Table 1 Results for the oxidation of alkanes and alkyl arenes catalysed by
Notes and references
a,b
1
†
Synthesis and selected data: to a solution of the diethyl ester derivative of
the ligand (1.54 g, 5.0 mmol) in methanol (50 mL) was added a 25%
methanol solution of Me NOH (8.0 mL, 20.0 mmol). Solid Mn(Me-
CO ·2H O (1.35 g, 5.0 mmol) was then added in small portions under
Entry
Substrate
Product
Yield (%)c
4
1
2
3
4
5
a
Cyclohexane
Adamantane
Toluene
Cyclohexanol
Cyclohexanone
1-Adamantanol
1.9 (3.5)d
2.2 (5.4)d
8.0
1.0
3.1
1.3
4.2
16.9
5.2
37.3
2
)
3
2
stirring, and the resulting reaction mixture was further stirred for 15 min at
room temperature. A brick-red microcrystalline solid formed abundantly
which was collected by filtration and dried under vacuum. The filtered deep
brown solution was reduced to a final volume of 25 mL in a rotatory
evaporator. Upon standing at 4 °C in a refrigerator, a second crop of crystals
separated from the concentrated solution which was also collected and dried
2-Adamantanol/one
Benzaldehyde
Benzoic acid
1-Phenylethanol
Acetophenone
Benzhydrol
Ethylbenzene
Diphenylmethane
(60%). Anal. Calc. for C14
Found: C 41.05, H 9.91, N 5.12%. (Me
mmol) was dissolved in water (50 mL) and the reaction mixture was filtered
on paper to eliminate a small amount of solid particles. A solution of Ph PCl
0.75 g, 2.0 mmol) in acetonitrile (25 mL) was then added to the filtered
H
16MnN
3
O
6
·2H
2
O: C 40.67, H 10.17, N 4.84.
4
N)[Mn(opba)]·2H
2
O (0.83 g, 2.0
Benzophenone
4
Reactions were carried out at room temperature by adding a solution of the
substrate (0.10 mmol) in CH Cl (0.2 mL) to a stirred mixture of the metal
catalyst (5.0 3 10 mmol) and Bu O
under an O atmosphere for a period of 24 h. In the absence of catalyst no
(
2
2
deep brown aqueous solution. Well-shaped, brick-red elongated prisms of 1
suitable for X-ray diffraction were deposited after a few hours of slow
evaporation at room temperature. They were filtered off and air-dried
23
t
2
2 2
H (0.30 mmol) in CH Cl (0.2 mL)
b
2
c
oxidation was observed. Yields refer to GLC determination based on the
starting substrate. With a reaction time of 72 h.
2
1
(
90%). n(KBr)/cm 3422s (O–H) from H
2
O, 2254w (C·N) from MeCN,
d
1
669vs and 1645vs (CNO), 1381s and 1280s (C–O) from opba. UV–Vis
2
1
21
5
(
1
‡
MeCN) lmax/nm: 210 (e/L mol cm 1.4 3 10 ), 225 (sh), 260 (4.0 3
4
3
0 ), 275 (sh), 340 (9.4 3 10 ) and 410 (sh).
Crystal data for C70 63Mn : M = 1434.1, triclinic, space group
H
2 5 18 2
N O P
¯
P1, a = 13.099(3), b = 15.446(3), c = 17.687(4) Å, a = 73.04(3), b =
7
=
3
9.94(3), g = 80.84(3)°, U = 3348(1) Å , T = 293 K, Z = 2, m(MoKa)
and alkyl arenes are summarised in Table 1. Complex 1
catalysed the oxidation of cyclohexane to the corresponding
alcohol and ketone, cyclohexanol and cyclohexanone, re-
spectively, with varying yields depending on the reaction time
2
1
0.50 mm , 11665 reflections measured, 7556 assumed as observed with
I 4 2s(I). Hydrogen atoms were located from a difference synthesis and
2
refined with an overall isotropic thermal parameter. Refinement on F of
8
75 variables with anisotropic thermal parameters for all non-hydrogen
(
entry 1). Interestingly, the cyclohexanol+cyclohexanone ratio
atoms gave R = 0.092 and wR = 0.251 with S = 0.94 (observed data).
