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Efficient Regio- and Enantioselective Mannich Reactions.

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filtered and cirr-drieci10 yield 2-2 PF, (232 mg. 95 %)as a yellow powder: m.p. 282 C
(dscomp.). FAB-MS 1 7 1 ; : 531 ( M - PF,)'. 386 ( M - 2PF,)':
' H NMR
(CD,CN). d = 6.75 ( 4 H . s). 7.51 7.55 (6H. m). 7.62-7.67 (4H.m). 8.81 (4H.s).
9 9 3 ( 4 H . ~ )"; C N M R ( C D , C N ) . & = 30.9.67.7. 130.6. 130.7, 130.9, 131.3. 142.3.
Anal.: found C 50.01. H 3.35. N 3.98. calcd for C,,H,,N,P,FI,: C 49.70. H 3.28.
N 4 14.
~
1-2PF,, Equimolar amounts (about 5 mM) of 2-2PF6 and 3'' were mixed in
CD,CN The solution turned red instantaneously: FAB-MS: 171:~ 1167 ( M - PF,)'.
1072 ( M - ?PF,,)'. 636 ( I 5DN38C10)+. 531 (DBnDAP - PF,)';
' H NMR
(CD,CN). 3 = 3.75 3 81 (8H. m). 3.82-3.88(8H. m),3.93-4.08(16H. m). 5.906.00(6H. m). 6.15 (4H. I . J = 8.0 Hz). 6.23(4H. m). 7.50 -7.70(6H. m). 7.88 (4H.
d . J = X 0 H ~ ) . X . l 5 ( 4 H . s ) , 9 . 7 1(4H.s): " C N M R ( C D , C N ) : h = 67.4.68.6.706.
71.9. 71 9. 105 3. 117.8. 117.8. 124.5. 125.0. 115 2. 129.8. 130.6. 130.7. 131.3, 142.0.
( M - PF,)
153.4. High resolution MS: found m I 1167.4315. C,,H,,N,O,,,F,P
requires i i r 1 1167.4359 Crystals suitable for X-ray structural analysis were grown
by vapor diffusion of iPr,O into an MeCN solution of a I : I mixture of DBnDAP[PE,], and 1 5DN38C10. The procedure and equipment for absorption and
luminescence meawrements were described previously [21].
Received October 24. 1995 [Z8494IE]
German version Angeu Chem 1996, 108. 1056- 1059
-
Keywords: charge-transfer complexes molecular machines
pseudorotaxanes . supramolecular chemistry
*
A. Aviram. J ,4111. Cheiii. Soc. 1988. 110. 5687-5692; A. Aviram. M. Ratner,
Clr~ir.PI7i.s. L r / / 1974. 29. 277-283
V. Balzani. L. Moggi. F. Scandola in Suprumolecukur Phorochemisrr!. (Ed.: V.
Balrani). Reidel. Dordrecht. 1987, 1-28.
I - M . Lehn. 4/i,qw. (%em. 1988. tO0. 91 - 116: A n p i . . Cliem. lnt. E d Enz/.
1988. 27. 90 112: ihid 1990. 102. 1347-1362 and 1990. 29, 1304-1319:
S i i ~ ~ r ~ i ~ r i o k ~('henii.srr~~.
~~uirii
VCH. Weinheim. 1995
MI^ i i / w El<,(rroiric /3e1+ce.s (Eds.: F. L. Carter. R. E. Siatkowsky. H.
Woltjicn). Elsevier. Amsterdam. 1988.
V Balzani. E Scandola. Siipp,niiiiolr.ciilrrr-Plioro~hi~iiihrr~i..
Horwood. ChiChester. 1991. Chap 12.
K . E Drexier. ~ V i i i i o . s ~ ~ . ~ / oMokwilur
iis
M u c l i i n e r ~ Munufucriiring.
~.
und Comp i i r u / i w . Wile!, New 'fork. 1992.
A. P De S i h a . H. Q N . Gunaratne, C P McCoy. Nururi, 1993. 364. 42- 44.
P Bull. L. Garwiii. N r u u r r 1992. 355, 761 -766.
~,
259, 890-892.
