Kinetic resolution of diiron acyl complexes - An approach to asymmetric bicyclic β-lactams

Article abstract of DOI:10.1002/(SICI)1521-3773(19990419)38:8<1116::AID-ANIE1116>3.0.CO;2-M

Kinetic resolution is achieved in the reaction of racemic diiron complexes like 1 with the chiral nitrone (-)-2. Oxidative removal of the metal and reductive cleavage of the N-O bond provides β-amino acids. This sequence was used in the synthesis of β-ami

Full text of DOI:10.1002/(SICI)1521-3773(19990419)38:8<1116::AID-ANIE1116>3.0.CO;2-M

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72%) or 5 (1.30 g, 87%). Recrystallization from hexane yielded very fine
needles of both compounds.
Kinetic Resolution of Diiron Acyl
ComplexesÐAn Approach to Asymmetric
Bicyclic b-Lactams**
Crystal data for 5: C84H126N12OSn4, Mr ˆ 1794.73, monoclinic, space group
P21/c (no. 14), a ˆ 22.911(4), b ˆ 18.441(6), c ˆ 22.250(13) Š, b ˆ 115.30(3)8,
3
Vˆ 8499(6) Š3, F(000) ˆ 3688; Z ˆ 4, 1calcd ˆ 1.40 gcm
,
m(MoKa) ˆ
Scott R. Gilbertson* and Omar D. Lopez
14.2 cm 1, crystal dimensions 0.3 Â 0.2 Â 0.1 mm, 12145 reflections collect-
ed for 2 < q < 238, 11805 independent reflections, R1 ˆ 0.047 for 8396
reflections with I > 2s(I), wR2 ˆ 0.09 (for all data), S ˆ 0.989. Data
collected at Tˆ 173(2) K, Enraf Nonius CAD-4 diffractometer, absorption
correction, structural solution by direct methods, full-matrix least-squares
refinement on F2 with SHELXL-93 with non-hydrogen atoms anisotropic.
The asymmetric unit contains two independent molecules of the Sn2
complex and one molecule of diethyl ether solvent. Crystallographic data
(excluding structure factors) for the structure reported in this paper have
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-107662. 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).
In the last few years we have been interested in the dipolar
cycloaddition of nitrones with diiron acyl complexes.[1, 2] This
chemistry has been shown to be effective in the diastereo- and
enantioselective addition of a variety of nitrones to mono- and
disubstituted a,b-unsaturated acyl complexes. It was found
that, after cycloaddition, oxidation of the resultant complex
gives a thioester isoxazolidine product.[1±3] It has been shown
that isoxazolidines can be converted to amino alcohols
through reduction of the N O bond.[4±6] In the case of the
cycloadducts discussed below, this results in the formation of
thioester derivatives of b-amino acids. Here in we show that
reaction of a cyclic nitrone derived from proline proceeds with
one enantiomer of the diiron complex significantly faster than
with the other enantiomer. Additionally the utility of this
approach is demonstrated through the synthesis of a simple
carbapenem.
Received: November 9, 1998 [Z12641IE]
German version: Angew. Chem. 1999, 111, 1185 ± 1187
Keywords: germanium ´ metal ± metal interactions ´ tin
Reaction of complex 1 with the Z-nitrone 2 gave the
expected isoxazolidine product, which could be oxidized to
the corresponding thioester 4. Reaction with zinc and acetic
acid then yielded the b-amino b-hydroxy thioester 5. The hope
was that treatment of the thioester with mercury trifluoro-
acetate would result in removal of the sulfur with commen-
surate trapping by the amine group to give the b-lactam.[7±9]
Since optically active diiron acyl complexes are accessible, this
approach would potentially provide a mild route to optically
active b-lactams.[2] Unfortunately the initial attempt to form
the b-lactam from amino alcohol 5 resulted in less than a 15%
yield of the desired product 6. It has been reported that the
cyclization to give b-lactams with groups cis on the adjacent
carbon atoms of the four-membered ring is difficult
(Scheme 1).[10]
Because of this observation, and the fact that a large
number of the known b-lactam antibiotics possess the
opposite stereochemistry, the dipolar cycloaddition was run
on an E-nitrone. The stereochemistry of acyclic nitrones is
typically Z. Consequently, it was necessary to attempt the
cyclization with a cyclic nitrone. Endo addition of such a
nitrone would give a b-amino acid with the correct stereo-
chemistry to readily form a b-lactam. Cyclization of nitrone 7
with diiron complex 1 followed by oxidative removal of the
[1] M. A. Della Bona, M. C. Cassani, J. M. Keates, G. A. Lawless, M. F.
