Improving Catalyst Activity in Hydrocarbon Functionalization by Remote Pyrene–Graphene Stacking

Article abstract of DOI:10.1002/chem.201900964

A copper complex bearing an N-heterocyclic carbene ligand with a pyrene “tail” attached to the backbone has been prepared and supported on reduced graphene oxide (rGO). The free and supported copper materials have been employed as homogeneous and heterogeneous catalysts in the functionalization of hydrocarbons such as n-hexane, cyclohexane, and benzene through incorporation of the CHCO₂Et unit from ethyl diazoacetate. The graphene-anchored complex displays higher reaction rates and induces higher yields than its soluble counterpart, features that can be rationalized in terms of a decrease in electron density at the metal center due to a remote net electronic flux from the supported copper complex to the graphene surface.

Full text of DOI:10.1002/chem.201900964

A Journal of
Accepted Article
Title: Improving Catalyst Activity in Hydrocarbon Functionalization by
Remote Pyrene-Graphene Stacking
Authors: Pilar Ballestin, David Ventura-Espinosa, Santiago Martín, Ana
Caballero, Jose A. Mata, and Pedro J. Pérez
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10.1002/chem.201900964
Chemistry - A European Journal
█ Remote Catalyst Tuning
Improving Catalyst Activity in Hydrocarbon Functionalization by
Remote Pyrene-Graphene Stacking
Pilar Ballestin,[a] David Ventura-Espinosa,[b] Santiago Martín,[c] Ana Caballero,*[a] Jose A.
Mata*[b] and Pedro J. Pérez*[a]
Abstract: A copper complex bearing an N-heterocyclic carbene ligand with a pyrene-tail attached to the backbone has been
prepared and supported onto reduced graphene oxide (rGO). Both copper materials have been employed as homogeneous
and heterogeneous catalysts in the functionalization of hydrocarbons such as hexane, cyclohexane and benzene upon
incorporation of the CHCO2Et unit from ethyl diazoacetate. The graphene-anchored complex displays higher reaction rates
and induces higher yields than its soluble counterpart, features which can be explained as the result of a decrease of electron
density at the metal center due to a remote net electronic flux from the supported copper complex to the graphene surface
through the pyrene tag.
the field of alkane C-H bond catalytic functionalization by carbene
insertion, using diazo compounds as the carbene source
(Scheme 1). [4] The appropriate election of the catalyst, usually a
group 11 metal complex bearing a trispyrazolylborate or an NHC
ligand, allowed the conversion of unreactive C-H bonds of linear,
branched or cyclic alkanes, even those of methane or ethane. [5]
To promote catalyst separation and recycling, we have previously
developed this transformation under biphasic conditions[ 6 ] or
using modified silica[7] as the support for tethered catalysts, in
both cases the catalyst performance being similar when
compared with the corresponding homogenous system. Following
this research program, we have now turned our attention into
Introduction
The outstanding development of homogeneous catalysis in
the last half-century has provided
a
plethora of novel
transformations[1] albeit very few have reached the use at the
industrial level. One of the main drawbacks toward that end
stands on the operations derived from catalyst separation and
further recycling, which is of particular interest when using
precious metals.[2 ] Because of this, the strategy of anchoring
tested homogeneous catalysts onto supports that would facilitate
such operations is gaining importance in this homogeneous-to-
heterogeneous frontier. [3] Two main factors must be considered
for the success of this transition: (ii) the catalyst activity in terms
of reaction kinetics and (ii) the selectivity of the transformation.
Ideally, the fixation of the catalyst on a solid support should
proceed without any alteration of the previous features. Also the
catalytic pocket must remain unaltered, the lack of interactions
between the latter and the support being crucial to ensure that the
catalytic reaction in the homogeneous phase also occurs in the
heterogeneous counterpart in the same manner.
One of our groups has been working in the last decades in
[a]
P. Ballestín, Dr. A. Caballero, Prof. Dr. P. J. Pérez
Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC
CIQSO-Centro de Investigación en Química Sostenible and
Departamento de Química
Universidad de Huelva, 21007-Huelva (Spain)
Fax: (+34)959219942
E-mail: perez@dqcm.uhu.es; ana.caballero@dqcm.uhu.es
D. Ventura-Espinosa, Dr. J. A. Mata
Institute of Advanced Materials (INAM),Universitat Jaume I, Avda.
