The concept of docking/protecting groups in biohydroxylation

Article abstract of DOI:10.1002/(SICI)1521-3773(19990917)38:18<2763::AID-ANIE2763>3.0.CO;2-M

A general principle for biohydroxylation, in which time-consuming screening and enrichment techniques are avoided, is demonstrated by the introduction of a docking/protecting group into the substrate. This facilitates acceptance by the microorganism and allows the use of a narrow range of microorganisms, for example Beauveria bassiana ATTC7159 (B.b.), for the hydroxylation of compounds with diverse structures. After the biohydroxylation, the docking/protecting group is removed (see scheme).

Full text of DOI:10.1002/(SICI)1521-3773(19990917)38:18<2763::AID-ANIE2763>3.0.CO;2-M

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[4] A. L. Balch, M. Mazzanti, B. C. Noll, M. M. Olmstead, J. Am. Chem.
Soc. 1994, 116, 9114.
[5] J. V. Bonfiglio, R. Bonnett, D. G. Buckley, D. Hamzetash, K. M.
Hursthouse, K. M. A. Malik, A. F. McDonagh, J. Trotter, Tetrahedron
1983, 39, 1865.
[6] a) A. L. Balch, M. Mazzanti, B. C. Noll, M. M. Olmstead, J. Am.
Chem. Soc. 1993, 115, 12206; b) S. Attar, A. L. Balch, P. M.
Van Calcar, K. Winkler, J. Am. Chem. Soc. 1997, 119, 3317; c) S.
Attar, A. Ozarowski, P. M. Van Calcar, K. Winkler, A. L. Balch,
the two end units of [Pd4(OEB)2]. The formation of
[Pd(OEB)] from the pyridine/ethanol solution is governed
by the ability of pyridine to coordinate to the central Pd2 unit
and thus to facilitate its dissociation from [Pd4(OEB)2].
The h2 coordination of the bilindione by a palladium center
not only produces the novel structure shown in Figure 1, but
also alters the chemical reactivity of the ligand. We will
describe the rearrangement of the ligand core in [Pd4(OEB)2]
elsewhere.[18]
Â
Chem. Commun. 1997, 1115; d) A. L. Balch, L. Latos-GrazÇynski, B. C.
Noll, M. M. Olmstead, N. Safari, J. Am. Chem. Soc. 1993, 115, 9056.
Â
[7] a) L. Latos-GrazÇynski, J. A. Johnson, S. Attar, M. M. Olmstead, A. L.
Balch, Inorg. Chem. 1998, 37, 4493; b) R. Koerner, L. Latos-
Experimental Section
Â
GrazÇynski, A. L. Balch, J. Am. Chem. Soc. 1998, 120, 9246.
[8] A compound in which two lithium ions are sandwiched between two
anionic porphyrins has been structurally characterized: C. S. Alexan-
der, S. J. Retig, B. R. James, Organometallics 1994, 13, 2542.
[9] K. K. Dailey, G. P. A. Yap, A. L. Rheingold, T. B. Rauchfuss, Angew.
Chem. 1996, 108, 1985; Angew. Chem. Int. Ed. Engl. 1996, 35, 1833.
[10] M. Senge, Angew. Chem. 1996, 108, 2051; Angew. Chem. Int. Ed. Engl.
1996, 35, 1923.
[11] C. Floriani, E. Solari, G. Solari, A. Chiesi-Villa, C. Rizzoli, Angew.
Chem. 1998, 110, 2367; Angew. Chem. Int. Ed. 1998, 37, 2245.
[12] C. Floriani, Chem. Commun. 1996. 1257.
