(Pyridyl)benzoazole ruthenium(II) and ruthenium(III) complexes: Role of heteroatom and ancillary phosphine ligand in the transfer hydrogenation of ketones

Article abstract of DOI:10.1039/c3dt51599k

The synthesis and structural characterization of ruthenium complexes supported by 2-(2-pyridyl)benzoazole ligands and their evaluation as catalysts in the transfer hydrogenation of ketones are reported. Reactions of 2-(2-pyridyl)benzoimidazole (L1), 2-(2-pyridyl)benzothiazole (L2) and 2-(2-pyridyl)benzoxazole (L3) with RuCl₃·3H₂O produced the corresponding complexes [RuCl₃(L1)] (1), [RuCl ₃(L2)] (2) and [RuCl₃(L3)] (3), respectively. Similarly, treatment of L1-L3 with RuCl₂(PPh₃)₂ afforded the corresponding Ru(ii) complexes [RuCl₂(PPh₃) ₂(L1)] (4), [RuCl₂(PPh₃)₂(L2)] (5) and [RuCl₂(PPh₃)₂(L3)] (6), respectively. Solid state structures of 1 and 2 confirmed the bidentate coordination mode of L1 and L2 to ruthenium. ³¹P{¹H} NMR spectroscopy revealed coordination of two PPh₃ ligands trans to each other in an octahedral environment in 4-6 as confirmed by the solid state structure of 6. Complexes 1-6 produced active catalysts in the transfer hydrogenation of ketones in 2-propanol at 82 °C. Ruthenium(II) complexes 4-6, containing the PPh ₃ ligand, exhibited higher catalytic activities than the corresponding ruthenium(III) compounds 1-3. Complexes 1 and 4 of L1 were more active than the corresponding complexes of L2 and L3. Density functional theoretical calculations showed that dipole moments of 1-6 control their catalytic activities. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c3dt51599k

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(Pyridyl)benzoazole ruthenium(II) and ruthenium(III)
complexes: role of heteroatom and ancillary
phosphine ligand in the transfer hydrogenation
of ketones†
Cite this: Dalton Trans., 2014, 43,
1228
Aloice O. Ogweno, Stephen O. Ojwach* and Matthew P. Akerman
The synthesis and structural characterization of ruthenium complexes supported by 2-(2-pyridyl)benzo-
azole ligands and their evaluation as catalysts in the transfer hydrogenation of ketones are reported. Reac-
tions of 2-(2-pyridyl)benzoimidazole (L1), 2-(2-pyridyl)benzothiazole (L2) and 2-(2-pyridyl)benzoxazole
(
L3) with RuCl
RuCl (L3)] (3), respectively. Similarly, treatment of L1–L3 with RuCl
(PPh (L1)] (4), [RuCl (PPh (L2)] (5) and [RuCl
state structures of 1 and 2 confirmed the bidentate coordination mode of L1 and L2 to ruthenium. P{ H}
NMR spectroscopy revealed coordination of two PPh ligands trans to each other in an octahedral
3
·3H
2
O produced the corresponding complexes [RuCl
(PPh
(PPh
3
(L1)] (1), [RuCl
afforded the corresponding
(L3)] (6), respectively. Solid
3
(L2)] (2) and
[
3
2
3 2
)
Ru(II) complexes [RuCl
2
3
)
2
2
3
)
2
2
3 2
)
3
1
1
3
environment in 4–6 as confirmed by the solid state structure of 6. Complexes 1–6 produced active cata-
lysts in the transfer hydrogenation of ketones in 2-propanol at 82 °C. Ruthenium(II) complexes 4–6, con-
taining the PPh3 ligand, exhibited higher catalytic activities than the corresponding ruthenium(III)
compounds 1–3. Complexes 1 and 4 of L1 were more active than the corresponding complexes of L2
and L3. Density functional theoretical calculations showed that dipole moments of 1–6 control their cata-
lytic activities.
Received 16th June 2013,
Accepted 21st October 2013
DOI: 10.1039/c3dt51599k
www.rsc.org/dalton
have been widely applied is the transfer hydrogenation of
ketones. Transition metal-catalyzed transfer hydrogenation of
Introduction
There is rapid growth in transition metal chemistry especially ketones is preferred to the traditional high pressure hydro-
1
2
in their syntheses and applications as homogeneous catalysts genation reactions due to its mild conditions. Ruthenium
1
in various organic transformation reactions. Notably, nitrogen complexes anchored on N and P-donor ligands have been
and phosphine-donor complexes continue to receive signifi- reported to form superior catalysts towards catalytic transfer
8
,12
cant attention due to their versatile coordination chemistry hydrogenation of ketones.
These mixed ligand complexes
and propensity to form stable and active homogeneous comprising ‘hard’ N and ‘soft’ P ligands have the ability to
2
–4
catalysts.
Ruthenium complexes are a classic example of stabilize the metal center and fine-tune the electronic pro-
1
3
compounds that continue to attract a lot of attention due to perties of the resulting catalysts. So far, the most significant
their promising role in both catalytic and stoichiometric and active catalysts are ruthenium(II) complexes derived from
5
–11
reactions.
One such reaction where ruthenium compounds monotosylated 1,2-diamine or amino-alcohols discovered by
8
Noyori and co-workers. These catalyst systems are highly
active due to the presence of the N–H functionality. In this
School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01,
Scottsville, Pietermaritzburg, 3209, South Africa. E-mail: ojwach@ukzn.ac.za;
Fax: +27 (33)260 5009; Tel: +27 (33)260 5239
contribution, we report the synthesis and coordination chemi-
stry of (pyridyl)benzoazole ruthenium(II) and ruthenium(III)
complexes. The role of the PPh ancillary ligand in regulating
3
†
Electronic supplementary information (ESI) available: ESI Fig. S1–S5 contain
3
1
the catalytic activities of these complexes in the transfer hydro-
ESI-MS spectra of complexes 1–4 and 6. Fig. S6a and S6b represent P{H} NMR
spectra of complexes 4 and 5 in DMSO-d
6
. The molecular structure of complex 6 genation of ketones would also be discussed. The findings in
1
is shown in Fig. S7. H NMR spectrum of L4 and ESI-MS spectrum of complex 7 this work demonstrate that the oxidation state of the metal
31
are given in Fig. S8 and S9 respectively. Fig. S10 and S11 show the P NMR spec-
center, the nature of the ligand and the phosphine donor
moiety control the activities of the complexes. We have also
used density functional theoretical calculations to rationalize
the catalytic trends obtained.
