A Ferrocenyl-Benzo-Fused Imidazolylidene Complex of Ruthenium as Redox-Switchable Catalyst for the Transfer Hydrogenation of Ketones and Imines

Article abstract of DOI:10.1002/cctc.201601025

A ferrocenyl-benzo-fused imidazolylidene complex of Ru^II was prepared and fully characterized. In the presence of acetylferrocenium tetrafluoroborate this complex can be oxidized to generate a complex with a cationic ligand. The neutral complex

Full text of DOI:10.1002/cctc.201601025

Accepted Article
Title: A ferrocenyl-benzo-fused imidazolylidene complex of ruthenium
as redox-switchable catalyst for the transfer hydrogenation of
ketones and imines
Authors: Eduardo Victor Peris, Macarena Poyatos, and Susana Ibáñez
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201601025
Link to VoR: http://dx.doi.org/10.1002/cctc.201601025
A Journal of
www.chemcatchem.org

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
A ferrocenyl-benzo-fused imidazolylidene complex of ruthenium
as redox-switchable catalyst for the transfer hydrogenation of
ketones and imines
[a]
[a]
[a]
Susana Ibáñez, Macarena Poyatos* and Eduardo Peris*
Abstract:
A
ferrocenyl-benzo-fused-imidazolylidene complex of
the ligand and some coordinated compounds, we concluded that
the oxidation of the ligand with acetylferrocenium
Ru(II) was prepared and fully characterized. In the presence of
acetylferrocenium tetrafluoroborate this complex can be oxidised
generating a complex with a cationic ligand. The neutral complex can
be recovered by reducing the oxidised cationic compound with
cobaltocene. The activity of the neutral and oxidized complexes was
tested in the transfer hydrogenation of ketones and imines, using i-
PrOH as hydrogen source. While the neutral complex is very active in
the reduction of all substrates, the oxidized species shows low activity
in the reduction of ketones. The rate of the reduction of acetophenone
could be modulated by addition of subsequent amounts of oxidant and
reductant. The addition of acetylferrocenium tetrafluoroborate caused
a decrease in the catalytic activity, while the addition of cobaltocene
restored the activity. The catalytic activity shown by both catalysts in
the reduction of N-benzylideneaniline is similar.
3
+
tetrafluoroborate afforded the corresponding oxidized (Fe )
species, together with a minor product product resulting from the
2
+
protonation of the ferrocenyl-imidazolylidene (Fe ) ligand
(Scheme 1). The minor protonated species was presumably
formed as a consequence of the hydrogen abstraction from the
produced cationic radical generated by the oxidation of the
ferrocenyl-imidazolylidene ligand. The two resulting cationic
ligands, which can be regarded as the product of the oxidation of
the starting ferrocenyl-imidazolylidene, reduced the electron
richness of the metal, as a consequence of the diminished
electron donor character of the cationic ligands compared to the
neutral one. This change in the electrondonating character of the
-1
ligand was quantified as 2.9 cm , considering the shift in the
av(CO) of the related [IrCl(Fc-NHC)(CO) ] complexes (with Fc-

2
NHC = ferrocenyl-imidazolylidene, or its related cationic forms).
This subtle, yet not negligible, electron-donor shift, was found to
be very useful for preparing a redox-switchable gold catalyst for
the cyclization of alkynes with furans. For this reaction, it was
observed that the activity of the neutral gold complex was
negligible, but it could be switched on by adding an oxidant that
transformed the gold complex into a very active catalyst.
Introduction
‘
Switchable catalysts’ are normally defined as all those catalysts
that are able to switch their activities by applying certain types of
stimuli, such as light, pH, redox processes or changes of reaction
conditions.[ Among this type of catalysts, those containing redox-
switchable ligands have been thoroughly studied. Redox active
ligands are sources of electrons that normally allow the metal
retaining its original oxidation state,[2] while facilitating the tuning
of the electron richness of the ligand and the bound metal.[3] The
participation of a redox active ligand in a catalytic process, may
be by accepting or releasing electrons, or by actively forming or
breaking covalent bonds.[4] Probably due to their great chemical
versatility, during the last decade a large number of N-heterocyclic
carbene ligands (NHCs) containing redox active moieties have
been reported,[5] although their use in homogeneous catalysis is
still relatively rare.[6]
1]
Scheme 1. Oxidation and further hydrogen abstraction of the ferrocenyl-benzo-
fused imidazolylidene Ir(I) complex
We recently described
a
redox-switchable benzo-fused-
imidazolylidene ligand, which was coordinated to iridium (I) and
gold (I).[7] From the experimental and computational analysis of
Based on this previous findings, we now report the preparation of
a
ruthenium (II) complex with a ferrocenyl-benzo-fused-
imidazolylidene ligand. The full characterization and the
electrochemical behavior of this complex will be fully analyzed.