[Pd4(OEB)2]: Under a dinitrogen atmosphere, a solution of palladium(ii)
acetate (115 mg, 0.512 mmol) in chloroform (5 mL) was added to a solution
of octaethylbiliverdin (30 mg, 0.054 mmol) in ethanol (25 mL). (Ethanol is
critical for the success of the reaction and serves as reductant.) After the
mixture was heated to 658C for 5 min and stirred for 1.5 h at 258C, the
solvent was evaporated. The residue was subjected to chromatography on
silica with chloroform as the eluant. The first dark green fraction was
collected and evaporated to dryness (yield: 27.5 mg, 66.5%). Crystals
suitable for X-ray crystallography were grown by slow diffusion of water
into a solution of the complex in THF. 1H NMR (300 MHz, CDCl3): d ˆ
6.759 (s, meso-CH), 6.007 (s, meso-CH), 5.156 (s, meso-CH), 2.575 ± 1.892
(m, CH2), 1.340 ± 0.863 (m, CH3). UV/Vis: lmax [nm] (e [m 1 cm 1]) ˆ 831
(2.2 Â 104), 358 (4.6 Â 104), 284 (3.7 Â 104). MALDI MS (positive ion):
parent cluster at 1527.00 amu.
[13] D. Cullen, E. Meyer, T. S. Srivstava, M. Tsutsui, J. Am. Chem. Soc.
1972, 94, 7603.
[14] S. Kato, M. Tsutsui, D. Cullen, E. Meyer, Jr., J. Am. Chem. Soc. 1977,
99, 620.
[15] D. J. Doonan, A. L. Balch, S. Z. Goldberg, R. Eisenberg, J. S. Miller, J.
Am. Chem. Soc. 1975, 97, 1961.
[16] N. M. Rutherford, M. M. Olmstead, A. L. Balch, Inorg.Chem. 1984,
23, 2833.
[17] A. L. Balch, Comments Inorg. Chem. 1984, 3, 51.
[18] P. Lord, M. M. Olmstead, A. L. Balch, unpublished results.
[19] S. Parkin, B. Moezzi, H. Hope, J. Appl. Crystalogr. 1995, 28, 53.
Crystal data for [Pd4(OEB)2] ´ THF: Dark green plate, dimensions 0.22 Â
Å
0.16  0.02 mm, triclinic, space group P1, a ˆ 14.7685(15), b ˆ 14.935(2),
c ˆ 16.328(2) Š, a ˆ 87.407(9), b ˆ 83.278(8), g ˆ 76.132(8)8, Vˆ
3
3472.0(6) Š3, l ˆ 1.54178 Š, Z ˆ 2, 1calcd ˆ 1.532 Mgm
;
m(CuKa) ˆ
8.665 mm 1; Siemens P4 diffractometer, rotating anode; 2V± w scans,
2Vmax ˆ 113; Tˆ 130 K; 9187 reflections collected; 9187 independent
reflections; min./max. transmission 0.2516/0.8458; solution by direct
methods (SHELXS-97, G. M. Sheldrick, 1990); refinement by full-matrix
least-squares methods on F 2 (SHELXL-97; G. M. Sheldrick, 1997); 806
parameters, R1 ˆ 0.0893, wR2 ˆ 0.1772 for all data; R1 ˆ 0.0649 for 6915
observed data (I > 2s(I)). An empirical absorption correction was ap-
plied.[19]
Crystal data for [Pd(OEB)]: Black needle, dimensions 0.44 Â 0.08 Â
0.08 mm, monoclinic, space group I2/a, a ˆ 13.274(3), b ˆ 18.655(4), c ˆ
14.144(3) Š, b ˆ 116.00(3)8, Vˆ 3141.3(11) Š3, l ˆ 0.71073 Š, Z ˆ 4,
The Concept of Docking/Protecting Groups in
Biohydroxylation**
3
1
1calcd ˆ 1.392 Mgm
;
m(MoKa) ˆ 0.628 mm
; Siemens R3m/V diffracto-
Gerhart Braunegg, Anna de Raadt,
Sabine Feichtenhofer, Herfried Griengl,*
Irene Kopper, Antje Lehmann, and Hans-Jorg Weber
metrer; 2V w scans, 2Vmax ˆ 45; Tˆ 140(2) K; 2198 reflections collected;
2030 independent relections; min./max. transmission 0.770/0.952; solution
by direct methods (SHELXS-97, G. M. Sheldrick, 1990); refinement by full-
matrix least-squares methods on F 2 (SHELXL-97; G. M. Sheldrick, 1997);
195 parameters, R1 ˆ 0.055, wR2 ˆ 0.0900 for all data; R1 ˆ 0.042 for 1715
observed data (I > 2s(I)). An empirical absorption correction was applied.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication nos. CCDC-113559 and
CCDC-114918. 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).
