ChemComm
Communication
19
Table 2 Results of the reaction tests over various metal catalysts hybridised with Thus, the quantum yield for BnCN is still as low as 0.22%.
a
the titanium dioxide photocatalyst
However, the discovery of the new simple catalytic route under mild
b
conditions should be important in view of green and sustainable
chemistry. There are still a few reports on precious metal catalysts
hybridised with a photocatalyst. The further development of such
hybrid catalysts and the optimisation of the reaction conditions will
improve the product yield, selectivity and photon efficiency and will
realise wide application in many kinds of reactions.
Products (mmol)
b
b
Entry
Catalyst
Pd/TiO
BnCN
PhOH
SN
H
2
Y (%)
b
S (%)
20
1
2
3
2
3.6 c
n.d.
tr.
0.3
tr.
0.3
0.4
5.9
3.2
3.6
14.4
5.2
0.32
0
92
0
d
Pt/TiO
Rh/TiO
2
2
0
0
a
Catalyst 0.2 g, benzene 0.1 mL (1.1 mmol), acetonitrile 3.9 mL
74.7 mmol). Reaction time was 3 h. The wavelength of the incident
The XAFS experiments were performed under the approval
See of the Photon Factory Program Advisory Committee (Proposal
No. 2011G575). This work was supported by a Grant-in-Aid for
Challenging Exploratory Research (No. 24656490).
(
ꢀ
2 b
light was 405 ꢂ 20 nm, the light intensity was 27 mW cm
.
c
d
footnotes b–d of Table 1. n.d. = not detected. tr. = trace.
showed almost no catalytic activity for the BnCN formation
Table 2). Although the cyanomethyl radical should be similarly
Notes and references
(
generated on the photocatalyst in these hybrid catalysts as sug-
gested from the formation of SN, the BnCN was scarcely produced
without the palladium catalyst. Thus, it suggests that the palla-
dium nanoparticles contribute not only to the separation of the
electron–hole pair and the successive reduction of protons to form
hydrogen (eqn (2) and (5)) but also the unique catalysis for the C–C
bond formation between benzene and the cyanomethyl radical
1 M. Kosugi, M. Ishiguro, Y. Negishi, H. Sano and T. Migita, Chem.
Lett., 1984, 1511.
2
3
L. Wu and J. F. Hartwig, J. Am. Chem. Soc., 2005, 127, 15824.
J. Velcicky, A. Soicke, R. Steiner and H.-G. Schmalz, J. Am. Chem.
Soc., 2011, 133, 6948.
4
5
D. A. Culkin and J. F. Hartwig, J. Am. Chem. Soc., 2002, 124, 9330.
M. E. Kurz, S. C. Lapin, K. Mariam, T. J. Hagen and X. Q. Qian, J. Org.
Chem., 1984, 49, 2728.
6 Y. Tamura, H. D. Choi, M. Mizutani, Y. Ueda and H. Ishibashi,
Chem. Pharm. Bull., 1982, 30, 3574.
(
eqn (4)). Since palladium has the lowest metal–carbon bond
7
M. A. Fox and M. T. Dulay, Chem. Rev., 1993, 93, 341; H. Kisch, J. Prakt.
Chem., 1994, 336, 635; P. Pichat, Catal. Today, 1994, 19, 313; A. Maldotti,
A. Molinari and R. Amadelli, Chem. Rev., 2002, 102, 3811; H. Yoshida, Curr.
Opin. Solid State Mater. Sci., 2003, 7, 435; O. Carp, C. L. Huisman and
A. Reller, Prog. Solid State Chem., 2004, 32, 33; A. Corma and H. Garcia,
Chem. Commun., 2004, 1443; H. Yoshida, Catal. Surv. Asia, 2005, 9, 1;
M. Fagnoni, D. Dondi, D. Ravelli and A. Albini, Chem. Rev., 2007, 107, 2725;
G. Palmisano, V. Augugliaro, M. Pagliaro and L. Palmisano, Chem.
Commun., 2007, 3425; L. Yuliati and H. Yoshida, Chem. Soc. Rev., 2008,
14b,16
dissociation energy among these metals,
it might moderately
adsorb the cyanomethyl radical to promote the cyanomethylation.
