Use of pyrazolyl ligands for the formation of a bimetallic cobalt-ruthenium complex

Article abstract of DOI:10.1016/j.poly.2011.04.023

A straightforward route to Ru(pyz)₂(Hpyz)₄ (Hpyz = pyrazole) has been developed. This has been found to react readily with a modified Co(pyrazolylborate)Cl complex in the presence of triethylamine as an HCl acceptor to yield a bimetallic cobalt-ruthenium complex, in which the two metals are each six-coordinate, and bridged by three pyrazolyl anions. Both species have been characterized structurally, as has a modified Co(pyrazolylborate)₂ complex.

Full text of DOI:10.1016/j.poly.2011.04.023

Polyhedron 30 (2011) 1899–1905
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Use of pyrazolyl ligands for the formation of a bimetallic cobalt–ruthenium complex
⇑
Yifan Shi, Atta M. Arif, Richard D. Ernst
Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, UT 84112-0850, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A straightforward route to Ru(pyz) (Hpyz) (Hpyz = pyrazole) has been developed. This has been found to
2
4
Received 26 February 2011
Accepted 19 April 2011
Available online 27 April 2011
react readily with a modified Co(pyrazolylborate)Cl complex in the presence of triethylamine as an HCl
acceptor to yield a bimetallic cobalt–ruthenium complex, in which the two metals are each six-coordinate,
and bridged by three pyrazolyl anions. Both species have been characterized structurally, as has a modified
2
Co(pyrazolylborate) complex.
Dedicated with pleasure to Uwe Rosenthal
on the occasion of his 60th birthday.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Bimetallic pyrazolyl complex
Cobalt pyrazolyl
Ruthenium pyrazolyl
1
. Introduction
The construction of molecules containing di- and poly-metallic
the preparation of the desired Co–Ru species, which often occurs
in relatively low yield. Additional approaches have led to bimetal-
lic salts, in which one metal occurs in the cation, the other in the
anion [5c,9]. In one report, pyrazolyl ligands have been used to link
cobalt and ruthenium, as well as other metal combinations, in
organometallic complexes [10]. Herein we extend this approach,
in order to link cobalt and ruthenium simultaneously in a non-
organometallic environment. Other heterobimetallic combinations
linked by the simple pyrazole ligand have been prepared, most [11]
but not all [12] being organometallic or carbonyl complexes. One
can certainly expect that this approach can be expanded to the
preparations of a much wider variety of bi- and poly-metallic
complexes.
units has been a topic of great interest for some time. Such species
have attracted attention as they may be characterized by interest-
ing metal–metal bonding interactions, mixed valency, complex
electronic and magnetic properties, and could potentially lead to
useful cooperative chemical reactivity. In the latter area, there
has been specific interest in the preparation of molecular cobalt–
ruthenium complexes, given these metals’ Fischer–Tropsch activi-
ties, and the fact that ruthenium is used commercially to improve
the activities of cobalt catalysts [1]. While the incorporation of the
ruthenium is at least initially non-selective, migration to the cobalt
domains occurs and leads to significant improvement in catalyst
properties.
2. Experimental
Although a more selective ‘‘redox targeting’’ approach has been
developed [2], in which cobalt is selectively delivered to ruthenium
oxide on various supports, much use has also been made of ligands
which can bridge two metal centers in close proximity. Excluding
compounds containing potentially deleterious species such as
other metals, metalloids, or phosphorus, cobalt–ruthenium bime-
tallics have readily been accessed using ligands such as cyanides
All reactions were carried out in Schlenk apparatus under a
nitrogen atmosphere. C D and THF were dried and deoxygenated
6
6
by distillation from sodium or sodium benzophenone ketyl under a
nitrogen atmosphere, while other solvents were passed through
activated alumina columns under a nitrogen atmosphere. Analyti-
cal data were obtained from E&R Microanalytical and Desert
Analytics Laboratories.
[
3] or poly(cyclopentadienyls) [4], or others which can at least
support the formation of bi- and poly-metallic clusters, and have
been definitively characterized structurally [5]. In general, these
ligands can be specialized and somewhat expensive, or for simple
ligands such as CO [6–8], may still require significant effort for
i
2
.1. K[HB(3- Pr-4-Br-pyz)
3
]
A modification of previously reported syntheses was used to
i
prepare this species [13]. First, 3- Pr-pyrazole, an air-stable and
colorless liquid, was prepared in a two-step reaction. Twenty mil-
liliters of ethyl formate was added to 10.8 g (0.20 mol) of sodium
methoxide in 100 mL of toluene. While being stirred, the colorless
⇑
Corresponding author.
