Metalated 2-alkenylsulfoximides in asymmetric synthesis: Diastereoselective preparation of highly substituted pyrrolidine derivatives

Full text of DOI:10.1002/(SICI)1521-3773(19981102)37:20<2883::AID-ANIE2883>3.0.CO;2-Y

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A number of methods are available for establishing the
five-membered heterocyclic ring with two to four substitu-
ents.[12] Many of these possible entries are restricted in their
constitutional and configurational versatility; these limits also
hold for approaches from natural precursors.[13] The 1,3-
dipolar cycloaddition of azomethine-ylides to olefins or
acetylene dipolarophiles controlled by chiral auxiliaries[14] is
a common way to obtain pyrrolidines. The electronic demands
of the dipolarophile necessitate the formation of 2-alkoxy-
carbonyl-substituted derivatives. However, this method has
been applied for the synthesis of combinatorial libraries,
which suggests the importance of these substances for
pharmaceutical purposes.[15]
Metalated 2-Alkenylsulfoximides in
Asymmetric Synthesis: Diastereoselective
Preparation of Highly Substituted Pyrrolidine
Derivatives**
Michael Reggelin* and Timo Heinrich
Enantiomerically pure metalated 2-alkenylsulfoximides
from cyclic sulfonimidates 1[1] were introduced in 1994 and
proved to be efficient asymmetric d3-synthons.[2, 3] The iso-
merically pure, highly substituted tetrahydofuranes 6 and 7[4]
(derived from the open-chain precursors 2 and 3) as well as
the oxabicyclic systems 8 and 9[3] (derived from 4 and 5) could
be synthesized efficiently by use of reagent 1 (Scheme 1).[2, 4]
Here we demonstrate that the addition of a-aminoalde-
hydes to titanated 2-alkenylsulfoximides offers a versatile
approach to a multitude of highly substituted pyrrolidines in
good yields (Scheme 2, Table 1). In contrast to the protocol
Scheme 1. Heterocyclic compounds available from the cyclic sulfonimi-
date 1. R2 ˆ alkyl, alkaryl, alkheteroaryl; R3 ˆ CH2S(O)(pTol)Nval, vinyl,
methyl. TMS ˆ trimethylsilyl, TBDMS ˆ tert-butyldimethylsilyl.
Based on these results, the extension of our method to the
synthesis of azamono- (10 and 11) and azabicycles (12 and 13)
seems to be rather promising. Here we describe the stereo-
selective synthesis of enantiomerically pure, highly substitut-
ed pyrrolidine derivatives 10 and 11. This structural element is
found in various biologically active alkaloids[5] such as
glycosidase inhibitors,[6] excitatoric aminoacid antagonists,[7]
or ACE inhibitors (ACE ˆ acetylcholinesterase).[8] Further-
more, pyrrolidine derivatives are important as catalysts in
asymmetric synthesis, for example in the addition of dialkyltin
compounds to aldehydes,[9] in the enantioselective reduction
of ketones,[10] or in asymmetric Diels ± Alder reactions.[11]
Scheme 2. Synthesis of pyrrolidines 18a ± f and 19a ± f, starting from open-
chain 2-alkenylsulfoximides. a) nBuLi, 788C. b) Chlorotris(isopropoxy)-
titanium, 08C. c) 21a ± c, 788C. d) Piperidine, 208C; (NH4)2CO3, NH4Cl.
e) K2CO3, MeOH; BOC2O, NaHCO3. f) SmI2. FMOC ˆ (9H-fluoren-9-
ylmethoxy)carbonyl.
