Selective activation of Ar-Cl and Ar-C bonds with iron(II) complexes

Article abstract of DOI:10.1002/(SICI)1521-3773(19980420)37:7<963::AID-ANIE963>3.0.CO;2-X

The electrophilic iron-carbene chelate complexes 1 and 2 react with alkoxides RO^- to give the neutral chelate complex 3 and the carbene complex 4, respectively. Depending on the nature of the chelating ortho substituent, selective activation of

Full text of DOI:10.1002/(SICI)1521-3773(19980420)37:7<963::AID-ANIE963>3.0.CO;2-X

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J. J. Schneider, U. Denninger, J. Hagen, C. Krüger, D. Bläser, R.
Boese, Chem. Ber. 1997, 130, 1433.
[16] J. Weiss, T. Priermeier, R. A. Fischer, Inorg. Chem. 1996, 35, 71.
[17] J. Weiss, A. Frank, E. Herdtweck, S. Nlate, M. Mattner, R. A. Fischer,
Chem. Ber. 1996, 129, 297.
[18] R. A. Fischer, M. Kleine, O. Lehmann, M. Stuke, Chem. Mat. 1995, 7,
1863.
Selective Activation of Ar± Cl and Ar± C
Bonds with Iron(ii) Complexes**
Â
Geraldine Poignant, Sourisak Sinbandhit, Loïc Toupet,
Â
and Veronique Guerchais*
Selective bond-activation reactions mediated by transition
metals are currently the focus of synthetic and mechanistic
interest. These fundamental processes are particularly impor-
tant in carbene and arene chemistry.[1, 2] In this context, the
electrophilic arylcarbene chelate complexes 1 (X ˆ Cl) and 2
(X ˆ OMe) are good candidates for promoting new reactions
within the coordination sphere, since the chelating group X
can be activated by the Lewis acidic organo-iron fragment[3, 4]
or dissociate to provide a vacant coordination site.[5, 6] Here
we report on the reactivity of 1 and 2[5] towards alkoxides. The
outcome of the reaction depends on the nature of the chelate
group; selective activation of Ar± Cl and Ar± C bonds was
achieved.
Scheme 1. a) RONa (3 equiv)/ROH, THF, 808C !room temperature.
TfO ˆ trifluoromethanesulfonate.
for the methyl and methylene groups, which indicates the
presence of two different ethoxy groups. Moreover, in the 1H
NMR spectrum (258C) one of the methylene groups gives rise
to an AB system at d ˆ 3.00 and 2.78 (2JH,H ˆ 10 Hz) when the
corresponding methyl signal at d ˆ 0.98 is selectively 1H-
decoupled.
Complex 1 reacts cleanly with alkoxides RONa to give the
unexpected neutral chelate complexes 3a (R ˆ Me) and 3b
(R ˆ Et), which were isolated as stable black crystals in 83 ±
89% yield from pentane (Scheme 1). Both contain two
additional alkoxy groups. The 1H NMR spectrum (C6D6,
258C) of 3a exhibits three broad signals for the methoxy
substituents, one of which corresponds to the coordinated
OMe group, while the other two methoxy groups are
diastereotopic. The coalescence of these signals on warming
(TC (300 MHz) ˆ 428C) to give a singlet at d ˆ 2.90, indicates
As expected the OMe ligand is labile, and treatment of 3a
with PMe3 quantitatively yields orange crystals of 4. In this
[Fe(C5Me5)(CO)(PMe3){h1-C6H4-o-C(OMe)3}]
4
case, the three OMe groups are magnetically equivalent in the
1H (d ˆ 3.29) and 13C (d ˆ 49.9) NMR spectra (258C). An X-
ray structure analysis confirms the proposed structure (Fig-
free exchange on the NMR time scale. For 3b, the 1H and 13
C
ure 1).[7] The FeC O unit deviates from the expected linear
NMR spectra each exhibit two well-resolved pairs of signals
ꢀ
geometry (Fe-C-O 171.0(3)8). The bond angles at Cipso of the
aryl group are quite different owing to the presence of the
bulky tris(methoxy)methyl substituent.
