H2O2-dependent Fe-catalyzed oxidations: Control of the active species

Article abstract of DOI:10.1002/1521-3773(20010302)40:5<949::AID-ANIE949>3.0.CO;2-4

Manipulation of the coordination sphere of an Fe¹¹ ion can be used to tune the balance between different catalytic pathways for oxidation (OH versus iron-based oxidant; see scheme). This reinvestigation of Fenton chemistry uses the iron complex shown as a mechanistic probe.

Full text of DOI:10.1002/1521-3773(20010302)40:5<949::AID-ANIE949>3.0.CO;2-4

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in italics: IR (film): nÄmax ˆ 2929, 1757, 1734, 1654, 1618, 1560, 1515,
Experimental Section
1
1448, 1396, 1247, 1124, 739, 618 cm
;
1H NMR (600 MHz, CDCl3):
d ˆ 9.04 (d, J ˆ 7.8 Hz, 1H; NH), 8.93 (s, 1H; H-1''), 7.23 and 6.84 (d Â
2, J ˆ 8.6 Hz, 1H  2; PMBM), 7.21 (d, J ˆ 8.1 Hz, 1H; H-4'), 7.19 (d,
J ˆ 8.0 Hz, 1H; H-5'), 7.04 (s, 1H; H-4''), 6.80 (s, 1H; H-5''), 6.34 (m,
1H; Allyl), 6.07 (d, J ˆ 2.2 Hz, 1H; H-12), 5.84 (m, 1H; Alloc), 5.73
(m, 1H; H-7'), 5.61 (br dd, J ˆ 2.2, 3.5 Hz, 1H; H-11), 5.49 and 5.29
(br dd  2, J ˆ 1.3, 17.1 Hz, 1H  2; Allyl), 5.41 and 5.23 (br dd  2,
J ˆ 1.0, 10.3 Hz, 1H  2; Alloc), 5.40 (br s, 1H; H-1''''), 4.81 and 4.78
(d  2, J ˆ 7.0 Hz, 1H  2; PMBM), 4.71 (sept, 1H; H-10''), 4.53 ± 4.48
(brs ‡ m, 6H; PMBM ‡ Allyl ‡ Alloc), 4.26 (dd, J ˆ 12.6, 6.0 Hz,
1H; Ha/b-14), 4.22 (d, J ˆ 8.6 Hz, 1H; Ha/b-8), 4.19 (d, J ˆ 3.6 Hz, 1H;
General protocol: The 2-deoxythioglycoside (0.1 mmol), alcohol
(1.5 equiv), and DTBMP (4.5 equiv) were dissolved in CH2Cl2 (1.0 mL)
under argon, using light-protected glassware. After the mixture had been
stirred for 1.5 h at 238C over molecular sieves (4 Š, <5 microns, freshly
activated), powdered AgPF6 (3 ± 4 equiv) was added at O8C. When the
reaction was complete (0.5 ± 2 h), pyridine (50 equiv) was added, and the
mixture was stirred for a further 0.5 h. Filtration (celite pad, diethyl ether/
n-hexane (1:4)), concentration, and chromatographic purification provided
the 2-deoxyglycoside.
Received: August 22, 2000 [Z15678]
H-10), 4.17 (d, J ˆ 12.6 Hz, 1H; Hb/a-14), 4.08 (d, J ˆ 8.6 Hz, 1H; Hb/a
-
8), 4.06 (s ‡ m, 4H; CH3-14'' ‡ H-5''''), 4.03 (d, J ˆ 6.2 Hz, 1H; H-13),
3.91 (s, 3H; CH3-13''), 3.72 (s, 3H; PMBM), 3.26 (d, J ˆ 9.3 Hz, 1H;
H-4''''), 3.13 (dd, J ˆ 14.7, 4.7 Hz, 1H; Ha/b-8'), 3.09 and 3.00 (brd and
d, J ˆ 16.4 Hz, 1H  2; CH2-5), 2.62 (dd, J ˆ 14.7, 11.6 Hz, 1H; Hb/a-8'),
[1] Reviews on the formation of 2-deoxyglycosides with special reference
to natural products: a) C. M. Marzabadi, R. W. Franck, Tetrahedron
2000, 56, 8385 ± 8417; b) K. Toshima, K. Tatsuta, Chem. Rev. 1993, 93,
1503 ± 1531.
