Ferrocenyl ligands with two phosphanyl substituents in the α,ε positions for the transition metal catalyzed asymmetric hydrogenation of functionalized double bonds

Full text of DOI:10.1002/(SICI)1521-3773(19991102)38:21<3212::AID-ANIE3212>3.0.CO;2-9

COMMUNICATIONS
In conclusion, we suggest that DAF-FM is a useful tool for
visualizing the temporal and spatial distribution of intra-
cellular NO.
Ferrocenyl Ligands with Two Phosphanyl
Substituents in the a,e positions for the
Transition Metal Catalyzed Asymmetric
Hydrogenation of Functionalized Double
Bonds**
Experimental Section
The synthesis of the indicators is described in the Supporting Information.
Tania Ireland, Gabriele Grossheimann, Catherine
Wieser-Jeunesse, and Paul Knochel*
Fluorescence spectroscopy: The DAFs were dissolved in DMSO to obtain
10mm stock solutions. Relative quantum efficiencies of fluorescence of
DAFs and DAF-Ts were obtained by comparing the area under the
corrected emission spectrum of the test sample upon excitation at 492 nm
with that of a solution of fluorescein in 0.1m sodium hydroxide, which has a
quantum efficiency of 0.85.[8] Bleaching of dyes (10 mm) was determined in
0.1m sodium phosphate buffer (pH 7.4). The solutions in 30-mL vials were
placed in full sunlight on a fine day in November in Tokyo and were
sampled every 1 h.
Dedicated to Professor Armin de Meijere
on the occasion of his 60th birthday
Chiral ferrocene ligands have found numerous useful
applications in asymmetric catalysis.[1] Recently, we described
a new family of C2-symmetrical ferrocenyl ligands called
Ferriphos 1, which proved to be efficient catalysts for the
hydrogenation of a-acetoamidoacrylic acid derivatives.[2, 3] We
have now discovered another class of chiral diphosphanylfer-
rocenyl derivatives 2a ± d which are excellent ligands for the
enantioselective hydrogenation of various functionalized
double bonds and carbonyl groups. The relatively broad area
Imaging: Primary cultured endothelial cells from bovine aorta were
passaged in Dulbeccoꢁs modified Eagleꢁs medium containing 10% fetal
bovine serum and antibiotics. Cells between the 13th and 16th passages
were used for these experiments. The cells were incubated for 1 h at 378C in
PBS(‡) (PBS ˆ phosphate buffered saline) containing 10 mm DAF-FM DA
(0.2% DMSO) for loading, and washed with PBS(‡). They were mounted
on an inverted fluorescence microscope (Olympus IX70, Tokyo, Japan)
equipped with an objective lens (Â20), an excitation filter (490 nm), a
dichroic mirror (505 nm), and a long-pass emission filter (515 nm). The air
temperature was maintained at 378C with a warming box (IX-IBM,
Olympus). Optical signals were recorded with an Argus 50 (Hamamatsu
Photonics, Shizuoka, Japan), which is an imaging system including a cooled
charge-coupled device (CCD) camera. Bradykinin and l-NAME were
purchased from Sigma (St. Louis, MO, USA).
R2
H
R
R1
PPh2
PPh2
Fe
Fe
PPh2
PPh2
R1
R2
Received: May 10, 1999 [Z13402IE]
German version: Angew. Chem. 1999, 111, 3419 ± 3422
2a : R = NMe2
2b : R = N-pyrrolidyl
2c : R = Me
1: Ferriphos
Keywords: dyes
´ fluorescence spectroscopy ´ nitrogen
2d : R = iPr
monoxide ´ sensors ´ signal transduction
of application of this new class of a,e-diphosphanes in
asymmetric catalysis as well as their short synthesis makes
these ligands especially attractive. The modular approach to
their synthesis means that a variety of substituents R (alkyl or
amino groups) can be introduced in the benzylic position. As
shown later, the nature of R is crucial to the enantioselectivity
observed with these ligands.