Lappert, M. Stürmann, M. Weidenbruch, J. Chem. Soc. Dalton Trans.
1998, 1187, and references therein.
[2] a) P. J. Davidson, M. F. Lappert, J. Chem. Soc. Chem. Commun. 1973,
317; b) D. E. Goldberg, D. H. Harris, M. F. Lappert, K. M. Thomas, J.
Chem. Soc. Chem. Commun. 1976, 261; c) D. E. Goldberg, P. B.
Hitchcock, M. F. Lappert, K. M. Thomas, A. J. Thorne, T. Fjeldberg,
A. Haaland, B. E. R. Schilling, J. Chem. Soc. Dalton Trans. 1986, 2387.
[3] K. W. Klinkhammer, W. Schwarz, Angew. Chem. 1995, 107, 1448;
Angew. Chem. Int. Ed. Engl. 1995, 34, 1334.
[4] M. Weidenbruch, H. Kilian, K. Peters, H. G. von Schnering, H.
Marsmann, Chem. Ber. 1995, 128, 983.
[5] U. Lay, H. Pritzkow, H. Grützmacher, J. Chem. Soc. Chem. Commun.
1992, 260.
[6] W.-P. Leung, W.-H. Kwok, F. Xue, T. C. W. Mak, J. Am. Chem. Soc.
1997, 119, 1145.
[7] S. Masamune, L. R. Sita, J. Am. Chem. Soc. 1985, 107, 6390.
[8] K. M. Baines, J. A. Cooke, C. E. Dixon, H. W. Liu, M. R. Netherton,
Organometallics, 1994, 13, 631.
Â
Â
[9] M.-A. Chaubon, J. Escudie, H. Ranaivonjatovo, J. Satge, Chem.
Commun. 1996, 2621.
[10] C. Drost, P. B. Hitchcock, M. F. Lappert, L. J.-M. Pierssens, Chem.
Commun. 1997, 3595.
[11] 1,8-Dineopentylaminonaphthalene was prepared from 1,8-diamino-
naphthalene by successive treatment with i) tBuC(O)Cl, NEt3 in THF
and ii) Li[AlH4] in THF (as for (tBuCH2N)2C20H12[12]).
[12] C. Drost, P. B. Hitchcock, M. F. Lappert, J. Chem. Soc. Dalton Trans.
1996, 1187, and references therein.
[13] C. Drost, P. B. Hitchcock, M. F. Lappert, Organometallics 1998, 17,
3838.
[14] a) N. Kuhn, T. Kratz, D. Bläser, R. Boese, Chem. Ber. 1995, 128, 245;
b) A. Schäfer, M. Weidenbruch, W.Saak, S. Pohl, J. Chem. Soc. Chem.
Commun. 1995, 1157.
[15] H. Braunschweig, B. Gehrhus, P. B. Hitchcock, M. F. Lappert, Z.
Anorg. Allg. Chem. 1995, 621, 1922.
[16] M. Weidenbruch, A. Stilter, H. Marsmann, K. Peters, H. G. von Sch-
nering, Eur. J. Chem. 1998, 1333.
[17] K. W. Zilm, G. A. Lawless, R. M. Merrill, J. M. Millar, G. G. Webb, J.
Am. Chem. Soc. 1987, 109, 7236.