[*] Dr. V. Guerchais, G. Poignant
Â
UMR 6509 CNRS-Universite de Rennes 1
Â
ªOrganometalliques et Catalyse: Chimie et Electrochimie
The formation of complexes 3a ± b involves cleavage of the
Ar± Cl bond. This cleavage is promoted by coordination of
the chlorine atom, as shown by the following experiment.
Â
Moleculairesº
Â
Beaulieu, Universite de Rennes 1
F-35042 Rennes Cedex (France)
Fax: (‡33)299-281646
‡
[5]
Treatment of the nonchelated complex 5 OTf
under the
E-mail: guerchai@univ-rennes1.fr
same conditions led to formation of the acetal complexes 6a
(R ˆ Me) and 6b (R ˆ Et) by addition of RO to the
electrophilic carbene carbon atom. Although stable in the
Dr. S. Sinbandhit
Â
Centre Regional de Mesures Physiques de lꢁOuest (C.R.M.P.O.)
Â
Beaulieu, Universite de Rennes 1
F-35042 Rennes Cedex (France)
‡
[Fe(C5Me5)(CO)2{h1-C(OMe)C6H4-o-Cl}]OTf
5 OTf
Dr. L. Toupet
Á
Â
Â
UMR 6626 Groupe Matiere Condensee et Materiaux
[Fe(C5Me5)(CO)2{h1-C(OMe)(OR)C6H4-o-Cl}]
6a,b
Â
Beaulieu, Universite de Rennes 1
F-35042 Rennes Cedex (France)
solid state as a yellow powder, these species undergo thermal
decomposition in solution at 08C. Addition of HBF4 ´ OEt2 to
a crude solution of 6a led quantitatively to the carbene
[**] This work was supported by the CNRS and HCM program (contract
Â
number 940501). We thank the ªRegion Bretagneº for a grant to G.P.
Â
and Dr. P. Guenot for mass spectrometric measurements.
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Figure 2. Crystal structure of 8. Selected bond lengths [Š] and angles [8]:
Fe ± C17 1.990(6), Fe ± C12 1.881(5), O2 ± C12 1.305(7), O3 ± C12 1.335(7),
O4 ± C23 1.423(7); Fe-C11-O1 173.2(6), O2-C12-O3 108.8(4), Fe-C12-O2
133.4(4), Fe-C12-O3 117.8(4).
Figure 1. Crystal structure of 4. Selected bond lengths [Š] and angles [8]:
C17 ± C18 1.519(6), O2 ± C18 1.382(4), O3 ± C18 1.411(4), O4 ± C18
1.413(5), Fe ± C12 2.033(3), Fe ± P 2.187(1), Fe ± C11 1.699(4), O2 ± C19
1.426(6), O3 ± C20 1.420(4), O4 ± C21 1.421(5); Fe-C11-O1 171.0(3), C11-
Fe-C12 99.6, P-Fe-C11 85.9(1), P-Fe-C12 89.2(1), Fe-C12-C17 133.3(3), Fe-
C12-C13 112.6(2).
(h2-C,O)[Fe(C5Me5)(CO){h2-C(OR)2C6H4-o-OMe}]
9
rearranges by Ar± Ca bond cleavage, that is, a-aryl elimina-
tion. Examples of hydride, alkyl, and aryl migration to a
carbene ligand are known;[11, 12] the reverse reaction is
probably induced by the presence of the labile ligand[13] and/
or the instability of the acetal complex (see above). Exchange
of the alkyl group of the carbene ligand occurs in the presence
of an excess of EtO /EtOH, a behavior already observed for
vinyl ether complexes.[14]
This study illustrates the dichotomy of reactivity of iron
complexes: exclusive Ar± Cl bond cleavage is promoted by
the Lewis acid ± base interaction, whereas the presence of a
labile chelate ligand activates the Ar± C bond.