described earlier,[2, 3] we used toluene instead of THF as
solvent for the deprotonation and transmetalation of the
allylsulfoximides 2a and 3a as well as their enantiomers (ent-
2a and ent-3a). Only in this solvent are high yields and very
high diastereoselectivities obtained (ds ꢀ 96%, determined by
NMR spectroscopy from the crude product). The FMOC-
protected a-aminoaldehydes were generated without racemi-
zation by Dess ± Martin oxidation[16] of the corresponding
[*] Priv.-Doz. Dr. M. Reggelin, T. Heinrich
Fachbereich Chemie der Universität
Marie-Curie-Strasse 11, D-60439 Frankfurt/Main (Germany)
Fax: (‡49)69-7982-9128
E-mail: re@krypton.org.chemie.uni-frankfurt.de
[**] This work was supported by the DFG (Re 1007/1 ± 4) and Solvay
Pharmaceuticals GmbH (Hannover, Germany). Continous support by
Prof. Dr. C. Griesinger is gratefully acknowledged. We thank the
Degussa AG for generous gifts of amino acids.
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Table 1. Highly substituted pyrrolidines from metalated 2-alkenylsulfox-
imides.
Compd R1
R2
Yield [%] ds [%][a] [a]D20 [8][b]
M.p [8C]
18a
18b
18c
18d
18e
18 f
19a
19b
19c[c]
19d
19e
19 f[c]
H
H
H
Bn
iBu
tBuOCH2 21
27
23
67
65
68
ꢀ 96
ꢀ 96
ꢀ 96
59
67
54
ꢀ 96
ꢀ 96
ꢀ 96
37.71 (0.4) 108.5
‡ 28.17 (0.6) oil
‡ 24.46 (0.8) 115.7
37.29 (1.0) 127.8
19.99 (0.9) 96.9
‡ 14.80 (0.3) oil
‡6.52 (1.4) 107.7
37.29 (1.0) oil
‡1.80 (0.3) 93.1
‡ 26.70 (1.0) 91.0
‡ 66.20 (1.0) 97.3
20.80 (0.3) 187.2
CH3 Bn
CH3 iBu
CH3 tBuOCH2 44
H
H
H
CH3 Bn
CH3 iBu
CH3 tBuOCH2 30
63
42
Bn
iBu
tBuOCH2 31
33
36
43
34
[a] Determined from the 1H NMR spectra of the crude products. [b] c in
dichloromethane. [c] Deprotected at nitrogen and isolated as the p-
toluenesulfonate; optical rotation recorded in methanol.
Figure 2. Part of the 15N ± 1H HMBC spectrum of 20. Verification of the
cyclization (thick bond) is provided by the correlation of the pyrrolidine
nitrogen atom to the protons (1, 1') of the sulfonimidoylmethyl group.
amino alcohols, and were allowed to react without further
purification.[17]
After deprotonation of the sulfoximides with nBuLi, trans-
metalation with chlorotris(isopropoxy)titanium (ClTIPT),
and addition of the protected aldehydes, O-titanated 5-ami-
no-4-hydoxyvinylsulfoximides 14a ± f and 15a ± f were formed
but not isolated (Scheme 2). After one hour piperidine
(10 equiv) was added at 788C to deprotect the nitrogen
atom, which attacked the acceptor-substituted double bond of
the vinylsulfoximide (Figure 1). After crystallization of the
atom (H-1 and H-1'). This is possible only if the cyclization
had taken place. The relative and absolute configuration of
the pyrrolidines derived from the crotylsulfoximide 3a (S
configuration at sulfur) could be verified by X-ray structure
analysis of the N-tosylated derivative prepared from 14d.[21]
As expected the absolute configurations of the pyrrolidine
alcohol center
(C-3) and the neighboring C-4 atom resulted from a Re-side
attack of the allyl moiety on the Re side of the a-amino-
aldehyde (lk process).[2, 3] In agreement with our interpreta-
tion of the stereochemical outcome of the cyclization process,
the sulfonimidoylmethyl fragment is always oriented trans to
the hydroxyl functionality at C-3.[4] As expected, for the series
of crotylsulfoximides obtained from ent-3a (R configuration
at sulfur), the induced absolute configurations were the result
of a Si,Si process. This was verified by X-ray structure analysis
of the pyrrolidine 19d.[22]
Figure 1. Stereochemical aspects of the cyclization. The topicity of the
attack of the nitrogen atom on the 5-position is directed by two conforma-
tional aspects: reduction of allylic strain and 1,5-repulsion.