1
trum of the isopropanol Ru complex and H NMR spectrum of 2-phenylethanol
product obtained from the transfer hydrogenation of acetophenone respectively.
CCDC 937657 for 1 and 937658 for 2. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c3dt51599k
1228 | Dalton Trans., 2014, 43, 1228–1237
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Due to the paramagnetic nature of complexes 1–3, NMR
spectroscopy was not useful in their structural elucidation.
Their identities were thus established by micro-analyses, mass
Results and discussion
Synthesis of ruthenium complexes
Ligands L1–L3 were synthesized according to literature pro- spectrometry (Fig. S1–S5†) and single crystal X-ray analyses for
1
4
cedures. Treatment of L1–L3 with RuCl ·3H O produced the 1 and 2. For example, the ESI-MS mass spectrum of 1
3
2
+
corresponding monometallic ruthenium complexes 1–3 in (Fig. S1†) showed m/z at 402.89 (M + 1) as the base peak
moderate yields (Scheme 1). On the other hand, reactions of corresponding to its molecular ion of 401.89. Elemental ana-
L1–L3 with RuCl (PPh ) afforded the respective ruthenium(II) lyses data of 1–3 were consistent with the proposed structures
2
3 3
compounds 4–6 (Scheme 1, route A). In another synthetic pro- in Scheme 1 and demonstrated their purity. Solid state struc-
tocol, reductions of ruthenium(III) complexes 1–3 with Et N in tures of 1 and 2 confirmed the bidentate coordination modes
the presence of two equivalents PPh also produced the corres- of L1 and L2 to the ruthenium atom.
3
3
1
31
1
ponding ruthenium(II) compounds 4–6 (Scheme 1, route B).
Route A gave compounds 4–6 in relatively higher yields the structural elucidation of ruthenium(II) compounds 4–6. For
58%–86%) compared to route B (53%–77%). It is important example, a broad signal at 13.07 ppm assigned to the N–H
to note that even the use of one equivalent of PPh in route B proton in L1 was recorded at 13.90 ppm in 4. Similarly, the 6H-
H NMR and P{ H} NMR spectroscopy were also used in
(
3
afforded the corresponding complexes 4–6, though at reduced pyridyl protons recorded at 8.73 ppm in L1 and L2 were
yields. The lower yields associated with route B could emanate observed downfield at 8.91 ppm and 9.42 ppm in 4 and 5
3
1
1
from partial reductions of 1–3. While compounds 1–3 were iso- respectively. P{ H} NMR spectroscopy was particularly useful
lated as dark brown solids, 4–6 were obtained as purple solids. in the characterization of 4–6 in establishing the nature of
3
1
coordination of the PPh ligand. Fig. 1a and 1b show P NMR
3
spectra of complex 6 recorded in DMSO-d
vely. Typical
6
and CDCl
P{ H} NMR spectra recorded in DMSO-d
showed three signals (Fig. 1a): one major peak at 34.43 ppm
4), 32.13 ppm (5), 32.48 ppm (6); a second minor signal
between 25.55 and 21.64 ppm; and a third peak at ≃
6.72 ppm typical of free PPh3.
Our initial interpretation of the P NMR spectra pointed to
the presence of free PPh and the formation of other side pro-
ducts or existence of two different geometric isomers of 4–6
3
respecti-
31
1
6
(
−
3
1
3
1
5
(
3
trans- and cis-dispositions of the two PPh ligands).
However, from the high purities of 4–6 obtained from micro-
analyses data, the presence of impurities was ruled out. A closer
inspection of the spectra and literature reports pointed to the
3 6
displacement of one coordinated PPh by DMSO-d (eqn (1))
1
6
used to acquire the NMR spectra. The DMSO-d coordinated
6
Scheme 1 Synthetic protocol for ruthenium(II) and ruthenium(III) ruthenium complexes (4a–6a) could thus be responsible for
compounds.
the peaks observed between 32.13 and 34.43 ppm. These
3
1
1
Fig. 1
P { H} NMR spectra of complex 6 (a) DMSO-d
6 3 3
, signal at −6.56 ppm reveals the generation of a free PPh (b) in CDCl , one signal at
29.83 ppm indicates that the two trans-PPh
3
ligands are chemically equivalent.
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values fall within the observed range of 31.4–33.8 ppm
16–19
reported in mono-coordinated PPh3 compounds.
The
signals at 24.20 ppm (4), 25.55 ppm (5) and, 21.64 ppm (6)
3
1
were therefore assigned to the trans-PPh
3
ligands. P{H} NMR
signals for similar phosphine ruthenium compounds have
1
5,18,20
been reported between 24.36 and 21.87 ppm.
These data
therefore reveals the partial substitution of one coordinated
PPh to establish an equilibrium mixture between 4 and 6 and
3
6
the corresponding DMSO-d adducts 4a–6a. ESI, Fig. S6a and
3
1
S6b† show the P NMR spectra of complexes 4 and 5 in
DMSO-d respectively.
6
Fig. 2 Molecular structure of 1 drawn at 50% probability ellipsoids. Bond
lengths (Å): Ru–N(1) 2.0630(16); Ru–N(2) 2.0471(15); Ru–N(4) 2.0406(17);
Ru–Cl(2) 2.3583(4); Ru–Cl(3) 2.3675(5). Bond angles (°): N(1)–Ru–N(3)
7
8.70(6); N(1)–Ru(1)–Cl(2) 89.07(4); N(3)–Ru(1)–Cl(2) 89.24(4); N(1)–
Ru(1)–Cl(3) 91.34(4); N(3)–Ru(1)–Cl(3) 88.15(4); Cl(1)–Ru(1)–Cl(2)
76.995(15); Cl(2)–Ru(1)–Cl(3) 92.475(16); Cl(3)–Ru(1)–Cl(1) 90.409(16).