The application of enzymes and microorganisms in organic
synthesis has become a valuable and indispensable tool of
synthetic chemistry within the last ten to fifteen years.[1] Since,
in general, nonnatural substrates are transformed, it is not
surprising that these compounds are not always well accepted
by the biocatalysts in question. With regard to biohydroxy-
lation, it was recognized at an early stage that the presence of
Received: February 23, 1999 [Z13075IE]
German version: Angew. Chem. 1999, 111, 2930 ± 2932
[*] Prof. Dr. H. Griengl, Prof. Dr. G. Braunegg, Dr. A. de Raadt,
S. Feichtenhofer, I. Kopper, Dr. A. Lehmann, Dr. H.-J. Weber
Spezialforschungsbereich F01 Biokatalyse
Keywords: N ligands ´ oligopyrroles ´ palladium ´ pi inter-
actions
Institut für Organische Chemie der Technischen Universität Graz
Stremayrgasse 16, A-8010 Graz (Austria)
[1] H. Falk, The Chemistry of Linear Oligopyrroles and Bile Pigments,
Springer, Vienna, 1989.
[2] R. Stocker, Y. Yamamoto, A. F. McDonagh, A. N. Glazer, B. N. Ames,
Science 1987, 235, 1043.
[3] T. Nakagami, S. Taji, M. Takahashi, K. Yamanishi, Microbiol.
Immunol. 1992, 36, 381; H. Mori, T. Otake, M. Morimoto, N. Ueba,
N. Kunita, T. Nakagami, N. Yamasaki, S. Taji, Jpn. J. Cancer Res. 1991,
82, 755.
Fax : (‡ 43)316-873-8740
E-mail: sekretariat@orgc.tu-graz.ac.at
[**] We thank Prof. K. Kieslich for performing initial screening experi-
ments, C. Illaziewicz for the measurement of NMR spectra, and M.
Kaube for help with preparing this manuscript.
Supporting information for this article is available on the WWW
under http://www.wiley-vch.de/home/angewandte/ or from the author.
Angew. Chem. Int. Ed. 1999, 38, No. 18
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certain functional groups has a positive influence on substrate
acceptance.[2] On the basis of this observation and extending a
strategy first suggested by Furstoss et al. for the hydroxylation
of compounds such as alcohols and alkenes,[3] we developed a
general concept which can be successfully applied for
biohydroxylation. Similar to the common practice of using
protective groups in organic chemistry, a docking/protecting
(d/p) group is first introduced, ideally under mild conditions
and in high yield, and subsequently the biotransformation is
performed. Under the conditions employed in this work,
without the d/p group hydroxylation did not take place or side
reactions occurred [Eq. (1) and (4)].[4] After the biotransfor-
2764
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mation, the d/p group is removed. Besides promoting
interaction of the substrate with the active site of the
hydroxylating enzyme, the d/p group should be UV-active to
facilitate detection (TLC, HPLC). In some cases, it would also
be beneficial to reduce the volatility of the parent substance
by the introduction of the d/p group to avoid substrate losses
during the fermentation. In accordance with these criteria, a
number of compounds were prepared and their suitability as
d/p groups experimentally accessed. This was achieved by
screening these substrates with a range of microorganisms
which were known to hydroxylate similar organic compounds.
