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Metalloporphyrin-Catalyzed Hydroxylation of Cyclohexane by Alkyl Hydroperoxides Pronounced Efficiency of Iron-Porphyrins.

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droperoxides, peracids, or iodosylbenzenel''. Evidence has
been presented for involvement of a high valency iron-oxo
species as the active oxygen transfer
Very few
chemical systems are known to efficiently catalyze alkane
hydroxylation under such mild conditions""]. Very recently,
iron-porphyrins have been shown to catalyze iodosylarenesupported hydroxylations of nonactivated C-H b o n d ~ l ~ . ~ ' .
As a part of our effort to understand the mechanisms of the
reactions between hemoproteins or metalloporphyrins and
two-electron oxidizing agentsIS1,and to define good catalysts
for hydroxylation of alkanes by readily available single oxygen donors, we have compared, in the present study, the abilities of various metalloporphyrins to catalyze cyclohexane
hydroxylation by alkyl hydroperoxides@'.
Cumyl hydroperoxide, C6H5C(CH3),00H, is stable for
days in benzene-cyclohexane (1:l) at 20°C. Addition of a
catalytic amount of rneso-tetraphenylporphyrin-iron(rrr)
chloride, Fe(TPP)Cl, to this mixture leads to fast decomposition of the hydroperoxide (&,2= 1 min) with formation of a
nearly stoichiometric amount of cumenol, C6H5C(CH3)20H,
(95%) and acetophenone in minor quantities (= 2-4%).
Study of the reaction mixture by HPLC and GLC also shows
a concomitant formation of cyclohexanol and cyclohexanone
with final yields (reached after about 10 min) of 40 and 20%
based on starting hydroperoxide171. These products were also
identified by IR and 'H-NMR after distillation or silica gel
chromatography of the reaction mixture. Visible spectroscopy shows that Fe(TPP)Cl is unchanged at the end of the
reaction and therefore behaves as a true catalyst. Very similar yields of cyclohexanol and cyclohexanone are obtained
under anaerobic conditions (argon), the reaction being only
slightly faster than in the presence of 02.Taking into account that two moles of oxidant are necessary for cyclohexa-
stabilization is reached for hy = 1/2 hx. A glance at the usual
parameter
shows that this situation cannot be
reached with the the common heteroatoms (N, 0, S, etc.) but
is more nearly approached the greater hx and the smaller hy,
i. e. the more pronounced the donor and acceptor properties
of the substituents.
Figure 2 shows, furthermore, that the stabilization of the
system substituted by captodative groups is greater than the
sum of the substituent effects: on using the given parameter
values, the interaction of the radical center with the acceptor
group -C=X or with the donor group -Y results in a stabilization of the =-system by 0.81 6 or 0.68 6, respectively;
the overall captodative stabilization is 1.676, i. e. O . l S @
greater than the sum of the individual effects.
A quantitative determination of the optimum radical stabilization on the basis of the donor and acceptor properties
of the substituents taking into consideration electron-interaction effects is possible[71with the LCFO modeF".
Received: June 2, 1980 [Z 597 IE]
German version: Angew. Chem. 92, 937 (1980)
[l] H G' Viehe, R. Merenyi, L. Stella, 2. Janousek, Angew. Chem. 91, 982
(1979); Angew. Chem. Int. Ed. Engl. 18,917 (1979).-I thank Prof. Viehe for
a strmulating discussion of the principle of captodative substitution.
[2] M. Klessinger, W. Lultke, Tetrahedron 19, Suppl. 2, 315 (1963).
[3] M J. S. Dewar, R. C. Dougherty: The PMO Theory of Organic Chemistry.
Plenum Press, New York 1975.
14) E. Hezibronner. H. Bock: Das HMO-Modell und seine Anwendung. Vol. 1 .
Verlag Chemie, Weinheim 1968, p. 179. The HMO Model and its Application. Wiley, London, and Verlag Chemie, Weinheim 1976, p. 179.