ð1Þ
1
In order to confirm the displacement of one PPh by the
3
3
1
DMSO-d
the non-coordinating CDCl
signal at ca. 29.9 ppm (Fig. 1b) was observed. This is consistent
with the trans-arrangement of the two PPh ligands and exist-
ence of one isomer in 4–6. Solid state structure of complex 6
Fig. S7†) confirmed the trans-disposition of the two PPh3
6
solvent, P{H} NMR spectrum of 6 was acquired in
3
NMR solvent. Indeed only one
3
(
ligands and bidentate coordination mode of L3 to give a six-
coordinate ruthenium center. The structure could not be satis-
factorily refined due to desolvation of the crystal, hence the
data obtained are not suitable for publication and discussion
of bond parameters. However, the coordination chemistry and
atom connectivity are not in doubt.
Fig. 3 Molecular structure of 2 drawn at 50% probability ellipsoids.
Bond lengths (Å): Ru–N(1) 2.0536(12); Ru–N(2) 2.0769(12); Ru–N(3)
Molecular structures of complexes 1 and 2
2
.0494(13); Ru–Cl(2) 2.3273(4); Ru–Cl(3) 2.3554(4). Bond angles (°):
N(1)–Ru(1)–N(3) 79.15(5); N(1)–Ru(1)–Cl(1) 91.01(3); N(3)–Ru(1)–Cl(1)
6.61(3); N(1)–Ru(1)–Cl(2) 89.34(3); N(3)–Ru(1)–Cl(2) 89.58(3); Cl(1)–
Ru(1)–Cl(2) 176.03(14); Cl(1)–Ru(1)–Cl(3) 91.43(14); N(3)–Ru(1)–Cl(3)
73.54(4); Cl(3)–Ru(1)–N(3) 85.04(4).
Single crystals suitable for X-ray analyses of 1 and 2 were
2
grown by slow evaporation of their MeCN–Et O solutions at
8
room temperature. Fig. 2 and 3 show the molecular structures
of 1 and 2 respectively while Table 1 contains data collection
and structural refinement parameters of 1 and 2. Complexes 1
and 2 both co-crystallized with one acetonitrile solvent. Both
L1 and L2 adopt bidentate coordination modes to ruthenium
in 1 and 2. The coordination environment around the ruthe-
nium atom in 1 and 2 consists of one ligand unit, three Cl
ligands and one NCMe molecule in the sixth position to give a
nominally octahedral coordination geometry. The bond angles
for Cl(2)–Ru(1)–Cl(3) of 92.47° (1) and Cl(1)–Ru(1)–Cl(3) of
1
Ru–Cl(3) (Cl trans to N ) bond length of 2.3675(5) Å. The
bz
elongation of the Ru–Cl(3) bond could be attributed to a stron-
ger trans effect of the benzoimidazole ring compared to the Cl
ligand. A similar trend is observed in the Ru–Cl bond dis-
tances in 2. The average Ru–Cl bond lengths of 2.348(5) Å in 1
and 2 are shorter than the average Ru–Cl bond distances of
5
,21–23
2.430(4) Å reported for similar ruthenium complexes.
An
9
1.43° (2) deviate from 90° as is typical of octahedral com-
interesting aspect in the solid state structures of 1 and 2 is the
coordination of one NCMe molecule to give an 18-electron
metal center. Thus the expected 16-electron trichloride species
are coordinatively unsaturated, a feature we have exploited in the
use of 1–3 as catalysts in the transfer hydrogenation of ketones.
plexes. Thus the geometry around the ruthenium atoms in 1
and 2 could be best described as a distorted octahedral. The
Ru–Npy bond lengths of 2.0630(16) Å and 2.0536(12) Å in 1 and
2
, respectively, are statistically similar. However, the Ru–Nbz
bond distance of 2.0471(15) Å in 1 is significantly shorter than
the Ru–Nbz bond distance of 2.0769(12) Å in 2, suggesting that
L1 has less trans-effect than L2. In the structure of 1, the
Transfer hydrogenation of ketones catalyzed by 1–6
Ru–Cl(1) and Ru–Cl(2) (trans to each other) bond distances of Preliminary investigations of complexes 1–6 in the catalytic
.3583(4) Å and 2.3305(4) Å, respectively, are shorter than the transfer hydrogenation of acetophenone as a model substrate
2
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Table 1 Crystal data collection and structural refinement parameters
for 1 and 2
Table 2 Summary of the transfer hydrogenation of acetophenone data
of complexes 1–6
a
b
c
Parameter
1
2
Entry
Catalyst
Conversion [%]
TOF
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C
16
H
15Cl
3
5
N Ru
C
16
H
14Cl
3
4
N RuS
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
4
5
4
1
91
77
88
95
92
93
57
59
79
59
92
23
19
22
24
23
23
14
30
40
59
23
484.75
100(2)
0.71073
Triclinic
Pˉ1
501.79
100(2)
0.71073
Triclinic
Pˉ1
8.6945(4)
9.5982(4)
8.5108(4)
9.7943(4)
d
d
11.3983(5)
102.453 (2)
90.168 (2)
99.820 (2)
914.44 (7)
2
1.761
1.310
482
11.4935(5)
100.446 (2)
90.126(2)
100.326(2)
926.33(7)
2
1.799
1.398
498
e
1
1
0
1
f
γ (°)
Volume (Å )
a
3
Conditions: acetophenone, 2.0 mmol; catalyst; 0.02 mmol (1.0 mol%);
base, KOH in 2-propanol (100 mol%); time, 4 h, temperature, 82 °C.
Z
D
b
1
c
−1
calcd (mg m−3
Determined by H NMR spectroscopy. TOF in mol substrate mol
1 d e f
)
catalyst h−
2
.
0.01 mmol catalyst (0.5 mol%). Time, 1 h. KOH,
−
1
Absorption coefficient (mm
F(000)
)
5 mol%.
Theta range for data
collection (°)
Reflections collected/unique
Completeness to theta (%)
1.83–26.56
1.80–26.83
13 981
97.3
0.838
13 956
96.5
1.129
2
Goodness-of-fit on F
R Indices (all data)
R
1
= 0.0208
2
R
1
= 0.0165
2
wR = 0.0929
wR = 0.0404
Largest diff. peak and hole
0.673 and
−0.367
0.417 and
−0.349
−
3
(e Å
)
Scheme 2 Catalytic transfer hydrogenation of acetophenone by 1–6.
