PPh3)2Cl] [13] were synthesized according to the
literature methods. 1,3,5-tris(pyridyl)-2,4,6-triazine
(tptz) was purchased from Loba Chemie Private Limited
and used as such.
2.1.4. [CpRu(PPh3)(tppz)]PF6 (5PF6)
1H NMR (d, CDCl3): 8.95 (m, 1H), 8.63 (d, 1H,
J ¼ 6 Hz), 8.19 (m, 1H), 8.03 (t, 1H, J ¼ 6:6), 7.92 (m,
1H), 7.62–6.75 (m, 26H), 4.95 (s, 5H, Cp).
31P {1H} NMR (d, CDCl3): 46.21 (m), )143 (sept).
Anal. Calc. for C47H36N6RuP2F6: C, 58.69; H, 3.74;
N, 8.73. Found: C, 58.75; H, 3.67; N, 8.81%.
UV–Vis (CH2Cl2, 10ꢀ3 M): kmax ¼ 461 nm.
2.1. Preparation of the complexes 2–5
The following general procedure was used for the
preparation of these mononuclear complexes.
The mixture of the complex [CpRu(PPh3)2Cl] (0.1 g,
0.110 mmol), the ligand (0.220 mmol) and NH4PF6
(0.220 mmol) were refluxed in methanol (40 ml) whereby
the orange color suspension gradually changes to intense
dark red color. It was refluxed for 5 h, then the solvent
was rotary evaporated. The residue was extracted with
CHCl3 and filtered through short silica gel column to
remove insoluble material, the filtrate was again con-
centrated to about 2 ml and addition of excess diethy-
lether precipitated the product as red-brown solid.
3. Crystal structure determination of 3PF6 and 5PF6
Suitable single crystals of 3PF6 were grown by slow
diffusion of hexane into acetone solution and of 5PF6
were grown from hexane into chloroform solution. A
suitable size crystal of complex 3PF6 was mounted on
the end of the glass fiber and mounted on a Nonius
MACH3 diffractometer where as complex 5PF6 was
mounted on Bruker Smart Apex CCD system equipped
with graphite monochromatized Mo Ka (k ¼ 0:70930
ꢀ
2.1.1. [CpRu(PPh3)(bpp)]PF6 (2PF6)
A) radiation at a temperature of 293 K for the cell de-
1H NMR (d, CDCl3): 9.53 (s, 1H), 9.32 (d, 1H,
J ¼ 4:8 Hz), 8.63 (d, 1H, J ¼ 4:7), 8.32 (s, 1H), 8.02 (t,
1H, J ¼ 6:8 Hz), 7.65 (d, 1H, J ¼ 7:6 Hz), 7.54 (t, 1H,
J ¼ 7:6 Hz), 7.33–6.98 (m, 17H), 6.56 (d, 1H, J ¼ 8:2
Hz), 4.84 (s, 5H).
31P {1H} NMR (d, CDCl3): 48.81 (s), )143 (sept).
Anal. Calc. for C37H20N4RuP2F6: C, 55.02; H, 3.74;
N, 6.96. Found: C, 55.20; H, 3.78; N, 7.00%.
UV–Vis (CH2Cl2, 10ꢀ3 M): kmax ¼ 489 nm.
termination and intensity data collection. Crystal data
collection parameters are summarized in Table 1. The
structure was solved by direct methods [14] (SHELXS
-
1997). Refinement was by full-matrix least-squares
based on F 2 using SHELXL-93 [15]. Lorentz and polar-
ization corrections were applied. Non-hydrogen atoms
were refined anisotropically only in the case of complex
3PF6 and hydrogen atoms were refined using a ‘‘riding’’
model. Figs. 1 and 2 are the ORTEP [16] representation
of the molecules with 50% probability thermal ellip-
soids displayed. Selected bond distances and angles are
given in Tables 2 and 3 for complexes 3PF6 and 5PF6,
respectively.
