Synthesis and characterization of ruthenium(II) pyrazole tertiary phosphine complexes

Full text of DOI:10.1081/SIM-100104791

This article was downloaded by: [University of Waterloo]
On: 04 June 2014, At: 01:18
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt19
SYNTHESIS AND CHARACTERIZATION OF RUTHENIUM(II)
PYRAZOLE TERTIARY PHOSPHINE COMPLEXES
E. Wynne Evans a & Mark T. Atlay b
a School of Applied Sciences, University of Glamorgan , Pontypridd, Mid. Glam., CF37 1DL,
Wales, United Kingdom
b University of Luton , Park Square, Luton, Bedfordshire, LUI 3JU, England, United Kingdom
Published online: 20 Aug 2006.
To cite this article: E. Wynne Evans & Mark T. Atlay (2001) SYNTHESIS AND CHARACTERIZATION OF RUTHENIUM(II) PYRAZOLE
TERTIARY PHOSPHINE COMPLEXES, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 31:4, 623-632, DOI:
10.1081/SIM-100104791
To link to this article: http://dx.doi.org/10.1081/SIM-100104791
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(4), 623–632 (2001)
SYNTHESIS AND CHARACTERIZATION
OF RUTHENIUM(II) PYRAZOLE
TERTIARY PHOSPHINE COMPLEXES
2
E. Wynne Evans1,* andMark T. Atlay
1School of Applied Sciences, University of Glamorgan,
Pontypridd, Mid. Glam., CF371DL, Wales,
United Kingdom
2University of Luton, Park Square, Luton,
Bedfordshire, LUI 3JU, England, United Kingdom
ABSTRACT
The product of the reaction of [RuCl2(PPh3)3] with two
equivalents of pyrazole (Hpz) in toluene, when precipitated
from
a toluene=hexane mixture was characterised as
1
[RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14 (1); the same reaction, effec-
2
ted in acetone, produced the acetone coordinated species
[RuCl2(Hpz)(Me2CO)(PPh3)2] (2). When the reaction was
carried out using 3,5-dimethylpyrazole (HDMpz), in either
acetone or toluene as solvent, the yellow five-coordinate
complex [RuCl2(HDMpz)(PPh3)2] (3) was produced. The
1
bromo compounds [RuBr2(Hpz)2(PPh3)2] ꢀ = C6H14 (4) and
2
[RuBr2(HDMpz)(PPh3)2] (5) have also been prepared using
*Corresponding author. E-mail: ewevans@glam.ac.uk
623
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

624
EVANS AND ATLAY
[RuBr2(PPh3)3] as precursor. Attempts to make the iodo
analogues from [RuI2(PPh3)2]n, resulted in a species identified
as [RuI2(HDMpz)(PPh3)2] on the basis of NMR and infrared
measurements. The novel derivatives (1)–(5) have been char-
1
acterised using microanalyses and infrared, H and 31P NMR
spectroscopy.
Reaction of (1) with CO resulted in displacement of Hpz
to eventually produce cis-[RuCl2(CO)2(PPh3)2]. The reaction
appeared to proceed through the a monosubstituted product
[RuCl2(CO)(Hpz)(PPh3)2], distinguished from spectroscopic
measurements. The reaction of (1) with oxygen is discussed.
INTRODUCTION
Ruthenium complexes containing tertiary phosphines have long been
found to have applications in the field of homogeneous catalysis whilst
neutral pyrazoles have been widely used as monodentate ligands in
coordination chemistry1, coordinating through the azomethine nitrogen
atom, N2 (Fig. 1). Moreover, 1-unsubstituted pyrazoles are weak acids;
deprotonation produces the pyrazolate anion which may be used as a
bridging ligand between metal centres over a wide range of intermetallic
separations2. In addition, ruthenium(II) complexes containing (Z5-py-
razole ligands recently have been reported3. For these reasons, therefore,
the preparation and characterisation of ruthenium=phosphine=pyrazole
species and their interactions with small molecules, such as CO, are of
interest4. Here we report results of the reactions of [RuCl2(PPh3)3] with
pyrazole (Hpz) and 3,5-dimethylpyrazole (HDMpz), in acetone and
toluene, together with investigations of the geometry of the products. Two
bromo and one iodo analogues have also been synthesised from the
Figure 1. Pyrazoles.