As can be seen from the selected entries presented (further
examples will be published in a forthcoming paper), this
concept could be successfully applied to a number of different
substrate classes.
acid (10) in acceptable chemical yield and enantiopurity. In
an analogous manner, cyclohexenecarboxylic acid derivative
11 [Eq. (7)], after treatment with Bacillus megaterium DSM
32 (B. m.),[11] furnished a mixture of alcohol 12 (43%, ee >
90%, absolute configuration was determined by X-ray
structure analysis) and the corresponding ketone (28%).
Suitable conditions to deprotect alcohol 12 and afford
derivative 13 are currently under investigation.
The biohydroxylation of alcohols according to this concept
was accomplished by the preparation of isosaccharine deriv-
atives, as shown with Equation (8). Derivative 14, obtained
from (R)-3-octynol (C8H13OH (1 equiv), C5H5N (2 equiv)
3-chloro-1,2-benzisothiazole-1,1-dioxide (2 equiv), CH2Cl2,
RT, 24 h) was hydroxylated regioselectively by Mortierella
alpina ATCC 8979[12] (M. a.) to give 15 (72% de) which was
deprotected (NaOCH3 (0.5 equiv), CH3OH (absolute), RT,
3 h) to yield diol 16. The absolute configuration of the second
hydroxy group in the molecule is currently under investiga-
tion.
To date, biohydroxylation of nonactivated C H bonds of
alkyl or cycloalkyl moieties has been mainly applied in the
area of steroids with considerable success regarding yield and
regio- and enantioselectivity. In comparison, biohydroxyla-
tion of other substrates is far removed from being a method of
general use in preparative organic chemistry. However, the
use of the d/p group concept broadens the applicability of
biohydroxylations in synthetic organic chemistry. Details of
this work, experimental methods, and the assignment of the
absolute configurations will be discussed in a forthcoming full
paper.
The fungus Beauveria bassiana ATCC 7159[5] (B. b.) is a
microorganism with broad substrate acceptance.[6] In partic-
ular, the presence of a benzamide group proved to be
beneficial for substrate acceptance.[2, 7] Taking this into
account for the biohydroxylation of aldehydes and ketones,
the transformation of these substrates into N-benzoyloxazol-
idines and N-benzoylspirooxazolidines, respectively, was
carried out as an application of the d/p group concept. Unlike
cyclopentanone which is not accepted by B. b. [Eq. (1)], after
introduction of the d/p group (one-pot reaction: 1)
NH2CH2CH2OH (1 equiv), K2CO3 (2 equiv), CH2Cl2, RT,
48 h; 2) BzCl (1 equiv), RT, 24 h) to give N-benzoylspiroox-
azolidine 1, biohydroxylation took place and (5R,7S)-4-
benzoyl-1-oxa-4-azaspiro[4.4]nonan-7-ol (2) was obtained in
60% yield and 40% de. This compound was then benzylated
(BnBr, NaH, THF/DMF, 208C) prior to the last deprotection
‡
step (IR 120 (H ), CH3CN, 208C) to avoid elimination.
Consequently, ketone 3 was afforded as the final product
(40% ee). The optical purity and yield of the hydroxylated
product improved dramatically when a chiral d/p group
was used. This is illustrated with one of the chiral derivatives
from this group of ketones, substrate 4 [Eq. (3)]. After
fermentation, spirononanol 5 was isolated in 84% yield
and 90% de. Since the benzyl derivative of 5 is crystalline
it is possible to further raise the enantiopurity by recrystal-
lization.
In a similar manner, cyclohexanone was also hydroxylated
to give 7 [Eq. (5)]. The benefits of chiral derivatives, such as 4,
may not be restricted to the improvement of product optical
purity and yield. These compounds may also be valuable as
ªactive siteº probes by changing the substitution on the d/p
group. Such minor variations in substrate structure and the
effect on the site of hydroxylation would give valuable
information on substrate structure requirements. In this
context, in an extension of work by Fonken et al,[8] Furstoss
et al.,[9] and Haufe et al.,[10] we are currently carrying out
molecular modeling investigations.