The total control of the absolute configurations at the newly
formed stereogenic centers at C-3 and C-4 in the pyrrolidines
19a ± f merits comment. The addition of a 2-alkenylsulfox-
imide with the absolute configuration R at sulfur to a S-
configurated a-aminoaldehyde represents an intermolecular
ªmismatched pairº,[23] because the preferred topicity of the
nucleophile (Si) does not correlate with the Cram side of the
aldehyde (Re). In perfect agreement with our results with the
lactaldehydes,[2, 3] the stereochemical bias excerted by the a-
chiral aldehyde is totally overcompensated (reagent control).
The absence of the terminal methyl group in the parent
systems (2a and ent-2a) results in a decrease in the stereo-
control at C-5, as already discussed for the THF derivatives
(Figure 1).[4] The topicity of attack of the nitrogen nucleophile
onto the 5-position is dominated by the attempt of the system
to minimize allylic strain and 1,5-repulsion. For the vinyl-
sulfoximides 3, which lead to the 4-methyl-substituted pyrrol-
idines, there exists an optimal solution, conformation A. In
contrast, derivatives 2, which lead to the 4-unsubstituted
pyrrolidines, can also react via conformation B. In this
arrangement the absolute topicity of the attack on the
5-position is inverted. With respect to the 1,5-interaction, B
dibenzofulvene ± piperidine adduct from methanol and col-
umn filtration, the silyl ether group in the auxiliary was
cleaved by solvolysis and the pyrrolidine nitrogen atom was
protected with a tert-butoxycarbamoyl group. The removal of
the auxiliary from the resulting 5-sulfonimidoylmethyl-sub-
stituted heterocycles 16a ± f and 17a ± f was successful with
samarium diiodide in methanol/THF (1/2). This way of
desulfuration is described here for the first time and is
superior to alternative methods described in the literature.[18]
It is essential to manipulate the heteroatoms as described
above. If the silyl ether is still present no reaction occurs,[19]
and an open-chain homoallylamine is formed if the pyrroli-
dine nitrogen atom is deprotected.
After recording a 15N ± 1H HMBC spectrum[20] of 20, the
cyclization product of 14e, we were able to verify the
successful pyrrolidine synthesis (Figure 2). The pyrrolidine
3
nitrogen atom resonates at d ˆ 56.6 and shows two JNH
correlations to the methylene group adjacent to the sulfur
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M.p. 127.88C; [a]D20
ˆ
37.29 (c ˆ 1.00 in dichloromethane); 1H NMR
is less stable than A. Within this model, the desired 3,5-trans
product, the result of a cyclization via A, should be formed in
slight excess, which is indeed the case (Table 1). Structural
verification was again achieved by X-ray structure analysis of
the minor compounds 5-epi-19a and 5-epi-18a, confirming the
predicted 3,5-cis relative configuration.[24]
(270 MHz, [D10]xylol, 808C): d ˆ 0.849 (d, 3J ˆ 6.9 Hz, 3H; 4-CH3), 1.230
(d, 3J ˆ 6.1 Hz, 3H; 5-CH3), 1.448 (s, 9H; C(CH3)3), 1.618 (dqq, 3J ˆ 8.8,
3
3
2
3J ˆ 6.9, J ˆ 6.1 Hz, 1H; 4-H), 2.459 (dd, J ˆ 9.4, J ˆ 13.6 Hz, 1H; A-H),
3
2
3
3
2.988 (dd, J ˆ 4.6, J ˆ 13.6 Hz, 1H; B-H), 3.427 (dq, J ˆ 8.8, J ˆ 6.1 Hz,
1H; 5-H), 3.591 (brs, 1H; 3-H), 3.934 (ddd, 3J ˆ 9.4, 3J ˆ 4.6, 3J ˆ 5.7 Hz,
1H; 2-H), 7.013 ± 7.177 (m, 5H; arom.); 13C NMR (67.9 MHz, [D10]xylol,
808C): d ˆ 11.12 (C-4'), 19.44 (C-5'), 28.88 (C(CH3)), 40.97 (C-A/B), 44.62
(C-4), 59.33 (C-5), 69.46 (C-2), 75.73 (C-3), 79.00 (C(CH3)), 126.71, 128.63,
129.23 (5C, arom.), 139.75 (ipso-arom.), 154.49 (C ˆ O); IR (KBr): nÄ ˆ
Our results can be summerized as follows:
1) The g-hydroxyalkylation of the enantiomeric allyl- and
crotylsulfoximides 2a/3a and ent-2a/ent-3a, respectively, with
a-aminoaldehydes results in the formation of isomerically
pure vinylsulfoximides 14 and 15, which can be transformed to
highly substituted pyrrolidines 16 and 17 with piperidine as a
deblocking agent.