Sos Baynat s/n, 12006 Castellón, Spain
E-mail: jmata@qio.uji.es;
Dr. S. Martín
Dept. de Química Física, Facultad de Ciencias, Instituto de Ciencias
de Materiales de Aragón (ICMA), Universidad de Zaragoza-CSIC,
50009 Zaragoza (Spain)
Scheme 1. (a) The metal-catalyzed functionalization of C-H bonds through
carbene insertions from diazo compounds. (b) This work. The
benchmarking reaction of cyclohexane with ethyl diazoacetate catalysed
by complex 1 or supported 1 in reduced graphene oxide (1-rGO). The
heterogeneous catalyst originates an increasing in the reaction rate and
the yield into the product.
[b]
[c]
graphene materials as solid supports for catalyst bearing
polyaromatic fragments, a well-known antenna that promotes
strong aromatic  stacking and therefore fixation on the
The ORCID identification number)s) for the authors of this article can be
found under https://doi.org/10.1002/chem.2018XXXXXt.
1
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10.1002/chem.201900964
Chemistry - A European Journal
graphene surface.[ 8 ] It has been recently disclosed that the
substituent on the pyrene fragment affect the conductivity of the
graphene material.[9] We reasoned that with a relatively close
metal center, such electronic flux could affect the performance of
As mentioned above, the presence of the pyrene moiety in
the LMes ligand is very convenient toward its adsorption onto
13
]
graphenic surfaces.[
We have now performed the
onto the surface of reduced
immobilization of complex
1
the former during catalysis, particularly in this transformation
graphene oxide (rGO) at room temperature by impregnation of a
rGO suspension with a dichloromethane solution of complex 1
(Scheme 2). After 24 h of stirring at room temperature, the solid
was filtered off, washed and dried. The use of mild conditions
ensures that the properties of the molecular complex and the rGO
are preserved during the immobilization step. The hybrid material
1-rGO has been characterized by different techniques such as
HRTEM, XPS, UV/vis and ICP/MS (see SI for full details).
Determination of the exact amount of copper on the surface of
graphene is crucial toward further catalytic uses: ICP/MS analysis
of 1-rGO reported an amount of 8.0 wt% of complex 1 onto the
graphene.
[ 10 ]
where an electrophilic metallocarbene is involved.
The
immobilization of pyrene-tagged complexes onto graphenic
surfaces and further use in catalytic reactions is an area in
[11]
continuous development.
In this contribution, we describe a
new copper complex bearing an NHC ligand bearing a pyrene tail
at the backbone (Scheme 1) that can be adsorbed onto reduced
graphene oxide (rGO), as well as their use as catalysts for
carbene transfer reactions to alkanes and benzene. Interestingly,
we have observed the increase of both the reaction rate and the
yields toward hydrocarbon functionalization with the supported
catalyst, features that we explain as the result of an electronic
effect on the metal center generated at the remote pyrene-rGO
interaction.
A comparative analysis of complex 1 and 1-rGO was
performed by X-ray photoelectron spectroscopy (XPS). The
Results and discussion
Synthesis of the discrete and supported copper
complexes.
We first targeted the synthesis of the imidazolium salt of the
NHC-modified ligand LMes (Scheme 2) bearing mesityl groups at
the N atoms and an O-CH2-pyrenyl fragment at the backbone.
Toward that end, we employed the strategy previously described
by Cesar and co-workers, 12 upon reaction of bromomethylpyrene
with the corresponding 4-hydroxylimidazolium salt, leading to the
isolation of LMesBr in 71% yield. LMesBr was straightforwardly
characterized from their NMR spectra and analytical data (see
Experimental Section).
The copper(I) complex bearing LMes was prepared upon
deprotonation of LMesBr in the presence of potassium carbonate,
leading to the isolation of LMesCuBr (1) in 74% (Scheme 2).