The redox-switchable properties of this new complex will be
described in the reduction of ketones and imines by transfer
hydrogenation using isopropanol as hydrogen source.
[
a]
Institute of Advanced Materials (INAM)
Universitat Jaume I
Avda. Sos Baynat. E-12071-Castellón. Spain
Fax: (+) 34 964387522
E-mail: eperis@uji.es, poyatosd@uji.es
Supporting information for this article is given via a link at the
end of the document.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
2
+
3+
Results and Discussion
redox potential for the Ru /Ru couple is in the higher region of
the redox potentials shown by other related [RuCl
2
(NHC)(p-
cymene)] complexes (typically ranging between 1.00-1.15 V),[
thus suggesting that the oxidation of the ferrocenyl-based ligand
influences the redox potential of ruthenium center.
8]
Scheme 2 displays the synthetic procedure to synthesize the
ferrocenyl-imidazolylidene ruthenium (II) complex 2. The reaction
of the ferrocenyl-imidazolium iodide 1 with silver oxide afforded
the corresponding Fc-NHC-Ag(I) complex, which reacted in situ
5
4
3
2
1
0
2 2
with [RuCl (p-cymene)] to afford the ferrocenyl-imidazolylidene
ruthenium (II) complex 2 in 70 % yield. Complex 2 was
characterized by NMR spectroscopy and mass spectrometry, and
gave satisfactory elemental analysis. As a diagnostic of the
formation of the Fc-NHC-Ru complex, the 13C NMR spectrum of
2
displayed the characteristic resonance of the carbene carbon at
-0,5
0
0,5
1
1,5
-1
188.0 ppm.
E (V)
-2
1
,8
,6
,4
,2
0
0
0
0
0
0
,8
0,9
1
1,1
1,2
1,3
1,4
1,5
1,6
E (V)
Scheme 2. Synthesis of Ru(II)-based complexes 3 and 3-H
Figure 1. Cyclic voltammetry diagram (above) and relevant section of the
differential pulse analysis of complex 2 (below). Measurements performed on a
1
2 2 4 6
mM solution of the analyte in dry CH Cl with 0.1 M [NBu ][PF ] as the
supporting electrolyte, 100 mV/s scan rate, Fc/Fc+ used as standard with E1/2
In order to see if we could isolate the product of the oxidation of
the ferrocenyl fragment of this new ruthenium complex, we
oxidized complex 2 with acetylferrocenium tetrafluoroborate at
room temperature in dichloromethane. The addition of the oxidant
produced an immediate darkening of the brownish solution. The
reaction produced the quantitative formation of acetylferrocene,
which could be separated by washing with diethyl ether the crude
solid resulting from the reaction. The resulting paramagnetic dark
brown solid was analyzed by elemental analysis and mass
spectroscopy. The 1H NMR spectrum of 3 showed the broad
signals expected for a paramagnetic compound. The mass
spectrum revealed a small peak at m/z 370.0, which is consistent
with the presence of a dicationic species resulting from the loss of
a chloride ligand in 3-H (see Scheme 2). These results are
consistent with our previously reported findings, which indicated
that the oxidized species may slowly evolve to a protonated
species resulting from the hydrogen abstraction from the
produced radical cationic species. Although we do not have a
clear explanation for the formation of this protonated species, we
+
(Fc/Fc ) = 0.46 V vs. SCE.
Figure 2. Molecular structure of complex 2. Ellipsoids at 50 % of probability.