[5] A . Slreitwieser. Molecular Orbital Theory for Organic Chemists. Wiley, New
York 1961
[6] M. Klessinger, Theor. Chim. Acta 49, 77 (1978).
171 M. Klessinger, W. Merker, unpublished; cf. W Merker, Diplomarbeit, Unlversitat Munster 1980.
Table 1 . Cyclohexane oxidation by cumyl hydroperoxide [a] with various catalysts (molar ratio 120:1:0.05) [b]
Catalyst
Yield (X;][cl
after 15 min
Fe(TPP)CI
Cyclohexanol
Cyclohexanone
1,,2 of
ChH5C(CH3)2-OOH
40
20
1-2
rnin
TPPHz
o r FeC13
or FeC12
Co"(TPP)
[d]
0 [el
45
M"(TPP)
M = Cu. Ni, Zn,
M'"(TPP)O
M = Ti, V
Mn"'(TPP)CI
Os(TPP)(CO)(py)
[dl
0
1
5%
2 5%
3.5 h
or Mg
0
14
0
23
0 [el
0
(25 after 10 d)
0.5
(12% after 10 d)
[el
0.3 min
M
lrl
3d
[a] Commercial (Fluka) samples containing 30% cumene; same results obtained with pure hydroperoxide with Fe(TPP)CI. [b] Addition of 50 m M hydroperoxide to 6 ml of
a benzene/cyclohexane mixture (1 : 1) containing 2.5 mmol I - ' catalyst. FeC12 and FeCI, were first dissolved in the minimum amount of CH3CN. [cl Based on starting hydroperoxide. [d] The visible spectrum of the porphyrin (in benzene for Os(TPP)(CO)(py) and in pyridine for Co(TPP)) is greatly modified at the end of the reaction. [el 5%
cyclohexanol after 20 d. [fl No significant decomposition of the hydroperoxide after 2 d.
Metalloporphyrin-Catalyzed Hydroxylation of
Cyclohexane by Alkyl Hydroperoxides:
Pronounced Efficiency of Iron-Porphyrins'"'
By Daniel Mansuy, Jean-Frangois Bartoli,
Jean-Claude Chottard, and Marc Lange'']
Cytochromes P450 are able to catalyze the hydroxylation
of nonactivated alkanes, either by O2 in the presence of a reducing agent, or by two-electron oxidants such as alkyl hy-
['I
Dr. D. Mansuy. Dr. J. F. Bartoli, Prof. Dr. J. C. Chottard, Dr. M. Lange
Laboratoire de Chimie de I'Ecole Normale Superieure,
Associe au CNRS
24. rue Lhomond, F-75231 Paris Cedex 05 (France)
?*I
We are indebted to Dr. P. Batlioni for supplying Os(TPP)(CO)(py) and
Ti(TPP)(O).
Angew. Chem. Int. Ed. Engi. 19 (1980) No. 11
none formation from cyclohexane, 80%of the oxidizing equivalents of the hydroperoxide are used for cyclohexane oxidation. Neither ferric or ferrous chloride nor the free porphyrin
(TPPH,) gives any cyclohexane oxidation in the reaction
conditions (Table 1) indicating that both the metal ion and
its porphyrin ligand are necessary for the catalysis to take
place.
Table 1 compares various rnetalloporphyrins~*~
as catalysts
for cyclohexane oxidation.
From these results, the metalloporphyrins studied can be
divided into three classes. (i) The Cull-, Nili-, Zn"-, Mgii-,
V1"-, and Ti'"-porphyrins are completely inactive in our
conditions. (ii) Co(TPP) and Os(TPP)(CO)(py) are able to
catalyze cyclohexane oxidation, the former even giving a
slightly faster reaction and better yields than Fe(TPP)(Cl),
0 Verlag Chemie, GmbH, 6940 Weinheim. 1980
0570-0833/80/1111~0909
$02.5010
909
but appear greatly modified at the end of the reaction, exhibiting a decreased activity upon further hydroperoxide addition to the reaction mixture. (iii) Fe- and Mn(TPP)CI are
true catalysts found unchanged at the end of the reaction and
exhibiting a constant activity upon new addition of hydroperoxide.
