Table 2 Substrate scope and oxidation conditionsa
Product yield(s) (%)
tolerance for substrates with coordinating functional groups.
Ethers were reactive: di-n-butyl ether was oxidized to butyl
butyrate in greater than 50% yield, (some saponification to
n-butanol was also observed during the reaction), but cyclic
ethers (e.g. tetrahydropyran) were not oxidized. While
additives such as acetone or acetic acid have no deleterious
effect on the oxidation, the presence of those functions in the
substrate rendered the target unreactive. Species such as
amides, lactones, carboxylic acids, and esters were all unreactive.
Examples tested include methyldecanoate, methyl adamantane
carboxylate, N,N-dihexyl-benzamide, g-valerolactone, cyclohexyl
acetate, octanoic acid, and 1-adamantane carboxylic acid.
In summary, we have shown that iron(II) salts can cause
folding and organization of pyridine-appended cavitand
scaffolds to create highly effective catalysts for the oxidation
of simple unactivated hydrocarbons. The catalysts are wide
in scope and oxidations are performed cleanly under mild
conditions without autooxidation of catalyst. The cavitands
retain the metal throughout the reaction, and can be recovered
by filtration after precipitation with ether. Further application
of these cavitands for supramolecular catalysis is underway in
our laboratory.
Substrate Solvent T (1C) Cat.
Total (%)
H2O :
MeCN
(1 : 1)
23
5ÁFe2 54
4
12
58
79
6ÁFex 67
H2O :
EtCN
(1 : 1)
60
5ÁFe2 32
6ÁFex 35
26
22
58
57
H2O : 60
EtCN
(1 : 1)
5ÁFe2 48
6ÁFex 52
20
17
68
69
H2O : 60
EtCN
(1 : 1)
5ÁFe2 40
6ÁFex 34
13
12
53
46
H2O :
EtCN
(1 : 1)
60
23
5ÁFe2
6ÁFex
47
42
47
42
Notes and references
1 A. E. Shilov and G. B. Shul’pin, Chem. Rev., 1997, 97, 2879.
2 J. H. Dawson, Science, 1988, 240, 433.
Bu2O
H2O :
MeCN
(1 : 1)
3 M. Merkx, D. A. Kopp, M. H. Sazinsky, J. L. Blazyk, J. Muller
and S. L. Lippard, Angew. Chem., Int. Ed., 2001, 40, 2782.
4 (a) D. J. Ferraro, L. Gakhar and S. Ramaswamy, Biochem.
Biophys. Res. Commun., 2005, 338, 175; (b) S. Taktak, W. Ye,
A. M. Herrera and E. V. Rybak-Akimova, Inorg. Chem., 2007,
46, 2929; (c) R. Mas-Balleste
2007, 129, 15964.
5 (a) L. Que Jr. and W. B. Tolman, Nature, 2008, 455, 333;
(b) M. S. Chen and M. C. White, Science, 2007, 318, 783;
(c) N. D. Litvinas, B. H. Brodsky and J. DuBois, Angew. Chem.,
5ÁFe2 51
6ÁFex 56
23
21
74
77
H2O :
MeCN
(1 : 1)
23
´
and L. Que Jr., J. Am. Chem. Soc.,
5ÁFe2
6ÁFex
88
87
88
87
a
All reactions were carried out using 10 mol% catalyst loading and
t
10 mol. eq. BuOOH. Reactions were performed in triplicate and the
Int. Ed., 2009, 48, 4513; (d) L. Gomez, I. Garcia-Bosch,
´
A. Company, J. Benet-Buchholz, A. Polo, X. Sala, X. Ribas and
M. Costas, Angew. Chem., Int. Ed., 2009, 48, 5720.
average yield is reported.
6 (a) M. Costas, M. P. Mehn, M. P. Jensen and L. Que Jr, Chem.
Rev., 2004, 104, 939; (b) M. M. Abu-Omar, A. Loaiza and
N. Hontzeas, Chem. Rev., 2005, 105, 2227.
7 M. A. Bigi, S. A. Reed and M. C. White, Nat. Chem., 2011, 3, 216.
8 M. A. Bigi, S. A. Reed and M. C. White, J. Am. Chem. Soc., 2012,
134, 9721.
a 2.5 : 1 ratio. Trans-decalin, on the other hand, was oxidized
to trans-2-decalone and trans-1-decalone in a 2 : 1 ratio with
an overall yield of 53%. No tertiary C–H oxidation was
observed in this case due to the unfavorable 1,3-diaxial interactions
in the product. Reaction selectivity was further investigated by
testing more reactive benzylic substrates. Methyl groups were not
oxidized under the conditions in Table 2: even toluene and p-xylene
were unreactive. Secondary C–H oxidation was facile and
4-ethyltoluene was selectively converted to 4-methylacetophenone
in 88% yield (with 5ÁFe2; 6ÁFex gave 87% conversion) at ambient
temperature. In each of these cases, performing the oxidation with
uncoordinated FeSO4 gave essentially stoichiometric conversion.
The cavitands do not undergo observable self-oxidation or
decomposition during the reaction: if the oxidation is quenched
by addition of ether, the catalyst can be recovered by filtration,
and still displays coordinated Fe (as determined by MALDI-MS).
Given the success of catalysts 5ÁFe2 and 6ÁFex for the
oxidation of unfunctionalized hydrocarbons, we tested the
9 (a) D. H. R. Barton, R. S. Hay-Motherwell and W. B. Motherwell,
Tetrahedron Lett., 1983, 24, 1979; (b) A. Mukherjee, M. Martinho,
E. L. Bominaar, E. Munck and L. Que Jr, Angew. Chem., Int. Ed.,
¨
2009, 48, 1780.
10 (a) M. S. Chen and M. C. White, Science, 2010, 327, 566; (b) D. H. R.
Barton, S. D. Beviere and D. R. Hill, Tetrahedron, 1994, 50, 2665.
´
11 J. England, Y. Guo, K. M. Van Heuvelen, M. A. Cranswick,
G. T. Rohde, E. Bominaar, E. Munck and L. Que Jr, J. Am. Chem.
Soc., 2011, 133, 11880.
¨
12 K. Chen and L. Que Jr, J. Am. Chem. Soc., 2001, 123, 6327.
13 (a) R. J. Hooley and J. Rebek Jr, Chem. Biol., 2009, 16, 255;
(b) L. G. Marinescu and M. Bols, Angew. Chem., Int. Ed., 2006,
45, 4590.
14 G. Thiabaud, G. Guillemot, I. Schmitz-Afonso, B. Colasson and
O. Reinaud, Angew. Chem., Int. Ed., 2009, 48, 7383.
15 K. E. Djernes, O. Moshe, M. Mettry, D. D. Richards and
R. J. Hooley, Org. Lett., 2012, 14, 788.
16 S. I. Presolski, V. Hong, S.-H. Cho and M. G. Finn, J. Am. Chem.
Soc., 2010, 132, 14570.
c
11578 Chem. Commun., 2012, 48, 11576–11578
This journal is The Royal Society of Chemistry 2012