3430.1 (OH), 2973.0, 2930.6 (CH3), 1672.4 (C O) cm 1; elemental analysis
ˆ
calcd for C18H27NO3 (305.41): C 70.79, H 8.91, N 4.59; found: C 70.59, H
8.93, N 4.63.
Received: May 28, 1998 [Z11917IE]
German version: Angew. Chem. 1998, 110, 3005 ± 3008
2) The absolute configuration at the newly formed stereo-
genic centers C-3 and C-4 is controlled by the absolute
configuration at sulfur (reagent control). The configuration at
C-5 is the result of conformational preferences of the
cyclization precursor. Therefore only 3-substituted derivatives
allow total control of this stereogenic center.
Keywords: asymmetric synthesis ´ heterocycles ´ pyrroli-
dines ´ samarium ´ sulfoximines
[1] a) M. Reggelin, H. Weinberger, Tetrahedron Lett. 1992, 33, 6959 ±
6962; b) M. Reggelin, R. Welcker, Tetrahedron Lett. 1995, 36, 5885 ±
5886.
[2] M. Reggelin, H. Weinberger, Angew. Chem. 1994, 106, 489 ± 491;
Angew. Chem. Int. Ed. Engl. 1994, 33, 444 ± 446.
[3] a) M. Reggelin, H. Weinberger, M. Gerlach, R. Welcker, J. Am. Chem.
Soc. 1996, 118, 4765 ± 4777; b) M. Reggelin, M. Gerlach, M. Vogt,
unpublished results.
[4] M. Reggelin, H. Weinberger, T. Heinrich, Liebigs Ann. 1997, 1881 ±
1886.
[5] W. H. Pearson in Studies in Natural Product Chemistry, Vol. 1 (Ed.:
Atta-Ur-Rahman), Elsevier, Amsterdam, 1988, pp. 323 ± 358.
[6] a) G. W. Fleet, Top. Med. Chem. 1988, 65, 149 ± 162; b) R. T. Schwarz,
R. Datema, Trends Biochem. Sci. 1984, 9, 32 ± 34; c) V. Wehner, V.
Jäger, Angew. Chem. 1990, 102, 1180 ± 1182; Angew. Chem. Int. Ed.
Engl. 1990, 29, 1169 ± 1171, and references therein.
3) Samarium diiodide was introducted as a superior desulfur-
ation agent.
The expansion of this new strategy to synthesize isomeri-
cally pure, saturated nitrogen heterocycles such as substituted
1- and 2-azabi- and -tricyclic derivatives by proper combina-
tion of open-chain or cyclic 2-alkenylsulfoximides with open-
chain or cyclic a-aminoaldehydes was already successful (e.g.
12, 13, Scheme 1) and will be published in due course.
Furthermore, we found that with certain pharmacophoric
substituents R2 and after installation of such substituents at
the free OH group (e.g. by benzylation), a number of
biologically active substances are available.[25]
[7] R. J. Bridges, F. E. Lovering, J. M. Humphrey, M. S. Stanley, T. N.
