Published on Web 10/30/2007
Remarkable Co-catalyst Effect of Gold Nanoclusters on Olefin
Oxidation Catalyzed by a Manganese-Porphyrin Complex
Yoshitaka Murakami and Katsuaki Konishi*
Contribution from the CreatiVe Research InitiatiVe ‘Sosei’ and Graduate School of
EnVironmental Science, Hokkaido UniVersity, North 21 West 10, Sapporo 001-0021, Japan
Received July 9, 2007; E-mail: konishi@ees.hokudai.ac.jp
Abstract: The effect of dodecanethiolate-protected metallic nanoclusters of gold (Au:SC12, 1), silver (Ag:
SC12), palladium (Pd:SC12), and platinum (Pt:SC12) on the catalytic activity of Mn(TPP)Cl (TPP )
tetraphenylporphinato) was investigated in styrene oxidation with iodosylbenzene. Among the four metal
clusters, only Au:SC12 led to appreciable acceleration of the catalytic reaction. The major role of the Au
cluster was to regenerate the active catalytic path involving Mn(III) and Mn(V) from the deactivated Mn(IV)
species. The binary 1/Mn(TPP)Cl catalyst system showed an absorption spectrum characteristic of Mn-
(III)-porphyrin after reaction, whereas a catalytically ineffective Mn(IV) species was observed as the sole
porphyrin species in the absence of the Au cluster or in the presence of Pd, Ag, and Pt clusters. Accordingly,
the slow oxidation reaction with Mn(TPP)Cl was accelerated by the addition of Au:SC12, and complete
conversion of Mn(IV) into Mn(III) was observed in the absorption spectrum. 1H NMR inspection of the
reaction of Au:SC12 and iodosylbenzene revealed that the surface dodecyl groups were partially oxidized
into dodecanal and eliminated from the cluster surface, thereby producing unprotected gold sites on the
surface. A reactivation mechanism involving the reaction of the Mn-porphyrin and the oxidant activated
on the gold surface is proposed.
Introduction
has been studied in relation to the mechanism of cytochrome
P450 enzymes.4,5 However, the catalytic turnovers are generally
Since the pioneering work by Haruta, the prominent catalytic
activity of gold nanoclusters has attracted special attention, not
only in its fundamental aspects but also in relation to practical
chemical syntheses.1 Extensive studies have been continuing
up to the present, especially on the aerobic oxidation of CO
and alcohols in gas and liquid phases, revealing their distinctive
capability to activate oxidants under mild conditions.2,3 Such a
unique feature may also arise in other oxidation catalytic
systems. For example, the activity of a certain catalyst would
be enhanced when gold clusters assist the oxidative formation
of a reactive intermediate (e.g., high-valent species). However,
such promoting effects of gold clusters have not been reported
to date.
low due to the catalyst deactivation during the catalytic cycle:
the oxoMn(V) intermediate, which is considered to be respon-
sible for high activity,6 is easily transformed into a less active
Mn(IV) species,7 resulting in low turnover numbers (TONs). It
has also been suggested that the less active Mn(IV) species is
labile and reverts to the reactive forms by the action of
appropriate additives that induce redox perturbation (e.g.,
reduction, disproportionation).8 Therefore, it is expected that
gold clusters having high catalytic activity for oxidation
may mediate these redox processes to improve the catalytic
activity.
(4) (a) Meunier, B. Chem. ReV. 1992, 92, 1411. (b) Dolphin, D.; Traylor, T.
G.; Xie, L. Y. Acc. Chem. Res. 1997, 30, 251. (c) Katsuki, T. Coord. Chem.
ReV. 1995, 140, 189.
(5) (a) Hill, C. L.; Schardt, B. C. J. Am. Chem. Soc. 1980, 102, 6374. (b)
Groves, J. T.; Kruper, W. J.; Haushalter, R. C. J. Am. Chem. Soc. 1980,
102, 6375. (c) Guilmet, E.; Meunier, B. Tetrahedron Lett. 1980, 21, 4449.