Fig. 4 Time-dependence of transfer hydrogenation of acetophenone
by complexes 1, 2 and 4 showing shorter induction period in 4.
were carried out using 2-propanol and KOH at 82 °C
(Scheme 2). The catalytic reactions were performed using
2
.0 mmol of acetophenone, 0.02 mmol of 1–6 (1.0 mol%), 4–6 already contain ruthenium(II) metal centers implies they
KOH in 2-propanol (100 mol%). The percentage conversions are easily activated, consistent with the relatively shorter induc-
1
were determined by H NMR spectroscopy by comparing the tion periods observed. In addition, the π-acceptor ability of the
intensity of the methyl signal of acetophenone (s, δ 2.59 ppm) PPh ligand in 4–6 as opposed to the σ-donor Cl ligand in 1–3
3
and methyl signal of 1-phyenylethanal (d, δ 1.49 ppm) of the might play a crucial role in the stabilization of low oxidation
crude products. All the compounds were found to form active state ruthenium(II)/(I) species resulting in higher catalytic
2
5
catalysts affording conversions between 77% and 95% within activities. In fact, it is expected that reduction of ruthenium(III)
h (Table 2). A blank experiment without any ruthenium complexes 1–3 to ruthenium(I) species would be energeti-
complex afforded only 17% conversion within 4 h under cally unfavorable. This is why the modest catalytic activities
similar conditions.
displayed by 1–3 in this work are quite intriguing. An inspec-
4
From Table 2, it is evident that both the identity of the tion of the literature reveals no examples (to the best of our
ligand and the oxidation state of the ruthenium metal deter- knowledge) where similar ruthenium(III) complexes have been
mined the activities of the resulting catalysts. Catalysts derived used as catalysts in the transfer hydrogenation of ketones. We
from ruthenium(II) complexes bearing PPh ligands (4–6) were largely assign this behavior to the coordinatively unsaturated
3
more active and exhibited shorter induction periods than 16-electron ruthenium centers in 1–3 which allows for ketone
the corresponding trichloride ruthenium(III) complexes 1–3 substrate coordination. The coordination of one NCMe solvent
(
Fig. 4). The active species in the transfer hydrogenation of in the solid state structures of 1 and 2 (Fig. 2 and 3) further
ketones is known to contain a low oxidation state ruthenium augments this hypothesis.
3
metal. It is therefore conceivable that longer induction
Catalyst concentration also influenced the catalytic transfer
periods displayed by 1–3 may be associated with the reduction hydrogenation reactions (Table 2, entries 4 vs. 8 and 5 vs. 9).
of ruthenium(III) to ruthenium(II)/ruthenium(I) species. That For example, reducing the catalyst loading of 4 from 1 mol%
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to 0.05 mol% was followed by a significant drop in activity Table 3 Transfer hydrogenation of different ketones and bases using
a
complex 4
from 95% to 59% (Table 2, entries 4 and 8). The TOFs of 1–6
of 22–60 h− were lower compared to the pre-activated cationic
1
b
TOF (h−)
24
Entry
1
Substrate
Base
KOH
Conv. [%]
bis-(pyrazolyl)pyridineandbis-(imadzolyl)pyridineruthenium(II)
1
6
complexes reported by Zeng et al. which gave TOFs as
high as 705 600 h− . This difference could be largely attributed
to the highly electrophilic metal centers in the Zheng catalysts
compared to our catalysts 1–6. However, complexes 1–6 gave
relatively higher catalytic activities than the dinuclear phos-
phite ruthenium(II) complexes reported by Aydemir et al.,
95
1
2
3
4
5
KOH
KOH
KOH
KOH
91
95
97
98
23
24
24
25
−
1 21
which gave a TOF of 10–16 h
.
The identity of the heteroatom in the ligand architecture
also significantly affected the catalytic activities of complexes
1
–6. In general, complexes 1 and 4 bearing the (pyridyl)benz-
imidazole ligand L1 were the most active, followed by the
pyridyl)benzoxazole complexes 3 and 6. The (pyridyl)benzo-
(
thiazole complexes 2 and 5 showed the lowest activities. From
the basicity of L1–L3, one would expect 3 and 6 which contain
the (pyridyl)benzoxazole ligand to be the most active. Oxygen
is more electronegative than N or S and hence would be
2
4
expected to give a more electrophilic ruthenium center.
Higher catalytic activities of 3 and 6 (O-atom) in comparison to
and 5 containing L2 (S-atom) agrees with this argument.
6
KOH
64
16
2
However, the greater activities observed for the (pyridyl)-
benzoimidazole complexes 1 and 4 contradict this hypothesis.
This may be attributed to the presence of the acidic amine
proton which facilitates the “outer sphere” mechanism by
enhancing deprotonation of the isopropanol as widely pro-
7
8
KOH
78
98
20
25
NaOH
2
5–29
posed in the literature.
N–H moiety, we synthesized the N-propyl protected ligand L4
and the corresponding ruthenium trichloride complex 7.
In order to establish the role of the
3
0
3
1
9
Na
2
CO
3
73
97
18
24
1
ESI, Fig. S8 and S9† show the H NMR spectrum of L4 and the
ESI-MS spectrum of complex 7 respectively. The percentage
conversion of complex 7 of 57% was significantly lower com-
pared to the 91% observed for the N–H complex 1 in the trans-
fer hydrogen of acetophenone under similar conditions
t
10
BuOK
(Table 2, entries 1 and 7). This confirms the role of the N–H
functional group in enhancing the activities of the resulting
catalysts. Indeed, complex 7 displayed lower activity even in
comparison to the S complex 2 (77%) and O complex 3 (88%).
Impressed by the catalytic activities of 1–6 in the transfer
hydrogenation of acetophenones, we explored the transfer
hydrogenation of various ketones using catalyst 4 (Table 3,
entries 1–4). Under similar conditions, complex 4 exhibited
comparable catalytic activity in other ketones achieving
maximum conversions of 97% for cyclohexanones (Table 3,
entry 4). It is important to note that even the presence of sub-
stituents in the ortho position in the phenyl ring as in 2-methyl-
acetophenone did not significantly affect the reactions
a
Conditions: ketone, 2 mmol; catalyst. 0.02 mmol (1 mol%); 0.4 M of
b
base in 2-propanol (5 mL), temperature 82 °C. Determined by
1
H NMR spectroscopy after 4 h.
dibenzolylmethane (64%) presumably due to the electronic
rich alkyl groups and the absence of π-delocalization in the
substrate.