2.14 (d, J ˆ 14.4 Hz, 1H; Ha/b-2''''), 1.85 (dd, J ˆ 14.4, 4.3 Hz, 1H; Hb/a
-
2''''), 1.49 and 1.43 (s  2, 3H  2; acetonide), 1.46 and 1.45 (d  2, J ˆ
5.9 Hz, 3H  2; CH3-12'' and CH3-13''), 1.33 (d, J ˆ 6.3 Hz, 3H; CH3-
6''''), 1.21 (s, 3H; CH3-7''''), 1.00 (m, 18 H; TES Â 2), 0.68 (m, 12 H,
[2] Indirect routes to stereoselectively prepare 2-deoxy-gluco-pyrano-
sides are well established: a) K. Takeuchi, S. Higuchi, T. Mukaiyama,
Chem. Lett. 1997, 969 ± 970, and references therein; b) W. R. Roush,
C. E. Bennett, J. Am Chem. Soc. 1999, 121, 3541 ± 3542, and references
therein. For notable direct procedures, see: c) K. C. Nicolaou, R. E.
Dolle, D. P. Papahatjis, J. L. Randall, J. Am. Chem. Soc. 1984, 106,
4189 ± 4192; d) R. W. Binkley, D. J. Koholic, J. Org. Chem. 1989, 54,
3577 ± 3581; e) S.-I. Hashimoto, A. Sano, H. Sakamoto, M. Nakajima,
Y. Yanagiya, S. Ikegami, Synlett 1995, 1271 ± 1273; f) H. Schene, H.
Waldmann, Synthesis 1999, 1411 ± 1422.
[3] For indirect a-selective methods to form 2-deoxy-allo-pyranosides,
see: a) K. Tatsuta, A. Tanaka, K. Fujimoto, M. Kinoshita, J. Am.
Chem. Soc. 1977, 99, 5826 ± 5827; b) J. Thiem, S. Köpper, Tetrahedron
1990, 46, 113 ± 138; c) K. Toshima, S. Mukaiyama, Y. Nozaki, H.
Inokuchi, M. Nakata, K. Tatsuta, J. Am. Chem. Soc. 1994, 116, 9042 ±
9051; d) K. Toshima, Y. Nozaki, S. Mukaiyama, T. Tamai, M. Nakata,
K. Tatsuta, M. Kinoshita, J. Am. Chem. Soc. 1995, 117, 3717 ± 3727; for
rare examples of direct approaches, see: e) K. C. Nicolaou, S. P. Seitz,
D. P. Papahatjis, J. Am. Chem. Soc. 1983, 105, 2430 ± 2434; f) D. A.
Evans, S. W. Kaldor, T. K. Jones, J. T. Clardy, J. Stout, J. Am. Chem.
Soc. 1990, 112, 7001 ± 7031; g) S. F. Martin, T. Hida, P. R. Kym, M.
Loft, A. Hodgson, J. Am. Chem. Soc. 1997, 119, 3193 ± 3194.
[4] Isolation of kedarcidin and chromophore structure: a) J. E. Leet,
D. R. Schroeder, D. R. Langley, K. L. Colson, S. Huang, S. E. Klohr,
M. S. Lee, J. Golik, S. J. Hofstead, T. W. Doyle, J. A. Matson, J. Am.
Chem. Soc. 1993, 115, 8432 ± 8443; b) revised structure: S. Kawata, S.
Ashizawa, M. Hirama, J. Am. Chem. Soc. 1997, 119, 12012 ± 12013;
c) paramagnetic behavior of chromoprotein complex, cf. C-1027: M.
Hirama, K. Akiyama, T. Tanaka, T. Noda, K.-I. Iida, I. Sato, R.
Hanaishi, S. Fukuda-Ishisaka, M. Ishiguro, T. Otani, J. E. Leet, J. Am.
Chem. Soc. 2000, 122, 720 ± 721.
‡
TES Â 2); HR-MS (MALDI-TOF) m/z for C76ClH101N2NaO20Si2
‡
[M‡Na] : calcd: 1475.6052, found: 1475.6000.
[10] Y. Kataoka, O. Matsumoto, K. Tani, Chem. Lett. 1996, 727 ± 728.