In reactions catalyzed by Fe(TPP)Cl, cumyl- and tert-butyl hydroperoxide give similar results but with better yields
for the former; iodosylbenzene gives lower yields of oxidation products with a very different cyclohexanol/cyclohexanone ratio with an almost exclusive formation of the alcohol
as reported previo~sly~~l
(Table 2). Moreover, an important
irreversible oxidation of the porphyrin ring takes place with
the latter
under our conditions.
Table 2. Cyclohexane oxidation by single oxygen donors catalyzed by
Fe(TPP)CI [a].
Oxidant
Yield [%] after 15 min
CbH,,OH
GHtoO
t1,2 for
reaction
bin1
C~HSC(CH~)~O~H
f-Bu02H
C~HSIO
[bl
40
20
12
1-2
5
15
20
12
1
fa] Same conditions as Table 1. [b] Not completely soluble in the medium at the
beginning of the reaction.
In biological systems, hydroperoxide reactions are generally catalyzed by iron-porphyrins; it is noteworthy that we also
found an iron-porphyrin to be the best catalyst in our systern[’’.
Received: March 21. 1980;
revised. September 15, 1980 [Z 598 I€]
German version: Angew. Chem. 92, 938 (1980)
CAS Registry numbers:
Cyclohexane, 110-82-7; cyclohexanol, 108-93-0 cyclohexanone, 108-94-1;cumyl
hydroperoxide, 80-15-9
a ) V. Ullrich, Top. Curr. Chem. 83, 68 (1979); b) A. I?. Rahrmtula, P. J
O’Brien. E. G. Hrycuy. J A . Peferson, R. W. Estabrook, Biochem. Biophys.
Res. Commun. 60, 695 (1974); c) E Lichfenberger, W. Nastainczyk, V. UII~
rich, ibrd. 70, 939 (1976); d) G. D. Nordblom, R. E. While, M. J Coon, Arch.
Biochem. Biophys. 175. 524 (1976).
J T. Groves. G. A. McClusky, R. E. While, M. J. Coon, Biochem. Biophys.
Res. Commun. 81, 154 (1978).
J T Groves, T E. Nemo, R. S. Myers, J. Am. Chem. SOC.101, 1032 (1979).
C. K . Chnng. M. S. Kuo, J. Am. Chem. SOC.101, 3413 (1979).
a) D. Mansuy, J. P. Bntlioni, J. C. Chortard, V. Ullrich, J . Am. Chem. SOC.
101. 3971 (1979); b) D. Monsuy, J C. Choftard, M . Lange. J. P. Battionr. J.
Mol. Catal. 7, 215 (1980).
Preliminary results concerning tBuOOH supported hydroxylation of cyclohexane catalyzed by an iron-porphyrin have been recently mentioned. J. T.
Groves,Symposium on Microsomes and Drug Oxidation, Ann Arbor 1979.
Treatment of 50 mmol of cyclohexanol (in benzene) by 50 mmol of cumyl
hydroperoxide in the presence of 2.5 mmol of Fe(TPP)Cl at 20°C leads to cyclohexanone in 10-15% yield.
a) J. H. Fuhrhop, K. M. Smith in K. M. Smifh: Porphyrins and Metalloporphyrins. Elsevier, Amsterdam t975, p. 757; b) J W. Buchler in D. Dolphin;
The Porphyrins. Vol. I. Academic Press, New York 1978.
Preliminary results show that Ru(TPP)(PEt,)2 is also an active catalyst leading to 35% cyclohexanol and 12% cyclohexanone within a few minutes at
20 “C under the conditions of Table I . but appears partially modified at the
end of the reaction.