The ferrocenyl derivatives 2 are readily prepared in five
steps starting from ferrocene (Scheme 1). Thus, a Friedel ±
Crafts acylation of ferrocene with 2-bromobenzoyl chloride
furnishes the ferrocenyl ketone 3 in 80% yield. The Corey-
Bakshi-Shibata (CBS) reduction[4] of 3 affords the corre-
sponding ferrocenyl alcohol in 95% yield and 96% ee. This
[1] Methods Enzymol. 1996, 269 (the reference refers to the whole issue).
[2] M. Bätz, H. G. Korth, R. Sustmann, Angew. Chem. 1997, 109, 1555 ±
1557; Angew. Chem. Int. Ed. Engl. 1997, 36, 1501 ± 1503.
[3] H. Kojima, N. Nakatsubo, K. Kikuchi, S. Kawahara, Y. Kirino, H.
Nagoshi, Y. Hirata, T. Nagano, Anal. Chem. 1998, 70, 2446 ± 2453.
[4] N. Nakatsubo, H. Kojima, K. Kikuchi, H. Nagoshi, Y. Hirata, D. Maeda,
Y. Imai, T. Irimura, T. Nagano, FEBS Lett. 1998, 427, 263 ± 266.
[5] I. Fleming, M. Hecker, R. Busse, Circ. Res. 1994, 74, 1220 ± 1226.
[6] NONOate ˆ (Z)-1-{N-[3-aminopropyl]-N-[4-(3-aminopropylammo-
nio)butyl]amino}diazen-1-ium-1,2-diolate; see: J. A. Hrabie, J. R.
Klose, D. A. Wink, L. K. Keefer, J. Org. Chem. 1993, 58, 1472 ± 1476.
[7] W. C. Sun, K. R. Gee, D. H. Klaubert, R. P. Haugland, J. Org. Chem.
1997, 62, 6469 ± 6475.
[8] Y. Nishikawa, K. Hiraki, Analytical Methods of Fluorescence and
Phosphorescence, Kyoritsu Publishing Company, Tokyo, 1984, pp. 76 ±
80.
[*] Prof. Dr. P. Knochel, Dipl.-Chem. T. Ireland, Dr. G. Grossheimann,
Dr. C. Wieser-Jeunesse
Fachbereich Chemie der Universität
Hans-Meerwein-Strasse, D-35032 Marburg (Germany)
and
Institut für Organische Chemie der Universität
Butenandtstrasse 5 ± 13, D-81377 München (Germany)
Fax: (‡49)89-2180-7680
E-mail: Paul.Knochel@cup.uni-muenchen.de
[**] We thank the DFG (SFB 260, Graduiertenkolleg, Leibniz-Programm)
and the Fonds der Chemischen Industrie for financial support. We
thank Dr. Klaus Harms for the crystal structure analysis as well as
Degussa-Hüls AG and Chemetall GmbH for the generous donation of
chemicals. C.W.-J. thanks the Alexander-von-Humboldt-Stiftung for a
stipendium.
3212
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3821-3212 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 21

COMMUNICATIONS
PPh2
O
R2N
NR2
Br
Br
a, b, c
d
PPh2
Fe
Fe
Fe
Table 1. Enantioselective hydrogenation of b-ketoesters with the ªRuº[a]
chiral ligand catalytic system.
4a : R = Me
4b : R2 = -(CH2)4-
2a : R = Me
2b : R2 = -(CH2)4-
3
90 %
89 %
88 %
64 %
Scheme 1. a) CBS catalyst (0.3 equiv), BH3 ± Me2S, 08C, 2 h; b) Ac2O,
pyridine, 12 h; c) HNR2, CH3CN, H2O, 12 h; d) tBuLi (3.5 equiv), 788C
to room temperature (RT), 1 h; then ClPPh2 (2.5 equiv), 788C to RT, 1 h.