‡
complex 5 BF4 , which still contains the chlorine atom, as
confirmed by mass spectrometry.
Activation of an Ar± F bond by an iron complex with
formation of an Ar± Fe bond has been previously postulated,
but no spectroscopic evidence for an Fe ± F interaction was
obtained.[8] Halohydrocarbon complexes [M(h1-XR)] (X ˆ
halogen; R ˆ alkyl, aryl) undergo nucleophilic attack at the
Ca atom.[3] However, similar activation is not observed for the
chlorobenzene complex 7 on addition of Lewis bases.[9] In our
Experimental Section
[Re(C5Me5)(NO)(PPh3)(h1-ClC6H5)]BF4
7
A solution of 1, 2, or 5 (1 mmol) in THF was treated at 808C with a
freshly prepared solution of RONa (3 equiv) in ROH (R ˆ Me, Et). After
stirring for 1 h, the solution was evaporated to dryness. The products were
extracted with pentane and crystallized.
case, the intermediate formation of an Ar± OMe bond by
nucleophilic substitution[10] was ruled out by the investigation
of the anisyl derivative 2. The formation of the Fe ± aryl bond
and the subsequent rearrangement processes are not yet
understood.
In contrast, the reaction of 2 with EtONa takes a
completely different course: the new carbene ± aryl complex
8 was isolated as a yellow solid in 80% yield (Scheme 1). The
presence of the carbene ligand is indicated by the downfield
signal at d ˆ 263.8 in the 13C NMR spectrum. The crystal
structure (Figure 2) clearly shows that the geometry of the
carbene ligand is distorted. There are two different Fe-C-O
bond angles due to the presence of the anisyl ligand.[7]
We assume that the ethoxide ion initially adds to the
carbene center and that the intermediate complex 9 then
1
3a (89% yield, dark brown crystals): H NMR (300 MHz, C6D6): d ˆ 7.84
(dd, 3J(H,H) ˆ 7.5, 4J(H,H) ˆ 0.8 Hz, 1H, Ar), 7.35 (td, 3J(H,H) ˆ 7.4,
4J(H,H) ˆ 1.6 Hz, 1H, Ar), 7.10 (td, 3J(H,H) ˆ 7.4, 4J(H,H) ˆ 1 Hz, 1H,
Ar), 6.99 (dd, 3J(H,H) ˆ 7.5, 4J(H,H) ˆ 1.5 Hz, 1H, Ar), 3.02 (brs, 3H,
OMe), 2.88 (brs, 3H, OMe), 2.73 (brs, 3H, OMe), 1.42 (s, 15H, C5Me5);
13C{1H} NMR (50.3 MHz, CDCl3): d ˆ 221.7 (CO), 174.6 (FeAr), 140.2
(Ar), 136.5 (ArC), 127.9 (Ar), 126.8 (C(OMe)3), 123.9 (Ar), 121.9 (Ar), 89.6
(C5Me5), 56.3 (OMe), 52.7 (OMe), 52.5 (OMe), 10.8 (C5Me5); IR
1
(pentane): nÄ ˆ 1917 cm (CO); C,H analysis calcd for C21H28O4Fe: C
63.01, H 7.05; found: C 62.78, H 7.12.