2.1.2. [CpRu(PPh3)(bpq)]PF6 (3PF6)
1H NMR (d, CD3CN): 9.23 (d, 1H, J ¼ 5:4 Hz), 8.74
(d, 1H, J ¼ 8:9 Hz), 8.58 (d, 1H, J ¼ 4:3 Hz), 8.10 (t,

R. Lalrempuia et al. / Polyhedron 23 (2004) 1069–1073
1071
Table 1
Crystal data and structure refinement for complex 5PF6 ꢁ 3CHCl3 and complex 3PF6 ꢁ C3H2O
Empirical formula
Formula weight
T (K)
C50H39Cl9F6N6P2Ru
1319.93
C44H34F6N4P2ORu
911.79
293 (2)
293 (2)
0.71073
ꢀ
Wavelength (A)
1.5418
monoclinic
P21=n
Crystal system
Space group
Unit cell dimensions
orthorhombic
Pbca
ꢀ
a (A)
15.2504(12)
19.1960(15)
37.199(3)
14.2780(10)
9.9760(10)
28.9110(10)
103.48
ꢀ
b (A)
ꢀ
c (A)
ꢀ
b (A)
3
ꢀ
V (A )
10889.8(15)
8
1.610
4004.6(5)
4
1.512
Z
Dcalc (Mg mꢀ3
Crystal size (mm)
)
0.6 ꢂ 0.5 ꢂ 0.3
1.73–15.07
0.6 ꢂ 0.6 ꢂ 0.2
0–70
h range for data collection (°)
Index ranges
ꢀ11 6 h 6 11,
ꢀ14 6 k 6 13,
ꢀ27 6 l 6 27
22 053
0 6 h 6 17,
0 6 k 6 12,
ꢀ35 6 l 6 34
7411
Reflections collected
Independent reflections
Absorption coefficient (mmꢀ1
2214 (Rint ¼ 0:0583)
0.851
5296
5586
4.517
)
F ð000Þ
1848
empirical
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices ½I > 2rðIÞꢃ
R indices (all data)
empirical (SADABS)
full-matrix least-squares on F 2
2214/9/352
5586/0/524
1.162
1.002
R1 ¼ 0:0665, wR2 ¼ 0:1598
R1 ¼ 0:0789, wR2 ¼ 0:1717
0.546 and )0.471
R1 ¼ 0:0819, wR2 ¼ 0:2046
R1 ¼ 0:1134, wR2 ¼ 0:2418
ꢀ3Þ
ꢀ
Largest different peak and hole (e A
Fig. 1. Molecular structure of [CpRu(PPh3)(bpq)]PF6 (3). The entire
hydrogen atoms, PF6 and part of acetone molecules are removed for
clarity.
Fig. 2. Molecular structure of [CpRu(PPh3)(tppz)]PF6 (3). The entire
hydrogen atoms, PF6 and chloroform molecules are removed for
clarity.
4. Results and discussion
The reaction of the complex [CpRu(PPh3)2Cl] (1)
where Cp ¼ g5-C5H5with excess of the ligands (Scheme
1) in methanol under refluxing condition resulted in the
dissociation of one of the triphenylphosphines and
chloride ligand to yield the monomeric chelate com-
plexes 2–5 (Scheme 2). We are unable to isolate the
anticipated dimeric complexes by changing the molar
ratio of the starting complex to the corresponding li-
gand. These complexes are soluble in most of the polar
solvents.
All these complexes showed a sharp singlet in the
region of 4.53–5.04 ppm in 1H NMR spectra, which can

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R. Lalrempuia et al. / Polyhedron 23 (2004) 1069–1073
Table 2
In the case of complex 5 a multiplet was observed at 46
ppm for triphenylphosphine, which may be due to the
interaction between the phosphorus and the protons of
the highly strained tppz ligand.