[18] C. Drost, B. Gehrhus, P. B. Hitchcock, M. F. Lappert, Chem. Commun.
1997, 1845.
[19] B. Gehrhus, P. B. Hitchcock, M. F. Lappert, Angew. Chem. 1997, 109,
2624; Angew. Chem. Int. Ed. Engl. 1997, 36, 2514.
[20] T. Fjeldberg, H. Hope, M. F. Lappert, P. P. Power, A. J. Thorne, J.
Chem. Soc. Chem. Commun. 1983, 639.
[*] Prof. S. R. Gilbertson, Dr. O. D. Lopez
Department of Chemistry, Washington University
St. Louis, Missouri 63130 (USA)
Fax : (‡ 1)314-935-4481
E-mail: srg@wuchem.wustl.edu
[**] This work was supported by the National Science Foundation (Grant
No. CHE-9316821) and Washington University. We also gratefully
acknowledge the Washington University High-Resolution NMR
Facility, partially supported by NIH RR02004, RR05018, and
RR07155, and the Washington University Mass Spectrometry Re-
source Center, partially supported by NIHRR00954, for their
assistance.
Supporting information for this article is available on the WWW
under http://www.wiley-vch.de/home/angewandte/ or from the author.
1116
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1433-7851/99/3808-1116 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 8

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Scheme 1. Synthesis of b-lactam 6 from 1 and 2.
Scheme 3. Compound 11 is predominately one diastereomer, at least 20:1.
The recovered starting material is highly enriched in favor of one
enantiomer. TBDMS ˆ tert-butyldimethylsilyl.
metal gives the thio-ester product. Reduction of the N O
bond provides an amino thioester (8) that, upon treatment
with mercury trifluoroacetate, readily cyclizes to the b-lactam
9.[11] The stereochemistry obtained in this reaction not only
facilitates cyclization to the b-lactam but corresponds to the
stereochemistry of important carbapenems, such as thiena-
mycin (Scheme 2).[12±17]
The selection of one enantiomer of the diiron complex by
the enantiomerically pure cyclic nitrone requires considera-
tion of a number of factors. First, the nitrone must approach
the olefin from one side, most likely the side opposite the
sulfur (Scheme 4). Second, given the product formed, the
nitrone must react selectively through an endo transition state.
Third, only one face of the nitrone can add to the complex;
this is likely to be the face opposite the large tert-butyldime-
thylsilyl group. The last issue to consider is what conformation
the complex reacts in, s-cis or s-trans. From the high selectivity,
we know that either enantiomer A reacts in the s-trans
conformation or enantiomer B reacts in the s-cis conforma-
tion (Scheme 4). Since we do not yet know the absolute sense
of chirality of the complex at the metal center, we do not know
which conformation the molecule reacts in. Given the high
diastereoselectivity, we know it must be predominately one.
All these issues combine to cause the enantiomerically pure
nitrone to react with one of the two enantiomers of the
racemic mixture with a significantly faster rate.
It is important to note that, while the stereochemistry at the
metal center has not been determined, the absolute stereo-
chemistry of the three stereogenic carbon atoms in the
product is known. They have been assigned relative to the
known chirality of the carbon atom which bears the hydroxy
group of the nitrone. When the nitrone from cis-hydroxy
proline ((‡)-10), the enantiomer of ( )-10, is used the other
enantiomer of the b-lactam is obtained.
Scheme 2. Synthesis of 9 from 1 and 7. a) Cycloaddition, b) CAN, CH3CN,
c) Zn, HOAc, d) Hg(CF3CO2)2.
Once it had been established that this approach was a viable
route to b-lactams, an attempt to use this reaction sequence in
the synthesis of carbapenem structures was undertaken.