3b (83% yield, dark brown crystals): 1H NMR (300 MHz, CDCl3): d ˆ 7.57
(d, 3J(H,H) ˆ 7.5 Hz, 1H, Ar), 7.17 (t, 3J(H,H) ˆ 6.7 Hz, 1H, Ar), 6.96 (t,
3J(H,H) ˆ 7 Hz, 1H, Ar), 6.84 (d, 3J(H,H) ˆ 7 Hz, 1H, Ar), 3.31 (q,
3J(H,H) ˆ 7 Hz, 2H, OCH2CH3), 3.15 (s, 3H, OMe), 3.00 (m, 1H,
OCH2CH3), 2.79 (m, 1H, OCH2CH3), 1.60 (s, 15 H, C5Me5), 1.14 (t,
964
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3J(H,H) ˆ 7 Hz, 3H, OCH2CH3), 0.98 (t, 3J(H,H) ˆ 7 Hz, 3H, OCH2CH3);
13C{1H} NMR (75.47 MHz, CDCl3): d ˆ 221.4 (CO), 173.5 (FeAr), 139.7
(Ar), 137.4 (ArC), 127.4 (Ar), 125.8 (C(OMe)(OEt)2), 123.4 (Ar), 121.5
(Ar), 89.2 (C5Me5), 60.2 (OCH2CH3), 59.8 (OCH2CH3), 55.8 (OMe), 15.3
0.11,
(DEFLT 1990),
12.12,
16.16). Lorentzian and polarization corrections
R ˆ 0.046,
Rw ˆ 0.047,
w ˆ 1/s(Fo)2 ˆ [s2(I) ‡
(0.04F2o)2] 1/2, Sw ˆ 0.890 (residual D1 < 0.44 eŠ 3). Crystal structure
of 8: Enraf-Nonius CAD4 diffractometer, MoKa radiation, m ˆ
1
1
(OCH2CH3), 14.8 (OCH2CH3), 10.1 (C5Me5); IR (pentane): nÄ ˆ 1914 cm
Å
7.086 cm , F(000) ˆ 456, Tˆ 294 K, triclinic, space group P1, a ˆ
(CO); C,H analysis calcd for C23H32O4Fe: C 64.49, H 7.53; found: C 64.82, H
8.773(6), b ˆ 9.185(9), c ˆ 14.572(9) Š, a ˆ 99.64(5), b ˆ 89.89(2),
‡
3
3
7.47; HRMS (70 eV): m/z: 428.1641 [M ], calcd for C23H32O4Fe: 428.1649.
g ˆ 108.34(5)8, Vˆ 1097(1) Š
,
Z ˆ 2, 1 ˆ 1.296 gcm
. Of 4133
1
3
reflections, 2364 observed with I > 4s(I) (w/2q ˆ 1, hkl: 0.10,
4 (65% yield): H NMR (200 MHz, CDCl3): d ˆ 7.84 (d, J(H,H) ˆ 7.6 Hz,
1H, Ar), 7.38 (dd 3J(H,H) ˆ 7.8, 4J(H,H) ˆ 1.7 Hz, 1H, Ar), 6.85 (td,
3J(H,H) ˆ 7.3, 4J(H,H) ˆ 1.4 Hz, 1H, Ar), 6.69 (td,3J(H,H) ˆ 7.3, 4J(H,H) ˆ
1.8 Hz, 1H, Ar), 3.29 (s, 9H, OMe), 1.65 (s, 15H, C5Me5), 1.12 (d, 2J(P,H) ˆ
8.4 Hz, 9H, PMe3); 31P{1H} NMR (81 MHz, CDCl3): d ˆ 36.51 (s, PMe3);
13C{1H} NMR (75.47 MHz, CDCl3): d ˆ 222.6 (d, 2J(P,C) ˆ 38 Hz, CO),
170.4 (d, 2J(P,C) ˆ 26 Hz, FeAr), 146.1 (d, 2J(P,C) ˆ 12 Hz, Ar), 145.8 (ArC),
129.2 (Ar), 122.6 (Ar), 119.3 (Ar), 117.7 (C(OMe)3), 92.1 (C5Me5), 49.9
(OMe), 17.6 (d, 1J(P,C) ˆ 26 Hz, PMe3), 10.2 (C5Me5); IR (CH2Cl2): nÄ ˆ
10.10,
17.17), Lorentzian and polarization corrections
(DEFLT 1990),
R ˆ 0.056,
Rw ˆ 0.051,
w ˆ 1/s(Fo)2 ˆ [s2(I) ‡
(0.04F2o)2] 1/2, Sw ˆ 1.13 (residual D1 < 0.46 eŠ 3). 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-100931. 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).