Complex 1 was characterized by NMR and elemental analysis.
Spectroscopic data is in agreement with the existence of an NHC
ligand coordinated to copper as inferred from the observance of a
resonance at 174.4 ppm in the 13C{1H} NMR spectrum.
Figure 1. Comparative XPS analysis of the core-level peak of N1s, Br3d
and Cu2p for the complex 1 (top) and the hybrid material 1-rGO (bottom).
Figure 2. HRTEM images of 1-rGO at different magnifications.
results for 1-rGO show the characteristic core-level peaks of Cu
2p, Br 3d and N 1s at the same binding energy of complex 1
(Figure 1). The binding energy of Cu 2p confirms the +1 oxidation
state in both complex 1 and 1-rGO. The XPS analysis suggests
the immobilization of complex 1 onto the surface of graphene
without alteration in its structure or oxidation state. Additional
HRTEM studies of hybrid material 1-rGO shows that graphene
maintains the same morphology after the immobilization process
(Figure 2). Also, the energy-dispersive X-ray spectroscopy (EDX)
elemental
analysis shows the presence of copper
homogeneously distributed on the surface of graphene. UV/Vis
measurement of a suspension of 1-rGO shows the presence of
the characteristic bands of the pyrene tag, confirming that
complex 1 is immobilized onto the graphene (Figure S7). All data
collected from those characterization techniques assess that the
Scheme 2. Synthetic route for the preparation of LMesBr, LMesCuBr (1)
and LMesCuBr-rGO (1-rGO).
2
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10.1002/chem.201900964
Chemistry - A European Journal
nature of complex 1 and the properties of the support are
preserved during the immobilization process. Thus, the solid 1-
rGO seems appropriate to compare its potential catalytic activity
with that of the soluble, discrete complex 1 and to evaluate the
differences due to the graphene support.
conditions of temperature, copper and EDA loadings and reaction
time, the three hydrocarbons shown in Scheme 3 were employed
as substrates with 1-rGO as the catalyst (with 2 equiv of NaBArF
4
as halide scavenger). Figure 3 displays the comparison of yields
of both homo- and heterogeneous catalytic systems, an increase
being observed with the latter: 15% in 2, 16% in 3a-c and 10% in
4. Again, EDA was not fully consumed, even after 4 days of
stirring at room temperature. HRTEM images of the 1-rGO
materials after catalysis revealed that the structure seems
unaltered, without the formation of aggregates or metal
nanoparticles (see Figure S10).
Intrigued by the lack of complete consumption of EDA, we
carried out experiments measuring the evolution of N2 with time
(Figure 4). First, the well-known, very active TpBr3Cu(NCMe)
catalyst[ 17 ] for cyclohexane functionalization with EDA was
employed, providing the exact amount of N2 that should be
released with the initial amount of EDA (0.25 mmol). Then, under
the same conditions, 1 and 1-rGO were employed as catalysts in
separate experiments. As shown in Figure 4, both catalysts
induced the exponential growth typically observed for N2
formation in these transformations.[18] However, the amount of
evolved gas did not reach the expected limit of 0.25 mmol,
marked by the experiment with the TpBr3Cu(NCMe) catalyst, but
stopped at ca. 60% of such amount (0.15-0.16 mmol) with both
the homogeneous and the heterogeneous catalysts, in line with
the observation of some unreacted EDA at the end of the catalytic
transformations shown in Scheme 3. The fact that the amount of
nitrogen evolved is nearly the same with 1 and 1-rGO points
Scheme 3. Catalytic activity of complex
cyclohexane, hexane and benzene.
1 toward carbene transfer to
Catalytic activity of 1 and 1-rGO toward hydrocarbon
functionalization with ethyl diazoacetate.