[11] For bioactive analogues of 21: H. Imai, T. Oishi, T. Kikuchi, M.
Hirama, Tetrahedron 2000, 56, 8451 ± 8459.
[12] Schene and Waldmann have also reported the direct formation of
2-deoxyglycosides under extremely mild conditions, but through the
prolonged exposure of glycosyl fluorides, trichloroacetimidates, or
phosphites to LiClO4/Et2O; interestingly, they too observed the
apparent superior a-selective effect of the PF6 counteranion, see
ref. [2f].
H2O2-Dependent Fe-Catalyzed Oxidations:
Control of the Active Species**
Â
Â
Yasmina Mekmouche, Stephane Menage,*
Carole Toia-Duboc, Marc Fontecave,
Jean-Baptiste Galey, Colette Lebrun, and
Â
Jacques Pecaut
In memory of Olivier Kahn
[5] Our synthetic studies: a) F. Yoshimura, S. Kawata, M. Hirama,
Tetrahedron Lett. 1999, 40, 8281 ± 8285; b) M. J. Lear, M. Hirama,
Tetrahedron Lett. 1999, 40, 4897 ± 4900; c) S. Kawata, M. Hirama,
Tetrahedron Lett. 1998, 39, 8707 ± 8710; d) M. Hirama, Pure Appl.
Chem. 1997, 69, 525 ± 530; e) S. Kawata, F. Yoshimura, J. Irie, H.
Ehara, M. Hirama, Synlett 1997, 250 ± 252; f) K. Iida, M. Hirama, J.
Am. Chem. Soc. 1995, 117, 8875 ± 8876; 1994, 116, 10310 ± 10311.
[6] Notable work from other groups: a) A. G. Myers, S. D. Goldberg,
Angew. Chem. 2000, 112, 2844 ± 2847; Angew. Chem. Int. Ed. 2000, 39,
2732 ± 2735; b) A. G. Myers, Y. Horiguchi, Tetrahedron Lett. 1997, 38,
4363 ± 4366; c) S. Caddick, V. M. Delisser, Tetrahedron Lett. 1997, 38,
2355 ± 2358; d) P. Magnus, R. Carter, M. Davies, J. Elliot, T. Pitterna,
Tetrahedron 1996, 52, 6283 ± 6306.
[7] a) D. Crich, S. Sun, J. Am. Chem. Soc. 1998, 120, 435 ± 436; b) Y. Ito, T.
Ogawa, Tetrahedron Lett. 1988, 29, 1061 ± 1064; c) P. Fugedi, P. J.
Garegg, Carbohydr. Res. 1986, 149, C9-C12; for other thioglycoside
activation methods, see: d) P. J. Garegg, Adv. Carbohydr. Chem.
Biochem. 1997, 52, 179 ± 205.
[8] K. Suzuki, H. Maeta, T. Matsumoto, Tetrahedron Lett. 1989, 30, 4853 ±
4856.
[9] Selected physical data for a-15; for ease of comparison to the
kedarcidin chromophore, the numbering system of ref. [4a,b] is used
and the key 1H NMR signals that define the a-l-mycaroside are given
The reaction of ferrous ion with hydroperoxides has been
investigated for more than a century (Fenton chemistry), and
yet the mechanism has still not been satisfactorily rational-
ized. The nature of the reactive species has always been a
matter of debate, oscillating between hydroxyl or alkoxyl
Â
[*] Dr. S. Menage, Y. Mekmouche, Dr. C. Toia-Duboc, Prof. M. Fontecave
Â
Laboratoire de Chimie et Biochimie des Centres Redox Biologiques
Â
Universite Joseph Fourier/DBMS/CEA, UMR CNRS 5047
Â
17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)
Fax : (‡33)476889124
E-mail: smenage@cea.fr
Dr. J.-B. Galey
Â
Â
LꢁOreal Research Recherche Avancee
Á
1 avenue Eugene Schueller, 93600 Aulnay sous bois (France)
Â
C. Lebrun, Dr. J. Pecaut
Service de Chimie Inorganique et Biologique
DRFMC CEA-Grenoble (France)
[**] We thank the EU for financial support (TMR program
(ERBMRFXCT980207).