1
1898 cm (CO); C,H analysis calcd for C24H37O4FeP: C 60.51, H 7.83;
[8] M. L. H. Green, J. Haggitt, C. P. Mehnert, J. Chem. Soc. Chem.
Commun. 1995, 1853 ± 1854; A. N. Chernega, A. J. Graham, M. L. H.
Green, J. Haggitt, J. Lloyd, C. P. Mehnert, N. Metzler, J. Souter, J.
Chem. Soc. Dalton Trans. 1997, 2293 ± 2303.
[9] T.-S. Peng, C. H. Winter, J. A. Gladysz, Inorg. Chem. 1994, 33, 2534 ±
2542.
[10] For a review, see L. Balas, D. Jurrhy, L. Latxague, S. Grelier, Y. Morel,
M. Hamdani, N. Ardoin, D. Astruc, Bull. Soc. Chim. Fr. 1990, 127,
401 ± 426.
[11] T. Braun, O. Gevert, H. Werner, J. Am. Chem. Soc. 1995, 117, 7291 ±
7292.
[12] J. Yang, W. M. Jones, J. K. Dixon, N. T. Allison, J. Am. Chem. Soc.
1995, 117, 9776 ± 9777.
[13] Y. Strentom, W. M. Jones, Inorg. Chem. 1986, 5, 178 ± 180; J. Yang, J.
Yin, K. A. Abboud, J. W. Jones, Organometallics 1994, 13, 971-978,
and references therein.
found: C 60.78, H 7.75.
6b (80% yield, isolated at 408C, yellow powder): 1H NMR (300 MHz,
CDCl3, 308C): d ˆ 7.58 , 7.47, 7.17, 6.98 (Ar), 3.55, 3.40 (brm, OCH2CH3),
3.31 (s, OMe), 3.25, 3.05 (brm, OCH2CH3), 2.98 (s, OMe), 1.73, 1.64 (s,
C5Me5), 1.35, 1.17 (brm, OCH2CH3); 13C{1H} NMR (75.47 MHz, CDCl3,
308C): d ˆ 219.1, 218.8, 218.2 (CO), 149.6, 147.9.(ArC), 131.3, 130.9 (Ar),
129.8, 129.2 (ArCl), 128.0, 126.9, 126.5, 125.9, 125.6 (Ar), 116.5, 114.9 (Ca),
97.9, 96.6 (C5Me5), 58.9, 57.1 (OCH2CH3), 51.5, 50.8 (OMe), 15.5, 15.0
1
(OCH2CH3), 10.0, 9.8 (C5Me5); IR (pentane): nÄ ˆ 1997 (CO), 1947 cm
(CO). Two isomers were observed at 308C owing to hindered CÃa ± Ar
rotation at low temperature. No coalescence was observed up to the
decomposition temperature of O8C.
8 (80% yield, yellow crystals): 1H NMR (300 MHz, C6D6): d ˆ 7.75 (d,
3J(H,H) ˆ 6.6 Hz, 1H, Ar), 7.11 (t, 3J(H,H) ˆ 7.5 Hz, 1H, Ar), 6.96 (t,
3J(H,H) ˆ 7 Hz, 1H, Ar), 6.59 (d,3J(H,H) ˆ 6.6 Hz, 1H, Ar), 4.05 (brm,
2H, OCH2CH3), 3.92 (brm, 2H, OCH2CH3), 3.48 (s, 3H, OMe), 1.61 (s,
15H, C5Me5), 0.92 (brm, 6H, OCH2CH3); 13C{1H} NMR (75.47 MHz,
[14] A. Davison, D. L. Reger, J. Am. Chem. Soc. 1972, 94, 9237 ± 9238. M.
Rosenblum, J. Organomet. Chem. 1986, 300, 191 ± 218.