Hydrogen atoms and solvent (CHCl omitted for clarity. Selected bond
3
)
distances (Å) and angles (º): Ru(1)-C(1) 2.087(8), Ru(1)-Cl(1) 2.410(2), Ru(1)-
Cl(2) 2.430(2), C(1)-N(1) 1.336(10), C(1)-N(2) 1.364(11), C(17)-C(18) 1.454(12),
N(4)-C(17) 1.380(10), N(3)-C(17) 1.311(11), C(1)-Ru(1)-Cl(1) 88.5(2), C(1)-
Ru(1)-Cl(2) 90.7(2).
2
know that the presence of traces of H O is favoring the process.
In any case, the reduction of 3 with cobaltocene allowed the
quantitative recovery of the neutral complex 2, therefore
suggesting that if 3-H had formed, it would only be present in a
trace amount.
The study of the electrochemical properties of 2 was carried out
by performing the cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) experiments (Figure 1). Both experiments
Figure 2 shows the molecular structure of complex 2. The
structure consists of a ferrocenyl-benzo-fused imidazolylidene
ligand coordinated to a ruthenium center, which completes its
coordination sphere with a p-cymene and two chloride ligands.
The Ru-Ccarbene bond distance is 2.087(8) Å. The plane of the
tricyclic-carbene ligand deviates from the substituted Cp ring of
the ferrocenyl fragment by an angle of 23.88º. The two N-C
distances of the imidazolyl ring bound to the ferrocenyl moiety are
different, in agreement with the existence of a double and a single
were carried out in dichloromethane, with [NBu
4
](PF
6
)
as
+
electrolyte, and using ferrocene as reference (E1/2 (Fc/Fc ) = 0.46
V vs. SCE). The cyclic voltammetry revealed two quasi-reversible
redox events at 0.89 and 1.15 V, attributed to the oxidations
occurring at the Fe and Ru centers, respectively. The value of the
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
C-N bonds (1.311(11) and 1.380(10) Å, respectively). The
distance of the iron center to the centroids of the Cp rings is 1.659
Å, for both the substituted and unsubstituted Cp rings. This
distance, together with the eclipsed orientation of the Cp rings, is
consistent with the presence of a Fe(II) center at the ferrocenyl
moiety.[9]
Table 1 shows the results that we obtained for the reduction of
several ketones and imines in isopropanol using 2 as catalyst. In
order to determine if the oxidation of the ferrocenyl ligand could
have an effect on the catalytic outcome of the process, the
reactions were also carried out under the same reaction
conditions, but with the addition of acetylferrocenium
tetrafluoroborate. We used the optimized reaction conditions that
we used in some previously published works.[ The reactions
were carried out using a 0.5 mol % of catalyst loading (same
amount of oxidant, when needed), in isopropanol at 80ºC for two
hours, in the presence of KOH. As can be seen from the results
shown in Table 1, catalyst 2 produced good to excellent yields of
the final reduced products.
In order to study the catalytic redox-switchable abilities of complex
15]
2, we decided to test its catalytic activity in the reduction of
ketones and imines by transfer hydrogenation using isopropanol
as hydrogen source.[10] We did not find any examples in which
redox-switchable catalysts were used in this important reaction.
The earliest examples of Ru-NHC catalysts for this type of
processes date from 2002[11] and 2003,[12] and since then a large
number of NHC-containing catalysts have proven great activity in
this reaction.[13] For Ru(arene)(NHC) catalysts detailed studies on
the mechanistic pathway of the process have been published[14] It
has been proposed that loss of the arene ligand is the slowest
step of the process,[14a] therefore strong electrondonating ancillary
ligands (which should favour this loss) may enhance the activity
of the catalyst. On the contrary, poor electrondonating ligands, as
the ones resulting from the oxidation of one of the ligands present
in the coordination sphere of the complex, may reduce the activity
of the catalyst.
The addition of the oxidant clearly reduced the activity of the
catalyst in the reduction of the ketones. This reduced activity
turned into a significant inhibition for the cases of the reduction of
acetophenone,
hexanophenone
and
2-acetonaphtone.
Interestingly, for the reaction of N-benzylideneaniline, the activity
of the neutral complex 2 was similar to the activity of the reaction
carried out in the presence of an oxidant. This result is particularly
relevant, because it indicates that the oxidized complex maintains
its abilities to reduce imines, while reduces its activity in the
reduction of carbonyl compounds, therefore suggesting that the
system may be used for the selective reduction of imine functional
groups in those cases where imines and carbonyl groups are
present.