The effect of the base used was also investigated using
t
KOH, NaOH, Na
activity trend was found to be in the order NaOH > BuOK >
KOH > Na CO , consistent with the relative strength of the
bases. The slight differences in the activities of NaOH, BuOK
and KOH highlight their similar strengths in deprotonating
2
CO
3
and BuOK (Table 3, entries 8–10). The
t
2
3
t
(Table 3, entry 1–4). Comparable conversions observed for aceto-
phenone (95%), 2-methylacetophenone (91%) and 2-chloro-
acetophenone (95%) thus indicate less steric and electronic
contributions in regulating the reactivities of ketone sub-
21
2
-propanol as previously observed by Aydemir et al.
3
2
Proposed transfer hydrogenation reaction mechanism
strates. High catalytic activity (98%) was also reported for the
strained benzophenone. However, we observed a drastic drop The mechanism of transition metal catalyzed transfer hydro-
in activities (50%) for the 3-methylpentanone and 1,3- genation of ketone has been proposed to involve the formation
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of Ru(II) hydride species from a catalyst precursor followed by coordinated PPh
3
were recorded at 21.44 ppm and 29.38 ppm
the addition of a ketone to the coordinatively unsaturated as opposed to one signal at 29.83 ppm in complex 6. Similar
3
,4
Ru(II) hydride species. Considering the lability of the PPh
3
displacement reactions of labile ligands to form coordinatively
ligand in complexes 4–6, we propose the dissociation of one saturated intermediates in the transfer hydrogenation reac-
6
,33,34
PPh group prior to the coordination of the ketone through an tions have been reported in the literature.
Furthermore,
3
inner-sphere mechanism (Scheme 3). Using complex 6 as an dissociation of one PPh
3
is sterically acceptable since a six-
illustration, the catalytic pathway starts by dissociation of one coordinated species would be too saturated and sterically
PPh , leading to the formation of a metal alkoxide intermedi- demanding to allow substrate coordination.
3
1
ate (6-I). Generation of a Ru–H intermediate 6-II is followed by
Attempts to establish the formation of the Ru–H by
H
coordination of the acetophenone substrate to produce the NMR spectroscopy or stoichiometric reactions did not materia-
intermediate 6-III. Subsequent insertion of the coordinated lise as no signal was recorded within the range of
3
5
acetophenone into the Ru–H bond forms the Ru(II)–alkoxide −10.00 ppm. This is a feature we attribute to the likely
-IV. Protonation of the coordinated substrate by 2-propanol instability of the intermediate Ru-hydride species formed.
6
affords the 2-phenylethanol product and the alkoxide 6-V.
β-Hydride elimination of the coordinated 2-propanal in 6-V
DFT calculations
results in regeneration of the active catalyst 6-I. Experimental To further understand the effect of the ligand and catalyst
evidence for the lability of PPh is derived from the displace- structure on the catalytic activities of complexes 1–6, density
3
3 6
ment of PPh by the DMSO-d NMR solvent. To further functional theoretical calculations were performed on simpli-
support this assumption, we monitored the formation of 6-I fied ruthenium(II) analogues [RuCl (L1)] 1a, [RuCl (L2)] 2a,
2
2
3
1
from 6 in a iprOH–KOH solution using P NMR spectroscopy and [RuCl (L3)] 3a. Frontier molecular orbitals of 1a–3a calcu-
2
3
(Fig. S10†). Indeed, generation of a free PPh was evident from lated at B3LYP using the LANL2DZ basis set is shown in Fig. 5.
the signal at −5.29 ppm. In addition, two signals for the Table 4 contains a summary of charge distribution data of
Scheme 3 Proposed catalytic cycle for the transfer hydrogenation of ketone by 6 in the presence of 2-propanol and KOH.
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Dalton Transactions
Fig. 5 Frontier molecular orbitals of ruthenium(II) complexes [RuCl
2
(L1)] (1a); 2a-[RuCl
2
(L2)] (2a) and [RuCl
2
(L3)] (3a) as determined by density func-
tional theory using B3LYP level of theory and LANL2DZ basis set (isovalue 0.02).
Table 4 Summary of the data obtained from the DFT calculations of
the Ru(II) complexes
Conclusions
Ruthenium(III) and ruthenium(II) complexes anchored on
bidentate (pyridyl)benzoazole ligands have been prepared and
structurally characterized. The coordinative unsaturation of
the ruthenium(III) trichloride complexes and the high lability
Band gap
(eV)
NBO
(Ru)
Charge on
heteroatom
Dipole
moment
Complex
1a
2a
3a
2.4540
2.3800
2.3799
0.344
0.345
0.350
−0.591
0.372
−0.496
12.41
9.36
9.52
3
of the coordinated PPh ligand are responsible for the catalytic
activities of these compounds in the transfer hydrogenation of
ketones. This work demonstrates examples of non-phosphine
donor ruthenium(III) catalysts in the transfer hydrogenation of
1
a–3a. The benzoimidazole complex 1a showed the largest ketones. Ruthenium(II) catalysts bearing the PPh3 ancillary
HOMO–LUMO gap while the benzothiazole and benzoxazole ligands form more active systems than the ruthenium(II) tri-
compounds 2a and 3a exhibited very similar energy gaps chloride counterparts. The N–H moiety imparts a higher cata-
(Table 4). Since the HOMOs are predominantly occupied by lytic performance in the complexes compared to the O and S
ruthenium d-orbital electrons, it is expected that smaller and N-protected groups. DFT studies show that the larger
energy gap would facilitate π-back donation of electrons from dipole moment induced by the N–H group enhances the activi-
ruthenium to the ligand thus creating an electrophilic metal ties of the resulting catalysts.
center. This should result in higher catalytic activities of 2 and
3
6
3
compared to 1. The observation that 1 was more active
than 2 and 3 thus indicates that the HOMO–LUMO gap does
not control the activities of 1–6. This is supported by compar-
able Ru NBO of 0.344, 0.345 and 0.350 for 1a, 2a and 3a
Experimental section
General methods and instrumentation
respectively. It is important to note that 1a exhibited a larger All manipulations were carried out under inert atmosphere
dipole moment of 12.41 compared to 9.36 (2a) and 95.2 (3a). using standard Schlenk techniques unless stated otherwise.