This photoassisted direct cyanomethylation with acetonitrile
can be applied to other aromatic compounds as listed in Table S2
17
(
ESI†). From several monosubstituted benzenes and pyridine, the
corresponding cyanomethylation products were obtained in vary-
ing yield and selectivity. Among them, 2-cyanomethyl pyridine was
produced from pyridine in high yield (1.1% for 1 h) and high
selectivity (78%) (Table S2 (ESI†), entry 7). Among the monosub-
stituted benzenes, cyanomethyl nitrobenzene was obtained in high
yield (0.43% for 1 h), and cyanomethyl benzonitriles were formed
with high selectivity (57%) (Table S2 (ESI†), entries 2 and 3). The
trend of the isomer distribution of the obtained cyanomethylation
3
7, 1592; Y. Shiraishi and T. Hirai, J. Photochem. Photobiol., C, 2008, 9, 157;
G. Palmisano, E. Garc ´ı a-L o´ pez, G. Marc ´ı , V. Loddo, S. Yurdakal,
V. Augugliaro and L. Palmisano, Chem. Commun., 2010, 46, 7074;
H. Yuzawa and H. Yoshida, Chem. Commun., 2010, 46, 8854; H. Yuzawa,
T. Mori, H. Itoh and H. Yoshida, J. Phys. Chem. C, 2012, 116, 4126.
8 K. Shimura, H. Kawai, T. Yoshida and H. Yoshida, Chem. Commun.,
011, 47, 8958 (ACS Catal., 2012, 2, 2126).
2
9
M. Nomura, Y. Koike, M. Sato, A. Koyama, Y. Inada and K. Asakura,
AIP Conf. Proc., 2007, 882, 896.
products for each monosubstituted benzene was very unique, i.e., 10 Turnover number, TON = (number of the obtained BnCN molecules)/
(
number of the Pd atoms in the hybrid catalyst).
the para-isomer was selectively produced in the case of nitro-
benzene (83%), and the ortho-isomers were preferentially produced
for anisole (60%), which might originate from that the reaction
proceeded on the catalyst surface in the heterogeneous reaction
system. The side reactions for these monosubstituted benzenes
took place at the substituent (e.g., reduction, oxidation, cyano-
methylation, coupling or substitution) and hydroxylation of the
aromatic ring. Further optimisation of the reaction conditions
would improve the yield and selectivity.
In conclusion, the photoassisted direct cyanomethylation of
benzene with acetonitrile can be selectively promoted by the
palladium catalyst hybridised with the titanium dioxide photo-
catalyst, in which the photocatalyst activates acetonitrile to form
the cyanomethyl radical and the palladium catalyst promotes the
1
1 H. Yoshida, H. Yuzawa, M. Aoki, K. Otake, H. Itoh and T. Hattori,
Chem. Commun., 2008, 4634; H. Yuzawa, M. Aoki, K. Otake,
T. Hattori, H. Itoh and H. Yoshida, J. Phys. Chem. C, 2012,
1
16, 25376. Adsorbed water on the photocatalyst would be used
for the photocatalytic hydroxylation of benzene.
1
1
2 S. Arimitsu, Koukaitokkyokouhou (Japanese Published Unexamined
Patent Application), No. 57-35525, 1982.
3 The yields of phenol, succinonitrile and hydrogen seem slightly
higher than the expected ones (Table 1, entry 3), implying that these
side reactions would be competitively enhanced under this condition.
14 (a) Y. R. Luo, Handbook of Bond Dissociation Energies in Organic
Compounds, CRC Press, 2002; (b) D. R. Lide, CRC Handbook of
Chemistry and Physics, CRC Press, London, 86th edn, 2006.
5 A. Maldotti, R. Amadelli, C. Bartocci and V. Carassiti, J. Photochem.
Photobiol., A, 1990, 53, 263.
1
1
6 J. A. M. Simoes and J. L. Beauchamp, Chem. Rev., 1990, 90, 629.
Metal–carbon bond dissociation energies (D298K) are 436, 580 and
6
0
ꢀ1
10 kJ mol for Pd, Rh and Pt, respectively.
successive substitution. This catalytic reaction proceeded continu- 17 For these examinations, the light around 365 nm in wavelength was
employed since the high yield of benzyl cyanide was obtained from
ously without deactivation in a fixed-bed flow reactor in the
benzene and acetonitrile under the conditions (Table S1 (ESI†), entry 2).
presence of water (Fig. S5, ESI†). Essentially, this reaction asso-
1
8 K. G. Joback and R. C. Reid, Chem. Eng. Commun., 1987, 57, 233.
ciated with the production of hydrogen (eqn (1)) cannot preferably 19 The quantum yield, QY(%) = 100 ꢃ YBnCN/Iphoton, where Iphoton stands
for the incident photon number, which was calculated from a result
proceed under mild conditions: the change of the Gibbs free energy
ꢀ2
recorded under the light of 365 nm and 5.0 mW cm in intensity.
0 Y. Shiraishi, Y. Sugano, S. Tanaka and T. Hirai, Angew. Chem.,
Int. Ed., 2010, 49, 1656.
0
ꢀ1
r
under standard conditions (D G298K = 41 kJ mol ) estimated by
2
1
8
the Joback method implies the thermodynamic difficulty.
This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 3793--3795 3795