D. Brndley. S ~ i m c 1993,
R. A. Bissell. A P De Silva, H. Q. N. Gunaratne, P. L M. Lynch, G. E. M.
Maguire. C. P McCoy. K. R A. S. Sandanayake. Top. Curr. Cheni. 1993,168.
223-264
V. Biilzani. F. Scandola in Coniprehensrve Sirprumolecukur Chemislr?. Vol. 10
(Ed D. N. Reinhoudt), Pergamon. Oxford, 1996. in press.
P. L. Anelli. N. Spencer, I. F. Stoddart. J A m . Clrerii. Soc. 1991. 113. 51315133. R. A. Bissell. E Cordova. A. E. Kaifer. I. F. Stoddart Nurur-e 1994.369.
133 137.
R . Ballardini. V. Balzani. M. T Gandolfi. L., Prodi. M. Venturi. D. Philp.
H. G. Rickettb. J. F Stoddart, A n g e w Cliem. 1993. 105. 1362-1365; Aiigeii.
Chriii.
Ed E q l . 1993. 32, 1301-1303; P. R. Ashton, R. Ballardini. V.
Balzsni. A. Crrdi. M. T. Gandolfi. S. Menzer, L. Perez-Garcia, L. Prodi. J. F.
Stoddart. M Venturi. A. I. P. White. D. J. Williams, J Am. Chem. Soc. 1995.
117. 11171 -11197.
P. R . Ashton. R Ballardlni. V. Balzani, M. T. Gandolfi, I-F., Marquis, L.
Perez-Garcia. L. Prodi. J. F. Stoddart. M. Venturi. J Chwn. Soc. Cheni. Comi i i r i i i . 1994. 171 180.
M Seller. H Diirr, I. Willner. E. Joselevich, A. Doron. I. F. Stoddart, J Am.
Cliciii. So(.. 1994, 116. 3399-3404: A. C. Benniston, A. Harriman. V. M.
Lynch. ihid 1995. /17, 5275 - 5291. and references cited therein; L. Zelikovich,
1. Libman. A Shiinzer. Nuture. 1995. 374, 790-792.
A. Lrcoreil. C' 0 Dietrich-Buchecker. L P . Sauvage, J A m . Cheni. Soc. 1994,
116. 93YY 9400.
D Philp. J. I; Stoddart, Svderr. 1991. 445-458: Angel!.. Chem. 1996. 108,
No I I : A i i p i ~ (%ern.
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Inr. E d Engl. 1996. 3 j . No. 11 ; H . W. Gibson, M. C.
Bhcd,i. P T Engen. Prc~g.Po/yiii. Sci. 1994, 19. 843-945
Liquid secondary ion mass spectrometry (LSIMS) was carried out on a VGZab Spec mass spectrometer (accelerating voltage 8 kV; resolution 2000). Samples of 1-2 PF, were dissolved in a small volume of 3-nitrobenzyl alcohol, which
had previous11 been coated onto a stainless steel probe tip. Spectra were
recorded in the positive-ton mode at a scan speed of 5 s per decade.
[I91 Crystal data for 1-2PF; triclinic. u = 13 799(3). h = 14.407(4). c =
16 3 3 6 ( 5 ) A. 1 = 110.09(2). fl = 90.33(2), ;= 91.12(2);, V = 3049 A3. T =
293 K. spice group Pi, Z = 2. prrlrd
= 1 430 g c m - 3 , 11 = 15.03 cm-', 9056
independent measured. 4034 with (I Fol >4olF,I, 8 5 6 0 ) refined lo R , = 0.1141
and i i R , = 0 2968. The data was collected on a Siemens P4 diffractometer with
graphite monochromated Cu,, radiation using w scans. The structure was
solved by direct methods and with the SHELXTL program package (version
Aiigeii. Cheiir. In!. E d Engl. 1996. 35. No. 9
$:.
5.03) (G. Sheldrick. Universitit Gottingen. 1995).Further dctails oi'the ci-ystal
structure investigation can he obtained from the Camhridgc Crystallographic
Data Centre. 12 Union Road. GB-Cambridge CB2 IEZ ( U K ) on quoting full
literature citation.