Experimental Section
As a representative example of this d/p concept, the biohydroxylation of
cyclopentanone is described [Eq. (3)].
By employing (R)-1-amino-2-propanol (Aldrich, 98% ee) as the d/p group,
4 was prepared in a manner similar to that given for 1, the procedure being
based on a procedure published by Saavedra.[13] Yield 75%; 98% ee; m.p.
65.5 ± 67.58C; [a]2D0
ˆ
79.8 (c ˆ 2.1 in CH2Cl2); 1H NMR (200 MHz,
CDCl3, 258C): d ˆ 0.96 (d, J ˆ 6.5 Hz, 3H; Me), 1.64 ± 1.98, 2.37 ± 2.71
(2 Â m, 6H, 2H; H6, 7, 8, 9), 3.60 (m, 1H; H2), 4.00 (m, 2H; H2,3), 7.40 (s,
‡
5H; benzoyl); GC-MS: m/z (%): 245 (8) [M ].
5: After exposure of 4 to B. bassiana ATCC 7159[5] and chromatographic
isolation, the crystalline compound 5 was obtained as the major diaster-
eoisomer in 84% yield and with 90% de; m.p. 106 ± 1088C; [a]2D0
ˆ
78.4
(c ˆ 0.9 in CH2Cl2); 1H NMR (200 MHz, CDCl3, 258C, minor diaster-
eoisomer given in italics;
implies that the assignment could be
*
interchanged): d ˆ 0.93 (d, J ˆ5.7 Hz, 3H; Me); 1.73 ± 2.41 (m, 4H; H6,
8, 9*, 9), 2.57 ± 2.69 (m, 2H; H8*, OH), 2.75, 2.94 (2  dd; J ˆ 5.7 Hz, J' ˆ
14.0 Hz, 1H ratio: 20:1; H6), 3.63 (dd, J ˆ 5.1 Hz, J' ˆ 11.3 Hz, 1H; H2),
3.98 (m, 2H; H2, H3), 4.42 (br.s, 1H; H7), 7.37 (s, 5H, benzoyl); GC-MS:
‡
m/z (%): 261 (2) [M ].
3: Benzylation of 5 under standard conditions[14] and d/p group removal
afforded 3 as a syrup. Yield (over two steps) 52%; 84% ee; [a]2D0
ˆ
43.0
This d/p group concept has also been applied to the
hydroxylation of cycloalkane carboxylic acids. Here, the
parent acid is transformed into a benzoxazole.[11] As can be
seen from Equation (6), benzoxazole 8 was hydroxylated by
Cunninghamella blakesleeana DSM 1906[11] (C. b.) and
deprotected (4n aq. HCl/EtOH (1:1, v/v), ZnCl2 (2 equiv),
reflux) to afford (1S,3S)-3-hydroxycyclopentanecarboxylic
(c ˆ 1.0 in CH2Cl2); NMR data in agreement with literature values.[15]
Received: December 30, 1998
Revised version: May 3, 1999 [Z12851IE]
German version: Angew. Chem. 1999, 111, 2946 ± 2949
Keywords: asymmetric synthesis ´ bioorganic chemistry ´
enzyme catalysis ´ hydroxylations ´ synthetic methods
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[1] a) Biotechnology: Biotransformations I, Vol. 8a (Ed.: D. Kelly), Wiley-
VCH, Weinheim, 1998; b) K. Faber, Biotransformations in Organic
Chemistry, 3rd ed., Springer, Berlin, 1997; c) Enzyme Catalysis in
Organic Synthesis (Eds.: K. Drauz, H. Waldmann), VCH, Weinheim,
1995.
