Fe-Only Hydrogenases
557 560
Table 1. Selected bond lengths [ä] for 5 and 6.
for C15H19Br2NO4: C 41.21, H 4.38, Br 36.56, N 3.20; found: C 41.71, H 4.58,
Br 35.67, N 3.21.
5
6
1,3-Dithioacetyl-2-(4-butoxycarbonylaminobenzoyl)propanol (3): The di-
bromo derivative 2 (0.219 g, 0.5 mmol) was dissolved in acetone (15 mL),
and then potassium thioacetate (4.5 equiv; 0.257 g, 2.25 mmol) was added.
The reaction was stirred under N2 at ambient temperature and followed by
TLC. When starting material disappeared (ca. 4 h) the precipitated KBr
was filtered off, and the filtrate was evaporated in vacuo. The residue was
purified by flash column chromatography with toluene/EtOAc (6:1) as
À
Fe1 S1
2.2699(7)
2.2603(7)
2.5093(5)
2.2528(7)
2.2466(7)
1.797(3)
1.798(3)
1.807(3)
1.807(3)
1.797(3)
1.799(3)
1.833(2)
1.824(2)
2.278(2)
2.257(2)
2.499(1)
2.256(2)
2.261(2)
1.794(7)
1.787(7)
1.808(7)
1.804(7)
1.789(7)
1.815(7)
1.824(6)
1.827(6)
À
Fe1 S2
À
Fe1 Fe2
À
Fe2 S1
À
Fe2 S2
À
Fe1 C1
À
Fe1 C2
1
eluent, giving 3 (177 mg, 82.5%) as an oil. H NMR (CDCl3): d 1.52 (s,
À
Fe1 C3
9H), 2.32 (s, 6H), 3.26 (dd, J 10.5, 4.8 Hz, 1H), 3.29 (dd, J 10.5, 3.9 Hz,
1H), 5.22 5.28 (m, 1H), 6.71 (s, 1H), 7.42 7.44 (m, 2H), 7.91 7.93 (m,
2H); elemental analysis calcd (%) for C19H25Br2NO6S2: C 53.38, H 5.89, N
3.28, S 15.00; found: C 53.20, H 5.97, N 3.17, S 15.14.
À
Fe2 C4
À
Fe2 C5
À
Fe2 C6
À
S1 C8
1,3-Dithiolo-2-(4-butoxycarbonylaminobenzoyl)propanol (4): The thioace-
tate derivative 3 (124 mg, 0.29 mmol) was dissolved in DMF (5 mL). To
solution hydrazine hydrate (3.5 equiv; 50 mL, 1.027 mmol) was added
dropwise under N2 at ambient temperature, and then the solution was
stirred for 10 min. Afterwards, acetic acid (3.5 equiv; 60 mL, 1.027 mmol)
was added dropwise under N2 at ambient temperature. The reaction was
followed by TLC, and when the starting material disappeared (ca. 30 min)
the mixture was diluted with water (10 mL) and ethyl acetate (10 mL).
After phase separation the organic layer was washed with 2 Â 10 mL of
water, and then the water phase was extracted with ethyl acetate. The
combined organic phase was washed with water (10 mL) and brine
(10 mL), dried with Na2SO4, filtered, and concentrated in vacuo. The
crude product was purified by flash column chromatography with toluene/
À
S2 C7
Conclusion
An amino-functionalized model 6 for the active site of the Fe-
only hydrogenases has been prepared by covalently linking
4-aminobenzoic acid to a 2Fe2S structure. The Fe dimers of 6
and its precursor 5 are fully stable during the reaction
conditions invetsigated. The crystal structures of 5 and 6 show
that the functional group and the Fe dimer are separated from
each other by about 11 ä. This suggests that these complexes
will be useful for protein modification and the build up of
supramolecular systems, where a 2Fe2S unit is linked to one or
more redox components for the study of electron transfer
processes.
1
EtOAc (6:1) as eluent, giving 4 (94.5 mg, 95.5%) as a thick oil. H NMR
(CDCl3): d 1.46 (t, J 8.8Hz, 2H), 1.53 (s, 9H), 2.97 (dd, J 5.7 Hz,1 Hz,
1H), 3.00 (dd, J 5.7 Hz, 1.5 Hz, 1H), 5.16 (app. pent., J 5.7 Hz, 1H),
6.66 (s, 1H), 7.43 7.46 (m, 2H), 7.96 7.99 (m, 2H); elemental analysis
calcd (%) for C19H25Br2NO6S2: C 52.45, H 6.16, N 4.08, S 18.67; found: C
52.45, H 6.21, N 4.03, S 18.58.
Synthesis of [m-(SCH2)2CHCO2C6H4NHCO2C(CH3)3]Fe2(CO)6 (5): T he
dithiol derivative 4 (90 mg, 0.207 mmol) was dissolved in dry THF (20 mL),
and then triiron dodecacarbonyl (105 mg, 0.208 mmol) was added. The
resulting solution was warmed up to 65 678C, stirred for 0.5 h under N2,
and then concentrated by evaporating the solvent in vacuo. The crude
product was purified by flash column chromatography on silica gel with
toluene/pentane (1:1) as eluent followed by pure toluene. The crystalline
product 5 was obtained by cooling the concentrated toluene solution at ca
À208C overnight (141.5 mg, 87%). 1H NMR (CDCl3): d 1.52 (s, 9H), 1.69
(dd, J 12.9, 12.0 Hz, 1H), 2.91 (dd, J 13.5, 4.5 Hz, 1H), 4.42 4.49 (m,
1H), 6.65 (s, 1H), 7.39 7.42 (m, 2H), 7.86 7.88 (m, 2H); elemental analysis
calcd (%) for C21H19Fe2NO10S2: C 40.6, H 3.08, N 2.25, S 10.32; found: C
43.76, H 3.46, N 2.11, S 9.37. The deviation is due to the presence of ca 20%
toluene solvent in the crystal structure.
