Fullerenes for catalysis: Metallofullerenes in hydrogen transfer reactions

Article abstract of DOI:10.1039/c7cc01267e

[60]Fullerene hybrids have successfully been used as catalysts in hydrogen transfer reactions, namely ketone reduction and N-alkylation with alcohols. Due to their poor solubility in polar solvents, these hybrids behave as homogeneous/heterogeneous catalysts that can be mechanically separated and reused several times while the final products do not need chromatographic separation.

Full text of DOI:10.1039/c7cc01267e

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
first methanofullerene derivatives of Sc
3
N@C2n (2n
=
68 and 80). Synthesis of the
3
N@D5h-C80
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DOI: 10.1039/C7CC01267E
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Fullerenes for Catalysis: Metallofullerenes in
Hydrogen Transfer Reactions
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a*
a,b*
Sara Vidal, Juan Marco-Martínez, Salvatore Filippone and Nazario Martín
DOI: 10.1039/x0xx00000x
www.rsc.org/
[60]Fullerene hybrids have succesfully been used as catalysts in properties of a homogeneous catalyst with those of carbon-
hydrogen transfer reactions, namely ketones reduction and N- based materials and, eventually, to find synergies with the
alkylation with alcohols. Due to the poor solubility in polar chemical properties of transition metals for chemical
solvent, these hybrids behave as homogeneous/heterogeneous transformations. So far, despite
fullerenes have been
3
catalysts that can be mechanically separated and reused for thoroughly investigated and a wide variety of derivatives,
4
several times while the final products do not need including chiral fullerenes, have been synthesized, their use in
5
chromatographic separation.
catalysis has been almost neglected.
Hydrogenation, dehydrogenation, hydrogen storage and
transfer constitute exciting and challenging topics for the
replacement of a fossil fuel-based economy by clean, safe and
easy accessible hydrogen-based processes. In particular, the
importance of avoiding hazardous gas, such as molecular
hydrogen, in organic chemistry has driven to the “golden age
of the transfer hydrogenation” by means of different strategies
and catalysts for hydrogenation reactions.1 Since these
catalysts are based on noble metal complexes, high efficiency,
mild conditions, low loading and recyclability are required.
On the other hand, transition metals have been very often
associated in catalysis to carbon-based structures. A classic
approach relies in the use of carbon materials as support for
active metals while, more recently, carbocatalysis has emerged
as an effort to remove completely metals by the use of carbon
Fig 1. Transfer hydrogenation by fullerenes hybrids.
In order to address this issue, we have prepared fullerene
hybrids where C60 is endowed with highly active metal atoms
[6]
[7]
[8]
in hydrogenation transfer reactions, such as Ir, Ru, or Rh,
2
nanostructures with metal-free active sites. As heterogeneous
6
and that present a metal centered chirality. Herein, we report
on the catalytic ability of these [60]fullerene hybrids in transfer
hydrogenation reactions such as ketones reduction and N-
Alkylation with alcohols by hydrogen autotransfer process
catalysis, both strategies benefit from an easy use (mechanical
separation of catalyst and products) while they suffer from the
lack of a defined structure of the catalyst, sometimes
reproducibility, and for the lack of a clear mechanism as it
happens for molecular homogeneous catalysts.
(borrowing hydrogen). Remarkably, as result of the very poor
solubility of fullerene cages in polar solvents, they merge the
advantages of the molecular homogeneous catalyst (defined
structures and stereochemical configurations) with those of
heterogeneous catalysts (products are readily isolated and the
catalyst recovered by mechanical means and reused).
In this regard, we wondered if fullerenes, as the sole
molecular carbon allotropes, were able to gather the
a.Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad
Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain). E-mail:
salvatorefilippone@ucm.es ; nazmar@quim.ucm.es
Hydrogen transfer is an alternative hydrogenation process that
avoids the use of potentially explosive and difficult to handle
b.
IMDEA-Nanociencia, C/Faraday 9, Campus de Cantoblanco, 28049 Madrid
gaseous
H
2
. In this process, hydrogen formed from
(Spain).