Separation of the Enantiomers of
2-Hydroxycarboxylic Acids on
Optically Active Stationary Phases
By Wilfried A . Konig, Susanne Sievers, and
Uwe Schulze“’
The direct gas chromatographic separation of optical antipodes on chiral stationary phases has already been achieved
r] Prof. Dr. W. A. Konig, DipLChem. S
Sievers, U. Schulze
lnstitut fur Organische Chemie und Biochemie
der Universitat
Martin-Luther-King-Platz 6, 0.2000 Hamburg 13 (Germany)
910
0 Verlag Chemie, GmbH, 6940 Weinheim, 1980
in the case of amino acids, amino alcohols, amines and 2-alkylcarboxamides[‘.21.In these cases the separation was attributed exclusively to selective hydrogen bonding interact i o n ~ [ * We
, ~ ~have
.
shown with several model species that e.g.
also dipole-dipole interactions effect an enantiomer separationc4’.
Stationary phases developed for the separation of amino
acids1’.’], however, are not suitable for the separation of enantiomers of nitrogen-free compounds. We have now succeeded for the first time in separating also the trifluoroacetylated esters of 2-hydroxycarboxylic acids on some novel stationary phases. Acids of this type are metabolic products of
higher organisms1s1and constituents of important brain glycolipidsI6].
As stationary phases we used the L-(9-mandelic acid derivatives (1)-(4) (Table I), coated on the inner surface of
glass capillary columns (borosilicate glass, 40 m, 0.2 mm internal diameter). The separation factors for the trifluoroacetylated compounds investigated are presented in Table 1. As
expected, the respective (9-enantiomers are always retarded
on phases (1)-(4) which contain the (5‘)-mandelic acid as
structural unit. The elution sequence was checked in the case
of the enantiomers of mandelic acid, alanine, valine, valinol,
2-aminopentane, and a-phenylethylamine.
The amino acid enantiomers are eluted in the reverse order on the phase diastereomeric to (I),with (R)-a-phenylethylamine. The separation factors are expectedly smaller
than in the case of (1) (e.g. DL-mandelic acid: a = 1.007 at
70 “C;DL-alanine: a = 1.012 at 80 “C; DL-valinol: a = 1.013 at
SOOC). It can be concluded from this behavior that both chiral centers of the stationary phase influence the separation.
As shown by the results with phase (3), a single asymmetic
center can also suffice for “chiral recognition” (cf. Table 1).
Interestingly, phases (1) and (4) show a noticeable selectivity for the enantiomers of mandelic acid, while the homologous racemic 3-phenyllactic acid is separated only on phases
(2) and (3). This is an indication that “chiral recognition” is
favored by a close structural relationship between the interacting chiral partners. Also on cyclohexyl O-benzyloxycarbonyl-(S)-mandelate as stationary phase, of the hydroxy
acids only DL-mandelic acid is separated. Remarkably, in
this case “chiral recognition” is even observed in a nitrogenfree system.
The phases (2) and (3), on which also aliphatic hydroxy
acids are separated, behave less specifically. Hydrogen bonding interactions are in any case of secondary importance for
the selectivity of the phases (2) and (3) for hydroxy acids,
since at most one hydrogen bridge can be formed between
the phase and the substrate. This argument is further supported by the observation that the phases (1) and (4),i.e. in
the cases where two hydrogen bridge bonds are possible,
show rather less selectivity towards hydroxy acids than the
other two phases. On the other hand, an essential contribution of hydrogen bonding interactions cannot be ruled out
for the separation of the amines on phase (4).
The possibility of separating enantiomeric hydroxy acids
on phases such as (2) and (3) or similar compounds extends
the scope of gas chromatography as a rapid method for configurational analysis. The partial separation of the enantiomers of trifluoroacetylated I-phenylethanol on O-benzyloxycarbonyl-(S)-3-phenyllactic acid tert-butylamide indicates
that diastereomeric interactions can be exploited for the separation of enantiomers also in the case of other nitrogen-free
compounds.
Preliminary results with polymer-based phases of this type
for enantiomer separation indicate that this method of analysis will undoubtedly gain practical importance.
0570-0833/80/1111-0910
$02.50/0
Angew. Chem. Int. Ed. Engl I 9 (1980) No. I I
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alkyl, efficiency, metalloporphyrins, hydroperoxide, pronounced, iron, cyclohexane, porphyrio, hydroxylation, catalyzed
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