Therefore, the racemic complex 1 was treated with enantio-
merically pure nitrone 10. This reaction resulted in a 50%
yield of the expected bicyclic isoxazolidine but, surprisingly, as
a single diastereomer. If both enantiomers of the racemic
complex reacted with the enantiomerically pure nitrone ( )-
10, two diastereomeric products (S,S and S,R) should have
been obtained. Isolation of the unreacted starting material
and measurement of its optical rotation revealed that the
unreacted starting material was optically active, which con-
firmed that reaction with the nitrone ( )-10 effected a kinetic
resolution of the racemic
The relative rates of the reaction between a matched and
mis-matched nitrone complex pair has been determined. This
was done by resolution of the complex through reaction with
the enantiomerically pure nitrone ( )-10. After resolution of
complex. It was subse-
quently observed that, if
allowed sufficient time,
the other enantiomer of
the iron complex also re-
acts with nitrone ( )-10
(Scheme 3).
Scheme 4. The two possible endo transition states for product formation.
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Angew. Chem. Int. Ed. 1999, 38, No. 8
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the racemic complex with nitrone ( )-10, the recovered,
optically active starting material was then allowed to react with
its matched and mismatched nitrones, ( )-10 and its enantiomer
(‡)-10. It was observed that the complex resolved through
reaction with ( )-10 (i.e. the recovered starting material)
reacted eleven times faster with nitrone (‡)-10.
be used in a variety of asymmetric cycloadditions. The
reaction of nitrone 10 with diiron complexes provides b-
amino acids that can be converted to b-lactams with absolute
stereochemistry that corresponds to the carbapenems, such as
thienamycin. We are currently developing chemistry for the
conversion of intermediates such as 13 into a series of
biologically active b-lactams. Additionally we are attempting
to determine the absolute sense of chirality of these com-
plexes at the metal centers.
To demonstrate the potential of this approach for the
synthesis of b-lactams, carbapenem 13 was synthesized
(Scheme 5).[18] Cycloadduct 14 was obtained from the cyclo-
Experimental Section
General synthesis of the a,b-unsaturated acyl complexes:
A 100 mL, round-bottomed flask was charged with [Fe3(CO)12] (5.00 g,
9.93 mmol) and flushed with nitrogen. THF (120 mL) was added, followed
by the addition of n-propanethiol (0.87 g, 11.40 mmol) and triethylamine
(1.17 g, 11.53 mmol). The solution was stirred for 20 min, during which time
a color change of green to yellow-brown occurred. Then trans-crotonyl
chloride (2.10 g, 20.25 mmol) was added. During this addition, gas
evolution was observed. The mixture was stirred for 15 h, during which
time the reaction mixture turned dark red and a white precipitate formed.
The solution was filtered and the solvent removed to leave a red oil. The
product was purified by silica gel chromatography (hexane) to give 3.40 g
(8.02 mmol, 81%) of a slightly air-sensitive, dark red oil. A product which
corresponded to the CO deinsertion product, as described by Seyferth
et al., eluted before the desired product.[3, 19±21]
Sample dipolar cycloaddition: Crotonyl acyl complex 1 (1.6 g, 3.78 mmol)
was dissolved in ethyl acetate (20 mL) and transferred to a 50 mL Schlenk
tube. Nitrone ( )-10 (974.0 mg, 4.53 mmol) was added and the mixture was
degassed by three freeze-pump-thaw cycles. Once degassed the reaction
mixture was stirred for 3 h. The product was purified by column
chromatography (silica gel, ethyl acetate/hexane 5/95) and isolated as a
red oil; 1.89 mmol, 50%. 1H NMR (300 MHz, CDCl3): d ˆ 4.33 (dd, J ˆ 7.8,
7.2 Hz, 1H), 4.25 (dq, J ˆ 6.0, 4.5 Hz, 1H), 3.85 (dd, J ˆ 9.0, 8.1 Hz, 1H),
3.72 (m, 1H), 3.04 (dd, J ˆ 10.0, 4.8 Hz, 2H), 2.81 (m, 2H), 1.86 (m, 2H),
1.53 (m, 1H), 1.38 (m, 2H), 1.13 (t, J ˆ 7.5 Hz, 3H), 1.01 (d, J ˆ 6 Hz, 3H),
0.87 (s, 9H), 0.06 (s, 3H), 0.05 (s, 3H); minor isomer: 4.40 (m, 1H), 3.77 (m,
1H), 3.11 (t, J ˆ 5.9 Hz, 1H), 2.97 (d, J ˆ 5.74 Hz, 1H), 1.14 (t, J ˆ 7.3 Hz,
3H), 1.00 (d, J ˆ 5.6 Hz, 3H), 0.86 (s, 9H); 0.03 (s, 3H); 0.02 (s, 3H);
13C NMR (75 MHz, CDCl3): d ˆ 300.3, 211.5, 211.2, 208.9, 208.7, 208.6, 81.4,
72.3, 72.0, 65.4, 65.0, 40.6, 37.3, 26.8, 25.8, 18.0, 17.4, 13.4, 4.7, 4.8; minor
Scheme 5. Synthesis of carbapenem 13 from 14. TBDPS ˆ tert-butyldi-
phenylsilyl.