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radicals and an oxene species.[1, 2] Moreover, the discovery
that non-heme ± iron proteins can oxidize inert substrates
(e.g., alkanes) selectively has stimulated chemists to reinves-
tigate the reaction of non-heme ± iron complexes with dioxy-
gen- and oxygen-derived oxidants.[3] In fact, dinuclear,
methane monooxygenase,[4] and mononuclear non-heme ±
iron enzymes such as isopenicillin N synthase, 2-oxo-gluta-
rate-dependent enzymes, and pterin-dependent phenylala-
nine, tyrosine, tryptophan hydroxylases are proposed to carry
out a two-electron oxidation via an FeIV ± oxo moiety.[5]
Herein, we report on the oxidation mechanism by using iron
complexes of the ligand N,N'-bis(pyridin-2-ylmethyl)-N,N'-
bis(3,4,5-trimethoxybenzyl)ethane-1,2-diamine (L) as a sub-
strate.[6] This ligand displays several potential oxidation sites,
in particular the methylene groups and phenyl rings from
benzylic moieties; the latter are known to be very reactive
towards hydroxyl radicals, leading to the formation of
phenol.[7] Herein we compare the catalytic properties of
two complexes, [FeIILCl2] ´ 0.25H2O (1 ´ 0.25H2O) and
[FeIIL(CH3CN)2(ClO4)2] ´ 3H2O (2(ClO4)2 ´ 3H2O), during ox-
idation of ligand L (Scheme 1) and of various substrates by
H2O2 in acetonitrile. With such probes we demonstrate that
complex 1 behaves as a typical Fenton reagent, whereas
complex 2 functions through metal-based mechanisms. This
shows that for this class of iron complexes the reactivity can
be tuned by modifying the simple monodentate ligand.
The synthesis of complexes 1 and 2 started with mixing
equimolar amounts of FeCl2 ´ 4H2O or Fe(ClO4)2 ´ 6H2O,
respectively, and the ligand L in CH3OH under argon.
Addition of diethyl ether to the CH3OH solution afforded
in both cases a yellow powder. Slow diffusion of diethyl ether
into a solution of these powders in acetonitrile afforded
crystals suitable for X-ray structure analysis (Figure 1).[8] The
crystal structures of 1 ´ CH3CN and 2(PF6)2 ´ 2.5 CH3CN ´
0.25 CH3OH ´ 0.5 H2O reveal that in each case the Fe center
is octahedrally coordinated; the coordination differs with
respect to the nature of the two ligands that occupy the two
cis-positioned open sites of the FeII coordination sphere: in
compound 1 they are filled by chloride ions, whereas in 2 they
are filled by acetonitrile solvent molecules. This difference
confers a different spin state to the ferrous ion in the solid
state only (shown by the longer Fe N distances in 1 than
in 2). Complexes 1 and 2 displayed significantly different
Figure 1. ORTEP representation of complexes 1 and 2. Hydrogen atoms
have been omitted for clarity. Selected bond lengths [Š]: for 1: Fe-N(1)
2.3272(7), Fe-N(2) 2.2120(6), Fe-N(3) 2.3012(6), Fe-N(4) 2.2228(6); for 2:
Fe(1)-N(11) 1.939(4), Fe(1)-N(12) 1.942(4), Fe(1)-N(2) 1.986(4), Fe(1)-
N(4) 1.988(4), Fe(1)-N(1) 2.055(4), Fe(1)-N(3) 2.061(4).
Scheme 1. Ligand oxidation of complexes 1 and 2 to give LOH and L1,
respectively.
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resonance signals in their 1H NMR spectra in acetonitrile
between d ˆ 160 and 20 (data not shown).
anone (yield based on the oxidant 38%; alcohol/ketone 8/1)
occurred only with complex 2, whereas equimolar amounts of
alcohol and ketone were detected with complex 1 as the
catalyst (yield based on the oxidant 6%). The origin of the
oxygen atom incorporated into cyclohexane has been deter-
mined in both cases.[18] When 10 equivalents of H218O2 were
mixed with 2 in the presence of 1000 equivalents of H216O,
47(Æ3)% of the cyclohexanol was 18O-labeled. This was
confirmed when 18O-labeled water and unlabeled H2O2 were
used. In contrast, with complex 1 and H218O2, cyclohexanol
was fully labeled with the oxygen atom from the oxidant; no
exchange with water was observed. Finally, only complex 2
was capable of epoxidizing cyclooctene (30% yield based on
the oxidant) and cyclohexene (20% yield based on the
oxidant) substrates.[19] Notably, in the case of cyclohexene,
allylic oxidation products were the major products regardless
of the catalyst (only 2-cyclohexen-1-ol was formed; yield
10%).