Entry
Substrate
R
Ligand
Product
% ee[b]
1
2
3
4
5
6
7
8
9
6a
6a
6b
6b
6c
6c
6d
6d
6d
Me
Me
nPr
nPr
iPr
iPr
Ph
2a
2d
2a
2c
2a
2c
2a
2d
2c
7a
7a
7b
ent-7b
7c
ent-7c
7d
7d
95.5 (93.2)[c]
95.9
96.5
92.7
95.9
96.5
95.0
96.0
93.7
alcohol is obtained almost enantiomerically pure (99.5% ee)
after recrystallization from heptane. Acylation of the alcohol
gives the intermediate acetate in a quantitative yield, which is
converted into the corresponding amino derivatives 4a and
4b by treatment with dimethylamine or pyrrolidine, respec-
tively. These are then converted into 2b and 2c, respectively,
in approximately 97% ee by the reaction with tBuLi followed
by the addition of ClPPh2,
Finally, 4a was dilithiated with tBuLi and converted into the
corresponding dibromide by reaction with Cl4Br2C2 (80%
yield, 97.5% ee; Scheme 2), which can then be directly
substituted with various organozinc reagents (Me2Zn and
Ph
Ph
ent-7d
[a] [Ru(cod)(C4H7)2]/HBr; [b] Determined by GC on
a
chiral phase
(Chirasil-L-Val) or by HPLC on a chiral phase (Daicel Chiralcel OD, OJ,
or AD columns). The absolute stereochemistry was established by
comparison with the literature. [c] Reaction performed with a substrate
to catalyst ratio of 5000 to 1.
Table 2. Enantioselective hydrogenation of various b-dicarbonyl com-
pounds.
R
Br
PPh2
Br
de (%)[a]
ee (%)[a,b]
Me2N
R
Entry Product
Ligand
c
a, b
Br
PPh2
Fe
Fe
Fe
1
2a
98.2
90.9 (1R,2R)
2c : R = Me, 92 % (d.r. : 96/4)
2d : R = iPr, 31 % (d.r. : 95/5)
5a : R = Me, 70 % (d.r. : 95/5)
5b : R = iPr, 83 % (d.r. : 94/6)
4a
2
3
4
5
6
ent-8
ent-9
2c
2a
2c
2a
2c
90.5
98.0
98.8
97.2
99.4
91.6 (1S,2S)
98.2 (1S,3S)
98.8 (1R,3R)
98.4 (1S,3R)
91.8 (1R,3S)
Scheme 2. a) tBuLi (3.5 equiv),
(2.2 equiv),
(2 equiv), R2Zn (4 equiv), THF, 788C to RT, 12 h; c) nBuLi (2.2 equiv),
788C, 15 min, then ClPPh2 (2.3 equiv), 788C to RT, 1 h.
788C to RT, 1 h; then Cl4Br2C2
788C to RT, 1 h, 80% yield, 97.5% ee; b) CH3COCl
iPr2Zn) using acetyl chloride as a promotor. This process leads
to the substitution products 5a and 5b with high retention of
configuration (d.r. > 94:6). The diphosphanes 2c and 2d were
obtained in 92 and 31% yield, respectively, after exchange of
the bromine atoms with lithium and reaction with ClPPh2.
Remarkably, the ligands 2a ± d are highly efficient for the
asymmetric hydrogenation of various b-ketoesters of type 6
(Table 1).[5, 6] The hydrogenation reactions were performed
using the standard conditions of [Ru(cod)(C4H7)2]/HBr[7]
(0.5 mol%; cod ˆ cycloocta-1,5-diene, C4H7 ˆ 2-methylallyl)
and ligands 2a ± d (0.5 mol%) in EtOH at 508C and under H2
(50 bar).
The same configuration for the hydrogenated products 7
are obtained using the ligands 2a, 2b, and 2d, while the b-
hydroxyesters having the opposite configuration (ent-7) result
from the use of 2c (R ˆ Me) (92 ± 96% ee; entries 4, 6, and 9
in Table 1).