isomer: 82.4, 72.9, 72.7, 65.9, 65.3, 40.8, 36.7, 25.7, 18.1, 13.5, 4.9; IR (thin
1
film): nÄ ˆ 2932, 2898, 2858, 2074, 2031, 1997, 1970, 1462, 1114, 1071 cm
;
addition of nitrone ( )-10 and a racemic mixture of complex
1. The resulting complex 14 was then treated with cerium
ammonium nitrate (CAN) to liberate thioester 15. To
complete the synthesis of 13, the hydroxy group that was
used to set the stereochemistry must be oxidized to a ketone.
It was found that the best time for this transformation was
before the b-lactam was formed. This was accomplished
through reduction of the N O bond with zinc and acetic acid,
to give b-amino thioester 16, followed by protection of the
free hydroxy group as the tert-butyldiphenylsilyl ether (17).
Selective removal of the tert-butyldimethylsilyl group with
tetrabutylammonium fluoride (TBAF) then gave the desired
alcohol (18) ready for oxidation. Jones oxidation of the free
alcohol followed by cyclization with mercuric trifluoroacetate
afforded optically active bicyclic b-lactam 13. When the
nitrone from cis-hydroxy proline ((‡)-10) was used, the
stereochemistry of the three stereogenic centers of b-lactam
13 corresponded to the stereochemistry of many therapeuti-
cally useful carbapenems, including thienamycin.
FAB-MS: m/z (%): 641 ([M ‡ H, 10), 133 (100); HRFAB-MS: calcd for
C23H34Fe2NO9SSi: m/z: [M ‡ H] 640.0422, found 640.0413; TLC: Rf: 0.52
(ethyl acetate/hexane 15/85).
Received: October 27, 1998 [Z12576IE]
German version: Angew. Chem. 1999, 111, 1188 ± 1190
Keywords: asymmetric synthesis ´ cycloadditions ´ iron ´
lactams
[1] S. R. Gilbertson, D. P. Dawson, O. D. Lopez, K. L. Marshall, J. Am.
Chem. Soc. 1995, 117, 4431 ± 4432.
[2] S. R. Gilbertson, O. D. Lopez, J. Am. Chem. Soc. 1997, 119, 3399 ±
3400.
[3] S. R. Gilbertson, X. Zhao, D. P. Dawson, K. L. Marshall, J. Am. Chem.
Soc. 1993, 115, 8517 ± 8518.
[4] R. Huisgen, H. Hauck, R. Grashey, H. Siedl, Chem. Ber. 1968, 101,
2568 ± 2584.
[5] A. Vasella, R. Voeffray, Helv. Chim. Acta 1982, 65, 1134 ± 1144.
[6] H. Iida, K. Kasahara, C. Kibayashi, J. Am. Chem. Soc. 1986, 108,
4647 ± 4648.
[7] S. Masamune, S. Kamata, W. Schilling, J. Am. Chem. Soc. 1975, 97,
3515 ± 3516.