RUTHENIUM(II) PYRAZOLE COMPLEXES
625
reactions of [RuBr2(PPh3)3] and [RuI2(PPh3)2]n with Hpz and HDMpz,
1
respectively. The reactions of [RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14 (1), with O2
2
and CO are also discussed.
RESULTS AND DISCUSSION
Structure of Pyrazole Complexes
The reaction of two equivalents of a nitrogen-donating ligand, such as
pyridine, with [RuCl2(PPh3)3] in acetone has been reported to result in
six-coordinate species with cis coordination of the nitrogen ligands; the
same reaction in toluene has resulted in the formation of the trans isomers5.
In this study, in an attempt to prepare the two isomers containing cis and
trans pyrazole groups, the same ruthenium compound was reacted with
pyrazole in both solvents. In toluene the diamagnetic, six-coordinate trans-
1
species [RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14 (1) was formed after addition of
2
hexane, whilst reaction of Hpz with [RuCl2(PPh3)3] in acetone gave the
acetone-coordinated species [RuCl2(Hpz)(Me2CO)(PPh3)2] (2). Reaction of
[RuCl2(PPh3)3] with HDMpz instead of Hpz, in either solvent, produced the
five-coordinate species [RuCl2(HDMpz)(PPh3)2] (3); presumably the steric
bulk of HDMpz, as compared with Hpz, prevents six-coordination. Both
1
of the bromo compounds [RuBr2(Hpz)2(PPh3)2] ꢀ = C6H14 (4) and
2
[RuBr2(HDMpz)(PPh3)2] (5) have been prepared by reaction of the appro-
priate pyrazoles with [RuBr2(PPh3)3]. Difficulty was encountered in pre-
paring the iodo analogues in a high degree of purity by the reaction of the
appropriate pyrazoles with [RuI2(PPh3)2]n. Reaction of Hpz with
[RuI2(PPh3)2]n gave an impure product with a 31P NMR resonance at 54 d,
suggesting a completely different structure as compared with the other
pyrazole complexes under consideration. Possibilities include five-coordi-
nate and cationic species of Ru(II) which tend to have similar 31P chemical
shifts6,7; such species might form because of the overcrowding resulting
from the increased size of the halogen. In contrast, 1H NMR of the product
of the reaction of HDMpz with [RuI2(PPh3)2]n indicated that an iodo
analogue of (3) and (5), probably [RuI2(HDMpz)(PPh3)2], had been formed.
Spectral information for the pyrazole products is shown in Table I.
The presence of a medium-intense band for n(N-H) at around 3200 cmꢁ1 in
the infrared spectrum of each one of the complexes is taken as evidence of
Z1-coordination of the pyrazoles7. Evidence for the trans configuration (D2h
symmetry, assuming the pyrazoles behave as point masses) of the complexes
(1) and (4) comes from 31P NMR and far-infrared (600–250 cmꢁ1) mea-
surements: a single resonance, at an appropriate chemical shift value for