ꢀ
Selected bond lengths (A) and bond angles (°) for
[CpRu(PPh3)(bpq)]PF6 (3PF6)
Bond lengths
Ru(1)–N(1)
Ru(1)–C(5)
Ru(1)–C(3)
Ru(1)–N(2)
Ru(1)–C(1)
Ru(1)–C(4)
Ru(1)–P(2)
Ru(1)–C(2)
2.090 (7)
2.172 (9)
2.217 (8)
2.070 (7)
2.188 (9)
2.203 (9)
2.322 (2)
2.230 (8)
In contrast to the above reactions, the product iso-
lated from the reaction between complex 1 and py-terpy
contains a mixture of products. The 1H NMR spectrum
shows three equally intense cyclopentadienyl peaks at
4.4, 4.38 and 4.36 ppm suggesting the presence of three
different environments for the cyclopentadienyl ligand.
31P {1H} NMR spectrum is also complicated and shows
peaks at 49.7 ppm (singlet), 45.9 ppm (singlet) and 42.8
ppm (multiplets). The UV–Vis spectrum also shows two
very broad bands at 450 and 520 nm. An attempt to
separate the mixture by crystallization and column
chromatography was unsuccessful.
Bond angles
N(2)–Ru(1)–N(1)
N(1)–Ru(1)–P(2)
N(2)–Ru–P(2)
76.11 (2)
94.00 (17)
95.01 (19)
Table 3
ꢀ
Selected bond lengths (A) and bond angles (°) for
[CpRu(PPh3)(tppz)]PF6 ꢁ 3CHCl3 (5PF6)
Bond lengths
5. Crystal structures
Ru(1)–N(12)
Ru(1)–C(01)
Ru(1)–C(04)
P(1)–C(11B)
Ru(1)–N(21)
Ru(1)–C(02)
Ru(1)–C(05)
P(1)–C(11A)
Ru(1)–P(1)
2.093(12)
2.207(11)
2.214(11)
1.837(9)
The complex [CpRu(PPh3)(bpq)]PF6 (3PF6) crystal-
lizes with one acetone per molecule but only two protons
of the acetone were located. The geometry about the
metal atom can be regarded as distorted octahedral with
the bpq ligand chelating the ruthenium atom with two
nitrogen atoms and the other coordination sites occu-
pied by triphenylphosphine and a pentahapto bound
cyclopentadienyl ligand. The average Ru–C (Cp) bond
2.113(12)
2.193(11)
2.220(11)
1.849(10)
2.336(5)
Ru(1)–C(03)
P(1)–C(11C)
2.197(10)
1.834(9)
ꢀ
length is 2.202 A where the individual bond length falls
Bond angles
ꢀ
within the range of 2.172–2.230 A. The two nitrogens
chelate the ruthenium (N1–Ru–N2) with an angle of
N(12)–Ru–N(21)
N(21)–Ru–P(1)
N(12)–Ru–P(1)
75.9(5)
92.4(3)
93.7(3)
76.11° and the bond lengths are almost the same with
2.090 and 2.070 A for Ru–N1 and Ru–N2, respectively.
ꢀ
The angle subtended by N1–Ru–P2 and N2–Ru–P2 is
94° and 95.01°, respectively. The distance between the
ruthenium atom and phosphorus atom of the triphe-
ꢀ
nylphosphine ligand is 2.322 A. Even with the low ac-
curacy of the results from the X-ray determination, all
the metrical parameters are in a close agreement with
those of complex 5 and other related works [1,2].
Scheme 2.
The complex [CpRu(PPh3)(tppz)]PF6 (5PF6) crystal-
lized with three molecules of chloroform per molecule.
The crystal diffracts weakly and the maximum angle at
which I > 2rðIÞ is 15°. Due to the small ratio of data to
parameter, only the PF6 and chloroform units were re-
fined anisotropicaly and the rest was refined isotropic-
be assigned unambiguously to the resonance of cyclo-
pentadienyl ligand. The analytical data, integration of
the spectrum and a rather complicated peaks originating
1
from the potentially bridging ligands in the H NMR
spectrum suggest the unsymmetrical coordinating na-
ture of this ligand to the metal center, i.e. two nitrogens
chelate the ruthenium centre leaving other pyridyl
groups uncoordinated which inturn reflects the mono-
meric nature of the complexes. The peaks corresponding
to the protons of the triphenylphosphine and the chelate
ligands appear in the aromatic region in the range of 7–9
ppm. The 31P {1H} NMR spectrum of these complexes
showed single peak at around 48 ppm and septet at )143
ppm for triphenylphosphine and PFꢀ6 ion, respectively.