We have chosen three hydrocarbons as model substrates to
test the capabilities of these copper-based materials toward the
catalytic transfer of the carbene CHCO2Et group from ethyl
diazoacetate (EDA). Cyclohexane, n-hexane and benzene were
reacted with EDA in the presence of catalytic amounts of 1, using
2 equiv of NaBArF , with respect to the catalyst as halide
4
scavenger. The experiments led to the incorporation (Scheme 3)
of such carbene group to cyclohexane (2) or hexane (3a-c), upon
copper-mediated insertion into the C-H bonds,[4] or the addition to
the double bond of benzene, affording a cycloheptatriene (4) in
the so-called Buchner reaction.[14] Albeit yields were lower than
those previously reported for related NHCCuCl catalysts,[15] these
values are large enough for comparative purposes with those of
the heterogeneized version of 1 (vide infra). It is worth noting that
EDA was not completely consumed after 21 h of stirring, and that
the products derived from catalytic carbene coupling, i. e. diethyl
fumarate and maleate accounted for a small fraction of initial EDA.
16]
Figure 4. Kinetic curves for the evolution of N2 in the reaction of
cyclohexane and EDA at room temperature. The grey curve
corresponds to TpBr3Cu(NCMe) as the catalyst, providing the expected
maximum amount of evolved N2. See Supporting Information for details.
product (%)
40
35
30
25
20
15
10
5
toward a deactivation process affecting the metal center in a
similar manner.
To evaluate the reversibility of this catalytic inhibition, catalyst
recycling was performed with heterogeneous 1-rGO by simply
filtering off the reaction mixture and reusing the solid residue (see
Experimental). As a representative example we employed n-
hexane as the substrate. Figure 5 displays the results of three
consecutive runs, showing that the catalyst remains active, in
spite of not consuming all the EDA at the end of each cycle. We
believe that the inhibition process along the catalytic reaction, can
be reversed at the end of the cycle when the reaction is filtered
and the solid washed before use. The observed decrease in
yields across the cycles should be due to the loss of a portion of
the solid catalyst during workup. It is also worth mentioning that
the filtrate obtained at the end of each cycle was not active
0
% 2
% 3a-c
% 4
1
1-rGO
Figure 3. Comparison of the catalytic activity of 1 and 1-rGO for the
reactions shown in Scheme 3. See experimental section for details.
Once the moderate catalytic activity of 1 was assessed, we
moved toward its supported version, 1-rGO. Under identical
3
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10.1002/chem.201900964
Chemistry - A European Journal
toward additional EDA, indicating the absence of substantial
catalyst leaching. At this stage, we do not have an explanation for
the inhibition of the catalyst avoiding the complete consumption of
EDA.
the substituents at the pyrene ring infer a variation in the
conductivity at graphene due to electron transfer from or to
pyrene. In our case, the –CH2-O-NHC substituent must act as an
electron-donating group, increasing electron density at graphene
with the corresponding decrease at the copper complex (Scheme
4). Also, Peris and co-workers have demonstrated a similar
pyrene-to-polyaromatic systems electron density flux.[ 20 ] This
remote pyrene-graphene stacking effect explains the
enhancement of reaction rate and yields observed with 1-rGO
when compared with those of soluble 1.
yield %
40
35
30
25
20
15
10
5
Conclusions
The copper complex bearing a NHC ligand with a pyrene tag
attached to the ligand backbone has been synthetized, fully
characterized and supported onto reduced graphene oxide. Both
the soluble complex 1 and the anchored derivative 1-rGO have
been employed as catalysts for the functionalization of hexane,
cyclohexane or benzene in transformations involving the
incorporation of the carbene unit CHCO2Et to the hydrocarbon
molecule. The catalytic activity of the heterogeneous catalyst 1-
rGO displays higher reaction rate as well as an enhancement of
the yields into the functionalized products, thus the anchored
complex being more effective than the homogeneous counterpart.
This behavior could be related[21] to an increase of electrophilicity
at the metal center due to an electronic flux from the copper
complex to the graphene surface through the pyrene tag.
0
1
2
3
cycle#
Figure 5. Catalyst recycling for n-hexane (left). Yields are referred to
initial EDA.