Table 1. Transfer hydrogenation of ketones and imines using complex 2[a]
In order to get a more detailed insight about the effect of the
addition of the oxidant in the reaction medium, we decided to
monitor the reduction of cyclohexanone. The reaction profile is
depicted in Figure 3. As can be seen from this profile, the addition
of the oxidant not only produces a lower yield of the product, but
also decelerates the reaction, therefore indicating that the higher
activity of the neutral catalyst (2) is maintained all along the
reaction course. This result suggests that the differences in
activity are due to kinetic reasons rather to reasons related to the
stability of both, 2 and 3. It is noteworthy to point out that the yields
shown in Figure 3 and Table 1 are significantly different, but this
is mainly due to the fact that the monitoring of this reaction
required interrupting the reaction at the selected reaction times for
taking the aliquots, and this has an effect in reducing the reaction
rates.
Entry
Substrate
Catalyst
Yield(%)[b]
1
2
3
4
5
6
7
8
9
acetophenone
2
94
24
75
66
94
20
60
6
acetophenone
2 + oxidant
cyclohexanone
2
cyclohexanone
2 + oxidant
hexanophenone
2
hexanophenone
2 + oxidant
2-acetonaphthone
2-acetonaphthone
4-bromoacetophenone
4-bromoacetophenone
4-methoxyacetophenone
4-methoxyacetophenone
N-benzylideneaniline
N-benzylideneaniline
2
70
60
50
40
30
2 + oxidant
2
68
51
40
18
85
81
10
11
12
13
14
2 + oxidant
Yield (%)
2
2 + oxidant
2
20
10
0
2
2
+ oxidant
2 + oxidant
0
5
10
15
20
25 Time (h)
[
a] Reaction conditions: 0.5 mmol ketone or imine, 0.05 mmol KOH, 0.5 mol%
of complex 2, 0.5 mol% of acetylferrocenium tetrafluoroborate (oxidant) and 2
mL of isopropanol at 80 ºC for 2 h. [b] Yields determined by GC using anisole
Figure 3. Time-dependent reaction profile of the transfer hydrogenation of
cyclohexanone. Reaction conditions as those described in Table 1. Oxidant =
acetylferrocenium tetrafluoroborate.
(0.5 mmol) as internal standard.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
Based on the observation that 2 and 3 catalyzed the reduction of
ketones at different constant rates, we decided to study if we
could modulate the activity of the catalyst over the course of the
reaction. We monitored the reduction of hexanophenone to 1-
The catalytic activity of the ruthenium complex 2 was tested in the
reduction of ketones and imines by the transfer hydrogenation
methodology. The complex showed good to excellent activity in
the transfer hydrogenation of a wide variety of ketones and one
imine. When the activity of the complex was compared with the
activity of the in situ generated oxidized catalyst 3, a clear
inhibition of the activity was observed for the cases in which the
substrates contained carbonyl groups. This allowed the
modulation of the activity of the catalyst by successively adding
acetylferrocenium tetrafluoroborate and cobaltocene. The
addition of acetylferrocenium tetrafluoroborate interrupted the
advance of the reaction, while the addition of cobaltocene
restored the catalytic activity. This result expands upon the
relatively few examples known of reversibly switching catalysts,
and to the best of our knowledge, this is the first one to be used
in the well-known reduction of ketones by transfer hydrogenation.
For the case of the imine, the activity of the neutral complex was
similar to that shown by its oxidized partner. All in all, our work
represents a new example among the very rare cases of known
NHC-based redox switchable catalysts.
o
phenylhexanol in iPrOH at 80 C using 2 (0,5 mol%). We chose
this substrate because it was the one to give us the largest
difference in catalytic activity when 2 or 3 were used (compare
entries 5 and 6 in Table 1). The reaction was monitored by gas
chromatography (GC) by taking aliquots at the selected times.
The result of the study can be observed in Figure 4. After one hour
(
50% yield) acetylferrocenium tetrafluoroborate (1 equivalent)
was added. This addition produced the deceleration of the
reaction, which after two more hours did not show any
measurable advance. Further addition of cobaltocene (1.1
equivalens), restored the activity of the catalyst, as expected for
the regeneration of the neutral catalyst 2 from the reduction of 3.