E-mail address: ernst@chem.utah.edu (R.D. Ernst).
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.023

1
900
Y. Shi et al. / Polyhedron 30 (2011) 1899–1905
solution was combined with 21.4 mL (0.20 mol) of 3-methyl-2-
butanone. An exothermic reaction ensued and the mixture turned
yellow immediately. After 30 min, 100 mL of distilled water was
added and the mixture was kept stirring for another 20 min. In an-
other flask, 10 g (0.20 mol) of hydrazine monohydrate was added
to 100 mL of 2 M HCl carefully, and the solution was cooled to
room temperature with a cold bath. Then, the mixture from the
first reaction was transferred to a separatory funnel, from which
the yellow aqueous phase was dripped into the hydrazine hydro-
chloride solution. The reaction mixture was stirred for 15 min
while an amber oil appeared. KOH (7.0 g) was added to yield a ba-
sic solution. The orange product was extracted with 40 mL of ether
and dried with magnesium sulfate. After the ether was removed
with a rotoevaporator, the mixture was heated to 150 °C and the
It is stable in air and can be further purified by recrystallization
from THF. Yield: 3.94 g, 45%.
2 4
2.3. Ru(pyz) (Hpyz) , 2
To 0.50 g (1.8 mmol) of [Ru(COD)Cl
under nitrogen were added 0.80 g (12 mmol) of pyrazole and
0.80 g (7.5 mmol) of ground Na CO in a heavy-wall borosilicate
2 x
] [14] in 10 ml of methanol
2
3
glass tube. The mixture was stirred under 3 bar of hydrogen at
50 °C for 40 h. The color of the solution changed from dark red to
orange. After cooling to room temperature, the slurry was trans-
ferred to a Schlenk flask. Fifteen milliliter of CH
tract the product from the last trace of Na CO
tube. After all the solvent was removed in vacuo, the residue was
extracted with 30 mL of CH Cl and filtered through a frit with a
2
Cl
2
was used to ex-
2
3
left in the reaction
i
product 3- Pr-Hpyz was distilled under dynamic vacuum (BP:
2
2
ꢀ3
5
9 °C at 10 torr). Yield: 10.8 g (49%).
Celite pad. The filtrate was dried in vacuo and washed with two
10 mL portions of ether and one 5 mL portion of acetone. Excess
pyrazole was removed by sublimation at 60 °C under vacuum.
The crude product often had a reddish tinge, though the pure prod-
uct should be yellow. However, NMR analysis showed that it was
pure enough for further reactions. Yield: 0.55 g, 60%. The solid
product appeared stable in the air for a short period of time. How-
ever in solution, it underwent decomposition on contact with oxy-
gen to give an uncharacterized oily product. It changed slowly to a
deep red color even in an inert environment. Crystals suitable for
an X-ray diffraction study were obtained by cooling a concentrated
In the next step, 5.0 mL (0.097 mol) of bromine was added to a
i
suspension of 10.8 g (0.097 mol) 3- Pr-Hpyz in 125 mL of water in a
flask cooled by a cold bath. After 30 min, the solution was neutral-
ized with 4.1 g (0.10 mol) of NaOH, yielding a yellow oil. It was ex-
2 2
tracted with 20 mL of CH Cl and dried with magnesium sulfate.
The concentrated product was heated to 160 °C slowly (overheat-
ing causes decomposition) and distilled under dynamic vacuum
ꢀ
3
i
(
BP: 75 °C at 10 torr). Yield: 11.8 g (62%). 3- Pr-4-bromopyrazole
is an air-stable, colorless liquid, but often is contaminated with
some light yellow impurity.
Subsequently, 0.54 g (0.010 mol) of KBH
.5 g (0.050 mol) of the above-prepared 3- Pr-4-Br-Hpyz, and there-
4
powder was added to
CH
2
Cl
Anal. Calc. for C18
3.86%.