covalent M N bonds (1.50 ± 1.60 Š), their electronic struc-
tures with strong axial ligand fields from the bound nitride,
and from the ability of these systems to engage in N-atom
transfer reactions. To date such reactions have been most
thoroughly investigated for nitridomanganese(v) complexes
containing tetrapyrrole or Schiff-base auxiliary ligands, where
transfer of the nitrogen atom to olefins has been demon-
strated.[3] N-transfer reactions between two metal ions, for
example, from nitrido(porphyrinato)manganese(v) to por-
phyrinatochromium(iii) has been demonstrated by Bottomley
and Neely.[4] The homometallic N-transfer reaction from a
nitridomanganese(v) complex to a different manganese(iii)
species has also been observed.[5] Thus, it is remarkable that
no nitrido-bridged manganese complexes have been descri-
bed to date. Here we report the synthesis and characterization
of the (m-nitrido)dimanganese complex [Mn2(m-N)(CN)10]6 .
Treatment of solutions containing [MnV(N)(salen)][3b]
(H2salen ˆ bis(salicylidene)ethylenediamine) and KCN with
reductants such as hydrazine or methanol produced intensely
colored red-purple solutions from which the salt K5H[Mn2-
(m-N)(CN)10] ´ 2H2O (1) was isolated in low yield. The same
compound was obtained in high yield from the reaction of an
MnII salt with an aqueous KCN solution of [NMe4]2-
Na[MnV(N)(CN)5] ´ H2O.[1b] The stability of aqueous solutions
of 1 depends strongly on the cyanide concentration. With no
added cyanide, the complex decomposes in seconds, whereas
it is stable for more than 30 min in 1m NaCN. From such
solutions the mixed sodium ± rubidium salt Na2Rb4[Mn2(m-N)-
(CN)10] ´ 6H2O (2) and [Rh(tn)3]2[Mn2(m-N)(CN)10] ´ 10H2O
(3) (tn ˆ propane-1,3-diamine) were isolated by addition of
RbCl or [Rh(tn)3]Cl3.
[2] G. S. Fonken, R. A. Johnson, Chemical Oxidations with Microorgan-
isms, Marcel Dekker, New York, 1972.
[3] R. Furstoss, A. Archelas, J. D. Fourneron, B. Vigne in Organic
Synthesis: an interdisciplinary challenge, IUPAC (Eds.: J. Streith, H.
Prinzbach, G. Schill), Blackwell, Oxford, 1985, pp. 215 ± 226.
[4] A. Kergomard, M. F. Renard, H. Veschambre, J. Org. Chem. 1982, 47,
792 ± 798.
[5] In this work, B. bassiana ATTC 7159 was cultivated in a manner
similar to that reported in reference [7c].
[6] H. L. Holland, Organic Synthesis with Oxidative Enzymes, VCH, New
York, 1992, pp. 72 ± 76.
[7] For recent examples of the application of benzamide groups in
biohydroxylation: a) R. A. Johnson, M. E. Herr, H. C. Murray, C. G.
Chidester, F. Han, J. Org. Chem. 1992, 57, 7209 ± 7212; b) C. R. Davis,
R. A. Johnson, J. I. Cialdella, W. F. Liggett, S. A. Mizsak, F. Han, V. P.
Marshall, J. Org. Chem. 1997, 62, 2252 ± 2254; c) H. F. Olivo, M. S.
Hemenway, M. H. Gezginci, Tetrahedron Lett. 1998, 39, 1309 ± 1312.
[8] R. A. Johnson, M. E. Herr, H. C. Murray, G. S. Fonken, J. Org. Chem.
1968, 33, 3217 ± 3221.
[9] R. Furstoss, A. Archelas, J. D. Fourneron, B. Vigne in Enzymes as
Catalysts in Organic Synthesis (Ed.: M. P. Schneider), D. Reidel, 1986,
pp. 361 ± 370.
[10] S. Peitz, D. Wolker, G. Haufe, Tetrahedron 1997, 53, 17067 ± 17078.