Although we observed that the recovery of the activity of the
catalyst was not complete, we attributed the attenuated activity to
partial decomposition of the catalyst due to the successive
removing of aliquots in the performance of the study, which made
us interrupt the reaction for a period of time by cooling the mixture
and restoring the temperature after each measurement.
Experimental Section
80
70
60
50
40
30
20
10
0
Yield (%)
General considerations. Compound 1[7] and acetylferrocenium
tetrafluoroborate,[ were prepared according to the method reported in
the literature. All other reagents were used as received from commercial
suppliers. NMR spectra were recorded on a Varian Innova 500 MHz, using
16]
3
CDCl as solvent. Electrospray mass spectra (ESI-MS) were recorded on
a Micromass Quatro LC instrument; nitrogen was employed as drying and
nebulizing gas. Elemental analyses were carried out on a TruSpec Micro
Series. Electrochemical studies were carried out by using an Autolab
Potentiostat (Model PGSTAT101) using a three-electrode cell. The cell
was equipped with platinum working and counter electrodes, as well as a
0
1
2
3
4
5
6
4 6
silver wire reference electrode. In all experiments, [NBu ](PF ) (0.1 M in
dry dichloromethane) was used as the supporting electrolyte with analyte
concentration of approximately 1 mM. Measurements were performed at
Time (h)
+
5
0 mVs-1 scan rates. All redox potentials were referenced to the Fc/Fc
Figure 4. Time dependent reaction profile of the reduction of hexanophenone
by transfer hydrogenation. The arrows indicate the addition of
+
couple as internal standard with E1/2(Fc/Fc ) vs. SCE = +0.46 V.
t
acetylferrocenium tetrafluoroborate (1 equivalnet) or cobaltocene (1.1
equivalents). The reactions were carried out using 0.5 mol% of catalyst, at 80 C,
under the same reaction conditions as those described in Table 1. Yields
calculated by GC using anisole as standard.
o
Synthesis of complex 2.
imidazolium salt 1 (100 mg, 0.17 mmol) and Ag
in dichloromethane, was stirred at room temperature overnight. Then,
RuCl (p-cymene)] (51.34 mg, 0.08 mmol) was added. Immediately, the
A
suspension of the ferrocene-based
2
O (19.63 mg, 0.08 mmol)
[
2
2
formation of a white precipitate was observed. To complete the reaction,
the suspension was stirred at room temperature for 7 h and then filtered
through a pad of Celite. The solution was concentrated nearly to dryness
and diethyl ether (5 mL) was added to precipitate the complex, which was
collected by filtration and further washed with diethyl ether. Complex 2 was
Conclusions
In summary, we prepared and fully characterized a new
ferrocenyl-benzo-fused imidazolylidene complex of ruthenium.
The reaction of this complex with acetylferrocenium
tetrafluoroborate afforded the product from the oxidation of the
ferrocenyl group to ferrocenium (3), although this compound may
contain some small amounts of 3-H, which can be regarded as
the protonated analogue of 2. The cationic nature of the ligand (in
1
isolated as a brown solid. Yield: 92.8 mg, 70 %. H NMR (500 MHz,
CDCl
3
):  = 7.71 (s, 1H, CHPh), 7.18 (s, 1H, CHPh), 5.50 (d, 3JH,H = 5.0 Hz,
3
2H, CHp-cym), 5.11 (d,
