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Chirality and Isomerism in Binuclear Iron Complexes with Sulfur Ligands [Fe(CO)(-УS4Ф)]2 a Model Complex for Oxidoreductases.

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arrangement. The nitrogen atoms are coordinated in the
form of a distorted pentagonal bipyramid, axially by two
calcium atoms and equatorially by two calcium and three
lithium atoms. The Ca,,-N-Ca,,
angle is nearly linear at
177.5(3)"; the Ca,,-N-(Ca, Li)eqangles lie between 81.5(2)"
and 96.9(2)". In the equatorial plane the angle subtended at
nitrogen between two calcium atoms is 94.7(1)"; that between two lithium atoms is 62.0(2)".
In the crystal structure of Li4SrN,1'61(bottom of Fig. 2)
the N atoms are also coordinated within distorted pentagonal bipyramids, in this case involving 2 x Li,, and 2 x
Sreq+ 3 x Li,,. The angular relationships are comparable to
those in the calcium compound (vide supra): LiaX-N-Li,,
174.4(3)"; Liax-N-(Sr,Li)eq 87.2(2)"-92.0(2)"; Sreq-N-Sreq
92.4(2)"; Lieq-N-Lieq 62.8(2)". As implied in Figure 2 (bottom), the Li,SrN, structure can be derived directly from the
structure of Li,N (Fig. 2, top)['31. The three-dimensional
framework of hexagonal bipyramids interconnected through
equatorial edges and axial vertices in Li,N (NLi,,zLi,,,) is
cut into layers which in Li,SrN, (NLiZ/,Li3,,Sr,/,) are in turn
made up of pentagonal bipyramids. The layers run along
[OOl]; each is turned 90" relative to the next, and they are
connected to one another through shared strontium atoms.
Strontium is therefore coordinated to four nitrogen atoms in
a distorted tetrahedral geometry (Sr-N: 2.648(3) b;; N-SrN: 92.4(2)"- 118.6(3)"). The Li-N bond lengths within the
layers (Liax-N: 1.913(2) A, Lie,-N: 2.112(2)-2.149(2) A) are
just as graded as those in the structure of Li,N113](Liax-N:
1.938 A, Lie,-N: 2.130(1). Impedance measurements show
Li,SrN, to be an ion conductor (activation energy 0.9(5) eV)
but with a considerably lower ionic conductivity than
Li,N'"'. At 430 "C the ionic conductivity of Li,SrN, is still
an order of magnitude lower than that of pure Li3N measured at room temperature.
Received: May 26,1989 [ Z 3359 IE]
German version: Angew. Chem. 101 (19S9) 1689
[l] R. Juza, K. Langer, K. von Benda, Angew. Chem. 80 (1968) 373; Angew.
Chem. Int. Ed. Engl. 7 (1968) 360.
121 R. D. Shannon, Aria Crystullogr. A 3 2 (1976) 751.
[3] R. Juza, F. Hund, Z. Anorg. Allg. Chem. 257 (1948) 1.
[4] R. Juza, F. Hund, Z. Anorg. Allg. Chem. 257 (1948) 13.
[ S ] R. Juza, H. H. Weber, E. Meyer-Simon, Z. Anorg. Allg. Chem. 273 (1953)
[6] R. Juza, W. Gieren, J. Haug, Z. Anorg. Allg. Chem. 300 (1959) 61.
171 R. Juza, E. Anschiitz. H. Puff, Angew. Chem. 71 (1959) 161.
[S] A. Gudat, R. Kniep, A. Rabenau, German Chem. Soc., 5th Annu. Conf.
Solid State Chem., Erlangen, September 28-30, 1988,
[9] G. Cordier, A. Gudat, R. Kniep, A. Rabenau, Angew. Chem. fOt (1989)
204; Angew. Chem. Int. Ed. Engl. 28 (1989) 201.
[lo] M. H. Gerss, W. Jeitschko, 2. Naturforsch. 8 4 1 (1986) 946.
[ l l ] R. Nesper, Z . Kristnllogr. manuscript in preparation. The observed distance d(Sr-N) = 2.6 A leads to a decidedly larger volume for the fluorite
structure type than for the YCoC structure type. For d(Sr-N) > 2.44 A,
the fluorite structure type will be energetically less favorable than the
[l2] J. Aubry, M. Fromont, R. Streiff, C.R. Hebd. Seances Acad. Sci. Ser. C262
(1966) 1785.