Blakely, M. F. Cristopharo, A. R. Chamberlin, Bioorg. Med. Chem.
Lett. 1993, 3, 115 ± 121, and references therein.
Experimental Section
[8] a) E. W. Petrillo, M. A. Ondetti, Med. Res. Rev. 1982, 2, 1 ± 41; b) H. S.
Cheung, D. W. Cushman, Biochim. Biophys. Acta. 1973, 293, 451 ± 463.
[9] K. Soai, S. Niwa, Chem. Rev. 1992, 92, 833 ± 856.
[10] E. J. Corey, R. K. Bakshi, S. J. Shibata, J. Am. Chem. Soc. 1987, 105,
5551 ± 5553.
18d: To a solution of 3a (329 mg, 0.89 mmol) in toluene (2 mL) was added
1
nBuLi (492 mg, 2.27 mmolg in hexane) at 788C by syringe. After
15 min ClTIPT (487 mg, 2.50 mmolg 1) was added, and the mixture was
warmed to 08C and stirred for 30 min. The mixture was again cooled to
788C, 21a (754 mg, 1.79 mmol) dissolved in THF (3 mL) was added, and
[11] S. Kobayashi, M. Murakami, T. Harada, T. Mukayama, Chem. Lett.
1991, 1341 ± 1344.
the mixture was stirred at
788C for 60 min. Piperidine (0.9 mL,
8.90 mmol) was added, and the temperature was raised to 08C. After
10 h the reaction mixture was poured onto a well-mixed, saturated solution
of (NH4)2CO3 (25 mL) layered with ethyl acetate (4 mL). After 30 min two
clear phases could be separated. The aqueous phase was extracted three
times with ethyl acetate (10 mL), and the combined organic layers were
extracted with a saturated solution of NH4Cl. After the organic phase was
dried over Na2SO4 and the solvent was evaporated in vacuo, the
benzofulvene ± piperidine adduct was crystallized from methanol. The
resulting crude product was purified by column filtration (eluent: diethyl
ether/hexane 1/1; ethyl acetate), and the obtained polar fraction was
treated with K2CO3 (136 mg, 0.99 mmol) in methanol (3 mL). The
pyrrolidine (desilylated 3a) nitrogen atom was protected with di-tert-
butoxycarbonate (BOC2O, 350 mg, 1.60 mmol) and NaHCO3 (100 mg,
1.2 mmol) in dioxane (4 mL) and water (8 mL). Then residual 3a and
unchanged BOC2O were removed by flash chromatography.
Á
[12] M. Pichon, B. Figadere, Tetrahedron: Asymmetry 1996, 7, 927 ± 964.
[13] a) R. H. Wightman, Tetrahedron 1993, 49, 3827 ± 3840; b) F. Nicotra,
Tetrahedron Lett. 1993, 34, 4555 ± 4558; c) C. Kibayashi, J. Org. Chem.
1987, 32, 1956 ± 1962; d) T. Livinghouse, J. Am. Chem. Soc. 1993, 115,
11458 ± 11489.
[14] a) P. Deprez, J. Royer, H. P. Husson, Tetrahedron: Asymmetry 1991, 2,
1189 ± 1192; b) P. Garner, W. B. Ho, J. Org. Chem. 1990, 55, 3973 ±
3975; c) P. Garner, F. Arya, W. B. Ho, J. Org. Chem. 1990, 55, 412 ±
414; d) R. M. Williams, W. Zhai, D. Aldous, S. C. Aldous, J. Org.
Chem. 1992, 57, 6527 ± 6532, zit. Lit.; e) W. J. Lown in 1,3-Dipolar
Cycloaddition Chemistry, Vol. 1 (Ed.: A. Padwa), Wiley, New York,
1984.
[15] a) G. Liu, J. A. Ellman, J. Org. Chem. 1995, 60, 7712 ± 7713. b) M. M.