Through the reaction of nitrone ( )-10, optically active
diiron acyl complexes can be obtained. These complexes can
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[8] S. Masamune, Y. Hayase, W. Schilling, W. K. Chan, G. S. Bates, J. Am.
Chem. Soc. 1977, 99, 6756 ± 6758.
[9] E. J. Corey, K. C. Nicolaou, J. Am. Chem. Soc. 1974, 96, 5614 ± 5616.
[10] J. J. Tufariello, D. J. P. Pinto, A. S. Milowsky, D. V. Reinhardt,
Tetrahedron Lett. 1987, 28, 5481 ± 5484.
[11] S.-I. Murahashi, Y. Imada, H. Ohtake, J. Org. Chem. 1994, 59, 6170±6172.
[12] D. B. R. Johnston, S. M. Schmitt, F. A. Bouffard, B. G. Christensen, J.
Am. Chem. Soc. 1978, 100, 313 ± 315.
[13] T. Kametani, S.-P. Huang, A. Nakayama, T. Honda, J. Org. Chem.
1982, 47, 2328 ± 2331.
[14] T. Kametani, T. Nagahara, T. Honda, J. Org. Chem. 1985, 50, 2327±2331.
[15] T. N. Salzmann, R. W. Ratcliffe, B. G. Christensen, F. A. Bouffard, J.
Am. Chem. Soc. 1980, 102, 6161 ± 6163.
[16] R. V. Stevens, K. Albizati, J. Chem. Soc. Chem. Commun. 1982, 104±105.
[17] J. J. Tufariello, G. E. Lee, P. A. Senaratne, M. Al-Nuri, Tetrahedron
Lett. 1979, 4359 ± 4362.
[18] W. S. Faraci, A. V. Bakker, R. W. Spencer, R. A. Williams, V. J. Jasys,
M. S. Kellogg, R. A. Volkmann, Bioorg. Med. Chem. Lett. 1993, 3,
2271 ± 2276.
[19] D. Seyferth, C. M. Archer, J. C. Dewan, Organometallics 1991, 10,
3759 ± 3763.
for producing and fabricating metallic structures. Acorga
P5000 (referred to as P50) is a modern corrosion inhibitor for
iron and comprises 5-nonylsalicylaldoxime as a mixture of
carbon-chain isomers.[1] P50 was developed as an extraction
agent for copper,[2] and bis-salicylaldoxime complexes of
many dipositive metal ions are known.[3] However, there is no
information on the mode of action of P50 on iron surfaces, and
data available on iron(ii) and iron(iii) salicylaldoximate
complexes are scant and contradictory.[4±7] We have already
identified a variety of bonding modes for salicylaldoxime
oligomers with vanadium and zinc.[8] When steel is treated
with P50, a purple coating is formed on the surface and
constitutes the protective film. Here we describe the iron
chemistry of salicylaldoxime and alkyl-substituted analogues
and compare the products of these reactions with correspond-
ing materials produced by treating mild steel with these
reagents.