1131 A. Rabenau, H. Schulz, J. Less Common M e / . 50 (1976) 155.
[14] J:F. Brice, J.-P. Motte, R. Streiff, C.R. Hebd. SiancesAcad. Sci. Ser. C269
(1969) 910.
1151 J:F. Brice, J. Aubry, C.R. Hebd. Seances Acad. Sci. Ser. C271 (1970) 825.
[16] Crystallographic data: LiCaN: orthorhombic, Pnma. a = 8.471(3), b =
3.676(2), c = 5.537(3) A. Z = 4 ; 670 measured, 268 independent reflections; R = 0.034. Li,SrN,: tetragonal, I4,/amd, a = 3.822(2), c =
27.042(9) A, Z = 4; 1192 measured, 188 independent reflections; R =
0.045. Phillips PW-1100 single crystal diffractometer, Mo,,. 300 K. Further details of the crystal structure investigation are available on request
from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG) hy quoting the depository number CSD 54206, the names
of the authors, and the journal citation.
(171 A. Rabenau, Solid Stale Ionics 6 (1982) 277.
Angen'. Chem. In!. Ed. Engi. 28 (1989) No. 12
Chirality and Isomerism in
Binuclear Iron Complexes with Sulfur Ligands:
[Fe(CO)(p-"S,")]z., a Model Complex
for Oxidoreductases **
By Dieter Sellrnann,* Robert Weiss, and Falk Knoch
Numerous oxidoreductases, including nitrogenases and
hydrogenases, have an active center consisting of iron atoms
in a coordination sphere of sulfur atoms. However, much
uncertainty remains about the precise structures of such
multinuclear centers and the molecular processes associated
with the corresponding catalytic reactions." Previously described model compounds of these centers are all only of the
structural type; i.e., they do incorporate iron atoms and
sulfido or thiolato ligands,"bl are usually highly symmetric,
but fail to react with such relevant substrates as CO, N,, or
H,. What has generally not been considered with respect to
model complexes is the fact that the metal centers in oxidoreductases are always chirotopic as a consequence of bonding to the protein shell.1z1This generalization applies even
when the catalyzed reaction involves only achiral substrates
or, as in the case of the iron centers in ferredoxins, when the
iron centers are constituents of highly symmetrical subunits
such as [Fe,S,(SR),] clusters.[1a1Metallic centers in oxidoreductases must also provide free or potentially free coordination sites for the attachment of substrates.
In our search for model complexes of the active centers in
nitrogenases and hydrogenases we have attempted to elaborate the iron complex 1 in such a way as to create multicentered chiral units with free or potentially free coordination
sites at the Fe centers. Since 1 itself is chiral, it was of particular interest to ascertain what diastereomers would form in
the course of a dimerization. We now report the isolation and
structural characterization of the binuclear complex
which represents a new type of chiral complex. 2 contains
two homochiral fragments with low-valent Fe centers that
bind 0'-n ligands, and it is formed upon dimerization of
racemic precursor complexes according to equation (a).'"]
Theoretically, the dimerization of [Fe(CO)("S,")] fragments might lead to ten diastereomers (Scheme 1, I-X). This
assertion is based on the assumption of configurational stability at the Fe centers, however, since otherwise the number
of diastereomers would be even larger (e.g., isomers with
planar orientation of the sulfur ligands). Molecular models
reveal that the conformation of the C,H, bridge in 1 is fixed
due to the rigid C,H,S, units (i.e., "inversion" of the bridge
would lead to serious distortion of the angles at the Fe atom).
Thus, dimerization can only lead to RR, RS and SS isom e r ~ . [In
~ ]contrast to previously known binuclear complexes with chiral fragments,r61each of these combinations in 2 is
in principle the source of four isomers. Members of two of
the resulting ''pairs'' are in fact identical, so the overall result
Prof. Dr. D. Sellmann, Dip1.-Chem. R. Weiss, Dr. F. Knoch
Institut fur Anorganische Chemie der Universitat Erlangen-Niirnberg
Egerlandstrasse 1, D-8520 Erlangen (FRG)
(''S,")20 = 2,2'-(ethylenedithio)dibenzenethiolate. Transition Metal
Complexes with Sulfur Ligands, Part 51. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Part 50: D. Sellmann, 0. Kappler, F. Knoch, M. Moll, 2. Narurforsch., in press.