JH,H =5.0 Hz, 2H, CHp-cym), 4.99-4.95 (m, 4H, 2H
NCH
2
CH
2
CH
2
CH
3
and 2H, CHCp), 4.52 (s, 2H, CHCp), 4.37-4.29 (m, 2H
), 4.23 (s, 5H CHCp), 4.10 (s, 3H NCH ), 3.09-2.94 (m,
), 1.97 (s, 3H, CH3 p-
NCH
2
CH
2
CH
2
CH
3
3
1H, CHisop p-cym), 2.31-2.10 (m, 4H, NCH
2
CH
2
CH
2
CH
3
3
cym), 1.75-1.62 (m, 4H, NCH
isop p-cym), 1.05 (t, 3
2
CH
H,H = 15.0 Hz, 3H, NCH
CH CH CH
2
CH
2
3
CH ), 1.28 (d, JH,H = 5.0 Hz, 6H, CH
3
3
makes the electron density at the ruthenium center be lower
than the electron density of the same metal at the mother complex
. Interestingly, the reaction of 3 with cobaltocene allows the
), 1.01 (t, 3
J
CH CH CH
2 2 2 3
J =
):  = 188.0
H,H
). 13C NMR (126 MHz, CDCl
15.0 Hz, 3H, NCH
2
2
2
3
3
2
(Ru-Ccarbene), 155.7 (NCN), 140.1 (Cq Ph), 134.3 (Cq Ph), 132.7 (Cq Ph), 132.4
(Cq Ph), 109.3 (Cq p-cym), 99.8 (Cq p-cym), 99.6 (CHPh), 89.6 (CHPh), 86.9 (CH
p-cym), 83.0 (CH p-cym), 73.8 (Cq Cp), 70.4 (CHCp), 69.8 (CHCp), 69.2 (CHCp),
quantitative recovery of 2, therefore indicating the full reversibility
of the process.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
5
0.4
(NCH
2
CH
2
CH
2
CH
3
),
50.2
(NCH
), 31.9 (NCH
CH CH ), 18.7 (CH3 p-cym), 14.2
CH ). Electrospray MS (20 V,
Cl FeRu·H O (792.62): C,
6.07; H, 6.10; N, 7.07. Found: C, 55.95; H, 6.09; N, 7.08.
2
CH
2
CH
2
CH
3
),
32.2
Acknowledgements
(NCH
2
CH CH CH
2
2
3
), 32.1 (NCH
2
CH CH
2
2
CH
3
3
), 30.8 (CHisop p-
cym), 22.7 (CH3 isop p-cym), 20.6 (NCH
2
CH
2
2
3
We gratefully acknowledge financial support from MINECO of
Spain (CTQ2014-51999-P) and the Universitat Jaume
(P11B2014-02, P11B2015-24). The authors are grateful to the
Serveis Centrals d’Instrumentació Científica (SCIC) of the
Universitat Jaume I for providing with spectroscopic and X-Ray
facilities.
(NCH
2
2 2
CH CH CH
3
), 14.1 (NCH
2
2
CH CH
2
3
+
I
m/z): 739.3 [M-Cl] . Anal. Calcd. for C37
5
H
46
N
4
2
2
Oxidation of complex 2, synthesis of complex 3. Complex 2 (20 mg,
.03 mmol) and acetylferrocenium tetrafluoroborate (8.13 mg, 0.03 mmol)
0
were placed together in a Schleck tube. The tube was evacuated and filled
with nitrogen three times. The solids were dissolved in dry
dichloromethane (10 mL) and the resulting mixture stirred at room
temperature for 2 h. The solution was then concentrated nearly to dryness
and dry diethyl ether (5 mL) was added. The brown solid so formed was
washed three times with dry diethyl ether in order to remove the formed
acetylferrocene, which is soluble in diethyl ether. Complex 3 was isolated,
along with 3-H, as a brown solid. Yield: 20.2 mg, 91%. Anal. Calcd. for
Keywords: N-Heterocyclic carbenes • Ruthenium • Transfer
hydrogenation • redox-switchable • Ferrocene
[1] V. Blanco, D. A. Leigh and V. Marcos, Chem. Soc. Rev. 2015, 44, 5341-5370.
[2] O. R. Luca and R. H. Crabtree, Chem. Soc. Rev. 2013, 42, 1440-1459.
[3] A. M. Allgeier and C. A. Mirkin, Angew. Chem. Int. Ed. 1998, 37, 894-908.
[4] a) V. Lyaskovskyy and B. de Bruin, ACS Catal. 2012, 2, 270-279; b) B. de
Bruin, Eur. J. Inorg. Chem. 2012, 340-342.
C
37
H
46
N
4
Cl
1.48; H, 5.42; N, 6.22. Electrospray MS (20 V, m/z): 370.0 [M-Cl+H]2+.
Electrospray MS negative mode (20 V, m/z): 87.3 [BF
]- .