[20] P. R. Ashton. D. Philp. M. V. Reddington. A. M. 2. Slawin. N. Spencer. J. E
Stoddart. D. J Williams. J Chem. Soc. Cliem. Coinmiiii. 1991. 1680- 1683.
1211 P. L. Anelli. P. R. Ashton. R. Ballardini. V. Balzani. M. Delgado. M T Gandolfi, T. T. Goodnow. A E. Kaifer. D Philp. M. Pietras~kiewicr.L. Prodi.
M V. Reddington. A. M Z . Slawin. N. Spencer. J. E Stodd'irt. C. Vicenr. D. J.
Williams. J Am. Client. Six. 1992, 114. 193 - 218.
[22] A. I. Blacker. J. Jazwinski. 1:M. Lehn. H d i . . Cliim Acta 1987. 70. 1 - 12. and
references therein.
[23] Z. D. Hill. P. MacCarthy, J Chrm. Ed. 1986, 63. 162- 167 and references
therein.
[24] S. Hiinig. J. Grosse. E. F. Lier. H. Quast. Liehip Ami. Clinir. 1973. 339-358.
[25] P. R. Ashton. C. L. Brown, E. J. T. Chrystal, T. T. Goodnow. A. E. Kaifer,
K. P. Parry, D. Philp, A. M. Z Slawin, N. Spencer, J. F. Stoddart. D. J
Williams. J. Chein. So<,.Clrrm. Conimun. 1991. 634-639. P R Ashton. E. J T.
Chrystal. J. P. Mathias. K. P. Parry. A. M 2. Slawin, 3 . Spencer. I. F Stoddart. D. J. Williams. Terrulredron Lrrt. 1987. 28. 6367-6370
Efficient Regio- and Enantioselective Mannich
Reactions**
Dieter Enden,* David Ward, Johannes Adam, and
Gerhard Raabe
The Mannich reaction,"] in which an aminomethyl group is
introduced in the 2-position to a carbonyl function, has found
a multitude of applications in organic chemistry.12]The resulting
Mannich bases are of particular interest due to their biological
activity (for example, analgesic, antineoplastic, and antibiotic
effects) ,[21 as bifunctional synthetic building
and as
precursors in the preparation of 2,P-unsaturated carbonyl comp o u n d ~ and
[ ~ ~?-amino alcohols.[4] The introduction of separately prepared iminium salts,[51 and the use of silyl enol
ethers,[61boron enolates,['] and enamines[*]has so extended the
range of application of the reaction that regioselective
aminomethylations can even be carried out in aprotic media in
good yields.
While some authors have already reported on the stereoselective Mannich reaction!']
very little is known about the enantioselective variants for the synthesis of B-amino ketones,["l
which is in sharp contrast to the plentitude of publications on its
oxa analogue, the enantioselective Aldol reaction." ' I A practical procedure for highly enantioseIective cc-aminomethylation of
ketones is, to the best of our knowledge, not yet available.
We now report an efficient, highly regio- and enantioselective
synthesis of Mannich bases, starting from cc-silyl ketones (S)-1,
which are accessible by the SAMPiRAMP hydrazone
method"'] in good yields (52-60%) and excellent enantioselectivities ( ~ ~ 2 9 8 %
(Table
) 1).
As illustrated in Scheme 1, the sc-dimethylthexylsilyl ketones
(S)-1 (thexyl = 1,1,2-trimethylpropyI, abbreviated as [Hex in
Scheme 1 ) are converted in quantitative yields to the (Z)-silyl
enol ethers (S)-2 (Z: E> 50: 1) by treatment with lithium diisopropylamide (LDA) and chlorotrimethylsilane (TMSCI) in
tetrahydrofuran/hexamethylphosphoric triamide (HMPA) at
['I
Prof. Dr. D. Enders, Dr. D. Ward, DipLChem. J. Adam, Dr. G . Raahe
Institut fur Organische Chemie der Technischen Hochschule
Professor-Pirlet-Strasse 1, D-52074 Aachen (Germany)
Fax: Int. code +(241)8888127
['*I This work was funded by the Deutsche Forschungsgemeinschaft (SFB 380 and
the Leibniz Prize) and by the Fonds der Chemischen Industrie. We thank the
firms Degussa AG. BASF AG. Bayer AG. and Hoechst AG for gifts of chemicals. D. W. thanks the Science and Engineering Research Council, Great
Britain for support (1994/1995).