When an excess of H2O2 was added to a solution of complex
1 (1 mm) in acetonitrile under argon, the solution immediately
turned blue. Titration studies showed that only two equiv-
alents of hydrogen peroxide were required to achieve
maximal intensity of a new transition at 740 nm. The new
species was characterized as a mononuclear phenolatoiron(iii)
complex [FeIII(LO)Cl2] (Scheme 1) based on the following
spectroscopic signatures: 1) the transition at 740 nm was
assigned to a charge-transfer band from an oxygen atom of
the phenolato ligand to an iron(iii) center;[9] 2) the positive-
ion mode ESI mass spectrum of the resulting solution
displayed only one molecular peak at m/z 708 (100%)
‡
attributed to [Fe(L H)Cl ‡ O] whose isotopic pattern was
in agreement with the theoretical one; 3) an isotropic signal
was observed at g ˆ 4.3 in the EPR spectrum of the resulting
solution.
The oxidized ligand was then extracted and characterized[10]
by ESI-MS and 1H NMR analysis as N-(2-hydroxy-3,4,5-
trimethoxybenzyl)-N,N'-bis(pyridin-2-ylmethyl)-N'-(3,4,5-tri-
methoxybenzyl)ethane-1,2-diamine which results from the
hydroxylation at the ortho position of one phenyl ring of the
ligand.[11] HPLC titration showed that more than 70(Æ10)%
of the ligand L had been transformed into LOH and only
6(Æ5)% of the starting ligand was found unconverted.[12]
Mass spectrometric analysis of the modified ligand LOH
obtained when H218O2 was used as an oxidant established that
the oxygen atom incorporated came exclusively from the
oxidant. Control experiments in the presence of H216O in the
H218O2-dependent reaction did not alter the yield of 18O-atom
incorporation. Aromatic hydroxylation of the ligand in iron
complexes has been previously reported.[6, 13]
All these data taken together imply two different oxidative
pathways depending upon the catalyst structure. In the case of
complex 1, the quasi-quantitative hydroxylation of the
pendant phenyl ring of the ligand, the origin of the oxygen
atom from the oxidant, the poor (stereo)selectivity during
alkane oxidation, and the lack of epoxidation strongly suggest
.
that freely diffusing OH is the active species.[20, 21] In contrast,
in the case of complex 2, the high stereoselectivity, the solvent
oxygen atom exchange, the oxidation of the closest C H bond
of the ligand (the methylene group of the benzyl ring), and the
reasonable yield of epoxides can be interpreted with the
involvement of an iron ± oxo complex as an active species,
allowing a better control of the substrate radicals (ªcaged
radicalsº) by the metal center. The participation of free
hydroxyl radicals when catalyst 2 was used is thus unlikely.
The presence of products labeled with oxygen atoms from
both water and the oxidant has already been observed in
oxidations dependent on heme± and non-heme ± iron com-
In contrast, addition of H2O2 to complex 2 ´ (ClO4)2 under
the same conditions as for 1 did not result in any intense color
change.[14] Moreover, extraction of the organic material from
the reaction mixture and analysis by HPLC led to the
recovery of 65(Æ10)% of the unconverted ligand L and the
isolation of a new modified ligand L1 in 14(Æ5)% yield (see
plexes and has been explained by a postulated ªoxo ± hydroxo
[22±25]
tautomerismº of the FeIV or FeV O intermediate.
ˆ
One possible explanation for the difference between 1 and
2 is the presence of labile sites only in 2, which thus allow the
binding of H2O2 to the metal center. Complex 1 would thus
react with H2O2 through an outer-sphere electron transfer
1
Scheme 1). L1 was characterized by ESI-MS and H NMR
analysis[15, 16] as N,N'-bis(pyridin-2-ylmethyl)-N-(3,4,5-trime-
thoxybenzyl)ethane-1,2-diamine which resulted from an N-
dealkylation of the L ligand. No evidence for the formation of
LOH in this reaction was obtained. Clearly, the nature of the
two monodentate ligands (Cl vs. CH3CN) influenced the
selectivity of the ligand oxidation, suggesting the participation
of different oxidative species.