The hydrogenation can be applied successfully to cyclic
ketoesters such as ethyl 2-oxocyclopentane carboxylate[8] to
give (1R,2R)-ethyl 2-hydroxy-1-cyclopentane carboxylate (8)
with 98% de and 90.9% ee after complete conversion (ªRuº/
2a (0.5 mol%), H2 (50 bar), CH2Cl2/EtOH 1/10, 508C, 65 h).
The enantiomeric product (1S,2S)-ent-8 is obtained with
90.5% de and 91.6% ee from 2c (ªRuº/2c (0.5 mol%),
ent-10
[a] Determined after complete conversion. [b] See Table 1.
H2 (50 bar), EtOH, 258C, 21 h; Table 2). Dibenzoylmethane
undergoes a double reduction using 2a (ªRuº/2a, H2 (50 bar),
EtOH, 508C, 10 h) to produce the C2-symmetrical 1,3-diol
(S,S)-9 with 98.2% ee. The opposite enantiomer (R,R)-ent-9
can be obtained in 98.8% ee using 2c with the same reaction
conditions. Unsymmetrical b-diketones such as 1-phenyl-1,3-
butanedione[9] is diastereoselectively reduced to (1S,3R)-1-
phenyl-1,3-butanediol 10 with 98.4% ee using 2a and (1R,3S)-
1-phenyl-1,3-butanediol (ent-10) in 91.8% ee using 2c (ªRuº/
2a or c, H2 (50 atm), EtOH, 508C, 10 h). Thus excellent
enantioselectivities are obtained with a broad range of b-
dicarbonyl compounds.[11]
We also found in preliminary experiments that (Z)-a-
methylacetamido cinnamate (11) is smoothly hydrogenat-
ed[5, 10] in the presence of 1 mol% of catalyst (H2 (1 ± 5 bar),
RT, 0.5 ± 5 h) to give the amino acid derivative 12 with
enantioselectivities up to 96.6% (Scheme 3).[12] Interestingly,
Angew. Chem. Int. Ed. 1999, 38, No. 21
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3821-3213 $ 17.50+.50/0
3213

COMMUNICATIONS
It is interesting to note the difference in the enantioselec-
tivity observed in the hydrogenation reactions using 2c. In an
attempt to explain these results, the complexes formed
between [Rh(nbd)2]BF4 and 2a ± d were isolated. All these
complexes are monomers according to FAB measurements
although the 31P NMR spectrum of the [Rh(nbd)2c]BF4
complex shows a smaller Rh,P coupling constant than the
other three complexes.[14] It seems that the presence of the a-
benzylic methyl group induces a particular space arrangement
of the chelating diphosphanes.
CO2Me
N(H)Ac
CO2Me
[Rh(nbd)2]BF4 (1 mol %)
Ligand 2a-d (1 mol %)
Ph
Ph
N(H)Ac
H2 (1 bar), 0.5-5 h
MeOH/toluene :1/1
11
12 : 95 % yield
with 2a : 95 % ee (R)
with 2b : 92 % ee (R) [a]
with 2c : 52 % ee (S) [a]
with 2d : 96.6 % ee (R)
Scheme 3. Enantioselective reduction of methyl a-acetamido cinnamates
(11) to the amino acid derivatives 12. [a] Reaction performed under H2
(5 bar).
In summary, we have developed a new family of ferrocenyl
ligands (2) with two phosphane substituents. These ligands
gave good to excellent enantioselectivities in the reduction of
various functionalized double bonds and b-dicarbonyl com-
pounds. Interestingly, the two opposite configurations of the
reduced products can be obtained just by modifying the
substituent R in the benzylic position. Further ligand mod-
ifications and applications in asymmetric catalysis are cur-
rently underway.
the ligand 2d also gives the best results for the hydrogenation
of dimethyl itaconate (13)[5, 10] (H2 (1 bar), MeOH, 14 h;
>95%; 98% ee; Scheme 4).