VCH Verlugsgeseklschufi mbH, 0.69451 Weinhemi, 1996
0570-0833,'9613509-0981$15.00f .25 0
98 1
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Fig 1. X-ray crystal structure of (S.R)-3f (hall-and-stick model).
Scheme I . Enaiitioselective synthesis of /<-dibenzylamino ketones (Rj-4 by the
asymmetric Mannich reaction. [a] LDA. THF. HMPA. -70 C: TMSCI:
[b] Bn,NCH,OCH,. BF, Et,O. CH,CI,. -95 C; [c] NH,E iiBu,NE THF.
- 70 C to room temperature. tHex = 1.1,2-trimethylpropyl.
Table 2. z-Dimethylthexylsilyl-/~-dibenzylamino ketones ( 5 3 - 3 prepared by
aminomethylation of the silyl enol ethers (S)-2.
3
R
Table I . z-DimethyIthexylelyI ketones (S)-1 prepared from butanone.
Yield
[z];"
["/.I
[c.
~
1
(S)-la
(S)-lb
(S)-lC
(S)-ld
(S)-le
(S)-lf
R
Me
Et
nPr
IBU
Bn
p-BrBn [c]
Yield [a]
[XI;'
re [h]
[%I
[c. benzene]
["A>]
51
54
57
60
52
58
- 196.4 (0.9)
99
99
98
98
99
99
-191.3(08)
- 133.3 (1 5 )
-115 3 (1.6)
-77.4 (2.2)
- 36.4 (1 2 )
[a] Overall yield (four steps) for the isolated z-silyl ketone starting from hutanone.
[b] Enantiomeric excesses were determined by gas chromatography of the corresponding alcohols by using a stationary phase consisting of 0-cyclodextrin.
polysiloxane The alcohols were prepared by the reduction of the z-silyl ketones
with LiAIH,. [c] p-BrBn = purmbromobenzyl
- 95 "C. The formation of regioisomeric tetrasubstituted silyl
enol ethers was never observed in these reactions. The high
selectivity of the deprotonation to the (Z)-enolate in the presence of HMPA[I3]is a prerequisite for a high asymmetric induction under the assumption that the bulky silyl group diastereofacially directs the introduction of the electrophilic aminomethyl
group.
In previous work, the handling of the hygroscopic iminium
salts was avoided by the in situ generation of the corresponding
iminium ions or similar reactive species by the treatment of
aminals o r geminal amino ethers in the presence of Lewis
acids.", 14] In the method described here, the alkylation of the
crude silyl enol ether was carried out by reaction with dibenzylmethoxymethyl amine" and BF;Et,O in CH,CI,. Aqueous
workup and flash chromatography afforded the desired dibenzylaminomethyl ketones (S,R)-3 in excellent yields (94-95 %)
and high diastereomeric excesses (de = 92 to 2 96%). The latter were determined by 'H N M R spectroscopy (Table 2).
The silylated Mannich bases 3 are stable compounds, which
show no tendency to epimerize or racemize and can be purified
without difficulty by flash chromatography o n silica gel. The use
of a kit-butyldimethylsilyl group rather than the dimethylhexylsilyl group led to a decrease in the diastereoselectivity to as
low as 81 % in the case of (S)-la, although the Z/E ratio was
high and similar to that observed for (S)-1a.[l6]The absolute
configuration was determined by the X-ray crystal structure
analysis of (S,R)-3f (Fig
(S)-3a
(S)-3b
(S)-3C
(.')-3d
(S)-3e
(.')-3f
~~
Me
Et
iiPr
IBU
Bn
p-BrBn [c]
95
95
95
94
94
95
Ill?
hcnzene]
[a]
["/.I
~~
+150.1 (0.4)
- 113.7 (0.6)
-97.6 (0.6)
-71.6 (0.5)
- 80.6 (0 9)
-32.1 (1.0)
9 2 ( t 9 6 [b])
t 96
t 96
t 96
2 96
2 96
[a] Determined hy ' H NMR spectroscopy (300MHz). [b] After flash chromatography [c] p-BrBn = puro-bromobenryl.