A second feature observed from the kinetic experiments is
that the reaction rate constant for nitrogen evolution (that is the
same for EDA consumption, since one molecule of EDA
generates one molecule of N2) with heterogeneous catalyst is
higher than that for the homogeneous counterpart: kobs(1-rGO) =
1.9 x 10-2 min-1 vs kobs(1) = 7.8 x 10-3 min-1 (Figure 4). It is well
established that N2 evolution in these transformations is the rate
determining step leading to the formation of a metallocarbene
intermediate, and that the rate is faster for more electrophilic
metal centers.[10,19] Additionally, it is also known that the higher
the electrophilicity at the metal-carbene intermediate, the higher
the yields into the C-H functionalization products.[10] With these
two ideas in mind, it seems reasonable assuming that the copper
center at 1-rGO is more electrophilic than that in 1, explaining the
observed behavior in yields and reaction rates. In other words,
the catalytic activity of 1 is enhanced when supported on rGO,
this adsorption generating a decrease in the electron density at
Experimental Section
General. All reactions were carried out under an oxygen free
nitrogen atmosphere by using an MBraun-Unilab glovebox containing
dry argon or nitrogen or conventional Schlenk techniques. Anhydrous
solvents were dried using a solvent purification system (SPS). EDA,
NaBArF and hydrocarbons for catalytic experiments were purchased
4
from Sigma-Aldrich and used without previous purification. r-GO was
purchased from Graphenea. Nuclear magnetic resonance (NMR)
spectra were recorded at room temperature with the appropriate
deuterated solvent on Bruker spectrometers operating at 300 or 400
MHz (1H NMR), and referenced to SiMe4. Elemental analysis were
carried out in a TruSpec Micro Series. Electrospray Mass Spectra
(ESI-MS) were recorded on a MicroMass Quatro LC instrument.
Methanol was used as mobile phase and nitrogen was used as the
drying and nebulizing gas. High-resolution images of transmission
electron microscopy (HRTEM) and high-angle annular dark-field. X-
ray photoelectron spectra (XPS) were acquired on a Kratos AXIS ultra
DLD spectrometer with a monochromatic Al Kα X-ray source (1486.6
eV) using a pass energy of 20 eV. To provide a precise energy
calibration, the XPS binding energies were referenced to the C1s
peak at 284.6 eV. UV-vis spectra were acquired on a Varian Cary 50
spectrophotometer. GC studies were ferformed on a Bruker GC-450
gas chromatography instrument with a FID detector using 30 m x 0.25
mm CP-Sil 8CB capillary column (catalytic reactions).
Synthesis of LMesBr. 4-hydroxy-1,3-dimesitylimidazolium chloride
(600 mg, 1.68 mmol) was suspended in 40 mL of dry acetonitrile.
Potassium carbonate (470.6 mg, 3.4 mmol) and potassium bromide
(614 mg, 5.1 mmol) were added and the mixture was stirred at room
temperature for 1 h. Then bromomethyl pyrene (516 mg, 1.74 mmol)
was added and the mixture was stirred at 60 ºC for 18 hours. The
solvent was removed, dichloromethane (35 mL) was added and the
Scheme 4. Electronic flux in 1-rGO accounting for the experimentally
observed enhanced reaction rate and yields. The red arrow shows the
electronic flux that originate a net decrease in electronic density at the
copper center.
the metal center. This proposal finds support in a recent
contribution by Lee and co-workers,[9] which demonstrated that
4
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10.1002/chem.201900964
Chemistry - A European Journal
mixture was filtered through a pad of celite to remove the insoluble
inorganic salts. The solvent was evaporated and the product was
filtered off, washed with 3 x 10 mL of the corresponding hydrocarbon
and dried under vacuum. The collected filtrates were investigated
using the same protocols mentioned above (see Supporting
Information for full description). The second run was set up upon
adding fresh hydrocarbon, halide scavaneger and the solution of EDA
in the corresponding substrate, this procedure being repeated for
several cycles.