ˆ
CD2Cl2): d ˆ 263.8 ( Ca), 226.6 (CO), 166.7 (FeAr), 154.3 (ArOMe), 143.9
(Ar), 122.5 (Ar), 119.8 (Ar), 108.2 (Ar), 95.5 (C5Me5), 66.7 (brs,
OCH2CH3), 55.1 (OMe), 14.6 (OCH2CH3), 9.7 (C5Me5); IR (pentane):
1
‡
nÄ ˆ 1936 cm (CO); HRMS (70 eV): m/z: 383.1314 [M
OEt], calcd for
OEt CO], calcd for C20H27O2Fe:
‡
C21H27O3Fe: 383.1310; 355.1355 [M
355.1361.
Synthetic Studies on Ciguatoxin: A Convergent
Strategy for Construction of the F ± M Ring
Framework**
Received: October 21, 1997 [Z11021IE]
German version: Angew. Chem. 1998, 110, 1009 ± 1012
Masayuki Inoue, Makoto Sasaki,* and
Kazuo Tachibana*
Keywords: carbene complexes ´ C ± C activation ´ C ± Cl
activation ´ iron
Ciguatoxin (CTX1B, 1) and its congeners, naturally occur-
ring polycyclic ethers found in marine unicellular algae, are
the principal toxins associated with ciguatera fish poison-
ing.[1, 2] These potent neurotoxins reportedly bind to the same
sites on voltage-sensitive sodium channels (VSSC) as breve-
toxins, another class of structurally related marine toxins.[3]
An important structural characteristic is the fact that the
hexahydrooxonin ring (the F ring) in 1 and its congeners
[1] V. V. Grushin, H. Alper, Chem. Rev. 1994, 94, 1047 ± 1062, and
references therein.
[2] Selective bond activation controlled by the choice of metal complex
was recently described: M. E. van der Boom, S.-Y. Liou, Y. Ben-
David, A. Vigalok, D. Milstein, Angew. Chem. 1997, 109, 636 ± 637;
Angew. Chem. Int. Ed. Engl. 1997, 36, 625 ± 626; M. Gandelman, A.
Vigalok, L. J. W. Shimon, D. Milstein, Organometallics 1997, 16,
3981 ± 3986.
[3] R. J. Kulawiec, R. H. Crabtree, Coord. Chem. Rev. 1990, 99, 89 ± 115,
and references therein.
[4] M. D. Butts, B. L. Scott, G. J. Kubas, J. Am. Chem. Soc. 1996, 118
11831 ± 11843.
[5] G. Poignant, S. Nlate, V. Guerchais, A. J. Edwards, P. R. Raithby,
Organometallics 1997, 16, 124 ± 132.
[*] Dr. M. Sasaki, Prof. Dr. K. Tachibana, M. Inoue
Department of Chemistry, School of Science
The University of Tokyo
Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Fax: (‡81)3-5800-6898
E-mail: msasaki@chem. s.u-tokyo.ac.jp
ktachi@chem.s.u-tokyo.ac.jp
Â
[6] S. Nlate, P. Guenot, S. Sinbandhit, L. Toupet, C. Lapinte, V. Guerchais,
Angew. Chem. 1994, 106, 2294Ð2296; Angew. Chem. Int. Ed. Engl.
1994, 33, 2218 ± 2219.
[**] This work was supported by the Japanese Ministry of Education,
Science, Sports, and Culture (grant-in-aid no. 08245103) and the Japan
Society for the Promotion of Science for Young Scientists through a
fellowship for M.I. We thank Dr. Keiichi Konoki and Professor
Michio Murata from our Department for binding assays and valuable
discussions and advice.
[7] Crystal structure of 4: Enraf-Nonius CAD4 diffractometer, MoKa
radiation, m ˆ 6.91 cm 1, F(000) ˆ 508, Tˆ 294 K, triclinic, space group
Å
P1, a ˆ 9.601(5), b ˆ 10.711(5), c ˆ 13.600(6) Š, a ˆ 75.55(4), b ˆ
84.46(4), g ˆ 67.88(3)8, Vˆ 1246(1) Š 3, Z ˆ 2, 1 ˆ 1.270 gcm 3. Of
4402 reflections, 3524 with I > 2s(I) were observed (w/2q ˆ 1, hkl:
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