The 1-silyl group can be removed readily at room temperature
by treatment with nBu,NF in THF, since the intermediate carbanion is stabilized as an enolate. However, this desilylation IS
accompanied by an almost complete racemization, the cause of
which lies in the formation of basic nBu,NOH. This problem
was solved by the addition of solid NH,F as a buffer and by
carrying out the reaction a t low temperatures to control the rate
of formation of the base. The enantiomeric excesses (ee =
91 -97 Yo)of the optically active b-amino ketones (R)-4 thus
formed were determined by 'H NMR spectroscopy (500 MHz)
using the chiral cosolvent (I?)-( -)-9-anthryl-2,2,2-trifluoroethanol (Table 3).
To explain the almost complete diasterofacial selectivity in the
formation of (S,R)-3,two transition states can be discussed: On
the one hand a cyclic transition state along the lines of the
can be envisZimmerman -Traxler model [TS,, (closed)]
Tahlc 3. /l-Dibenzylamino ketones (R)-4. prepared by desilylation of the ketones
( S .R)-3.
4
(R)-4a
(Rj-4b
(R)-4c
(R)-4d
(R)-4e
(R)-4f
R
Me
Et
iiPr
{Bu
Bn
p B r B n [b]
Yield
[4:'
[",I
[c,
96
97
98
99
91
98
- 8.3 (0.6)
-2.5 (0.7)
- 1.2 (0.5)
-2.2 (0.4)
+7.2 (1.1)
+9.7 (0.6)
l'<'
benzene]
Id]
["/.I
91
93
93
94
91
93
[a] Determined by ' H N M R spectroscopy (500MHz) using a solution of (R)-4
(3 mg) and (R)-( -)-9-anthryl-2,2.2-trifluoroethanol(10 mg) as chirdl cosolvent in
C,D,, (0.7 mL) [b] p-BrBn = prm-hromohenzyl.
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~~
aged. while on the other an open transition state [TS,,,
(open)][211
can also be considered. In both cases the diastereoselectivity is caused by shielding of the Si-side by the bulky
dimethylthexylsilyl group. The models lead, via (S,R)-3.to the
Mannich bases 4 with R configuration at the newly generated
stereogenic center (Scheme 2).
Scheme 2. Postulated transition states for the asymmetric Mannich reaction
To summarize. it has been shown that Mannich bases can be
prepared regioselectively in high enantiomeric purity and excellent overall yield by the procedure detailed here. To the best of
our knowledge, this procedure is the first practical. generally
applicable asymmetric Mannich reaction for the preparation of
/I-amino ketones. The extension of the method leading to the
generation of two new stereogenic centers in the 2- and 8-positions is currently the object of intensive investigations.[221
E.uprr.inwntul Procedure
~-Dimethylthex)lsilqIketone (S)-l.(.')-I was prepared by successiw silylation and
alkylation of hutanone-SAMP hydrdzone with chlorodimerhylthexylsilane and a n
'ippropriatc . i l k \ l iodide o r bromide [12]
Silyl en01 ether I.S)-2-A bolution of L D A ( 1 . 1 mmol) in T H F (10 mL. freshly
prepared f r o m nBuLi (0.7 m L of a I 6 u solution) a n d diisopropylamine (0.15 inL)
w a s treated with H M P A (2.5 mL) and cooled to -95 C. To this vigorously stirred
d u t i o n . ii wlutioii of (S)-2 ( I mmol) in T H F ( I mL) was added dropwiae over a
period 015 inin Finally. TMSCI ( I .2 mmol) was added in one portion. After 30 min
ihe reiictioti mixture was treated with saturated aqueous N a H C O , solution
110inL). T h e product was extracted with ti-pentane (60 mL). dried over MgSO,.
nnd the wlvent removed on a rotary evaporator under reduced pressure. T h e crude
product wits iiiimcdi;itely used in the next step without further purification.
x-Dimethyltliex~l~il4]r'-dihenzylaminom~thyl
ketone (S.R)-3: Dibenzylmethoxymethylainine(l.l5 iniiiol)[l5]wasaddedtoCH,CI, (10inL)andcooled to -95 C
The ci-ude product (S)-2. diluted with CH,CI, (2 mL) was added dropwisc to this
wlutioii. After thc addition of BF,-Et,O (1 15 mmol). the reaction mixture ?vas
allowed t o warm to -70 C.All conversions were compleie within 3 h ( T L C control) The rcitctioii mixture was worked up by treatment with p H 7 buffer (5 mL).