2
solution to ꢀ30 °C overnight.
i
9
22
H N
12Ru: C, 42.60; H, 4.34. Found: C, 42.04; H,
after stirred at 125 °C for 5 h, during which time about 100 mL of
hydrogen gas was generated. The temperature of the mixture was
raised to 180 °C and the reaction continued for 10 h or until another
00 mL of hydrogen was evolved. After being cooled down, the flask
was carefully evacuated and the residual pyrazole was distilled at
85 °C under dynamic vacuum. The crude product was cooled and
1
H NMR (300 MHz, CD
2
Cl
2
, ppm): 7.79 (d, 6H, J = 2.4 Hz,
0
0
0
0
0
0
H1,1 ,4,4 ,7,7 ), 6.68 (d, 6H, J = 1.9 Hz, H3,3 ,6,6 ,9,9 ), 6.18 (dd, 6H,
J = 2.3, 2.0 Hz, H2,2 ,5,5 ,8,8 ).
ppm): 143.4 (C1,4,7), 132.5 (C3,6,9), 105.6 (C2,5,8).
0
0
0
13
1
6
3
C{ H} NMR (75 MHz, CDCl ,
1
i
mixed with 30 mL of hexane. It was stirred until the white solid
2.4. Ru(Hpyz)
3
(l-pyz)
3
Co( Pr-Br-pyz)
3
BH, 4
was well dispersed. The product was collected by filtration and
i
washed with hexane. Yield: 2.9 g (46%). KHB(3- Pr-4-Br-pyz)
an air-stable, white solid that dissolves easily in THF.
3
is
To a slurry of 0.20 g (0.39 mmol) of Ru(pyz)
Cl
at ꢀ78 °C was added 0.26 g (0.39 mmol) of CoCl[HB( Pr-Br-
pyz) ] [13a] in 5 mL of CH Cl under nitrogen. The green mixture
was stirred for several minutes, at which time 55 L of NEt
2 4
(Hpyz) in 15 ml of
i
CH
2
2
The distillations in the first two steps were very important,
because the impurities are extremely hard to separate from the thick
oily product by other means. In the third step, the reaction progress
can be difficult to control, leading to some bis- or tetrakis-(pyrazol-
yl)borate salt as minor byproducts. These may be separated by
crystallization or filtration.
3
2
2
l
3
(0.39 mmol) was added dropwise, while all solids dissolved to pro-
duce a red solution. The flask was allowed to warm to room tem-
perature over the course of 2 h, during which time much orange
solid precipitated out and the solution changed to a lighter color.
All volatiles were removed in vacuo. The powder was washed with
two 8 mL aliquots of ether, and then was extracted with 25 ml of
toluene with sonication, which was required to help dissolution.
The solution was filtered through a medium frit with a Celite pad
and the solvent was removed in vacuo. The product was collected
as an orange powder. Yield: 0.32 g, 71%. Crystals suitable for an
X-ray diffraction study were grown by evaporating an ether solu-
i
2
.2. K[B( Pr-Br-pyz)
4
]
The potassium salt of the tetrapyrazolylborate ligand was
prepared similar to Trofimenko’s [13c] method for other poly-
pyrazolylborate ligands. Under nitrogen, 0.61 g (11 mmol) of
potassium borohydride was suspended in 12.5 g (66 mmol) of dis-
tilled 3-isopropyl-4-bromopyrazole (see Section 2.1). With vigor-
ous stirring, the mixture was heated to 120 °C with the evolved
hydrogen gas being passed through a ꢀ78 °C cold trap to a wet-test
meter. In the reaction mixture, borohydride started to dissolve into
the pyrazole. The slurry was kept at 120 °C for 3 h and then the
temperature was raised to 180 °C and the reaction continued for
another 12 h or until 750 mL of hydrogen gas, as monitored by
the wet-test meter, was generated. To eliminate all unsaturated
side products, the temperature was ultimately kept at 210 °C for
two further hours. Once cooled to below 70 °C, the flask was care-
fully evacuated and the unreacted pyrazole was distilled at 180 °C
and 0.3 Torr. The remaining material was mixed with 40 mL of
hexane and sonicated until it became well dispersed. A white solid
was collected by filtration on a frit, washed with hexane, and dried.
tion in an H-tube to CH
Ph
2 2
.