2 4
RuFeBF (861.41): C, 51.59; H, 5.38; N, 6.50. Found: C,
5
4
[5] a) U. Siemeling, C. Faerber, M. Leibold, C. Bruhn, P. Muecke, R. F. Winter,
B. Sarkar, M. von Hopffgarten and G. Frenking, Eur. J. Inorg. Chem.
2
009, 4607-4612; b) U. Siemeling, C. Faerber and C. Bruhn, Chem.
Reduction of complex 3, recovery of complex 2. Complex 3 (10 mg,
.01 mmol) and cobaltocene (2.19 mg, 0.01 mmol) were placed together
Commun. 2009, 98-100; c) D. M. Khramov, E. L. Rosen, V. M. Lynch and
C. W. Bielawski, Angew. Chem. Int. Ed. 2008, 47, 2267-2270; d) A. G.
Tennyson, R. J. Ono, T. W. Hudnall, D. M. Khramov, J. A. V. Er, J. W.
Kamplain, V. M. Lynch, J. L. Sessler and C. W. Bielawski, Chem. Eur. J.
0
in a Schleck tube. The tube was evacuated and filled with nitrogen three
times. The solids were dissolved in dry dichloromethane (5 mL) and the
resulting mixture stirred at room temperature for 1 h. The solution was then
concentrated nearly to dryness and dry diethyl ether (5 mL) was added.
The brown solid so formed was washed three times with dry diethyl ether.
The filtrate was concentrated under reduced pressure affording the
desired product. The spectroscopic data were in agreement with those
described above for complex 2. Yield: 8.5 mg, 95%.
2010, 16, 304-315; e) K. Arumugam, J. Chang, V. M. Lynch and C. W.
Bielawski, Organometallics 2013, 32, 4334-4341; f) A. Labande, N.
Debono, A. Sournia-Saquet, J.-C. Daran and R. Poli, Dalton Trans. 2013,
42, 6531-6537; g) A. Labande, J.-C. Daran, N. J. Long, A. J. P. White
and R. Poli, New J. Chem. 2011, 35, 2162-2168; h) B. Bildstein, J.
Organomet. Chem. 2001, 617, 28-38; i) B. Bildstein, M. Malaun, H.
Kopacka, K. Wurst, M. Mitterbock, K. H. Ongania, G. Opromolla and P.
Zanello, Organometallics 1999, 18, 4325-4336; j) B. Bildstein, M. Malaun,
H. Kopacka, K. H. Ongania and K. Wurst, J. Organomet. Chem. 1999,
Catalytic experiments
General procedure for the transfer hydrogenation. Complex 2 (0.0025
mmol) and KOH (0.05 mmol) were placed in a Schlenk tube fitted with a
Teflon cap. The tube was then degassed and filled with nitrogen three
times. Isopropanol (2 mL) and the corresponding ketone or imine (0.5
mmol) were added, and the mixture was stirred at 80 ºC for 2 h. Yields
were determined by GC analyses using anisole (0.5 mmol) as internal
standard. Some of the products were identified according to commercially
5
72, 177-187; k) B. Bildstein, M. Malaun, H. Kopacka, K. H. Ongania and
K. Wurst, J. Organomet. Chem. 1998, 552, 45-61; l) N. Debono, J.-C.
Daran, R. Poli and A. Labande, Polyhedron 2015, 86, 57-63; m) L. Bechki
and T. Lanez, Asian J. Chem. 2010, 22, 5523-5527.
[
6] a) M. Sussner and H. Plenio, Angew. Chem. Int. Ed. 2005, 44, 6885-6888;
b) K. Arumugam, C. D. Varnado, S. Sproules, V. M. Lynch and C. W.
Bielawski, Chem. Eur. J. 2013, 19, 10866-10875; c) C. D. Varnado, Jr.,
E. L. Rosen, M. S. Collins, V. M. Lynch and C. W. Bielawski, Dalton Trans.
available samples: 1-phenylethanol, cyclohexanol,
-methyl-2-
naphtalenemethanol, 4-bromo--methylbenzyl alcohol, 4-methoxy--
2013, 42, 13251-13264; d) L. Hettmanczyk, S. Manck, C. Hoyer, S.
methylbenzyl alcohol and N-benzylaniline. The spectroscopic features of
Hohloch and B. Sarkar, Chem. Commun. 2015, 51, 10949-10952; e) E.