recrystallized using
a mixture (1:1) of acetone/pentane. The
imidazolium salt LMesBr was obtained as a pale yellow powder. Yield:
740 mg (71 %). 1H NMR (300 MHz, CD3OD) δ 8.89 (d, J = 1.7 Hz, 1H,
NCHN), 8.26 (d, J = 7.2 Hz, 2H, CHpyr ), 8.23 – 7.89 (m, 7H, CHpyr),
7.81 (d, J = 1.7 Hz, 1H, CHimid), 7.15 (s, 2H, CHMes), 6.74 (s, 2H,
CHMes), 6.04 (s, 2H, CH2), 2.37 (s, 3H, CH3Mes), 2.20 (s, 3H, CH3Mes),
2.10 (s, 6H, CH3Mes), 1.61 (s, 6H, CH3Mes). 13C{1H} NMR (75 MHz,
CD3OD) δ [148.2, 142.9, 142.8, 136.1, 135.6, 134.2] (Cpyr, CHMes),
Kinetic experiments on dinitrogen evolution. Catalyst 1 or 1-
rGO (0.0025 mmol) was dissolved/suspended in cyclohexane (5 mL)
in a Man on the Moon© apparatus (see Supporting Information)
capable of measuring pressure variation. After 15 minutes of stirring
133.7 (NCHN), [132.8, 132.5, 132.0, 131.3, 130.8, 130.4, 130.0] (Cpyr
,
CHMes, Cimid), [129.6, 129.5] (CHMes) [128.3, 128.2, 127.8, 127.6, 127.1, for pressure stabilization, 0.005 mmol of NaBArF was added. Then,
4
127.0, 126.1, 125.4, 125.3, 123.7] (Cpyr, CHMes, Cimid), 106.7 (CHimid),
76.3 (CH2), [21.1, 21.1, 17.2, 17.2] (CH3Mes). Electrospray MS (Cone
20 V) (m/z, fragment): 535.2 [M-Br]+. Anal. Calculated for
C38H35BrN2O: C, 74.1; H, 5.7; N, 4.5 Found: C 74.0, H 5.4, N, 4.4.
Synthesis of complex 1. In a pyrex tube, imidazolium salt
(LMesBr) (575mg, 0.93 mmol), CuBr (134.8 mg, 0.93 mmol), K2CO3
(767.7 mg, 5.58 mmol) and 5 mL of acetone were heated at 60 ⁰ C for
18 h. Then, the solvent was removed under vacuum, dichloromethane
was added (10 mL) and the mixture was filtered through silica. The
pad of silica was washed with dichloromethane (10 mL). The solvent
was reduced to approximately 2 mL and pentane was added,
affording a pale yellow solid, which was filtered off and dried in
vacuum. Yield: 480 mg (76%). 1H NMR (300 MHz, CDCl3) δ 8.23 (d, J
= 7.6 Hz, 2H, CHpyr), 8.14 – 7.98 (m, 6H, CHpyr), 7.87 (d, J = 7.6 Hz,
1H, CHpyr), 6.93 (s, 2H, CHMes), 6.93 (s, 2H, CHMes), 6.37 (s, 1H,
CHimid), 5.66 (s, 2H, CH2), 2.31 (s, 3H, CH3Mes), 2.29 (s, 3H, CH3Mes),
2.04 (s, 6H, CH3Mes), 1,97 (s, 6H, CH3Mes). 13C{1H} NMR (75 MHz,
CDCl3) δ 174.4 (Ccarbene-Cu), [146.9, 139.1, 139.0, 135.4, 134.9, 134.4,
132.0, 131.0, 130.8, 130.3, 129.3, 129.1, 129.0, 128.1, 128.0, 127.1,
126.9, 126.7, 126.1, 125.6, 125.5, 124.6, 124.1, 123.9, 122.1, 100.9]
(Cpyr, CHMes, Cimid), 73.5 (CH2), [20.8, 20.8, 17.6, 17.3] (CH3Mes)]. Anal.
Calcd. for C38H35BrN2O: C, 67.3; H, 5.0; N, 4.1. Found: C, 67.1, H 5.4,
N 4.4.
100 equivalent of EDA (0.25 mmol, 31.14 μL) were added in one
portion and the mixture was stirred at room temperature. The nitrogen
evolution was measured until the pressure remained constant.