626
EVANS AND ATLAY
Table I. Spectroscopic Data Describing the Ruthenium(II) Phosphine=Pyrazole
Complexes
Compound
1H NMR (d)a
11.7(br, 2H, NH)
8.1 (d, 2H, C3{Hpz})
7.3 (m, 32H, [2H, C5{Hpz};
30H,{PPh3}])
5.9(t, 2H,C4{Hpz})
11.7(br, 1H, NH)
8.1 (d, 1H, C3{Hpz})
7.1 (m, 31H, [1H, C5{Hpz};
30H,{PPh3}])
31P NMR (d)b Infrared Data (cmꢁ1
)
c
(1)
28.4
29.1
n(N-H) 3270 m
n(Ru-Cl) 326d w
c
(2)
n(N-H) 3260 m
n(C ¼ O) 1710e s
n(Ru-Cl) 330 w
5.9 (s, 1H, C4{Hpz})
1.5 (s, 6H, {Me2CO)f
10.8 (br, 1H, NH)
7.1 (m, 30H, {PPh3})
5.3 (s, 1H, C4{HDMpz})
1.8 (s, 6H, -CH3{HDMpz})
11.7(br, 2H, NH)
(3)
(4)
26.1
n(N-H) 3250 m
n(Ru-Cl)
300 w, 312d w
c
28.4
n(N-H) 3260 m
8.1 (d, 2H, C3{Hpz})
7.3 (m, 32H, [2H, C5{Hpz};
30H, {PPh3}])
5.9 (t, 2H, C4{Hpz})
10.9 (br, 1H, NH)
(5)
26.0
n(N-H) 3255 m
7.2 (m, 30H, {PPh3})
5.4 (s, 1H, C4{HDMpz})
1.8 (s, 6H, -CH3{HDMpz})
c
aIn CDCl3, bin CDCl3 relative to 85% H3PO4, appropriate to trans-phosphines8,
d
5
e
ꢁ1
¼
trans to another chlorine atom , acetone in CCl4 exhibited n(C O) at 1720 cm
ffree acetone occurs at 2.1d.
,
equivalent trans-phosphine groups8, is found in the 31P NMR spectra of
each species; for the chloro complex (1), one appropriate value for n(Ru-Cl)
trans to another Cl atom5 is shown in the far-infrared spectrum. The
structures of (1) and (3) are shown in Fig. 2.
In transition metal pyrazole complexes, often the hydrogen atom on
the pyrrole-type nitrogen forms hydrogen bonds with anionic ligands. Also
apparent in the infrared spectrum of (1) is a medium-intensity broad band at
2850 cmꢁ1, possibly indicating N-Hꢀ ꢀ ꢀCl association9–11. Similar bands are
not observed in the infrared spectra of any of the other pyrazole species
reported.

RUTHENIUM(II) PYRAZOLE COMPLEXES
627
Figure 2. Suggested structures of (1) and (3).
Reactivity of Pyrazole Complexes with Air
The species (1)-(5) proved stable to air in the solid state, but in solution
turned green. The coordinatively unsaturated HDMpz species (3) and (5)
proved particularly unstable; their solutions rapidly changed colour in the
presence of air. Investigation of the oxidation of (1) and (3) in CDCl3
solution was carried out using 31P NMR. When exposed to air, a solution of
(1) turned from yellow to dark green over a period of 1–2 h. The green
¼
solution showed resonances at d 29 and d -6, assigned to free O PPh3 and
free PPh312, respectively. The same spectrum showed a signal at d 42 which
could not be identified; this may be due to a [Ru-OPPh3] species, which
resonates in this area–such complexes have been identified as products of the
oxidation13 of [RuCl2PPh3)3]. Coordinatively unsaturated (3) proved even
more sensitive to oxidation than (1), solutions turned green very rapidly
when exposed to air and an unidentified resonance at d 36 together with
signals indicative of free phosphine and phosphine oxide were observed in
the 31P NMR spectrum.
1
Reaction of CO with [RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14 (1)
2
The reaction of CO with (1) in toluene solution at ambient tempera-
ture leads to the replacement of Hpz by CO (a stronger-field ligand and
softer base) and spectroscopic measurements indicate that initially mono-
substituted [RuCl2(CO)(Hpz)(PPh3)2] is formed. Under more forcing con-
ditions further substitution occurs and pale green cis-[RuCl2(CO)2(PPh3)2] is
13
ꢂ
the product ; the infrared of which shows no n(N-H) band and n(C O)
absorptions at 2000 and 2064 cmꢁ1; also n(Ru-Cl) is evident in the far-
infrared at 300 and 280 cmꢁ1
.