L. Rosen, C. D. Varnado, A. G. Tennyson, D. M. Khramov, J. W.
Kamplain, D. H. Sung, P. T. Cresswell, V. M. Lynch and C. W. Bielawski,
Organometallics 2009, 28, 6695-6706; f) A. G. Tennyson, V. M. Lynch
and C. W. Bielawski, J. Am. Chem. Soc. 2010, 132, 9420-9429.
1
-phenylhexan-1-ol were obtained from the literature.[17]
Redox-switching experiments using complex 2. Complex 2 (0.0025
mmol) and KOH (0.05 mmol) were placed together in a Schlenk tube fitted
with a Teflon cap. The tube was degassed and filled with nitrogen three
times. Isopropanol (2 mL) and hexanophenone (0.5 mmol) were added,
and the resulting mixture stirred at 80ºC for 1h. The oxidant,
acetylferrocenium tetrafluoroborate (0.0025 mmol), was then added and
the resulting mixture was stirred at 80ºC for 2h. After this time, the
reductant, cobaltocene (0.00275 mmol), was added to the reaction vessel
and the resulting mixture was stirred at 80ºC. Aliquots were extracted at
the desired times, and analysed by GC using anisole (0.5 mmol) as internal
standard.
[
7] S. Ibanez, M. Poyatos, L. N. Dawe, D. Gusev and E. Peris, Organometallics
2016, 35, 2747-2758.
[
[
8] L. Mercs, A. Neels and M. Albrecht, Dalton Trans. 2008, 5570-5576.
9] a) R. Martinez and A. Tiripicchio, Acta Crystallogr. Sect. C-Cryst. Struct.
Commun. 1990, 46, 202-205; b) X. C. Wang, Y. P. Tian, Y. H. Kan, C. Y.
Zuo, J. Y. Wu, B. K. Jin, H. P. Zhou, J. X. Yang, S. Y. Zhang, X. T. Tao
and M. H. Jiang, Dalton Trans. 2009, 4096-4103; c) T. Y. Dong, B. R.
Huang, S. M. Peng, G. H. Lee and M. Y. Chiang, J. Organomet. Chem.
2002, 659, 125-132; d) N. J. Mammano, A. Zalkin, A. Landers and A. L.
Rheingold, Inorg. Chem. 1977, 16, 297-300.
[
[
10] D. Wang and D. Astruc, Chem. Rev. 2015, 115, 6621-6686.
11] A. A. Danopoulos, S. Winston and W. B. Motherwell, Chem. Commun. 2002,
1376-1377.
[
12] M. Poyatos, J. A. Mata, E. Falomir, R. H. Crabtree and E. Peris,
Organometallics 2003, 22, 1110-1114.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
[
13] V. Dragutan, I. Dragutan, L. Delaude and A. Demonceau, Coord. Chem.
Rev. 2007, 251, 765-794.
[15] S. Ruiz-Botella and E. Peris, Chem. Eur. J. 2015, 21, 15263-15271.
[16] N. G. Connelly and W. E. Geiger, Chem. Rev. 1996, 96, 877-910.
[17] M. Victoria Jimenez, J. Fernandez-Tornos, F. Javier Modrego, J. J. Perez-
Torrente and L. A. Oro, Chem. Eur. J. 2015, 21, 17877-17889.
[
14] a) J. DePasquale, M. Kumar, M. Zeller and E. T. Papish, Organometallics
2013, 32, 966-979; b) W. W. N. O, A. J. Lough and R. H. Morris,
Organometallics 2011, 30, 1236-1252.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201601025
FULL PAPER
Entry for the Table of Contents
FULL PAPER
A ferrocenyl-benzo-fused-
Susana Ibañez, Macarena Poyatos,
Eduardo Peris
imidazolylidene complex of Ru(II) was
used as a redox-switchable catalyst in
the transfer hydrogenation of ketones
and imines. The activity of the catalyst
significantly decreases in the
Page No. – Page No.
Title
presence of an oxidant.
This article is protected by copyright. All rights reserved.