Acknowledgements
The authors would like to thank the financial support of the
MINECO (CTQ2017-82893-C2-1-R and CTQ2015-69153-C2-2-
R), Junta de Andalucía (P12-FQM-1765) and Universitat Jaume I
(UJI-B2018-23). D. V-E thanks the MINECO for
a grant
(FPU15/03011). The authors thank the ‘Servei Central
d’Instrumentació Científica (SCIC)’ of the Universitat Jaume I.
Conflict of interest
The authors declare no conflict of interest.
Keywords: alkane C-H functionalization • carbene transfer •
graphene supported catalysts • pyrene graphene interaction •
catalyst anchoring
Synthesis of 1-rGO. A suspension of 315 mg of commercial
reduced graphene oxide in 10 mL of CH2Cl2 was inmersed in an
ultrasound bath for 30 min. Then, 70 mg of 1 were added to the
mixture. The suspension was stirred at room temperature for 24 h.
The black solid was isolated by filtration and washed with 200 mL of
CH2Cl2 affording the hybrid material as a black solid. The exact
amount of supported complex was determined by ICP-MS analysis.
The results accounted for a 8 wt% of complex 1 in the hybrid material
1-rGO, that was characterized by UV/Vis, XPS and HRTEM.
[1]
Homogeneous Catalysis, Understanding the Art. P. W. N.
Leeuwen. Kluwer Academic Publishers, Dordrecht, 2004.
D. J. Cole-Hamilton. Science 2003, 299, 1702 – 1706.
a) R. Augustine, S. Tanielyan, S. Anderson, Y. Gao, P. Goel, N. Mahata,
J. Nair, C. Reyes, H. Yang, A. Zsigmond in Methodologies in Asymmetric
M van
[2]
[3]
Catalysis, ACS Symposium Series, Vol. 880, chapter
2 Anchored
Homogeneous Catalysts: The Best of Both Worlds, 2004. b) S. Vidal, J.
Marco-Martínez, S. Filippone, N. Martín, Chem. Commun. 2017, 53,
4842-4844.
A. Caballero, M. M. Díaz-Requejo, M. R. Fructos, A. Olmos, J. Urbano,
P. J. Pérez. Dalton Trans. 2015, 44, 20295-20307.
A. Caballero, E. Despagnet-Ayoub, M. M. Díaz-Requejo, A. Díaz-
Rodríguez, M. E. Gonzꢀlez-Nꢁꢂez, R. Mello, B. K. Muꢂoz, B. K.; W.
Solo-Ojo, G. Asensio, M. Etienne, P. J. Pꢃrez Science, 2011, 332, 835-
838
M. A. Fuentes, B. K. Muñoz, K. Jacob, L. Vendier, A. Caballero, M.
Etienne, P. J. Pérez, Chem. – Eur. J., 2013, 19, 1327-1334.
J. T. Sarmiento, A. Olmos, T. R. Belderrain, A. Caballero, T. Varea, P. J.
Pérez, G. Asensio. ACS Sustainable Chem. Eng. 2019,
10.1021/acssuschemeng.9b00523.
Catalytic experiments with complex 1. In a Schlenk flask,
complex 1 (0.01 mmol, 7 mg) was dissolved in the hydrocarbon
[4]
[5]
(cyclohexane, hexane, or benzene; 15 mL) and 2 eq. of NaBArF
4
(17.8 mg) were added as halide scavenger. The mixture was stirred
for 15 min. A solution of EDA (1 mmol, 124.56 µL) in the hydrocarbon
(5 mL) was then added over 21 h with the aid of a syringe pump. In
the case of cyclohexane and hexane, the yields were determined by
GC analysis by using calibration curves. In the case of benzene, the
yields were determined by NMR analysis by using internal standard
(see Supporting Information for more details).
[6]
[7]
Catalytic experiments with complex 1-rGO. Following the
previous procedure, complex 1-rGO (0.005 mmol, 21 mg) was
dissolved in the hydrocarbon (cyclohexane, hexane, or benzene; 15
[8]
a) B. F. Machado, P. Serp. Catal Sci. Technol. 2012, 2, 54-75. V.
Georgakilas, M. Otyepka, A. B. Bourlinos, V. Chandra, N. Kim, K. C.
