4
A. Dhakshinamoorthy et al. / Journal of Catalysis 267 (2009) 1–4
III
t-Bu-O-O-H
t-Bu-O-O
Fe(III)
CH2
Fe-O-O-t-Bu
Fe(II) + t-Bu-O-O
t-Bu-O-O
C
O
CH
O-O-t-Bu
CH
t-Bu-O-H
Scheme 1. Proposed mechanism for the oxidation of benzylic compounds by iron(III) with TBHP.
of xanthene and other benzylic compounds with t-butylhydroper-
5000000
oxide in acetonitrile. For those products that can access the MOF
micropore system the reaction takes place with high to moderate
yields. The solid catalyst can be easily reused maintaining the par-
ticle integrity and with some gradual decay in activity. The avail-
ability of MOFs and the simple product isolation make this
system quite attractive for academic as well as industry
communities.
4000000
3000000
2000000
1000000
0
-1000000
-2000000
-3000000
-4000000
Acknowledgment
Financial support by the Spanish DGI (CTQ06-6857 and
CTQ2007-67805/PPQ) is gratefully acknowledged.
3460
3480
3500
3520
3540
3560
G
Appendix A. Supplementary material
Fig. 3. EPR spectrum recorded for the treatment of TBHP with Fe(BTC) at 70 °C in
the presence of PBN (see Supplementary material for simulation).
Supplementary data associated with this article can be found, in
of magnitude lower than that when catalyst, TBHP, and nitrone are
present. After generation of alcoxyl radicals, hydrogen abstraction
at the benzylic methylene groups will generate a carbon-centered
radical.
References
[1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem. Int. Ed. 38 (1999) 3268.
[2] M. Eddaoudi, D.B. Moler, H.L. Li, B.L. Chen, T.M. Reineke, M. O’Keeffe, O.M.
Yaghi, Acc. Chem. Res. 34 (2001) 319.
[3] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 43 (2004) 2334.
[4] S. Kitagawa, R. Matsuda, Coord. Chem. Rev. 251 (2007) 2490.
[5] L. Alaerts, C.E.A. Kirschhock, M. Maes, M.A. van der Veen, V. Finsy, A. Depla, J.A.
Martens, G.V. Baron, P.A. Jacobs, J.E.M. Denayer, D.E. De Vos, Angew. Chem. Int.
Ed. 46 (2007) 4293.
[6] F.X. Llabres i Xamena, A. Abad, A. Corma, H. Garcia, J. Catal. 250 (2007) 294.
[7] Z. Wang, G. Chen, K. Ding, Chem. Rev. 109 (2009) 322.
[8] J.Y. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Chem. Soc.
Rev. 38 (2009) 1450.
[9] L. Alaerts, E. Seguin, H. Poelman, F. Thibault-Starzyk, P.A. Jacobs, D.E.D. Vos,
Chem. Eur. J. 12 (2006) 7353.
[10] A. Henschel, K. Gedrich, R. Kraehnert, S. Kaskel, Chem. Commun. (2008) 4192.
[11] K. Schlichte, T. Kratzke, S. Kaskel, Micropor. Mesopor. Mater. 73 (2004) 81.
[12] J.W. Han, C.L. Hill, J. Am. Chem. Soc. 129 (2007) 15094.
[13] C. Bolm, J. Legros, J. Le Paih, L. Zani, Chem. Rev. 104 (2004) 6217.
[14] M. Nakanishi, C. Bolm, Adv. Synth. Catal. 349 (2007) 861.
[15] N. Komiya, T. Naota, Y. Oda, S.-I. Murahashi, J. Mol. Catal. A 117 (1997) 21.
[16] S. Menage, J.M. Vincent, C. Lambeaux, G. Chottard, A. Grand, M. Fontecave,
Inorg. Chem. 32 (1993) 4766.
[17] G. Huang, C.C. Cai, J. Luo, H. Zhou, Y.A. Guo, S.Y. Liu, Can. J. Chem. 86 (2008)
199.
[18] S.H. Cho, M.S. Cheong, K.D. Jung, C.S. Kim, S.H. Han, Appl. Catal. A 267 (2004)
241.
The shape selectivity of Fe(BTC) as heterogeneous catalyst was
demonstrated using a large molecule that cannot access the inte-
rior of the pores. The structure of Fe(BTC) has a pore size of
0.6 nm [19]. It has been previously shown that triphenylmethane
(1.1 nm molecular size) is size-excluded from the pores of zeolite
Y and the same can be assumed that occurs for Fe(BTC) [24]. Thus,
it could be anticipated that triphenylmethane should not undergo
oxidation if the reaction takes place inside the MOF micropores in
spite of the higher reactivity of C–H in the tertiary benzylic carbon.
Not surprisingly, the attempts to oxidize triphenylmethane re-
sulted in the formation of triphenylmethanol with low yield, sup-
porting that the benzyl oxidation takes place predominantly inside
the micropores of MOF particles.
Interestingly, oxidation of adamantane gives 1- and 2-ada-
mantanol in a 5:1 ratio and no detectable quantity of the corre-
sponding ketones. The product distribution in adamantane
oxidation has been proposed to be a hallmark of a free radical
aerobic oxidation when there is low selectivity for the oxidation
of the tertiary vs. the secondary carbon and when the 1-/2-ada-
mantanol ratio is low [15]. Thus, the adamantane product distri-
bution together with hydroquine quenching suggests that
Fe(BTC)-catalyzed oxidation occurs mainly through the oxidation
of free radicals.
[19] P. Krawiec, M. Kramer, M. Sabo, R. Kunschke, H. Fröde, S. Kaskel, Adv. Eng.
Mater. 8 (2006) 293.
[20] P. Horcajada, S. Surble, C. Serre, D.-Y. Hong, Y.-K. Seo, J.-S. Chang, J.-M.
Greneche, I. Margiolaki, G. Ferey, Chem. Commun. (2007) 2820.
[21] D.H.R. Barton, T.-L. Wang, Tetrahedron 50 (1994) 1011.
[22] A.M. Khenkin, R. Neumann, J. Am. Chem. Soc. 124 (2002) 4198.
[23] D.H.R. Barton, V.N. Le Gloahec, Tetrahedron 54 (1998) 15457.
[24] M. Alvaro, H. Garcia, A. Sanjuan, M. Espla, Appl. Catal. A 175 (1998) 105.
4. Conclusions
In summary, we have successfully shown the utility of inexpen-
sive Fe and Cu MOFs as effective catalysts for the aerobic oxidation