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
dehydrogenation of a donor molecule (typically an alcohol that
is used as solvent or in a large excess) is added to a hydrogen
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acceptor molecule. In this regard, transition metal-catalyzed (entry 3). These results reveal a strong increase ofVitehweArctiaclteaOlynltinice
hydrogen transfer reactions are undergoing a growing interest efficiency with respect to the iridium dimDOerI:,1b0e.1i0n3g9/aCm7CoCn0g12t6h7eE
since they fulfil the needs for safe, clean and atom economy most efficient iridium-based catalysts. Furthermore, it is
7
processes. Thus, we focused our attention on the racemic worthy to note two other important advantages in the use of
metallo-pyrrolidino[60]fullerenes (metallo-fulleropyrrolidines) this new hybrid catalyst. Firstly, at room temperature, it is
6
1
Ir
,
1Rh
,
1Ru, previously prepared (see also SI for their mostly insoluble in isopropanol as well as in other polar
synthesis and configurational details), with the aim to evaluate solvents and, therefore, it can be removed from the reaction
their efficiency as catalysts in such a kind of chemical medium by mechanical means, thus featuring at the same time
transformations.
the advantages of both homogeneous and heterogeneous
catalysis. Therefore, after filtration or centrifugation, the
catalyst could be removed from the solution or recovered for a
further use, respectively, keeping the product pure without
any further purification but solvent elimination.
Secondly, the recovered catalyst has successfully been reused
for up to 5 times without observing any loss of catalytic
efficiency (entries 4-8). However, exposition to oxygen and/or
light has to be carefully avoided since it is the main cause of
decreasing efficiency (entry 9).
Table 1. Ketones hydrogenation with isopropanol as solvent/hydrogen
source.
H
Cl
O
OH
Cl
K CO
2
3
Ir
Ir
Catalyst
Cl
Cl
R
R'
R
R'
H
IPA, 18h, D
[
Cp*IrCl
2 2
]
iPr
Me
Cl Ir
N
Cl Rh
N
Cl Ru
N
O
O
O
H
H
H
In addition, catalyst 1Ir was also able to efficiently reduce
O
O
O
cyclohexanone, cyclohexanecarboxaldehyde and pentanal
8
(entries 10-12).
Finally, 1Rh and 1Ru did not display the same efficiency and
afforded 76% and 17% yield, respectively (entries 13, 14).
1
Ir
1Rh
1Ru
Catalyst
mol% Ir)
Cp*IrCl
0.5)
Isolated
yield (%)
Entrya
R-; R’-
Based on the aforementioned results, we wondered if these
hybrid catalysts could be useful in hydrogen auto-transfer
processes where hydrogen donor and acceptor stem from the
same source as it occurs in the N-alkylation of amines with
(
[
]
2 2
1
Ph-; -CH
3
65
(
9
2
3
4
5
6
7
8
9
1Ir (0.5)
1Ir (0.1)
1Ir (1.0)
1Ir (rc.)c
1Ir (rc.)c
Ph-; -CH
Ph-; -CH
Ph-; -CH
Ph-; -CH
Ph-; -CH
Ph-; -CH
Ph-; -CH
Ph-; -CH
3
3
3
3
3
3
3
3
>99
alcohols (see scheme in table 2).
66b
We have chosen the N-alkylation of aniline with p-
methoxybenzylic alcohol as reaction model to study the
efficiency of the new hybrid catalyst and the effect of the
fullerene cage in the process.
>99
>99
>99
>99
Cp*Ir complex dimer was firstly used in 5% mol by Fujita and
Yamaguchi affording the corresponding amine in 95% yield
(Table 2, entry 1) and it has frequently been used as
1Ir (rc.)c
1Ir (rc.)c
>99
10
1Ir (rc.)c
15b
benchmark for this reaction. While the iridium prolinate (2)
was one of the more efficient complex able to afford the N-
1
1
1
1
1
0
1
2
3
4
1Ir (0.5)
1Ir (0.5)
1Ir (0.5)
1Rh(0.5)
1Ru(0.5)
-(CH
2 5
) -
>99
>99
>99
benzylated aniline in 93% yield in a 2% of catalytic loading,
Cyclohexyl-; -H
11
after 24 h. Notably, the use of the iridium-fullerene hybrid
nBu-; -H
1
Ir promotes a quantitative yield with just 1.25% of catalyst
Ph-; -CH
Ph-; -CH
3
76b
(92% isolated yield, entry 3).
The scope of this catalyst has also been extended to other
substrates such as aliphatic alcohols or amines and, as a
17b
3
[
a] Reactions were carried out in refluxing isopropanol by using 40 mg of acetophenone
in 2 mL of isopropanol and K CO
2
3
in the same amount as the catalyst. [b] Conversions general rule, the efficiency and yields obtained depend on the
have been determined by NMR. [c] rc.: recycled catalyst. Iridium fulleropyrrolidine 1Ir facility of formation of the intermediate imine.
recovered after centrifugation from a previous reaction.