Murphy, J. R. Schullek, E. M. Gordon, M. A. Gallop, J. Am. Chem.
Soc. 1995, 117, 7029 ± 7030.
[16] a) D. B. Dess, J. C. Martin, J. Am. Chem. Soc. 1991, 113, 7277 ± 7287;
b) D. B. Dess, J. C. Martin, J. Org. Chem. 1983, 48, 4156 ± 4158.
[17] After addition of 84 mol% of the chiral shift reagent Pr(hfc)3, the
enantiomeric excess of the aldehydes could be determined by
integration of the 1H NMR signal of the aldehyde protons: M.
Reggelin, T. Heinrich, unpublished results.
[18] Raney Nickel requires a large excess (>10 equiv) to provide satisfying
results, and much of the pyrrolidine formed is absorbed. Lithium
naphthalenide works fast, but ring-opened by-products are formed.
To remove the chiral auxiliary samarium (545 mg, 3.63 mmol) was
suspended in THF (12 mL), and diiodomethane (860 mg, 3.21 mmol) was
added by syringe at 08C. After 15 min the reaction was maintained at room
temperature for 60 min, and the pyrrolidine was added in methanol
(1.5 mL) and THF (3 mL). To quench the reaction, the mixture was poured
into a saturated solution of NH4Cl (20 mL), and 0.5n HCl was added until
two clear phases resulted. After the organic layer was extracted three times
with diethyl ether (20 mL), and the pyrrolidine was purified by flash
chromatography (diethyl ether/hexane 1/1) to yield 129 mg of 18d (63%).
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[19] Desilyation of the TMS-protected derivative occurs by solvolysis
during the desulfuration. More stable silyl ethers must be previously
cleaved in an extra step.
C5Me5). Unusual bonding modes prevail in 2, in which La
atoms are coordinated in two different ways. According to the
crystal-structure analysis,[8] La1 and La2 are positioned above
opposite rings of the pyrene molecule in a h6 coordination
hitherto unknown in polyarene complexes of the lanthanoids,
and the La ± C bond lengths lie between 2.76 and 3.07 Š
(Figure 1). La3 is h2-bound to one of the middle rings of the
[20] 13C ± 1H HMBC: A. Bax, M. F. Summers, J. Am. Chem. Soc. 1986, 108,
2093 ± 2094.
[21] M. Bolte, Acta Crystallogr. Sect. C 1997, C53, IUC 9700029.
[22] J. Bats, T. Heinrich, M. Reggelin, Acta Crystallogr. Sect. C, submitted.
[23] S. Masamune, W. Choy, J. S. Petersen, L. R. Sita, Angew. Chem. 1985,
97, 1 ± 31; Angew. Chem. Int. Ed. Engl. 1985, 24, 1 ± 30.
[24] J. Bats, T. Heinrich, M. Reggelin, Acta Crystallogr. Sect. C, eingereicht.
[25] M. Reggelin, T. Heinrich, B. Junker, J. Antel, U. Preuschoff, DE-B
19821418.9, 1998.