0 VCH VerlagsgesellschuftmhH. 0-6940
Wernherm. 1989
0570-0833/89/1212-17033 02.5010
Scheme 1. Theoretically possible isomers of 2 , with schematic representations of the pp-Z(SS), aa-E(RS),and Ba-E(SS) isomers, n = C,H,.
is ten structures that differ in the following ways:
a) The two CO ligands may point either in the same ( Z
isomers) or the opposite ( E isomers) direction.
b) The bridging of the Fe centers takes place via two kinds
of thiolato-S atoms which differ in only one respect: The
ortho thioether-S atom at the respective benzene ring
stands either trans to the remaining CO ligand (a-bridging) or trans to the second thiolato bridge @-bridging).
Furthermore, in the case of the RR and SS isomers the Z
form is only possible with ua-or pp-, the E form only with
pa- or @-linkage. The opposite is true for the RS isomers:
the 2 form is only possible with ap- or pa-, and the E form
only with au- or PP-bridging. The inversion-symmetric
ua-E(RS) and pP-E(RS)isomers VI and VII are meso forms
of 2.
Steric hindrance to dimerization is most likely to be associated with the various Z isomers. It was thus surprising to
discover that the product 2 isolated upon reaction according
to equation (a) could be shown by X-ray structural analysisL3]to consist of the enantiomeric pair aa-Z(RR)/aaZ(SS). Figure 1 illustrates the structure of the aa-Z(Ss>
isomer of 2.
The diamagnetic complex 2 contains two homochiral
[Fe(CO)("S,")] fragments connected by thiolato ligands,
and the resulting complex is also chiral. 2 possesses nearly C ,
symmetry, and the Fe" centers, which have 18e-configurations, are each coordinated pseudo-octahedrally to one CO
ligand and five S atoms. Both the 18, rule and the large
Fel -Fe2 separation argue against direct metal-metal interaction. The [Fel-Fe2-Sl-S5] four-membered ring is slightly
folded, with a dihedral angle of 171". The Fe-S distances are
225.1(3)-233.0(3) pm, and thus within the range regarded as
typical for such complexes.
The differing steric requirements within the Fe coordination spheres in 2 is rather striking. One "half" of each molecule appears heavily overloaded due to the steric demands of
the "S," ligands, while the other "half" is occupied only by
the two CO ligands. In this respect, therefore, the structure
of 2 is reminiscent of metalloproteins in which the folding of
a peptide chain produces a distinctive spatial environment
for the free coordination site. The two coordination sites on
2 that would result from release of CO should make it possible for bicentric and enantiofacial reactions to take place.
That free coordination sites actually do result upon cleavage
of CO from 2 is demonstrated by preliminary experiments
leading to the isolation of [Fe,(CO)(NO)(p-"S,")2]PF,.
According to X-ray structural analysis, the homochiral
[Fe(CO)("S,")] fragments in 2 display exclusively a-bridging. This suggests that the regioselectivity observed during
dimerization is due not to steric, but rather to electronic
factors associated with the differing characteristics of the
thiolate S atoms in the [Fe(CO)("S,")] fragments. Attempts
are currently being made to separate the racemic mixture.
Experimental Procedure
Fig. 1. Structure of aa-Z(SS)-2 in the crystal (without H atoms). Important
distances lpm] and angles I"]:Fel-Fe2 342.0(1), Fel-Sl 230.2(3), Fel-S2
230.5(3), Fel-S3 225.8(3), Fel-S4 229.8(3), Fel-S5 232.7(3), Fel-C1 174.4(11),
Fe2-Sl 233.0(3), Fe2-S5 229.4(3), Fe2-S6 231.3(3), Fe2-S7 225.1(3), Fe2-S8
230.5(3),Fe2-C2 174.5(30);Fe2-SI-Fel 95.1(1), Fe2-S5-Fel 95.4(1), SS-Fel-Sl
84.3(1), S5-Fe2-Sl 84.4(1), Cl-Fel-S2 174.4(4), C2-Fe2-S6 177.1(4).