Thus, this hybrid catalyst successfully carries out the alkylation
of aniline with aliphatic alcohols such as cyclohexanol, 2-
octanol or 3-hexanol in the presence of MgSO , as dehydrating
agent, with conversions that depend on the stability of the
corresponding imines (99%, 91% and 40% respectively, entries
Firstly, we tested the catalytic activity of iridium-fullerene 1Ir
in the reduction of ketones by hydrogen transfer from
isopropanol that is also used as solvent. Iridium dimer has
been used as reference and, indeed, the presence of 0.5%
iridium equivalents of this catalyst affords the acetophenone
reduction with a 65% yield after 18 hours (Table 1, entry 1).
For our delight, iridium-fulleropyrrolidine 1Ir gives rise to a
quantitative reduction of acetophenone after 18 hours with
only 0.5% of catalyst loading (entry 2). The use of minor
amounts of catalyst led to 66% of conversion after 18 hours
4
4
, 5 and 6). Alkylation of N-methylaniline with p-
methoxybenzylic alcohol was carried out using 4% of catalysts:
Cp*Ir dimer affords dialkylated aniline in 65% conversion
(entry 7) while fullerene-iridium complex displayed a better
efficiency (86%, entry 8). A similar behaviour was observed in
the N-benzylation of piperidine that occurs with 6% yield with
Cp*Ir dimer and in 32% yield with fullerene-iridium catalyst
2
| J. Name., 2012, 00, 1-3
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(
entries 9, 10). Finally, benzylamine was quantitatively the reduction of ketones and N-alkylation of amVinieewsArstihcloe wOnilninge
alkylated by cyclohexanol (entry 11). When Rh or Ru-fullerene high efficiencies and some important advDaOntI:a1g0e.1s0.3I9n/Cp7aCrCti0c1u2l6a7rE,
derivatives were used, the reactions occurred with a those merged from acting as a molecular homogeneous
remarkably lower yield in comparison to the related Ir catalyst (defined structures and stereochemical configurations)
derivatives.
with those of heterogeneous catalysts (products are easily
isolated and the catalyst recovered by mechanical means and
reused), when compared to other alternative catalysts.12
Financial support by the European Research Council (ERC-
Table 2. Amine N-alkylation by hydrogen borrowing.
R3
R2
OH
Fullerene hybrid
320441-Chirallcarbon), the Ministerio de Economıa
́
y
+
R2 NHR1
N
,
.
,
Competitividad (MINECO) of Spain (project CTQ2014-52045-R)
and the Comunidad Autónoma de Madrid (PHOTOCARBON
project S2013/MIT-2841) is acknowledged.
base tol anh ∆
R3
R4
R
4
R
1
h
y
d
r
o
i
m
g
Notes and references
e
i
n
n
e
a
t
1.
D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621-6686.
(a) S. Navalon, A. Dhakshinamoorthy, M. Alvaro and H.
Garcia, Chem. Rev., 2014, 114, 6179-6212; (b) D. S. Su, S.
Perathoner and G. Centi, Chem. Rev., 2013, 113, 5782-
5816; (c) D. R. Dreyer and C. W. Bielawski, Chem. Sci.,
2011, 2, 1233.
i
o
n
2
.
O
R3
R2
R2 NHR1
N
imine
R3
R4
3.
(a) J. L. Delgado, S. Filippone, F. Giacalone, M. Á. Herranz,
B. Illescas, E. M. Pérez and N. Martín, Journal, 2014, 350,
R1
f
orma on
ti
R4
-
H O
2
1
-64; (b) A. Hirsch and M. Brettreich, Fullerenes:
Chemistry and Reactions, Wiley VCH Weinheim, Germany,
2005.
Catalyst
mol% Ir)
Conversion
%)
Entrya
Product
(
(
4
.
(a) E. E. Maroto, M. Izquierdo, S. Reboredo, J. Marco-
Martínez, S. Filippone and N. Martín, Acc. Chem. Res.,
2014, 47, 2660-2670; (b) E. E. Maroto, S. Filippone, M.
Suárez, R. Martínez-Álvarez, A. De Cózar, F. P. Cossío and
N. Martín, J. Am. Chem. Soc., 2014, 136, 705-712; (c) J.
Marco-Martínez, S. Reboredo, M. Izquierdo, V. Marcos, J.
L. López, S. Filippone and N. Martín, J. Am. Chem. Soc.,
[
Cp*IrCl
2
]
2
MeO
H
N
1
95
(5.0)
Ph
Cp*
Cl Ir
O
HN
2c
93
O
“
“
2
014, 136, 2897-2904; (d) J. Marco-Martínez, V. Marcos,
S. Reboredo, S. Filippone and N. Martín, Angew. Chem.
Int. Ed., 2013, 52, 5115-5119; (e) E. E. Maroto, S.