628
EVANS AND ATLAY
EXPERIMENTAL
Reactions and manipulations were carried out in a dry nitrogen
atmosphere, using standard Schlenk-type apparatus. Solvents were distilled,
dried and degassed, prior to use. 1H and 31P NMR spectra were obtained in
CDCl3 at 298 K using a JEOL EX 270 MHz Fourier transform spectro-
photometer. Infrared spectra (4000-250 cmꢁ1) were recorded on Perkin
Elmer 881 and 457instruments using KBr and CsI discs, respectively. All
products were dried in vacuo. Analyses were carried out by Butterworth
Laboratories Ltd., Middlesex and MEDAC Ltd., Brunel University, Mid-
dlesex. The complexes [RuCl2(PPh3)3] and [RuBr2(PPh3)3] were prepared as
described in the literature14 from commercial RuCl3 ꢀ xH2O, obtained from
Aldrich. Magnetic susceptibilities were measured using a Johnson Matthey
magnetic susceptibility balance.
Preparation15 of [RuI2(PPh3)2]n
Ruthenium trichloride hydrate (0.20 g) was stirred with AgClO4
(0.48 g, 2.30 mmol) in methanol (30 mL) for 24 h. The resulting white pre-
cipitate was removed by centrifugation and filtration and potassium iodide
(0.38 g, 6.00 mmol) added to the filtrate. This mixture was refluxed under
nitrogen for 15 min and triphenylphosphine added (1.20 g, 4.57mmol). The
mixture was then refluxed for 4 h and the dark brown precipitate obtained
washed with methanol (20 mL) and diethyl ether, then dried under suction.
Yield, 0.65 g (96%).
Preparation of Ruthenium Chloro andBromo Pyrazole Compounds
Two methods could be employed for the preparation of the pyrazole
derivatives:
(a) [RuX2(PPh3)3] (0.20 mmol) was added to two equivalents of
the pyrazole dissolved in degassed acetone (30 mL) and the
mixture refluxed for 2 h. The yellow=orange=brown precipitate
obtained was filtered, washed with acetone and dried in vacuo at
353 K.
(b) The pyrazole (0.40 mmol) was reacted with [RuX2(PPh3)3]
(0.20 mmol) in degassed toluene (25 mL) as solvent. The mixture
was stirred for 30 min at room temperature. Concentration of the
solution to ca. 5 mL and addition of degassed hexane gave yellow

RUTHENIUM(II) PYRAZOLE COMPLEXES
629

630
EVANS AND ATLAY
microcrystals. The product was filtered, washed with a small
amount of hexane (5 mL) and dried in vacuo at 353 K.
Method (a) proved the most convenient for the isolation of most of the
pyrazole complexes and reported yields are based on this method. However
method (b) had to be employed for the preparation of
1
[RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14 (1); the reaction of [RuCl2(PPh3)3] with Hpz
2
in acetone gave the acetone coordinated species [RuCl2(Hpz)(Me2CO)
(PPh3)2] (2). For analytical data relating to (1)–(5), see Table II.
Reaction of [RuI2(PPh3)2]n with HDMpz
This was effected by refluxing 3,5-dimethylpyrazole (0.08 g, 0.83 mmol)
with [RuI2(PPh3)2]n (0.52 g) in acetone (25 mL), under nitrogen, for 6 h. The
resulting light brown precipitate was obtained by filtration and washed with
acetone (5 mL). Identified as [RuI2(HDMpz)(PPh3)2] from: IR (cmꢁ1):
1
3245 m, n(N-H). H NMR (d ppm):10.9, br, 1H, (NH{HDMpz}); 7.3, m,
30H, (PPh3); 5.4, s, 1H, C4(HDMpz);1.8, s, 6H, -CH3(HDMpz). 31P NMR
(d ppm): 25.0. Yield, 0.38 g (65%).
1
Reaction of [RuCl2(Hpz)2(PPh3)2] ꢀ = C6H14, (1) with CO
2
(i) Carbon monoxide was bubbled through a solution of (1) (0.18 g,
0.20 mmol) in degassed toluene (20 mL) for 2 h at ambient tem-
perature and pressure. A pale yellow product was obtained by
concentration of the toluene solution to about 2 mL and addition
of a few drops of hexane. This product was thought to contain
[RuCl2(CO)(Hpz)(PPh3)2] as identified from the following spec-
troscopic measurements: IR (cmꢁ1): 3270 w, n(N-H); 1940 s,
n(C O); 1430 s, (P-aryl); 327w, n(Ru-Cl). 1H NMR (d ppm):
ꢂ
11.3, br, 1H, (NH, {Hpz}); 7.3, m, 31H, (C3{Hpz} and 30H,
{PPh3}); 6.8, s, 1H, C5 (Hpz); 5.8, br, 1H, C4(Hpz). 31P NMR
(d ppm): 31.0, appropriate for trans-phosphines8.
(ii) A mixture prepared as in (i), was refluxed for three hours. A pale
green product was obtained by concentration of the solution and
precipitation with hexane. The product was subsequently char-
acterised as cis-[RuCl2(CO)2(PPh3)2], by comparison with pub-
lished spectroscopic data13.