Experimental Section
All reagents and solvents were purchased from Aldrich and used as
received. 1H NMR spectra were recorded on a Varian 400 spectrometer.
Elemental analysis was performed in Analytische Laboratorien, Lindlar
(Germany).
4-Butoxycarbonylaminobenzoic acid (1): 4-Aminobenzoic acid (2.74 g,
20 mmol) was suspended in water (40 mL) and then tert-butanol (30 mL)
was added. To this solution di-tert-butyl-dicarbonate (8.73 g, 40 mmol) and
solid NaOH (0.88 g, 22 mmol) were added and the temperature was
increased to 608C. After completion of reaction the mixture it was diluted
with water (100 mL), washed with CH2Cl2 (2 Â 50 mL) and the water phase
was cooled to 0 58C. Ethyl acetate was added (50 mL), and under
intensive stirring the pH was lowered to 2 by the addition of 2m HCl. The
organic phase was separated and the extraction was repeated with ethyl
acetate (2 Â 50 mL). Combined extracts were dried over Na2SO4, and
evaporated in vacuo giving 4-butoxycarbonylaminobenzoic acid (1; 4.62 g,
97.5%). The solid off-white powder was directly used for the next step.
1H NMR ([D6]DMSO): d 1.48 (s, 9H), 7.54 7.56 (m, 2H), 7,82 7.84 (m,
2H), 9.72 (s, 1H), 12.59 (s, 1H).
Crystal data for 5: C21H19Fe2NO10S2: M 621.20, monoclinic space group,
P21/c (No. 14), a 11.1598(10), b 11.9372(12), c 22.735(3) ä, b
92.002(12)8, V 3026.8(6) ä3, Z 4, T 170 K, 1calcd 1.466 gcmÀ3
,
m(MoKa) 1.15mmÀ1, F(000) 1356, 22301 reflections measured, 5651
unique (Rint 0.048), 4956 observed (I > 2s(I)), 365 parameters refined,
absorption correction (numerical): Tmin/Tmax 0.788/0.916. R1 0.0335, (I
> 2s(I)), wR(F2) 0.1050, S 1.11 (all data). Max./min. residual electron
density: 0.52/ À 0.46. Data collection: STOE-IPDS image plate diffrac-
tometer with a rotating-anode using MoKa radiation (l 0.71073 ä). The
intensities of the reflections were integrated with the STOE software, and
the numerical absorption correction was performed with the programs
X-RED and X-SHAPE.[31] The structure was solved by direct methods[32]
and refined by full matrix least-squares on F2.[33]
1,3-Dibromo-2-(4-butoxycarbonylaminobenzoyl)propanol (2): DMAP
(0.128 g, 1.05 mmol) and 1,3-dibromopropan-2-ol (0.26 mL, 2.54 mmol)
were added to a suspension of compound 1 (0.6 g, 2.53 mmol) in dry CH2Cl2
(50 mL). The resulting suspension was stirred at room temperature for
15 min, and then a CH2Cl2 (15 mL) solution of DCC (0.87 g, 4.21 mmol)
was added dropwise (ꢀ15 min) under N2 atm at ambient temperature. The
reaction was followed by TLC, and when the starting material disappeared
(ꢀ4 h) the solvent was evaporated in vacuo. The residue was purified by
column chromatography on silica with toluene/EtOAc (6:1) as eluent.
After evaporation of the solvent 2 was obtained as a white powder (0.905 g,
Synthesis of [m-(SCH2)2CHCO2C6H4NH2]Fe2(CO)6 (6): Trifluoroacetic
acid (0.51 mL, 3 mmol) was added to a solution of the diiron complex 5
(90 mg, 0.14 mmol) in dry dichloromethane (10 mL), and then stirred at
ambient temperature. The reaction was followed by TLC, and when the
starting material disappeared (3 4 h) the solvent and unreacted TFA were
evaporated in vacuo. The residue was purified by flash chromatography
with toluene/EtOAc (6:1) as eluent to give 6 (67 mg, 89%). A single
crystalline product was obtained by cooling the concentrated toluene/
1
86%). H NMR (CDCl3): d 1.53 (s, 9H), 3.72 (dd, J 11.0, 5.4 Hz, 1H),
1
3.77 (dd, J 11.0, 4.9 Hz, 1H), 5.35 (app. pent., J 5.4 Hz, 1H), 6.67 (s,
pentane (1:1) solution of 6 at about À208C overnight. H NMR (CDCl3):
1H), 7.44 7.47 (m, 2H), 7.98 8.01 (m, 2H); elemental analysis calcd (%)
d 1.67 (dd, J 13.0, 11.5 Hz, 1H), 2.90 (dd, J 13.0, 4.1 Hz, 1H), 4.09 (s,
Chem. Eur. J. 2003, 9, No. 2
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0902-0559 $ 20.00+.50/0
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