[ Rh(nbd)2]BF4 (1 mol %)
MeO2C
CO2Me
MeO2C
CO2Me
2a-d (1 mol %, 4-14 h)
MeOH, H2 (1 bar)
13
14 : 95 % yield
Received: May 11, 1999 [Z13406IE]
German version: Angew. Chem. 1999, 111, 3397 ± 3400
with 2c : 19 % ee (R) [ a]
with 2d : 98 % ee (S)
with 2a : 91 % ee (S)
with 2b : 81 % ee (S) [ a]
Scheme 4. Enantioselective reduction of dimethyl itaconate (13). [a] Re-
action performed in MeOH/toluene (1/1).
Keywords: asymmetric catalysis ´ homogeneous catalysis ´
hydrogenations ´ metallocenes ´ phosphanes
The complex [Rh(nbd)2a]BF4 (15, nbd ˆ norbornadiene)
was isolated and characterized by X-Ray crystallography
(Figure 1).[13] Remarkably, the ligand 2a acts as a tridentate
ligand and forms two six-membered metallocycles with an
unusual pentacoordinated RhI atom. The coordination of the
amino group seems not to be important to the catalytic
hydrogenation since the ligand 2d (R ˆ iPr) gives similar
enantioselectivities.
[1] a) A. Togni, R. L. Halterman, Metallocenes, Vol. 2, WILEY-VCH,
Weinheim, 1998, pp. 685 ± 721; b) C. J. Richards, A. J. Locke, Tetrahe-
dron: Asymmetry 1998, 9, 2377.
[2] a) J. J. Almena Perea, A. Börner, P. Knochel, Tetrahedron Lett. 1998,
39, 8073; b) J. J. Almena Perea, M. Lotz, P. Knochel, Tetrahedron:
Asymmetry 1999, 10, 375.
[3] J. Kang, J. H. Lee, J. S. Choi, Tetrahedron Lett. 1998, 39, 5523.
[4] a) L. Schwink, P. Knochel, Chem. Eur. J. 1998, 4, 950; b) J. Wright, L.
Framkes, P. Reeves, J. Organomet. Chem. 1994, 476, 215.
[5] For reviews, see a) K. E. Koenig in Asymmetric Synthesis, Vol. 5 (Eds.:
J. D. Morrison), Academic Press, Orlando, FL, USA, 1985, p. 71; b) H.
Takaya, T. Ohta, R. Noyori in Catalytic Asymmetric Synthesis (Ed.: I.
Ojima), VCH, New York, 1993, p. 1; c) R. Noyori, Asymmetric
Catalysis in Organic Synthesis, Wiley, New York, 1994, p. 16.
[6] M. J. Burk, M. F. Gross, T. G. Harper, C. S. Kalberg, J. R. Lee, J. P.
Martinez, Pure Appl. Chem. 1996, 68, 37.
Ã
Â
[7] a) J. P. Genet, C. Pinel, S. Mallart, S. Juge, S. Thorimbert, J. A. Laffitte,
Ã
Tetrahedron: Asymmetry 1991, 2, 555; b) J. P. Genet, C. Pinel, V.
Ratovelomanana-Vidal, S. Mallart, X. Pfister, L. Bischoff, S. Darses,
C. Galopin, J. A. Laffitte, Tetrahedron: Asymmetry 1994, 5, 675.
[8] M. Kitamura, H. Ohkuma, M. Tokunaga, R. Noyori, Tetrahedron:
Asymmetry 1990, 1, 1.
[9] M. Kitamura, T. Ohkuma, S. Inoue, N. Sayo, H. Kumobayashi, S.
Akutayawa, T. Ohta, H. Takaya, R. Noyori, J. Am. Chem. Soc. 1988,
110, 629.
[10] a) M. J. Burk, F. Bienewald, M. Harris, A. Zanotti-Gerosa, Angew.
Chem. 1998, 110, 2034; Angew. Chem. Int. Ed. 1998, 37, 1931; b) A.