.
resulting in formation of OH . In contrast, with complex 2 an
iron ± peroxo species, similar to peroxo complexes previously
observed during H2O2-dependent reactions, can be transiently
formed as a precursor for a metal-based oxidative species.[26]
The nature of this species remains to be established. We favor
To distinguish between these reactive species, the catalytic
properties of the 1/H2O2 or 2/H2O2 combination towards
external substrates was studied.[17] Only 2 led to catalytic and
stereoselective alkane hydroxylation under anaerobic condi-
tions. For example, the reaction of cis-1,2-dimethylcyclohex-
ane with 2/H2O2 led to the catalytic formation of cis-1,2-
dimethylcyclohexanol and trans-1,2-dimethylcyclohexanol in
a 10:1 ratio (yield based on the oxidant 20%), whereas the
analogous reaction with the 1/H2O2 combination led to an
equimolar mixture of cis- and trans-1,2-dimethylcyclohexanol
(yield 7%). Furthermore, catalytic oxidation of cyclohexane
to give cyclohexanol and only minor amounts of cyclohex-
a homolytic cleavage of the FeO OH bond, leading to a caged
.
[FeIV O OH ] radical pair.
ˆ
This work further supports the notion that high-valent
.
iron ± oxo species (and not only OH radicals) can be
generated and used as active species in non-heme ± iron
catalysis. Furthermore, it shows that the balance between
.
different catalytic pathways for the oxidation (OH vs. metal-
based oxidant) can be tuned through the manipulation of the
coordination sphere of the ferrous ion.
Received: July 3, 2000
Revised: November 20, 2000 [Z15380]
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COMMUNICATIONS
[1] a) C. Walling, Acc. Chem. Res. 1975, 8, 125; b) P. A. Mc Faul, D. D. M.
Wayner, K. U. Ingold, Acc. Chem. Res. 1998, 31, 159.
higher concentration. Other minor products have been detected but
their structures remain unknown.
[2] a) S. H. Bossman, E. Oliveros, S. Göb, S. Siegwart, E. P. Dahlen, L.
Payawan, M. Straub, M. Wörner, A. M. Braun, J. Phys. Chem. A 1998,
102, 5542; b) D. T. Sawyer, A. Sobkowiak, T. Matsushita, Acc. Chem.
Res. 1996, 29, 409; c) M. Kremer, Phys. Chem. Chem. Phys. 1999, 1, 3595.
[3] a) R. M. Buchanan, S. Chen, J. F. Richardson, M. Bressan, L. Forti, A.
Morvillo, R. H. Fish, Inorg. Chem. 1994, 33, 3208; b) J. Kim, R. G.
Harrison, C. Kim, L. Que, Jr., J. Am. Chem. Soc. 1996, 118, 4373; c) C.
[13] S. J. Lange, H. Miyake, L. Que, Jr., J. Am. Chem. Soc. 1999, 121, 6330.
[14] The reaction mixture contains both mononuclear FeII and FeIII L and
L1 complexes.
[15] 1H NMR (300 MHz, CD3CN, 258C): d ˆ 2.66 (m, 4H; NCH2CH2N),
3.52 (s, 2H; CH2Bz), 3.62 (s, 3H; OCH3), 3.67 (s, 2H; CH2py), 3.69 (s,
6H; OCH3), 3.72 (s, 2H; CH2py), 6.63 (s, 2H; o-HPh); 7.13 (td, 2H; m-
H
py); 7.23 (d, 1H; p-Hpy), 7.43 (d, 1H; p-Hpy), 7.61 (t, 2H; m-Hpy), 8.41
Â
Duboc-Toia, S. Menage, C. Lambeaux, M. Fontecave, Tetrahedron
(dd, 2H, o-Hpy). ESI/MS (CH2Cl2; positive-ion mode): m/z: 423
‡
Lett. 1997, 38, 3727, and references therein; d) M. Kodera, H.
Shimakoshi, K. Kano, Chem. Commun. 1996, 1737; e) D. T. Sawyer,
C. Kang, A. Liobet, C. Redman, J. Am. Chem. Soc. 1993, 115, 5817;
f) D. H. R. Barton, S. D. Beviere, W. Chavasiri, E. Cshuai, D. Doller,
W.-G. Liu, J. Am. Chem. Soc. 1992, 114, 2147.