Synthesis and Properties of Lanthanum ±
Pyrene ComplexesÐStructure of
[(Cp*La)3(m-Cl)3(thf)(m-h2:h6:h6-C16H10)],
the First Complex with a Pyrene Trianion**
Karl-Heinz Thiele,* Sergio Bambirra, Joachim Sieler,
and Svea Yelonek
Figure 1. Structure of 2 in the crystal. Selected bond lengths [Š] and angles
[8]: La1 ± C1 3.047(9), La1 ± C6 3.072(8), La1 ± C7 2.951(8), La1 ± C8
2.843(8), La1 ± C9 2.766(8), La1 ± C10 2.936(9), La2 ± C2 3.014(8), La2 ±
C3 3.061(8), La2 ± C16 2.951(9), La2 ± C15 2.872(11), La2 ± C14 2.903(10),
La2 ± C13 2.959(9), La3 ± C4 2.823(9), La3 ± C5 2.841(8), La ± Cl 2.810(3) ±
2.894(2), La3 ± O1 2.694(7), C11 ± C12 1.35(2), C4 ± C5 1.417(13); La3-Cl1-
La1 93.96(8), La3-Cl2-La2 94.04(6), La1-Cl3-La2 102.10(6)
The reduction of polyarenes with alkali metals in ethers
leads to compounds in which ether-stabilized contact-ion
pairs,[1] triples,[2] or even quintuples[3] occur. The known
magnesium anthracene[4] and probably also some naphthalene
complexes of europium, samarium, and ytterbium[5] are
similarly built. Complexes of trivalent lanthanoids with
naphthalene and anthracene have also been described in the
last few years.[6] In this context, the reduction of benzanthra-
cene, pyrene, and acenaphthylene with decamethylsamaro-
cene to form dinuclear complexes is of particular interest.[7] In
these compounds, h2, h3, h4, and h5 bonds are found between
the metal atom and the arene.
Most organolanthanoid compounds examined so far con-
tain {(C5H5)2Ln} and {(C5Me5)2Ln} units. Reactions of
[CpLnX2] derivatives, for which diverse conversions with
condensed aromatic hydrocarbons in the presence of alkali
metals can be expected, have been far less extensively
investigated. We report here on the synthesis, structure, and
bonding of lanthanum ± pyrene complexes with partly novel
and completely unexpected coordination modes.
pyrene molecule. The La3 ± C4 and La3 ± C5 distances of 2.82
and 2.84 Š, respectively, are almost identical. Thus, La3 is
coordinatively unsaturated and sterically less shielded, which
is compensated at least in part by the addition of a THF
molecule. Therefore, La1 and La2 form the centers of
distorted tetrahedrons and both have a coordination number
(CN) of eight, whereas La3 with CN ˆ 7 is arranged in a
distorted trigonal bypramid. Pyrene, which is planar when
uncoordinated, is slightly twisted in 2. The atoms C9 and C14
lie 0.115(9) and 0.095(9) Š, respectively, above the plane
determined for the C16H10 system, with C11 and C12 both
lying 0.095(10) Š below it. As with the {La3(pyrene)}system,
the pyrene unit thus adopts trianionic character.[9] Compound
2 can also be understood as a trinuclear complex with a
phenanthrene bridge to which a noncoordinated double bond
is attached; this view is supported by the strongly differing
bond lengths C4 ± C5 and C11 ± C12 of 1.41 and 1.35 Š,
respectively. The angles of the perpendiculars of the Cp*La
and LaC6 fragments are 128.138 and 128.568, respectively, for
In the reaction of [Cp*LaCl](m-Cl)2Li(thf)2] (1) in toluene
with pyrene and potassium under the strictest exclusion of air
and moisture, a red-violet solution is obtained from which the
pyrene complex [(Cp*LaCl)3(C16H10)] ´ thf (2) was isolated in
the form of red-violet, extremely air-sensitive crystals (Cp* ˆ
La1 and La2, and thus lie between those values for
[*] Prof. Dr. K.-H. Thiele, Dr. S. Bambirra
Institut für Anorganische Chemie der Universität Halle-Wittenberg
Kurt-Mothes-Strasse 2, D-06120 Halle (Germany)
Fax: (‡49)345-55-27028
[11]
[{Cp3La}n][10] and {Cp2 La} systems.
*
These results indicate that the formation of 2, a compound
with different coordination modes for La atoms bound in the
complex, can be described by Equation (1). The reaction of
Prof. Dr. J. Sieler, Dipl.-Chem. S. Yelonek
Institut für Anorganische Chemie der Universität Leipzig (Germany)
toluene
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
!
3 1 ‡ 3 K ‡ C16H10
2 ‡ 3LiCl ‡ 3KCl
(1)
5 THF
2886
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3720-2886 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1998, 37, No. 20