CCDC reference number 166256. See http://www.rsc.org/suppdata/cc/
b1/b105132f/ for crystallographic data in CIF or other electronic format.
dropped from 0.9 to 0.6 with longer reaction times, suggesting
that secondary alcohols are further oxidised to ketones under the
experimental conditions. It is also noteworthy that for our
catalytic system the tertiary to secondary C–H bond relative
reactivities (ktert/ksec; on a per bond basis) for the oxidation of
adamantane was as high as 24 (entry 2). On the other hand, alkyl
arenes such as toluene, ethylbenzene or diphenylmethane were
oxidised selectively at the benzylic position to give the
corresponding benzylic oxygenation products, and no traces of
the corresponding aromatic ring hydroxylation products were
detected by GLC analysis in any case. As expected, the
oxidation of toluene gave some minor amounts of benzoic acid
together with the main product benzaldehyde, whereas no
benzyl alcohol was observed among the oxygenation products
1 N. A. Law, M. T. Caudle and V. L. Pecoraro, Adv. Inorg. Chem., 1998,
46, 305.
2
(a) G. S. Schimpff-Weiland, H. Follmann and G. Auling, Biochem.
Byophys. Res. Commun., 1981, 102, 1276; (b) A. Willing, H. Follmann
and G. Auling, Eur. J. Biochem., 1988, 178, 603; (c) U. Griepenburg, G.
Lassmann and G. Auling, Free Radical Res., 1996, 26, 473.
3
(a) P. Nordlund, B. M. Sjöberg and H. Eklund, Nature, 1990, 345, 593;
(b) M. Atta, P. Nordlund, A. Aberg, H. Eklund and M. Fontecave, J. Biol.
Chem., 1992, 267, 20682; (c) P. J. Riggs-Gelasco, L. Shu, S. Chen, D.
Burdi, B. H. Huynh, L. Que, Jr. and J. Stubbe, J. Am. Chem. Soc., 1998,
120, 849.
4 R. Hage, Recl. Trav. Chim. Pays-Bas, 1996, 115, 385; M. T. Caudle, P.
Riggs-Gelasco, A. K. Gelasco, J. E. Penner-Hahn and V. L. Pecoraro,
Inorg. Chem., 1996, 35, 3577; K. Wang and J. M. Mayer, J. Am. Chem.
Soc., 1997, 119, 1470; R. Ruiz, A. Aukauloo, Y. Journaux, I. Fernández,
J. R. Pedro, A. L. Roselló, B. Cervera, I. Castro and M. C. Muñoz, Chem.
Commun., 1998, 989; G. B. Shul'pin, G. Süss-Fink and L. S. Shul'pina, J.
Mol. Catal. A, 2001, 170, 17 and references cited therein.
(
entry 3). The oxidation of ethylbenzene and diphenylmethane
afforded mixtures of the corresponding alcohol and ketone
exclusively (entries 4 and 5, respectively). The total yields of
benzylic oxygenation products followed the trend toluene <
ethylbenzene < diphenylmethane (entries 3–5). Indeed, the
oxidation efficiency along this series of alkyl arenes PhCH
=
2
R (R
5
R. L. Rardin, W. B. Tolman and S. J. Lippard, New J. Chem., 1991, 15,
417.
H, Me, Ph) correlates directly with the C–H bond strength,
thus suggesting that C–H bond cleavage is the rate-determining
step of the catalytic cycle. Further kinetic studies are in progress
to determine the detailed mechanism and the exact chemical
nature of the active oxidant in these biomimetic oxidations.
This work was supported by the Dirección General de
Enseñanza Superior e Investigación Científica (Spain) through
projects PB97-1411 and PB97-1397. R. R. thanks the Minis-
terio de Ciencia y Tecnología (Spain) for a grant. We are
specially thankful to Pedro Palanca for the assistance with the
GLC measurements.
6 (a) K. Wieghardt, U. Bossek, B. Nuber, J. Weiss, J. Bonvoisin, M.
Corbella, S. E. Vitols and J. J. Girerd, J. Am. Chem. Soc., 1988, 110,
7
398; (b) J. B. Vincent, H. L. Tsai, A. G. Blackman, S. Wang, P. D. W.
Boyd, K. Folting, J. C. Huffman, E. B. Lobkovsky, D. N. Hendrickson
and G. Christou, J. Am. Chem. Soc., 1993, 115, 12353; (c) T. Tanase and
S. J. Lippard, Inorg. Chem., 1995, 34, 4682; (d) R. Ruiz, C. Sangregorio,
A. Caneschi, P. Rossi, A. B. Gaspar, J. A. Real and M. C. Muñoz, Inorg.
Chem. Commun., 2000, 3, 361.
H. Oshio, E. Ino, I. Mogi and T. Ito, Inorg. Chem., 1993, 32, 5697; J.
Cano, G. De Munno, J. L. Sanz, R. Ruiz, F. Lloret, J. Faus and M. Julve,
J. Chem. Soc., Dalton Trans., 1994, 3465.
7
Chem. Commun., 2001, 2102–2103
2103