(100%) for [L1 ‡ H ].
[16] Accordingly, the pendant product of the N-dealkylation of the ligand,
3,4,5-trimethoxybenzaldehyde, has been quantitatively detected.
[17] Experimental conditions: complex/alkane/H2O2 1/1100/10 in acetoni-
trile inside a glove box (dioxygen content less than 1 ppm) using
syringe pump conditions; delivering time ˆ 30 min [complex] ˆ
0.7 mm.
Â
Á
[4] a) A. C. Rosenzweig, C. A. Frederick, S. J. Lippard, P. Nordlund,
Nature 1993, 366, 537; b) J. B. Wallar, J. D. Lipscomb, Chem. Rev. 1996,
96, 2625.
[5] a) L. Que, Jr., R. Y. N. Ho, Chem. Rev. 1996, 96, 2607; b) T. J.
Kappock, J. P. Caradonna, Chem. Rev. 1996, 96, 2659.
[6] S. Menage, J. B. Galey, J. Dumats, G. Hussler, M. Seite, I. Gautier-
Luneau, G. Chottard, M. Fontecave, J. Am. Chem. Soc. 1998, 120,
13370.
[7] G. V. Buxton, C. L. Greenstock, W. P. Helman, A. B. Ross, J. Phys.
Chem. Ref. Data 1988, 17, 513.
[18] The isotope ratio in cyclohexanol has been analyzed by GC/MS on a
reaction mixture directly after reaction. Cyclohexanol was not labeled
in the presence of 18O water under standard conditions.
[19] No 1,2-cyclohexanediol was detected.
[20] A. M. Khenkin, A. E. Shilov, New. J. Chem. 1989, 13, 659.
[21] Notably, [(bpmen)FeIICl2]/H2O2 showed the same stereoselectivity,
selectivity, and catalytic properties as complex 1 (bpmen ˆ N,N'-
dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine). Thus, the
concomitant formation of [Fe(LO)Cl2] is not responsible for the poor
catalytic properties.
Â
Â
[8] Selected physical data for 1: Elemental analysis for 1 ´ 0.25H2O
(C34H42.5Cl2FeN4O6.25)(Mr ˆ 733.4): calcd: C 55.62, H 5.79, N 7.63, Cl
9.68, Fe 7.63; found: C 55.45, H 5.87, N 7.64, Cl 9.75, Fe 7.68; ESI/
[22] a) W. Nam, J. S. Valentine, J. Am. Chem. Soc. 1993, 115, 1772; b) K. A.
Lee, W. Nam, J. Am. Chem. Soc. 1999, 121, 1916.
‡
MS(CH3CN): m/z: 693 (100%) [FeLCl] ; UV/Vis (CH3CN): lmax (e,
1 cm 1): 415 nm (1050). Crystal data of 1 ´ CH3CN: C36H45Cl2Fe-
m
[23] K. Chen, L. Que, Jr., Chem. Commun. 1999, 1375.
[24] J. Bernadou, B. Meunier, Chem. Commun. 1998, 2167.
[25] No hydrogen peroxide dismutation was observed for either complex
in the absence of substrate, apart from the involvement of dioxygen as
an oxygen-atom donor (autooxidation mechanism).
Å
N5O6, Mr ˆ 770.52, triclinic, space group P1, a ˆ 13.1459(2), b ˆ
15.5146 (2), c ˆ 18.5430 (2) Š, a ˆ 92.19(1), b ˆ 98.22(1), g ˆ
99.93(1)8, Vˆ 3679.34(8) Š3, Z ˆ 4, 1calcd ˆ 1.391 gcm
,
m ˆ
3
0.607 mm 1, l ˆ 0.71073 Š, direct methods, R[I > 2s(I)] ˆ 0.0305 for
12229 independent reflections of the 17177 collected, R(all data) ˆ
0.046. Selected physical data for 2: Elemental analysis for 2(ClO4)2 ´
3H2O (C34H48Cl2FeN4O17)(Mr ˆ 911.3): calcd: C 44.80, H 5.26, N 6.15,
Cl 7.78, Fe 6.15; found: C 44.80, H 5.44, N 6.16, Cl 8.22, Fe 5.75; ESI/
Â
[26] a) C. Duboc-Toia, S. Menage, R. Y. N. Ho, L. Que, Jr., C. Lambeaux,
M. Fontecave, Inorg. Chem. 1999, 38, 1261; b) Y. Mekmouche, C.
Â
Duboc-Toia, S. Menage, C. Lambeaux, M. Fontecave, J. Mol. Catal. A
2000, 156, 85; c) C. Kim, K. Chen, J. Kim, L. Que, Jr., J. Am. Chem.