This reflects that the N–H moiety in L1 increases the polarity Starting materials, RuCl ·3H O, RuCl (PPh ) , isopropanol,
3
2
2
3 3
of the respective ruthenium complex and thus accelerates its absolute ethanol and deuterated solvents, were obtained from
reactions with 2-propanol to generate the active Ru–H species. Sigma Aldrich and used as received. 2-(2-Pyridyl)benzoimid-
This might explain the higher catalytic activities observed for azole (L1), 2-(2-pyridyl)benzothiazole (L2), 2-(2-pyridyl)benzox-
the benzoimidazole (L1) complexes 1 and 4 compared to the azole (L3) were prepared following literature procedures.14
benzothiazole (L2) and benzoxazole (L3) complexes. The Dichloromethane was dried over P O and distilled prior
2
5
higher activities of benzoxazole complexes 3 and 6 in compari- to use. NMR spectra were recorded on
son to the benzothiazole analogues 2 and 5 are consistent with ( H, 400 MHz; C, 100 MHz; P, 162 MHz) Ultrashield
a
Bruker 400
1
13
31
this argument.
instrument at room temperature in CDCl3 and DMSO-d6
1234 | Dalton Trans., 2014, 43, 1228–1237
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Paper
solvents. Chemical shifts are reported in δ (ppm) and refer- C, 64.85; H, 4.41; N, 4.71%. Found: C, 65.19; H, 4.35; N,
enced to the residual proton in the solvents. All coupling con- 4.35%.
stants are measured in hertz (Hz). Elemental analyses were
The two synthetic procedures (methods A and B) described
performed on a Thermal Scientific Flash 2000 and mass for 4 were employed in the synthesis of 5 and 6.
spectra were recorded on an LC Premier micro-mass
spectrometer.
Synthesis of [{2-(2-pyridyl)benzothiazole}RuCl (PPh ) ] (5).
2 3 2
2 3 3
Method A: RuCl (PPh ) (0.10 g, 0.11 mmol) and L2 (0.02 g,
3
Synthesis of [{2-(2-pyridyl)benzimidazole}RuCl ]
(1). A 0.11 mmol) were used. Yield = 0.06 g (58%). Method B:
mixture of RuCl ·3H O (0.10 g, 0.48 mmol) and L1 (0.09 g, Complex 2 (0.10 g, 0.24 mmol), PPh (0.13 g, 0.50 mmol) and
3
2
3
0
.48 mmol) was refluxed in absolute EtOH (15 mL) for 4 h. A Et
3
N (1.00 mL, 7.16 mmol) were used. Recrystallization from
brown precipitate was collected by filtration, washed with CH
excess EtOH and dried to afford an analytically pure com- Yield = 0.08 g (53%). H NMR (400 MHz, DMSO-d ): δ 7.00 (t,
2
2
Cl –hexane solution mixture afforded 5 as a purple solid.
1
6
3
3
pound 1 as a brown solid. Single crystals suitable for X-ray ana- 3H, PPh
lysis of 1 were grown by slow evaporation of the acetonitrile– (m, 12H, PPh
Et O solution. Yield = 0.06 g (40%). (ESI-MS) m/z (%) 402.89 7.6 Hz); 7.64 (d, 2H, bzthio, J
3
, JHH = 7.6 Hz); 7.08 (t, 3H, PPh
3
, JHH = 7.6 Hz); 7.24
); 7.46 (t, 1H, py,
= 11.6 Hz); 7.82 (t, 1H, py,
HH
3
3
); 7.39 (m, 12H, PPh
3
J
HH
=
3
2
+
3
3
(
1
M , 100). Anal. Calcd For C12
H
9
Cl
0.44%. Found: C, 35.98; H, 2.19; N, 10.66%.
Synthesis of [{2-(2-pyridyl)benzothiazole}RuCl3] (2). The (d, 1H, py, JHH = 8.4 Hz). P {H} NMR (DMSO-d ): δ 25.55
3
N
3
Ru: C, 35.80; H, 2.25; N,
JHH = 7.2 Hz); 8.06 (d, 1H, py, JHH = 7.2 Hz) 8.17 (d, 1H,
3
3
bzthio, JHH = 7.2 Hz); 9.17 (d, 1H, bzthio, JHH = 5.6 Hz); 9.42
3
31
6
1
3
3 6
procedure used to prepare 1 was followed for the synthesis of (s, PPh ). C NMR (400 MHz, DMSO-d ): δ 137.16, 137.07,
3
1
2
3 2 3
, using RuCl ·3H O (0.20 g, 0.98 mmol) and L2 (0.21 g, 133.78, 133.63, 129.45, 129.26, 129.21. P NMR (CDCl ):
0
.98 mmol) to afford 2 as a light brown solid. Single δ 26.16 (s, PPh ). Anal. Calcd For C H Cl N P RuS: C, 63.44;
3
48 38
2 2 2
crystals suitable for X-ray analysis were grown by slow evapor- H, 4.21; N, 3.08%. Found: C, 63.14; H, 4.07; N, 3.12%.
ation of an acetonitrile solution of 2. Yield = 0.23 g (56%). Synthesis of [{2-(2-pyridyl)benzoxazoles}RuCl (PPh
ESI-MS) m/z (%) 420.87 (M + H, 20). Anal. Calcd For Method A: RuCl (PPh ) (0.10 g, 0.11 mmol) and L3 (0.02 g,
2
3 2
) ] (6).
+
(
2
3 3
C
12
H
8
Cl
H, 2.08; N, 6.91%.