Togni, C. Breutel, A. Schnyder, F. Spindler, H. Landert, A. Tijani, J.
Am. Chem. Soc. 1994, 116, 4062.
[11] However, preliminary experiments show that 2-substituted b-dicar-
bonyl compounds give moderate diastereoselectivities but also
excellent enantioselectivities under our conditions. Hydrogenation
of ethyl 2-methyl-3-oxo-butyrate with ligand 2a affords ethyl 3-hy-
droxy-2-methyl-butyrate with 40% de, 91.4% ee (2R,3S), and
86.0% ee (2S,3S).
‡
Figure 1. Structure of the complex cation [Rh(nbd)(2a)] in the crystal
(the hydrogen atoms are omitted for clarity). Selected bond lengths [Š] and
angles [8]: Rh-P1 2.337(1), Rh-P2 2.433(1), Rh-N1 2.233(4); P1-Rh-P2
107.53(4), N1-Rh-P1 86.86(10), N1-Rh-P2 91.65(9).
[12] Enantiomeric excesses were determined by GC or HPLC on a chiral
phase (Chirasil-L-Val, and Diacel Chiralcel columns OD, OJ, AD).
3214
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3821-3214 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 21

COMMUNICATIONS
protein shell[8] have not been intensively investigated using
model compounds and are less well understood.
[13] Crystal data for 15: Mr ˆ 1001.44, monoclinic, space group P21, a ˆ
1073.7(1), b ˆ 2317.0(2), c ˆ 1756.3(1) Š, b ˆ 97.03(1)8, Vˆ
3
4336.4(6) Š3, Z ˆ 4, 1calcd ˆ 1.534 Mgm
,
MoKa radiation (l ˆ
We have already reported the use of dendritic iron
porphyrins[9, 10] as model compounds for cytochromes in
which the protein shell around the buried electroactive core
is mimicked by the dendritic superstructure. These investiga-
tions revealed a strong correlation between the redox
potential and the degree of dendritic branching. In these
early systems, however, the nature of the axial ligation to the
iron center, which is known to have a very strong influence on
the redox properties[3] was not controlled. Therefore, the
observed shifts in redox potential caused by the dendritic shell
could not be quantified independently from axial ligation
effects and no general conclusions concerning the effects of
the dendritic superstructure could be drawn.
We now present a new series of dendritic cytochrome
mimics, which contain a defined and stable axial ligation
pattern. This allows, for the first time, a quantitative evalua-
tion of the effect of an insulating dendritic shell on the
redox properties of the embedded iron porphyrin core. The
three novel dendrimers of generation zero ([1 ´ Fe]Cl), one
([2 ´ Fe]Cl), and two ([3 ´ Fe]Cl) feature controlled axial
ligation at the iron center by two imidazoles tethered to the
porphyrin core. This stable ligation pattern, which is kineti-
cally inert towards coordinating solvents, is found in the
cytochrome b5 family of electron transfer proteins.[11] The
optimal length of the alkyl tethers between the iron-coordi-
0.71073 Š), m ˆ 0.847 mm 1. Data were collected on a STOE IPDS
system at 193 K. The structure was solved by direct methods and
refined on F20 by full-matrix least-squares methods (SHELXS-97,
SHELXL-97, SHELDRICK, 1997). All non-hydrogen atoms were
refined anisotropically. wR2 ˆ 0.0893 (all unique data), R1 ˆ 0.0367