Reaction[9] of iron(iii) chloride with salicylaldoxime
(H2SalH)[8] led to crystals formulated as [{Fe(SalH)(H-
SalH)}4] ´ H2SalH ´ 2C8H10 (1).[10] Compound 1 comprises two
molecules of xylene, a molecule of H2SalH, and a cluster
containing four FeIII centers, each of which has a distorted
octahedral coordination environment with four O and two cis-
N donor atoms (Figure 1). Each FeIII center is ligated by a
terminal, bidentate HSalH N,O-donor ligand (those contain-
ing N1, N3, N5, and N7 function in this manner) and four
atoms (1N and 3O) of three of the four bridging SalH ligands
(those containing N2, N4, N6, and N8). Each of these bridging
ligands joins two FeIII centers through its oximate oxygen
atom (m-O); the attached nitrogen atom links this Fe-O-Fe
moiety to a third FeIII center (m-ON), and the phenolate
oxygen atom is bound to this FeIII ion to form a six-membered
FeNCCCO chelate ring. The structure of the cluster is further
stabilized by four intramolecular hydrogen bonds between a
terminal oxime NOH group of the bidentate HSalH ligand
and the adjacent phenolate oxygen atom of another such
ligand. A similar diversity in the bonding modes of this type of
ligand occurs in [{VO(SalEt)(HSalEt)}2].[8]
The four FeIII centers of the tetranuclear cluster of 1 have a
distorted tetrahedral arrangement with Fe ´´´ Fe distances of
about 3.6 Š for linkage by one m-O and one m-ON, and about
4.1 Š for linkage by two m-ON groups. Tetranuclear FeIII
clusters, albeit with different structures, were identified in
[FeIII{FeIII(salicylhydroximato)(MeOH)(acetate)}3] ´ 3MeOH,
in which three FeIII centers are arranged about a central FeIII
ion,[12a] and [L2Fe2III(m3-O2)(m2-CH3COO)3(SalH)2FeI2IIL2]X
(L ˆ 1,4,7-trimethyltriazacyclononane; X ˆ ClO4, PF6), the
cation of which contains a butterfly arrangement of the four
FeIII centers formed by two edge-sharing Fe3III(m3-O) triangu-
lar units in which deprotonated NO groups bridge the wing
and body pairs of iron atoms.[12b]
[20] D. Seyferth, C. M. Archer, D. P. Ruschke, Organometallics 1991, 10,
3363 ± 3380.
[21] D. Seyferth, G. B. Womack, C. M. Archer, J. C. Dewan, Organo-
metallics 1989, 8, 430 ± 442.
Surface Coordination Chemistry: Corrosion
Inhibition by Tetranuclear Cluster Formation of
Iron with Salicylaldoxime**
Jacqueline M. Thorpe, Roy L. Beddoes,
David Collison,* C. David Garner,*
Madeleine Helliwell, Jeremy M. Holmes, and
Peter A. Tasker
The corrosion of metals represents a waste of both natural
resources and money. Corrosion can cause catastrophic
accidents because of premature failure of metallic equipment.
The worldꢁs supply of metals is limited, and wastage due to
corrosion leads to consumption of energy and water reserves
[*] Dr. D. Collison, Prof. C. D. Garner, Dr. M. Helliwell,
Dr. J. M. Thorpe, R. L. Beddoes
Department of Chemistry
The University of Manchester
Manchester M139PL (UK)
Fax: (‡44)161-275-4616
E-mail: david.collison@man.ac.uk
dave.garner@man.ac.uk
Dr. J. M. Holmes
Zeneca Specialties
Hexagon House, PO Box 42
Blackley, Manchester M93DA (UK)
Prof. P. A. Tasker
Department of Chemistry
The University of Edinburgh
Edinburgh EH93JJ (UK)
Elemental analyses, spectroscopic data, and other physical
measurements[13] have demonstrated that the predominant
constituent of the red-brown product obtained when an Fe
salt reacts with salicylaldoxime is the tetranuclear cluster
characterized in 1. The 57Fe Mössbauer isomer shift
[**] We thank Zeneca Specialties (J.M.T.) and The Royal Society (D.C.)
for financial support, Dr. J. M Charnock (EXAFS), Prof. A. X.
Trautwein, and Dr. E. Bill (Mössbauer), and ICI surface analysis
service, Runcorn, (XPS) for assistance with measurements, P. R.
Bolton and J. J. A. Cooney for assistance with the production of
Figure 1, and a referee for drawing to our attention the contents of
ref. [22].
1
1
(0.53 mms at 77 K, 0.54 mms at 4.2 K) and quadrupole
1
1
splitting (1.02 mms at 77 K, 1.05 mms at 4.2 K) are
consistent[16±18] with a high-spin FeIII system. The linewidth
Angew. Chem. Int. Ed. 1999, 38, No. 8
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