Synthesis of [{2-(2-pyridyl)benzoxazole}RuCl3] (3). This Et N (1.00 mL, 7.16 mmol) were used. Purple solid. Yield =
3
N
2
RuS: C, 34.44; H, 1.92; N, 6.67%. Found: C, 34.62; 0.10 mmol) were used. Yield = 0.08 g (86%). Method B:
Complex 3 (0.10 g, 0.25 mmol), PPh (0.13 g, 0.50 mmol) and
3
3
1
complex was prepared following the procedure described for 0.12 g (77%). H NMR (400 MHz, DMSO-d
1
6
): δ 7.03 (t, 2H, py,
3
3
using RuCl
3
·3H
2
O (0.20 g, 0.98 mmol) and L3 (0.21 g,
JHH = 7.6 Hz); 7.12 (t, 2H, bzox, JHH = 7.2 Hz); 7.24 (m, 12H,
3
0
.98 mmol) to give 3 as a brown solid. Yield = 0.26 g (66%). PPh ); 7.39 (m, 12H, PPh ); 7.49 (t, 2H, PPh , J = 9.6 Hz);
3
3
3
HH
+
+
3
3
(ESI-MS), m/z (%) 404.92 (M + H, 20); 333.96 (M − 2Cl, 40). 7.74 (d, 1H, py, JHH = 8.4 Hz); 7.89 (t, 1H, py, JHH = 7.6 Hz)
3
3
8 3 2 HH
Anal. Calcd For C12H Cl N RuO: C, 35.71; H, 2.00; N, 6.94%. 8.09 (d, 1H, bzox, JHH = 7.6 Hz); 8.49(d, 1H, bzox, J =
Found: C, 35.42; H, 1.83; N, 7.27%.
3
31
7.6 Hz); 8.88 (d, 1H, py, J = 5.6 Hz). P {H} NMR (DMSO-
HH
1
3
Synthesis of [{2-(2-pyridyl)benzimidazole}RuCl
2
(PPh
3
)
2
] (4).
6 3 6
d ): δ 21.65 (s, PPh ). C NMR (400 MHz, DMSO-d ): δ 137.14,
(0.20 g, 0.21 mmol) in 137.06, 133.77, 133.61, 129.44, 129.25, 129.20.
3
1
Method A: To a solution of RuCl
CH Cl (5 mL) was added L1 (0.04 g, 0.21 mmol) in CH Cl
2
(PPh
3
)
3
P NMR
+
(CDCl ): δ 29.93 (s, PPh ). (ESI-MS), m/z (%) 892.90 (M , 42).
2
2
2
2
3
3
(5 mL). A light brown precipitate was formed immediately. The Anal. Calcd For C48
H
2 2 2
38Cl N OP Ru: C, 64.58; H, 4.29; N,
mixture was stirred at room temperature for 4 h and filtered to 3.14%. Found: C, 64.73; H, 4.31; N, 3.22%.
obtain a purple precipitate. The precipitate was washed with
CH Cl (10 mL) to afford 4 as an analytically pure solid. Yield
2 2
=
0
0
0.14 g (73%). Method B: To a suspension of 1 (0.10 g,
Transfer hydrogenation of ketones
.25 mmol) in CH Cl (5 mL) were added PPh3 (0.13 g,
2
2
3
.50 mmol) and Et N (1.00 mL, 7.16 mmol) and the mixture A typical procedure for the catalytic transfer hydrogenation of
stirred at room temperature for 4 h. The solution was filtered ketones was as follows. A mixture of acetophenone (0.23 mL,
and the filtrate concentrated to about 3 mL and hexane (5 mL) 2.0 mmol), KOH in 2-propanol (100 mol%) and catalyst
was added to the concentrated solution. Slow evaporation of (0.02 mmol, 1 mol%) was introduced into a two-neck round
the mixture afforded purple single crystals of 4 in quantitative bottom flask fitted with a condenser under inert atmosphere.
1
amounts. Yield = 0.12 g (54%). H NMR (400 MHz, DMSO-d ): The mixture was stirred at 82 °C and the samples withdrawn at
6
3
δ 6.96 (t, 12H, PPh
m, 6H, PPh
PPh ); 7.77 (t, 1H, py, J = 6.8 Hz); 7.99 (d, 1H, bzim, J
3
, JHH = 8.0 Hz); 7.08 (m, 2H, bzim); 7.23 regular intervals. The percentage conversions were determined
3
1
(
3
); 7.29 (t, 1H, py, JHH = 6.4 Hz); 7.39 (m, 12H, using H NMR spectroscopy by comparing the intensities of
3
3
=
the methyl signal of acetophenone (s, δ 2.59 ppm) and methyl
3
HH
HH
3
7
.6 Hz); 8.52 (d, 1H, bzim,
J
HH = 8.4 Hz); 8.91 (d, 1H, py, signal of 2-phenylethanol (d, δ 1.49 ppm) of the crude pro-
HH = 5.6 Hz). P {H} NMR (DMSO-d
3
31
13
J
6
): δ 24.21 (s, PPh
3
).
C
ducts. After the reaction period, the solvent was evaporated to
NMR (400 MHz, DMSO-d ): δ 137.15, 137.05, 133.80, 133.60, dryness to afford a dark brown crude product which was iso-
6
3
1
1
1
29.46, 129.28, 129.21. P {H} NMR (CDCl
3
): δ 28.18 (s, PPh
PPh 20); 594.04 (Fig. S11†). The catalytic reactions were done in duplicates to
− ClPPh3, 20). Anal. Calcd For C H Cl N P Ru: ensure the reproducibility of the results.
3
). lated, recrystallized and characterized by H NMR spectroscopy
+
(
(
ESI-MS), m/z (%) 631.66 (M
−
3
,
+
M
48
39
2 3 2
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Density functional theoretical (DFT) modeling
8 C. A. Sandoval, T. Ohkuma, K. Muniz and R. Noyori, J. Am.
Chem. Soc., 2003, 125, 13490.
DFT calculations were performed in gas phase using a well-
established approach for the third row transition metal com-
plexes, to identify the energy-minimized structures based on
9
Y. Jiang, J. Qiongzhong and X. Zhang, J. Am. Chem. Soc.,
998, 120, 3817.
1
3
7,38
10 M. P. Araujo, A. T. Figueiredo, A. L. Bogado, G. V. Poelhsitz,
J. Ellena, E. E. Castellano, C. L. Donnici, J. V. Comasseto
and A. A. Batista, Organometallics, 2005, 24, 6159.
B3LYP/LANL2DZ
(Los Alamos National Laboratory 2
double ζ) level theory, with inner core electrons of the Ru atom
replaced by relativistic effective core potential (ECP). The
singlet states were used due to low electronic spin of Ru(II)
complexes. The Gaussian09 suite of programs was used for all
11 A. Grabulosa, A. Mannu, A. Mezzetti and G. Muller,
J. Organomet. Chem., 2012, 696, 4221.
12 D. Elma, F. Durap, M. Aydemir, A. Baysal, N. Meric, B. Ak,
3
9
the computations.