Verlagsgrsellschafl mbH, 0-6940 Weinheim. 1989
1270 mg (3.0 mmol) of I 171 was dissolved in 50 m L of djmethylformamide
(DMF). The raspberry-colored solution was then filtered and warmed to 90 "C,
causing it to turn reddish brown, and dark brown crystals of 2 began to separate. These were isolated after 48 h. Yield 70% (not optimized); 1R (KBr).
? = 1965 cm-' (CO); 'H NMR ([DJDMF): 6 = 6.8-8.4 (m, 16H). 0.8-2.5
(m, 8H); correct elemental analysis.
Received: August 9, 1989 IZ 3488 IE]
German version: Ange:ew.Chem. 101 (1989) 1719
Angew. Chem. h i . Ed. Engl. 28 (1989) No. 12
[l] Compare a) T. G. Spiro (Ed.): Mefal Ions in Biology. Vul. 4 (Iron Sulfur
Proteins) and Vul. 7 (Molybdenum Enzymes), Wiley, New York 1982 and
1987; b) M . J. Nelson, P. A. Lindahl, W. H. Orme-Johnson in G . L. Bchhorn, L. G . Marzilli (Ed.): Adv. Inorg. Biochemistry, Vut. 4 , Elsevier, Amsterdam 1982, p. 1.
[2] Regarding terminology cf. K. Mislow, J. Siegel, J Am. Chem. Suc. 106
(1984) 3319.
[3] X-ray structure analysis of 2: P2,/c, a = 1272.8(5), b = 1534.1(23), c =
1633.6(16)pm, p = 104.76(8)"; V = 3085(2) x lo6 pm3; Z = 4. T = 200 K,
Mo,. irradiation; w-scan; 3.0 .c w < 15" min-I, 4" 2 8 < 52". 5328 independent reflections, for 3287 of which F > 6m(F). SHELXTL-PLUS, direct
methods, R = 0.078, R, = 0.065. Further details of the crystal structure
investigation are available on request from the Fachinformationszentrum
Karlsruhe. Gesellschaft fur wissenschaftlich-technische Information mhH,
D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository
number CSD-54803, the names of the authors, and the journal citation. A
comparison between experimental and simulated powder diagrams (LAZYPulverix) for aa-Z(RR)/act-Z(S.S)-2 shows that the isolated product, consisting of blocks and intertwined prisms, must contain an additional isomer
of 2.
141 Regarding the dimerization of homochiral fragments or racemic heterochiral fragments cf. F. A. L. Anet, S . S . Miura, J. Siegel, K. Mislow, J. Am.
Chem. SOC.105 (1983) 1419.
[S] R . S assignment according to R. S. Cahn, C. K. Ingold, V. Prelog, Angew.
Chem. 78 (1966) 413; Angew. Chem. hi[.Ed. Engf. 5 (1966) 385; based on
IUPAC nomenclature the Rand S isomers would be referred to as A and A
isomers. respectively; cf. Deutsches ZentralausschuD fur Chemie (Ed.): Internaliunale R q e l n fur die chemische Nomenklatur und Terminolugie, Band
1 , Gruppe I, Verlag Chemie, Weinheim 1976, p. 100. As indicated in this
source, the IUPAC nomenclature for describing octahedral complexes with
multidentate ligands remains unsatisfactory.
[6] Compare a ) C. H. Winter, A. M. Arif, J. A. Gladysz, Organometallics 8
(1989) 219; b) G . Wilkinson, R. D. Gillard, J. A. McCleverty (Ed.): Cumprehrnsive Coordination Chemistry, Pergamon, Oxford 1987; c) J. M. B.
Harrowfield, S. B. Wild in [6h], Vul. 1, p. 179; D. A. House in [6b], Vul. 2,
p. 23, G. B. Kaufmann, Cuurd. Chem. Rev. 12 (1974) 105.
[7] D. Sellmann. H. E. Jonk, H. R. Pfeil, G. Huttner, J. von Seyerl, .l
OrRanumet. C'hem. 191 (1980) 171.
Scheme 1. HC
unsaturated hydrocarbon.
case of the dialkyl(tetracarbony1)osmium compounds cis[R,OS(CO),],[~] the hydrocarbon bridges in 1-4 are cis to
each other.