for data with I > 2s(I). 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-134965. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge
CD21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
[14] Selected 31P NMR data (81 MHz, CDCl3) of the phosphane ligands 2
and their complexes with RhI: 2a: d ˆ 16.7 (d, JP,P ˆ 19.1 Hz), 23.2
(d, JP,P ˆ 19.1 Hz); [Rh(nbd)(2a)]BF4: d ˆ 23.1 (dd, JP,P ˆ 22.0, JP,Rh
129.7 Hz), 8.6 (dd, JP,P ˆ 22.0, JP,Rh ˆ 117.6 Hz); 2b: d ˆ 17.1 (d, JP,P
ˆ
ˆ
20.3 Hz), 22.4 (d, JP,P ˆ 20.3 Hz); [Rh(nbd)(2b)]BF4: d ˆ 24.4 (dd,
JP,P ˆ 30.5, JP,Rh ˆ 155.1 Hz), 5.1 (dd, JP,P ˆ 30.5, JP,Rh ˆ 153.2 Hz); 2c:
d ˆ 12.9
(d,
JP,P ˆ 18.4 Hz),
22.4
(d,
JP,P ˆ 18.4 Hz);
[Rh(nbd)(2c)]BF4: d ˆ 17.9 (dd, JP,P ˆ 23.5, JP,Rh ˆ 101.9 Hz), 16.0
(dd, JP,P ˆ 23.5, JP,Rh ˆ 101.9 Hz); 2d: d ˆ 17.8 (d, JP,P ˆ 26.7 Hz),
22.8 (d, JP,P ˆ 26.7 Hz); [Rh(nbd)(2d)]BF4: d ˆ 24.8 (dd, JP,P ˆ 31.1,
JP,Rh ˆ 155.1 Hz), 12.3 (dd, JP,P ˆ 31.1, JP,Rh ˆ 155.1 Hz).
RHNOC
CONHR
[1·Fe]Cl R =
O
O O
Dendritic Iron Porphyrins with Tethered
Axial Ligands: New Model Compounds for
Cytochromes**
N
O
O
O
O
N
O
O
O
O
O
N Fe N
N
N
O
O
N
[2·Fe]Cl R =
O
O
Philipp Weyermann, Jean-Paul Gisselbrecht, Corinne
Boudon, François Diederich,* and Maurice Gross
O
O
O
O
N
O
CONHR
RHNOC
O
O
O
O
O
O
Cl
O
Dedicated to Professor Jean-Marie Lehn
on the occasion of his 60th birthday
O
O
O
O
O
O
O
O
O
O
O
O
The most intriguing characteristics of the cytochrome
family of electron transfer proteins is the very broad range
of redox potentials featured by the FeIII/FeII couple at the
electroactive heme core.[1] A variety of model studies have
identified a dependency of this potential from the nature of
substituents at the porphyrin ring,[2] axial ligation to the iron
center,[3] hydrogen bonding to the axial ligands,[4] and ruffling
of the porphyrin macrocycle.[5] In contrast, the influence of
environmental effects such as heme solvation,[6] polarity of the
heme microenvironment,[7] and the nature of the surrounding
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
HN
NH
O
O
O
HN
NH
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O O
O
O O
HN
O
NH
O
HN
NH
O
O
O
O
O
O
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N Fe N
N
N
N
O
O
O
O
O
O
O
N
O
O
O
O
O
O
O
O
O
O
O
O
O
HN
O
[*] Prof. Dr. F. Diederich, Dipl.-Chem. P. Weyermann
Laboratorium für Organische Chemie, ETH-Zentrum
Universitätstrasse 16, CH-8092 Zürich (Switzerland)
Fax: (‡41)1-632-1109
NH
O
O
HN
NH
O
O
O
O O O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Cl
NH
HN
O
O
O
O
HN
NH
O
O
O
O
O
O
O
O
O
O
O
O
E-mail: diederich@org.chem.ethz.ch
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Dr. J. P. Gisselbrecht, Dr. C. Boudon, Prof. Dr. M. Gross
Laboratoire dꢁElectrochimie et de Chimie Physique du Corps Solide
Faculte de Chimie, Universite Louis Pasteur and CNRS, UMR
no. 7512
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
4, rue Blaise Pascal, F-67000 Strasbourg (France)
O
O
[3·Fe]Cl
[**] This work was supported by the ETH Research Council.
Angew. Chem. Int. Ed. 1999, 38, No. 21
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3821-3215 $ 17.50+.50/0
3215