Soc. 1997, 119, 5964.
‡
MS (CH3CN): m/z: 757 (100%) [FeLClO4] ; UV/Vis (CH3CN): lmax
(e, m 1 cm 1): 377 nm (1700). Suitable crystals for an X-ray analysis
were obtained after a metathesis of ClO4 for PF6 anions. Crystal data
of 2(PF6)2 ´ 2.5 CH3CN´ 0.25 CH3OH´ 0.5 H2O: C43.25H57.5F12P2FeN8.5
-
Å
O
6.75, Mr ˆ 1144.22, triclinic, space group P1, a ˆ 13.3988(9), b ˆ
14.5835(9), c ˆ 27.8533 (17) Š, a ˆ 98.096(1), b ˆ 94.746(1), g ˆ
A Route to a Germanium ± Carbon Triple
Bond: First Chemical Evidence for a
Germyne**
94.264(1)8, Vˆ 5349.4(6) Š3, Z ˆ 4, 1calcd ˆ 1.421 gcm
,
m ˆ
3
0.437 mm 1, R[I > 2s(I)] ˆ 0.0748 for 24469 independent reflections
of the 34761 collected, R(all data) ˆ 0.1708. Crystallographic data
(excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-146454 (1) and
CCDC-146455 (2(PF6)2). Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
Â
Á
Christine Bibal, Stephane Mazieres, Heinz Gornitzka,
and Claude Couret*
Since the isolation of the first disilene, a compound
containing a silicon ± silicon double bond, in 1981,[1] many
stable compounds with a double bond involving the Group 14
elements Si, Ge, and Sn have been synthesized.[2] In contrast,
compounds containing a triple bond to a Group 14 element
other than C remained unknown. Power[3] described recently
a lead analogue of an alkyne (ArPbPbAr) but more consistent
with a diplumbylene form. However, some compounds with
triple bonds to Si were identified by spectroscopy or by
[9] See for example: a) C. J. Carrano, M. W. Carrano, K. Sharma, G.
Backes, J. S. Sanders-Loehr, Inorg. Chem. 1990, 29, 1865; b) A. B. P.
Lever, Inorganic Electronic Spectroscopy, Elsevier, New York, 1984,
p. 311.
[10] The resulting solution was concentrated and diluted in water in the
presence of excess dithionite and bathophenanthroline. The organic
material was extracted from the solution by using dichloromethane
and choloroform.
[11] Comparisons between 1H and 13C NMR spectra of L and LOH
allowed us to unambiguously attribute the inserted oxygen position. In
fact, the signal at d ˆ 6.63 corresponding to the o-H for L is replaced
by two signals at d ˆ 6.63 and 6.42 in a 2:1 ratio for LOH. A similar
trend is observed in the 13C NMR spectrum (for the o-C of the phenyl
ring signals appear at d ˆ 108.5 and 105.5 for LOH, but only at d ˆ
105.0 for L). ESI-MS for LOH (CH2Cl2; positive-ion mode): m/z: 619
Á
[*] Prof. Dr. C. Couret, C. Bibal, Dr. S. Mazieres, Dr. H. Gornitzka
 Â
Â
Laboratoire Heterochimie Fondamentale et Appliquee
Â
Universite Paul Sabatier
118, route de Narbonne, 31062 Toulouse cedex 04 (France)
Fax : (‡33)5-61-55-82-04
‡
E-mail: couret@ramses.ups-tlse.fr
(100%) for [LOH ‡ H ].
[12] The HPLC titration has been carried out on authentic pure samples of
L, L1, and LOH obtained by extraction of the reaction mixture at
[**] We thank Prof. Dr. Josef Michl (University of Colorado at Boulder,
USA) for helpful discussions.
952
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Angew. Chem. Int. Ed. 2001, 40, No. 5