2
(2.0)
99 (92)b
Filippone, A. Martín-Domenech, M. Suarez and N. Martín,
J. Am. Chem. Soc., 2012, 134, 12936-12938; (f) K. Sawai, Y.
Takano, M. Izquierdo, S. Filippone, N. Martin, Z. Slanina,
N. Mizorogi, M. Waelchli, T. Tsuchiya, T. Akasaka and S.
Nagase, J. Am. Chem. Soc., 2011, 133, 17746-17752; (g) E.
E. Maroto, A. de Cózar, S. Filippone, Á. Martín-Domenech,
M. Suarez, F. P. Cossío and N. Martín, Angew. Chem. Int.
Ed., 2011, 50, 6060-6064; (h) S. Filippone, E. E. Maroto, A.
Martín-Domenech, M. Suárez and N. Martín, Nat. Chem.,
3
4
1Ir (1.25)
1Ir (1.25)
H
N
99
Ph
H
N
5
6
1Ir (1.25)
1Ir (1.25)
Ph
91
40
n-C H
6
13
H
N
Ph
N
C
3
H
7
2
009, 1, 578.
MeO
MeO
[
Cp*IrCl
4.0)
2
]
2
7
65
86
6
5.
6.
(a) E. Sulman, V. Matveeva, N. Semagina, I. Yanov, V.
Bashilov and V. Sokolov, J. Mol. Catal. A: Chem., 1999,
146, 257-263; (b) A. L. Balch and K. Winkler, Chem. Rev.,
(
Ph
8d
9d
1Ir (4.0)
Cp*IrCl
“
“
2
016, 116, 3812-3882.
[
2
]
2
N
J. Marco-Martínez, S. Vidal, I. Fernández, S. Filippone and
N. Martín, Angew. Chem. Int. Ed., 2017, 56, 2136-2139.
(a) L. A. Oro and C. Claver, eds., Iridium Complexes in
Organic Synthesis, Wiley-VCH, Weinheim, 2009; (b) M.
Kitamura and R. Noyori, in Ruthenium in Organic
(2.0)
1
0d
1Ir (2.0)
32
99
7
.
H
Ph
N
1
1
1Ir (1.25)
Synthesis, Wiley-VCH Verlag GmbH & Co. KGaA, 2005,
DOI: 10.1002/3527603832.ch2, pp. 3-52; (c) Y. Chi, W.
Tang and X. Zhang, in Modern Rhodium-Catalyzed Organic
Reactions, ed. P. A. Evans, Wiley-VCH Verlag GmbH & Co.
KGaA, 2005, DOI: 10.1002/3527604693.ch1, pp. 1-31.
[
a] The reactions are carried out at mmolar scale with 1 eqv. of amine, 1.2 eqv. of
alcohol and the same equivalents of K CO as that of the catalyst. [b] Isolated yield.
c] Data reported in the literature. [d] MgSO was used.
2
3
11
[
4
In conclusion, new C60-based catalysts have shown their
efficiency in fundamental hydrogen transfer reactions such as
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8
.
These catalysts, in their optically active form, have shown
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a weak chiral induction leading to chiral alcohols only with
modest enantiomeric excesses. Despite this finding
demonstrates a promising behaviour as asymmetric
catalysts, a much deeper study (expecially on nature
ligands modifications) is ongoing to achieve higher and
remarkable values of enantioselectivity
DOI: 10.1039/C7CC01267E
9
.
(a) G. Guillena, D. J. Ramón and M. Yus, Chem. Rev., 2010,
1
10, 1611-1641; (b) G. E. Dobereiner and R. H. Crabtree,
Chem. Rev., 2010, 110, 681-703; (c) M. H. S. A. Hamid, P.
A. Slatford and J. M. J. Williams, Adv. Synth. Catal., 2007,
3
49, 1555-1575.
1
1
0.
1.
K.-i. Fujita, Z. Li, N. Ozeki and R. Yamaguchi, Tetrahedron
Lett., 2003, 44, 2687-2690.
A. Wetzel, S. Wöckel, M. Schelwies, M. K. Brinks, F.
Rominger, P. Hofmann and M. Limbach, Org. Lett., 2013,
1
5, 266-269.
1
2.
(a) R. Kawahara, K.-i. Fujita and R. Yamaguchi, J. Am.
Chem. Soc., 2010, 132, 15108-15111; (b) H. Liu, D.-L.
Wang, X. Chen, Y. Lu, X.-L. Zhao and Y. Liu, Green
Chemistry, 2017, 19, 1109-1116.
4
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