ꢀ
aly. The average Ru–C (Cp) bond length is 2.211 A. The
nitrogen atoms N12 and N21 chelate the ruthenium
atom with an angle of 75.9°. The bond distance between
the ruthenium and N12, N21 and P of PPh3 is 2.093,
ꢀ
2.113 and 2.336 A, respectively. The angle subtended by
N12–Ru–P1 and N21–Ru–P1 is 93.7° and 92.4°, re-
spectively. The bond angles and bond lengths are com-
parable in both these structures as well as with those of
related complexes.

R. Lalrempuia et al. / Polyhedron 23 (2004) 1069–1073
1073
6. Conclusion
References
[1] (a) R. Lalrempuia, M.R. Kollipara, P.J. Carroll, Polyhedron 22
(2003) 605;
The reaction of [CpRu(PPh3)2Cl] with equimolar or
excess amount of some potential bridging polypyridyl
ligands L, where L ¼ bpp, bpq, tppz and tptz in meth-
anol in refluxing condition yielded mononuclear com-
plexes of the formulations [CpRu(PPh3)(L)]þ which
apparently results from the dissociation of one triphe-
nylphosphine and the chloride ligands.
(b) R. Lalrempuia, M.R. Kollipara, Polyhedron 22 (2003) 3155.
[2] K.M. Rao, C.R.K. Rao, P.S. Zacharias, Polyhedron 16 (1997)
2369.
[3] R. Lalrempuia, P.J. Carroll, M.R. Kollipara, Polyhedron 22
(2003) 1391.
[4] M.R. Kollipara, E.K. Rymmai, Polyhedron 22 (2003) 307.
[5] (a) A.M.W. Thompson, Coord. Chem. Rev. 160 (1997) 1;
(b) 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.
7. Supplementary material
[6] (a) E.C. Constable, Adv. Inorg. Chem. 34 (1989) 1;
(b) E.C. Constable, Adv. Inorg. Chem. Radiochem. 30 (1986) 69;
(c) E.C. Constable, Prog. Inorg. Chem. 42 (1994) 67.
[7] F. Fagalde, N.E. Katz, J. Chem. Soc., Dalton Trans. (1993) 571.
[8] (a) J.A. Bailey, V.M. Miskowski, H.B. Gray, Inorg. Chem. 32
(1993) 369;
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre (CCDC), CCDC Nos. 222042 for complex 3 and
222043 for complex 5, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033; email: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(b) H.K. Yip, L.K. Cheng, K.K. Cheng, C.M. Che, J. Chem. Soc.,
Dalton Trans. (1993) 2933.
[9] W.I. Sundquist, S.J. Lippard, Coord. Chem. Rev. 100 (1990) 293.
[10] R. Lalrempuia, unpublished work.
[11] H.A. Goodwin, F. Lions, J. Am. Chem. Soc. 81 (1959) 6415.
[12] E.C. Constable, A.M.W. Cargill Thompson, J. Chem. Soc.,
Dalton Trans. (1992) 2947.
[13] M.I. Bruce, N.J. Windsor, Aust. J. Chem. 30 (1977) 1601.
[14] SIR-92: A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C.
Giacovazzo, A. Guagliardi, G. Polidoro, J. Appl. Crystallogr. 27
(1994) 435.
Acknowledgements
[15] G.M. Sheldrick, SHELXL-93: Program for the Refinement of
K.M.R. thanks the DST (DST SERC: SP/S1/F-22/
98), New Delhi for financial support. We also thanks the
S. Dey and T.P. Singh, AIIMS, New Delhi for providing
help in solving single crystal structure.
€
Crystal Structures, University of Gottingen, Gottingen, Germany,
€
1993.
[16] C.K. Johnson, ORTEP-II: A Fortran Thermal Ellipsoid Plot
Program for Crystal Structure Illustrations, ORNL-5138, 1976.