RUTHENIUM(II) PYRAZOLE COMPLEXES
ACKNOWLEDGEMENTS
631
We thank Johnson Matthey for a generous loan of ruthenium.
REFERENCES
1. Trofimenko, S. The Coordination Chemistry of Pyrazole-Derived
Ligands. Prog. in Inorg. Chem. 1986, 34, 115–210.
2. La Monica, G.; Attilio Ardizzoia, G. The Role of the Pyrazolate
Ligand in Building Polynuclear Transition Metal Systems. Prog. in
Inorg. Chem. 1997, 46, 151–238.
3. Perera, J.R.; Heeg, M.J.; Schlegel, H.B.; Winter, C.H. Ruthenium
Complexes Bearing Z5-Pyrazolato Ligands. J. Am. Chem. Soc. 1999,
121, 4536–4537.
4. Taqui Khan, M.M.; Khan, N.H.; Kureshy R.I.; Venkatassu-
bramanian, K. Synthesis, Characterization and X-ray Crystal Struc-
ture Studies of Ruthenium(II) Pyrazole Complexes and their
Interaction with Small Molecules. Polyhedron. 1992, 11 (4), 431–441.
5. Gilbert, J.D.; Wilkinson, G. New Complexes of Ruthenium(II) with
Triphenylphosphine and Other Ligands. J. Chem. Soc. 1969, (A) ,
1749–1753.
6. Thornback, J.R.; Wilkinson, G. Schiff base Complexes of Ruthe-
nium(II). J. Chem Soc., Dalton Trans. 1978, 110–115.
7. Pandey, D.S.; Pandeya, K.B.; Tripathi, I.P. Reactions of [RuH
(CO)Cl(PPh3)3] with Imidazole, 2-Methylimidazole, 2-Ethylimidazole
and Pyrazole. Ind. J. Chem. 1994, 33A, 354–356.
8. Hoffman, P.R.; Caulton, K.G. Solution Structure and Dynamics of
Five-Coordinate d6 Complexes. J. Am. Chem. Soc. 1975, 97, 4221–4227.
9. Carmona, D.; Ferrer, J.; Oro, L.A.; Apreda, M.C.; Foces-Foces, C.;
Cano, F.H.; Elguero, J.; Jimeno, M.L. Synthesis, X-ray Structure and
Nuclear Magnetic Resonance (H-1 and C-13) Studies of Rutheniu-
m(II) Complexes Containing Pyrazolyl Ligands. J. Chem. Soc. Dalton
Trans. 1990, 4, 1463–1476.
10. Oro, L.A.; Carmona, D.; Lamata, M.P.; Tiripicchio, A.; Lahoz, F.J.,
Dinuclear and Tetranuclear Mixed-Valence Complexes of Rhodiu-
m(III, I) and Rhodium(III) Iridium(I) with the 2,20-Bi-imidazolate(2-)
Anion (BIM) as Bridging Ligand. J. Chem. Soc. Dalton Trans. 1986, 1,
15–21.
11. Ten Hoedt, R.W.M.; Driessen W.L.; Vershoor, G.C. Structure of
Hexakis(pyrazole)nickel(II) Bis(tetrafluoroborate). Acta Cryst. 1983,
C39, 71–72.

632
EVANS AND ATLAY
12. Mann, B.E.; Masters, C.; Shaw, B.L. Nuclear Magnetic Resonance
Studies on Metal Complexes. Part VII. The 31P NMR Spectra of Some
Complexes of the Type trans-RhCl(CO)L2 [L ¼ Tertiary Phosphine or
P(OMe)3]. J. Chem. Soc. 1971, (A) , 1104–1106.
13. Cenini, S.; Mantovani, A.; Fusi, A.; Keubler, M. Low Oxidation States
Ruthenium Chemistry. I. The Reactions of Ru(PPh3)2Cl2 and Related
Complexes with Small Molecules. Gazz. Chim. Ital. 1975, 105, 255–
273.
14. Stephenson, T.A.; Wilkinson, G. New Complexes of Ruthenium(II)
and (III) with Triphenylphosphine, Triphenylarsine, Trichloro-
stannate, Pyridine and Other Ligands. J. Inorg. Nucl. Chem. 1966, 28,
945–956.
15. Atlay, M.T. The Catalysis of Homogeneous Co-oxidation. 1979, PhD
Thesis, Exeter University.
Received: November 6, 2000
Accepted: February 20, 2001
Referee I: M. Herberhold
Referee II: H. Berke