Kemp, P. Hobza, R. Zboril, K. S. Kim. Chem. Rev. 2012, 112, 6156-
6214.
mL) and 2 eq. of NaBArF (17.8 mg) were added. A solution of EDA
4
(0.5 mmol, 62.28 µL) in the alkane (5 mL) was then added over 21 h
with the aid of a syringe pump. Once finished, the solid catalyst was
5
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10.1002/chem.201900964
Chemistry - A European Journal
-[9]
J. Lee, E. Hwang, E. Lee, S. Seo, H. Lee. Chem. Eur. J. 2012, 18, 5155-
5159.
[15] M. R. Fructos, M. Besora, A. A. C Braga, M. M. Díaz-Requejo, F.
Maseras, P. J. Pérez. Organometallics 2017, 36, 172-179.
[10] A. Caballero, P. J. Pérez, J. Organomet. Chem. 2015, 793, 108-113.
[11] a) S. Ruíz-Botella, E. Peris, ChemCatChem 2018, 10, 1874-1881. b) S.
Ruíz-Botella, E. Peris Chem. Eur. J. 2015, 21, 15263-15271. c) S.
Sabater, J. A. Mata, E. Peris. ACS Catal. 2014, 4, 2038-2047. (d) D.
Ventura-Espinosa, S. Sabater, J. A. Mata. J. Catal. 2017, 352, 498-504.
[12] L. Benhamou, V. César, H. Gornitzka, N. Lugan, G. Lavigne. Chem.
Commun. 2009, 4720–4722.
[16] I. Rivilla, W. M. C. Sameera, E. Álvarez, M. M. Díaz-Requejo, F.
Maseras, P. J. Pérez. Dalton Trans. 2013, 42, 4132-4138.
[17] A. Caballero, M. M. Díaz-Requejo, T. R. Belderrain, M. C. Nicasio, S.
Trofimenko and P. J. Pérez, J. Am. Chem. Soc., 2003, 125, 1446-1447.
[18] See for example: A. Pereira, Y. Champouret, C. Martín, E. Álvarez, M.
Etienne, T. R. Belderraín, P. J. Pérez, Chem. – Eur. J., 2015, 21, 9769-
9775.
[13] a) D. Ventura-Espinosa, C. Vicent, M. Baya, J. A. Mata. Catal. Sci.
Technol. 2016, 6, 8024–8035; b) D. Ventura-Espinosa, A. Carretero-
Cerdán, M. Baya, H. García, J. A. Mata. Chem. Eur. J. 2017, 23, 10815–
10821; c) D. Ventura-Espinosa, S. Sabater, A. Carretero-Cerdán, M.
Baya, J. A. Mata. ACS Catal. 2018, 8, 2558–2566.
[19] A. Olmos, R. Gava, B. Noverges, D. Bellezza, K. Jacob, M. Besora, W.
M. C. Sameera, M. Etienne, F. Maseras, G. Asensio, Ana Caballero, P.
J. Pérez. Angew. Chem. Int. Ed. 2018, 57, 13848-13852.
[20] H. Valdés, M. Poyatos, E. Peris, Inorg. Chem. 2015, 54, 3654-3659.
[21] A referee has suggested that this behavior could be related to the
formation of a dimeric species formed upon pyrene p-stacking of the
molecular complex.
[14] E. Buchner, T. Curtius, Ber. Dtsch. Chem. Ges. 1885, 18, 2371-2377.
Received: ((will be filled in by the editorial staff))
Revised: ((will be filled in by the editorial staff))
Published online: ((will be filled in by the editorial staff))
6
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Anchoring a NHC-
Cu(I) complex onto
graphene through a
pyrene antenna
█ Remote Catalyst Tuning
Pilar Ballestin, David Ventura-
Espinosa, Santiago Martín Ana
Caballero,* Jose A. Mata* and Pedro
J. Pérez*
induces the
enhancement of the
catalytic properties of
the copper center
toward hydrocarbon
functionalization by
carbene transfer from
ethyl diazoacetate
■■ – ■■
Improving Catalyst Activity in
Hydrocarbon Functionalization by
Remote Pyrene-Graphene Stacking
7
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