[11] A. de Raadt, H. Griengl, M. Petsch, P. Plachota, N. Schoo, H. Weber,
G. Braunegg, I. Kopper, M. Kreiner, A. Zeiser, K. Kieslich,
Tetrahedron: Asymmetry 1996, 7, 467 ± 496.
[12] M. alpina ATCC 8979 was cultured in the same manner as that
described for C. blakesleeana DSM 1906, reference [11].
[13] J. E. Saavedra, J. Org. Chem. 1985, 50, 2379 ± 2380.
[14] T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis,
2nd ed., Wiley, New York, 1991.
[15] T. H. Eberlein, F. G. West, R. W. Tester, J. Org. Chem, 1992, 57, 3479 ±
3482.
The structure of the anion in 2 is shown in Figure 1.[6] It
consists of an eclipsed [Mn2(m-N)(CN)10]6 ion,[7] which
possesses crystallographic 2/m symmetry; the center of the
complex resides on an inversion center. Inspection of the
thermal parameters of the atoms C(10) and N(1) (Figure 1a)
reveals that these atoms are severely disordered. This disorder
was successfully modeled by using a split-atom model for
these atoms with isotropic thermal parameters (Figure 1b).
The refinement converged smoothly to give two equally
populated sites for each of these atoms. Thus, the anion in 2 is
The Mixed-Valent (m-Nitrido)dimanganese
Complex Anion
[(CN)5MnV(m-N)MnII(CN)5]6 **
Jesper Bendix,* Thomas Weyhermüller, Eckhard Bill,
and Karl Wieghardt*
ꢀ
asymmetric with a short Mn N bond (1.58(1) Š) and a long
ꢀ
Mn ± N bond (1.84(1) Š). The shorter Mn N bond is only
ꢀ
0.05 ± 0.08 Š longer than the Mn N bond in monomeric
nitridocyanomanganates(v).[1b] The Mn C bond trans to the
The synthesis and reactivity of complexes of the first-row
transition metals with terminal and bridging nitrido ligands is
a rapidly expanding area of research. Complexes with
terminal nitrido ligands are known for V, Cr, and Mn,[1]
whereas nitride-bridged complexes have been described for
V, Cr, and Fe but not for Mn.[2] Interest in these systems
derives from their unique molecular structures with very short
ꢀ
short Mn N bond is then considered to be the long one
(2.19(2) Š) due to a trans influence and the short Mn C bond
(1.95(2) Š) is trans to the longer Mn ± N bond. Interestingly,
the four equatorial Mn C distances in [MnII(CN)6]4 and
[MnV(N)(CN)5]3 (1.95(1) Š and 1.985(8) ± 2.001(8) Š,[8] re-
spectively) are nearly equidistant despite the fact that these
Mn ions differ in formal oxidation states by three.[9] In 2 the
equatorial average Mn C distance is 2.005(4) Š. This inter-
pretation of the structure of 2 renders the anion [Mn2(m-N)-
(CN)10]6 a mixed-valent MnV ± MnII species which is statisti-
cally disordered over two sites in the crystal.
[*] Dr. J. Bendix, Prof. Dr. K. Wieghardt, Dr. T. Weyhermüller,
Dr. E. Bill
Max-Planck-Institut für Strahlenchemie
Stiftstrasse 34 ± 36, D-45470 Mülheim an der Ruhr (Germany)
Fax: (‡49)208-306-3952
E-mail: wieghardt@mpi-muelheim.mpg.de
The effective magnetic moment of solid 3 increases from
1.72 mB at 4 K to 2.03 mB at 300 K. The salts 1 and 2 also have
magnetic moments in this range, but they are less temper-
[**] This work was supported by the Fonds der Chemischen Industrie. J.B.
acknowledges support from the Danish Research Councils. We thank
Dr. K. P. Simonsen for supplying the [Rh(tn)3]Cl3.
2766
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Angew. Chem. Int. Ed. 1999, 38, No. 18