Y. Turgut and B. Gumgum, J. Organomet. Chem., 2013,
7
29, 46.
X-ray crystallography analyses
1
3 (a) S. Enthaler, R. Jackstell, B. Hagemann, K. Junge, G. Erre
The X-ray data were recorded on a Bruker Apex Duo equipped
with an Oxford Instruments Cryojet operating at 100(2) K and
an Incoatec microsource operating at 30 W power. The data
were collected with Mo Kα (λ = 0.71073 Å) radiation at a crystal-
to-detector distance of 50 mm. The following conditions were
used for the data collection: omega and phi scans with
exposures taken at 30 W X-ray power and 0.50° frame widths
and M. Beller, J. Organomet. Chem., 2006, 691, 4652;
(b) Z. R. Dong, Y. Y. Li, S. L. Yu, G. S. Sun and J. X. Gao,
Chin. Chem. Lett., 2012, 23, 533.
4 N. Park, Y. Heo, M. R. Kumar, Y. Kim, K. H. Song and
S. Lee, Eur. J. Org. Chem., 2012, 1984.
1
1
5 N. J. Beach and G. J. Spivak, Inorg. Chim. Acta, 2003, 343,
244.
4
0
using APEX2. The data were reduced with the program
1
1
6 F. Zeng and Z. Yu, Organometallics, 2009, 28, 1855.
7 M. Serratrice, M. A. Cinellu, L. Maiore, M. Pilo, A. Zucca,
C. Gabbiani, A. Guerri, I. Landini, S. Nobili, E. Mini and
L. Messori, Inorg. Chem., 2012, 51, 3161.
8 A. Valore, M. Balordi, A. Colombo, C. Dragonetti,
S. Righetto, D. Roberto, R. Ugo, T. Benincori,
G. Rampinini, F. Sannicolò and F. Demartine, Dalton
Trans., 2010, 39, 10314.
4
1
SAINT using outlier rejection, scan speed scaling, as well as
standard Lorentz and polarisation correction factors.
SADABS semi-empirical multi-scan absorption correction was
A
4
2
applied to the data. Direct methods, SHELXS-97 and WinGX
1
were used to solve all three structures. All non-hydrogen atoms
were located in the difference density map and refined aniso-
tropically with SHELXL-97. All hydrogen atoms were included
as idealised contributors in the least squares process. Their
positions were calculated using a standard riding model with
C–Haromatic distances of 0.93 Å and Uiso = 1.2Ueq. The imidazole
N–H were located in the difference density map, and refined
isotropically.
1
9 J. Weiwei, W. Laindi and Y. Zhengkun, Organometallics,
2012, 31, 5664.
2
0 A. A. Batista, M. O. Santiago, C. L. Donnici, I. S. Moreira,
P. C. Healy, S. J. Berners-Price and S. L. Queiroz, Poly-
hedron, 2001, 20, 2123.
21 M. Aydemir, N. Meric and A. Baysal, J. Organomet. Chem.,
2012, 720, 38.
22 Y. Cheng, X. Lu, H. Xu, Y. Li, X. Chen and Z. Xue, Inorg.
Chim. Acta, 2010, 363, 430.
Acknowledgements
The authors are grateful for the financial support received 23 S. J. La-Placa and J. A. Ibers, Inorg. Chem., 1965, 4, 778.
from the University of KwaZulu-Natal.
24 S. P. Baran and J. M. Ritcher, Heterocycl. Chem., Lecture
Notes. Retrieved from http://www.scripps.edu/baran/
heterocycles/
2
5 S. E. Clapham, A. Hadzovic and R. H. Morris, Coord. Chem.
Rev., 2004, 248, 2201.
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30 Synthesis of 1-propyl-2-(pyridin-2-yl)-1H-benzo[d]imidazole
(L4). Dimethyl sulphoxide (15 mL) was added to ground
KOH (1.14 g, 20.4 mmol) and the mixture was stirred
for 5 min and L1 (1 g, 5.1 mmol) was added. The mixture
was further stirred for 1 h. 1-Bromopropane (1.26 g,
I. Moldes, E. de la Encarnacion, J. Ros, A. Alvarez-Larena
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7
1236 | Dalton Trans., 2014, 43, 1228–1237
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Paper
1
0.2 mmol) was then added and stirred for 12 h. The 37 (a) A. D. Becke, Chem. Phys., 1993, 98, 5648; (b) C. T. Lee,
solution was filtered and the solvent removed under
W. T. Yang and R. G. Parr, Phys. Rev. B: Condens. Matter,
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38 P. J. Hay and W. R. Wadt, Chem. Phys., 1985, 82, 270.
vacuum to obtain L4 as an orange oil. Yield = 0.65 g (53%).
1
3
H NMR (400 MHz, DMSO-d
6
): δ 0.96 (t, 3H, CH
3
, JHH
=
8
J
8
.0 Hz); 1.93 (m, 2H, CH -CH ); 4.81 (t, 2H, CH -C H , 39 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
2 3 2 2 5
3
3
HH = 8.0 Hz); 7.33 (m, 1H, bzim) 7.47 (d, 1H, py, JHH
=
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
GAUSSIAN 09 (Revision A.1), Gaussian, Inc., Wallingford CT,
2009.
3
.0 Hz); 7.85 (d, 1H, bzim, JHH = 8.0 Hz); 8.42 (t, 1H, bzim,
3
3
JHH = 4.0 Hz); 8.69 (d, 1H, py, J = 5.6 Hz). Anal. Calcd
HH
For C15
5.81; H, 6.98; N, 17.37%.
1 The procedure used to prepare complex 1 was followed for
the synthesis of 7 using RuCl ·3H O (0.10 g, 0.48 mmol)
15 3
H N : C, 75.92; H, 6.37; N, 17.71%. Found: C,
7
3
3
2
and L4 (0.11 g, 0.48 mmol) to afford 7 as a brown solid.
Yield = 0.185 g (89%). (ESI-MS) m/z (%) 408 (M − Cl, 20).
+
Anal. Calcd For C15
.45%. Found: C, 40.42; H, 3.83; N, 9.27%.
2 J. W. Faller and A. R. Lavoie, Organometallics, 2001, 20,
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