Anal. Calc. for C36 46BBr
H
3
N18RuCo: C, 37.85; H, 4.03; N, 22.08.
Found: C, 38.82; H, 3.98; N, 21.16%.
i
i
2 2 2
2.5. Co[( Pr-Br-pyz) B( Pr-Br-pyz) ] , 5
To 8 mL of an aqueous solution containing 0.75 g (2.6 mmol) of
Co(NO O and 0.77 g (10.0 mmol) of KCl was added an equal
ꢁ6H
volume of methanol, followed by 0.82 g (1.0 mmol) of KB( Pr-Br-
pyz) in 8 mL of THF. The color of the solution changed to purple
3
)
2
2
i
4
immediately. After several minutes, it was diluted to twice its ori-
ginal volume with water, which resulted in precipitation of a pur-
ple solid, while the solution changed back to orange-red. The
mixture was filtered though a medium frit, washed with two
2 2
15 mL aliquots of toluene, followed by 10 mL of CH Cl , yielding

Y. Shi et al. / Polyhedron 30 (2011) 1899–1905
1901
0
.66 g (42%) of purple solid. The product is air stable, soluble in
CH Cl and sparingly soluble in toluene. Crystals suitable for an
X-ray diffraction study were obtained by slowly evaporating a con-
centrated CH Cl solution from one side of an H-shaped tube to
CH Ph in the other side.
Anal. Calc. for C48
Found: C, 36.09; H, 3.90; N, 14.05%.
tions, six pyrazoles were incorporated, two of which were
deprotonated, to yield trans-Ru(pyz) (Hpyz) (2).
2 4
2
2
2
2
2
2
N
N
64 2 8
H B Br N16Co: C, 36.24; H, 4.04; N, 14.14.
H
1
2.6. Crystallographic studies
Single crystals for the diffraction studies were attached to glass
2 4
The structure of Ru(pyz) (Hpyz) , 2, is presented in Fig. 1, while
fibers using Paratone oil, and then transferred to a Nonius Kappa
CCD diffractometer, where they were maintained at 150(1) K for
unit cell determination and data collection. The structures were
solved using direct methods and Fourier programs in SIR-97, and
thereafter further refined using the SHELXL-97 program package.
All non-hydrogen atoms were refined anisotropically. The hydro-
gen atoms in 2 were refined isotropically, while for 4 and 5, the
hydrogen atoms were allowed to ride on their attached atoms.
Pertinent crystal and data collection parameters are provided in
Table 1.
pertinent bonding parameters are provided in Table 2. The com-
plex has crystallographically imposed inversion symmetry. As no
disorder between the Hpyz and pyz ligands was observed, this
necessitates a trans orientation of the two pyrazolyl anions. The
Ru–N distances for their coordinated nitrogen atoms (N1) can be
seen to be longer than those for the Hpyz ligands, 2.1155(14) ver-
sus 2.0838(14) and 2.0891(14) Å. The N–N distance for the anionic
pyz ligands, 1.384(2) Å, is longer than those for the neutral ligands,
which average 1.357(1) Å. The angles between the Hpyz and pyz
ligands are all quite close to expectation, falling within 0.13(5)°
of 90°, while the cis angles between the Hpyz ligands alternate
between 87.83(6)° and 92.17(6)°. An interesting distortion is
observed about the coordinated nitrogen atoms, such that the
2.7. TPR studies of supported Ru/CO species
Two FTS catalysts were prepared in the same way except for
0
Ru–N–N angles (122.57(10)°, 123.51(11)°, 122.89(11)°) are signif-
icantly smaller than the Ru–N–C angles (130.11(12)°, 131.51(12)°,
their metal sources. One catalyst precursor was compound 2, while
the other was a mixture of Ru(acac) and Co(NO O in a 1:1 M
3
3
)
2
ꢁ6H
2
1
32.39(12)°).
ratio, used in an amount designed to give the same metal content
as obtained from the bimetallic complex. They were loaded sepa-
rately onto alumina supports by solution phase (bimetallic in tolu-
ene; others in THF) and calcined at 300 °C.