Directed Synthesis of
Trinuclear Hydrocarbon-Bridged Complexes such as
[(OC),ReCH,CH,Os(CO),CH,CH,Re(CO),] **
By Wolfgang Beck,* Burkhard Niemer, and Barbara Wagner
Dedicated to Professor Alfred Schmidpeter on the occasion
of his 60th birthday
The nucleophilic addition of carbonylmetalates to coordinated, unsaturated hydrocarbons in cationic complexes is a
method that lends itself to the directed synthesis of a variety
of hydrocarbon-bridged complexes.l'] Previously we have
utilized only monoanions for this purpose, for example
[Re(CO),]", leading to heterobimetallic complexes. We are
now able to report that the dianion [Os(CO),]'@ ['* 3l permits
the efficient synthesis of trinuclear hydrocarbon-bridged
complexes (Scheme 1).
The complexes 1-4 were obtained in good yield by treatment of [OS(CO),]~~
with the cations 5-8 (in THF). The
Re, compound 9 was identified as a byproduct of 1.As in the
[*] Prof. Dr. W. Beck, DipLChem. B. Niemer, Dip].-Chem. B. Wagner I + ]
Institut fur Anorganische Chemie der Universitit
Meiserstrasse 1. D-8000 Munchen 2 (FRG)
['I X-ray structural analysis
I**] Hydrocarbon-Bridged Complexes, Part 14. This work was supported by
the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen
Industne. We wish to thank Professor Dr. F: R. Kreissl, Technische Universitat Munchen, for mass spectra, and Professor Dr. G. Hutfner,Universitit
Heidelberg, and Dr. K . Karaghiusoff, Universitat Munchen, for helpful
discussions. Part 13: J. Breimair, M. Steimann, B. Wagner, W. Beck, Chem.
Ber., in press.
Angen,. Chem. Int. Ed. Engl. 28 (1989) Nu. 12
Compounds 1-4 were characterized on the basis of
spectroscopic data (Table 1); in addition, 2-4 were the
subject of X-ray structural analysis.r91The mass spectrum of
1 reveals signals not only for the molecular ion but also
for the cleavage products [(OC),OsC,HaRe(CO),]@ and
[(OC),Re(C,H,)]@ and fragments corresponding to succes-
Table 1. IR[a] together with 'H- and "C-NMR spectroscopic data for 1-4.
1 (in pentane):
= 2119w, 21 low, 2033%2009vs, 1983m
2 (in C,H,): V = 2113w. 2067vw, 2040s,sh. 2030s, 2013vs, 2006vs,
3 (in pentane): V = 2138w, 2070m, 2053vs. 2044m, 2022m,sh, 2015~s.2005vw,
194Os, 1926s
4 (in CH,CI,): i = 2121w, 2040s, 2015m, 1978vs,br, 1907s,br,
1 (CD2C12,270 MHz): A A B B spectrum, 6 = 2.08 - 1.91. 14 lines
2 [D],toluene, 90MHz, -72°C): 6 = 5.20 (t, 4-H), 3.76 (dd. 3.5-H), 2.95
(t,l-H), 2.47 (dd,2,6-H); (+26 "C): b = 3.73 (br); (+52"C): b = 3.80(s)
3 (C,D,): 6 = 5.08 (br.1 H). 5.05 (br, 1 H), 4.71 (br, 2 H). 3.86 (br, 1 H), 3.79
(br, 1 H). 2.92 (br, 1 H), 2.86 (hr,t H)
4 (CD2C1,): 6 = 6.23 (dd,4,5-H), 4.50 (m, 3,6-H), 4.26 (t. 2,7-H), 3.68 (t,l-H)
I(CD,CI,, 67.8 MHz): 6 = 187.26(ReCOe,), 181.90(ReCO,,), 172.44(OsCO),
12.04, 4.45
3 (C,D,): 6 = 174.65 (OsCO,,), 168.54 (OsCO.,), 88.93. 88.75, 69.27, 69.19,
68.95, 68.75, 49.07, 48.63. MnCO signal not detectable
4 (CDKI,): 6 = 176.71 (OsCO.,). 169.57 (OsCO,,), 100.87 (C-4.5) 97.94 (C3,6), 82.77 (C-2,7), 18.09 (C-l), MoCO signal not detectable
[a] v(C0) bands in cm-'.
Verlagsgese//schaf~mbH, 0.6940 Weinheim. 1989
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binucleata, complex, mode, isomerism, iron, sulfur, complexes, уs4ф, chirality, ligand, oxidoreductases
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