(d) Battioni, P.; Renaud, J. P.; Bartolo, J. F.; Reina-Artiles, M.; Fort, M.;
Mansuy, D. J. Am. Chem. Soc. 1988, 110, 6462. (e) Lee, R. W.; Nakagaki,
P. C.; Bruice, T. C. J. Am. Chem. Soc. 1989, 111, 1368. (f) Groves, J. T.;
Lee, J.; Marla, S. S. J. Am. Chem. Soc. 1997, 119, 6269. (g) Collman, J.
P.; Zeng, L.; Decreau, R. A. Chem. Comm. 2003, 2974.
(6) The true active species is not yet clear, see: (a) Gross, Z.; Golublov, G.;
Simkhovich, L. Angew. Chem., Int. Ed. 2000, 39, 4045. (b) Wang, S. H.;
Mandimutsira, B. S.; Todd, R.; Ramdhanie, B.; Fox, J. P.; Goldberg, D. P.
J. Am. Chem. Soc. 2004, 126, 18. (c) Song, W. J.; Seo, M. S.; George, S.
D.; Ohta, T.; Song, R.; Kang, M.; Tosha, T.; Kitagawa, T.; Solomon, E. I.;
Nam, W. J. Am. Chem. Soc. 2007, 129, 1268.
(7) (a) Schardt, B. C.; Hollander, F. J.; Hill, C. L. J. Am. Chem. Soc. 1982,
104, 3964. (b) Groves, J. T.; Stern, M. K. J. Am. Chem. Soc. 1988, 110,
8638. (c) Park, S.-E.; Song, W. J.; Ryu, Y. O.; Lim, M. H.; Song, R.;
Kim, K. M.; Nam, W. J. Inorg. Biochem. 2005, 99, 424.
We herein studied Mn-porphyrin-catalyzed olefin oxidation
as a model reaction and investigated the effects of metallic
clusters on the reaction rate. Olefin oxidation catalyzed by
manganese(III) complexes of porphyrin and related macrocycles
(1) (a) Haruta, M.; Kobayashi, T.; Sano, H.; Yamada, N. Chem. Lett. 1987,
405. (b) Haruta, M. Nature 2005, 437, 1098.
(2) (a) Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44,
7852. (b) Hughes, M. D.; Xu, Y-J.; Jenkins, P.; McMorn, P.; Landon, P.;
Enache, D. I.; Carley, A. F.; Attard, G. A.; Hutchings, G. J.; King, F.;
Stitt, E. H.; Johnston, P.; Griffin. K.; Kiely, C. J. Nature 2005, 437, 1132.
(c) Chowdhury, B.; Bravo-Suarez, J. J.; Date, M.; Tsubota, S.; Haruta, M.
Angew. Chem., Int. Ed. 2006, 45, 412. (d) Bokhoven, J. A. van.; Louis,
C.; Miller, J. T.; Tromp, M.; Safonova, O. V.; Glatzel, P. Angew. Chem.,
Int. Ed. 2006, 45, 4651.
(3) (a) Comotti, M.; Pina, C. D.; Matarrese, R.; Rossi, M. Angew. Chem., Int.
Ed. 2004, 43, 5812. (b) Tsunoyama, H.; Sakurai, H.; Ichikuni, N.; Negishi,
Y.; Tsukuda, T. Langmuir 2004, 20, 11293. (c) Tsunoyama, H.; Sakurai,
H.; Negishi, Y.; Tsukuda, T. J. Am. Chem. Soc. 2005, 127, 9374.
(8) (a) Merlau, M. L.; Cho, S.; Sun, S.; Nguyen, S. T.; Hupp, J. T. Inorg.
Chem. 2005, 44, 5523. (b) Merlau, M. L.; Grande, W. J.; Nguyen, S. T.;
Hupp, J. T. J. Mol. Catal. A: Chem. 2000, 156, 79.
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10.1021/ja075051b CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 14401-14407
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