N
H
N
NH
N
N
3
. Results and discussion
N
Ru
N
N
As [RuCl
2
(1,5-COD)]
n
(COD = cyclooctadiene) has been shown to
(tmeda) (tme-
H
N
N
HN
N
be a useful reagent for the formation of RuCl
2
2
da = tetramethylethylenediamine) under hydrogenation condi-
tions [15], an analogous reaction was attempted using pyrazole
(
2 3
Hpyz, 1), in the presence of Na CO which could serve to neutral-
2
ize any HCl that might be generated. Indeed, under these condi-
Table 1
Crystallographic parameters for Ru(pyz)
2
(Hpyz)
4
, HB(3-i-C
3
7
H -4-Br-C
3 2
N H)
3
Co(C
3
2
N H
3
)
3
Ru(C
3
N H
2 4
)
3
, and Co[
j
2-(3-i-C
3
H
7 3 2 4 2
-4-Br-C N H) B] .
Formula
C
18
H
22
N12Ru
C
36
H
46BBr
3
CoN18Ru
48 64 2 8
C H B Br CoN16
Formula weight
Temperature (K)
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
507.55
150(1)
0.71073
orthorhombic
Pnaa
1141.5
150(1)
0.71073
cubic
1585
150(1)
0.71073
monoclinic
P2
1
3
C2/c
7.4189(2)
16.6616(3)
17.0220(5)
90
2104.10(9)
4
16.9893(5)
16.9893(5)
16.9893(5)
90
4903.7(2)
4
25.9481(6)
11.3503(3)
21.3567(3)
98.0603(12)
6227.8(2)
4
b (Å)
c (Å)
b (°)
Volume (Å )
3
Z
D
calc
1.602
7.79
1.546
31.37
1.69
54.55
Absorption coefficient (cmꢀ1)
h Range (°)
Limiting indices
3.4–27.5
ꢀ9 6 h 6 9
2.7–27.5
2–27.5
ꢀ22 6 h 6 22
ꢀ15 6 k 6 15
ꢀ14 6 l 6 14
3607
ꢀ33 6 h 6 33
ꢀ14 6 k 6 13
ꢀ27 6 l 6 27
12147
ꢀ
ꢀ
21 6 k 6 21
21 6 l 6 22
Number of reflections collected
4442
Number of independent reflections [I > 2
r
(I)]
2418; 2
0.0238
0.0588
0.31, ꢀ0.73
99.80%
3607; 2
0.0682
0.171
7133; 2
0.0472
0.1075
R (F)
2
R
w
(F )
Maximum/minimum differences Fourier peak (e Åꢀ3)
Data completeness
1.12, ꢀ0.75
0.70, ꢀ1.14
98.30%
99.60%

1
902
Y. Shi et al. / Polyhedron 30 (2011) 1899–1905
2 4
Fig. 1. The structure of Ru(pyz) (Hpyz) .
Fig. 2. The structure of the HB(3-i-C
complex.
3
7
H -4-Br-C
N
3 2
H)
3
3
Co(C N
2
H
3 3 3 2 4 3
) Ru(C N H )
Table 2
2 4
Selected bonding parameters for Ru(pyz) (Hpyz) .
Bond distances (Å)
Br
Ru–N1
Ru–N3
Ru–N5
2.1155(14)
2.0838(14)
2.0891(14)
N1–N2
N3–N4
N5–N6
1.384(2)
1.355(2)
1.359(2)
NH
Ru
N
N
N
Bond angles (°)
N1–Ru–N3
N1–Ru–N5
N3–Ru–N5
Ru–N1–N2
Ru–N3–N4
Ru–N5–N6
N
N
N
N
0
0
0
H
90.13(5)
89.91(5)
92.17(6)
122.57(10)
123.51(11)
122.89(11)
N1–Ru–N3
N1–Ru–N5
N3–Ru–N5
Ru–N1–C1
Ru–N3–C4
Ru–N5–C7
89.87(5)
90.09(5)
87.83(6)
130.11(12)
131.51(12)
132.39(12)
N
N
N
Co
N
BH
Br
N
N
N
N
HN
N
Br
4
Br
The structure of the bimetallic complex may be seen in Fig. 2,
while pertinent bonding parameters are listed in Table 3. The com-
N
N
plex lies along a C axis of symmetry, resulting in one unique pyr-
3
Br
azole ligand, and two unique pyrazolyl ligands, one bridging the
Cl Co
BH
two metals, the other bridging the cobalt and boron centers. The
metal ions are linked by three bridging pyrazolyl ligands, and for
cobalt the pseudo octahedral coordination sphere is completed
by the anionic pyrazolylborate ligand, while for ruthenium, there
are three additional pyrazole ligands. This is consistent with the
expected presence of Co(II) and Ru(II) centers. The Co–Ru distance
of 3.666(2) Å is sufficiently long that one can discount the presence
of significantly favorable Co–Ru bonding. For other bonding com-
parisons, reference can be made to the parameters set out in
Scheme 1. Regarding the distances, one can observe that the Co–
N distances to the boron-attached ring are substantially longer
than those to the ruthenium-attached ring, indicative of the partic-
ularly strong interaction of nitrogen with the electropositive boron
atom. For ruthenium, the distances to the neutral pyrazole ligands
appear to be slightly shorter than those for the bridging pyrazolyl
N
N
N
N
Br
3
The CoCl[(3-i-C
3
H
7
-4-Br-C
3
N
2
H)
3
BH] complex (3) appeared to
be an ideal candidate for reaction with 2, as 3 had been previously
used to prepare an organobimetallic cobalt–ruthenium complex
10]. The bromo and isopropyl substituents prevent incorporation
[
3
of two
j pyrazolylborates into the cobalt coordination sphere,
while perhaps allowing for subsequent incorporation of three sim-
2 4
ligands, consistent with the results for Ru(pyz) (Hpyz) (vide
ple, bridging pyrazolyl ligands. Indeed, the combination of 2 and 3
supra). All Co–N distances are longer than the Ru–N distances,
7
2
in CH Cl
2
, in the presence of triethylamine, led to the formation of
due to the former metal ion’s high spin d configuration, and the
6
the desired bimetallic, 4, in good yield.
latter’s low spin d configuration.

Y. Shi et al. / Polyhedron 30 (2011) 1899–1905
1903
Table 3
Not surprisingly, significant distortion of the bond angles about
the nitrogen donor centers in the pyrazolylborate ligand occurs, in
order to optimize the B–N and Co–N interactions. Thus, the
Co–N5–N6 angle of 115.8(5)° is much smaller than the Co–N5–
C7 angle, 135.5(6)°. For these two angles to become more similar,
without further angular distortion, the Co–N bonds would need to
be lengthened. There is also a smaller distortion of the angles about
N6, which prevented an even greater difference in angles about N5.
Interestingly, while there is little such distortion for the bridging
pyrazolyl ligands, the neutral pyrazole ligands show a significant
difference in the respective Ru–N1–N2 and Ru–N1–C1 angles,
Selected bonding parameters for HB(3-i-C
H
3 7
-4-Br-C
3
N
2
H)
3
Co(C
N
3 2
3
H )
3
Ru(C
3
N
2
H
4
)
3
.
Bond distances (Å)
Ru–N1
Co–N4
B–N6
N3–N4
Co–Ru
2.060(7)
2.102(8)
1.544(9)
1.333(10)
3.666(2)
Ru–N3
Co–N5
N1–N2
N5–N6
2.080(7)
2.233(7)
1.328(13)
1.358(10)
Bond angles (°)
0
0
N1–Ru–N1
N1–Ru–N3
N1–Ru–N3
N1–Ru–N3
N3–Ru–N3
Ru–N1–N2
Ru–N3–N4
Ru–N1–C1
Ru–N3–C4
92.8(3)
86.0(3)
89.2(3)
177.7(3)
91.9(3)
119.0(6)
123.9(5)
136.8(7)
127.7(6)
109.4(6)
N4–Co–N4
N4–Co–N5
N4–Co–N5
N4–Co–N5
N5–Co–N5
Co–N4–N3
Co–N5–N6
Co–N4–C6
Co–N5–C7
91.6(3)
175.6(3)
90.8(3)
0
0
0
0
00
0
0
92.0(3)
1
19.0(6)° versus 136.8(7)°.
85.4(3)
123.3(5)
115.8(5)
127.2(6)
135.5(6)
Although the presence of bromo and isopropyl substituents on
the pyrazole ligand may prevent the incorporation of two triden-
tate ligands in a metal coordination sphere, it has been found that
with two equivalents of these disubstituted pyrazolyl ligands, both
may be incorporated as bidentate ligands. The structure of the
0
N6–B–N6
resulting species, Co[(3-i-C
Fig. 3, with pertinent bonding parameters presented in Table 4.
The complex has crystallographically imposed C symmetry, lead-
ing to pseudo-tetrahedral coordination as a result of the
nation by each ligand. Clearly the presence of the i-C
3 7 3 2 4 2
H -4-Br-C N H) B] (5) can be seen in
3
.666(2)
Ru
Co
B
2
2
2
.080(7)
2.233(7)
j
coordi-
, and
) coordination for
the complex. The two unique Co–N distances are similar, averaging
.984(2) Å. The chelating N1–Co–N3 angle is naturally the smallest
N
N
2.060(7)
.328(13)
N
1
N
2.102(8)
N
N
1
.544(9)
3 7
H
.333(10)
1.358(10)
3
1
perhaps Br, substituents has prevented bis(j
R
1
observed, at 99.24(12)°, with the four non-chelating N–Co–N an-
gles coming at 108.72(19)°, 112.02(12)° (two), and 125.28(19)°.
Nonetheless, the N1–Co–N3 angle is significantly larger than its
counterparts in the bimetallic complex, and is accompanied by a
larger N2–B–N4 angle, 113.4(3)°. As in complex 4, some angular
distortion about the Co-bound nitrogen centers is observed. Thus,
the Co–N1–N2 and Co–N3–N4 angles are again smaller, at
118.3(2)° and 123.4(2)°, while the Co–N1–C1 and Co–N3–C7 an-
gles are 131.4(3)° and 128.4(3)°, respectively. The lesser difference
in this case seems then to lead to less distortion about N2 and N4.
Br
1
36.8(7)
Ru 124.1(5) 123.2(5)
19.0(6)
Co 115.8(5) 122.2(8)
B
1
127.1(7)
127.3(9)
N
N
N
N
N
1
03.4(9)
1
27.9(6)
135.6(6)
107.9(7)
108.5(7)
110.6(7)
N
108.9(8)
R
Br
Br
Br
Br
Br
Scheme 1. Pertinent bonding parameters for the bimetallic Ru–Co complex.
N
N
N
N
N
N
N
N
N
N
N
N
The coordination angles around the metals show slight distor-
tions. The N–Co–N angles involving the pyrazolylborate ligand
are 85.4(3)°, which likely leads to an expansion of the N–Co–N an-
gles for the other three nitrogen atoms, to 91.6(3)°. A similar differ-
ence arises around ruthenium, whose N–Ru–N angles involving the
nitrogen atoms of the bridging pyrazolyl ligands are 91.9(3)°, close
to the value of cobalt, while the corresponding angles for the non-
chelating pyrazole ligands are 92.8(3)°.
B
Co
B
N
N
N
N
Br
Br
Br
Br
5
Temperature Programmed Reduction (TPR) was performed on
two mixed Co/Ru samples supported on alumina, one prepared
from bimetallic complex 4, while the other was prepared by load-
Table 4
3 7 3 2 4 2
Selected bonding parameters for Co[j H -4-Br-C N H) B] .
2-(3-i-C
Bond distances (Å)
Co–N1
B–N2
B–N5
N1–N2
N5–N6
1.978(3)
1.547(5)
1.520(5)
1.374(4)
1.375(5)
Co–N3
B–N4
B–N7
N3–N4
N7–N8
1.990(3)
1.552(5)
1.513(6)
1.374(4)
1.368(5)
Bond angles (°)
N1–Co–N1
0
0
0
125.3(2)
99.2(1)
118.3(2)
118.3(3)
131.4(3)
128.7(4)
N3–Co–N3
N1–Co–N3
Co–N3–N4
B–N7–N8
Co–N3–C7
B–N7–C19
108.7(2)
112.0(1)
123.4(2)
119.7(3)
128.4(3)
129.4(3)
N1–Co–N3
Co–N1–N2
B–N5–N6
Co–N1–C1
B–N5–C13
3 7 3 2 4 2
Fig. 3. The structure of Co[(3-i-C H -4-Br-C N H) B] .

1
904
Y. Shi et al. / Polyhedron 30 (2011) 1899–1905
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
Ru + Co
1
1
0
0
.6
.2
.8
.4
0
RuCo Bimetallic
0
33; or e-mail: deposit@ccdc.cam.ac.uk.
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