Iblloued b> cxlr.iction with CH,CI, (60 mL). drying over Na2S0,. removal of
aporator under reduced pressure. and flash chromatography
(silica gcl. diethyl ether n-pentane 1.10).
~ ~ L ~ i h e n i ~ l a m i n o i n cketone
t h y l (R)-4-To a cooled (-70 C) solution of (.S.R)-3
( I minol) i n T H I ( 5 0 m L ) were added sequentially solid NH,F (1 85 g. 50 mmol)
a n d nBti,NF ( I 2 niL. 1 c solution in T H F : 1 2 mmol). T h e reaction mixture w a b
allowed to wiiriii t o room temperature. after which time p H 6 buffer (10 m L ) w a s
added a n d the product extrdCtCd with ,?-penrane (90 m L ) . After the product had
heen dricd o \ e r S,i,S0,. it was purified by flash chromatography (silica gel. diethyl
etlicr //-pciitanc I 2 0 )
Keywords: amino ketones - asymmetric Mannich reactions
enolates . ketones . SAMP hydrazones
.
[ I ] C. Mannich. W Kriische. A i - d . Phnriii 1912. 2711. 647
['I Reviews: E F. Kleinman i n C'oiii/~re/ioi,sii.c.Or,qo,iic Si i ? / / i i , . \ / \ . C d 2 (Ed>
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~~rii~ig.
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Schicss. W B Schwcizer. C/ii!iiio 1985. 39. 271. W. Oppolrer. 'I Schneidcr.
Heir. Ciiiiii . 4 C / u 1986. 69. 1817; C. C h n a r i . I . Venturini. G Giclon. G.
Schimperna. Ti.rrn/i[&on Lcvc. 1987. 28. 227: W Oppdier. R. Morctri. S.
Thomi. ihid. 1989. 311. 5603. H. Kunz. W Pfrengle. A i i y c i i . C/iiw 1989. 101.
1041: A i l p i C h ~ /ti/.
i Ed €!i,q/. 1989. -7X. 1067. H . K U W . D Schan7enb;ich.
h d 1989. 101. 1042 and 1989. 2X. 1068: A. R. Katritzk!. I' A . Hariis. Prrm
i i i 4 o i i 1990. 46. 987. D. A Evans. F. Urpi. T C. Somcr,. J S. Clark. M . T
Bilodeau. J .4w. C/imi.Soc 1990. 112. 8215: T Ai-en%.H 1,r;iuenr;ith. Aii,qlw
Ciiriii. 1990. /02. 929: . 4 1 i p i . . Chcni. 1111 0 1 . Eii,q/. 1990. 39. 932: K. T. Wanner. 1. Praschak. U. Nagel. Arch P/ior?,i 1990. 323. -335. f:. G h o l e n . A
Aliocco. M . Broody. A. Zuppi. Tcwohrih-o~iLei/. 1991. 32. 73: H F~rauciirath.
T Arenr. G. Raabe. M Zorn. , 4 i , q v C/im 1993. 1O.i. 71. ;lii,qiw ('/i?/ii.
liii.
Ed. Eiigl. 1993. 32. 83. P. C. B. P q e . S M. Allin. E. W ('ollington. K.A. E
Carr. J Org. Chew 1993. 3.
6902: N . Risch. M.Arend. l q m . <'/mi 1994.
lfJ6. 2531: .4ii,qeeii. Clioii. I f i f . M Gi,q/ 1994. 33. 2412. Y Matscimura. T
Toinita. E,iro/icv/ror?Lrli. 1994. 35. 3737. M.Arend. i\: Rihch. i l i i p c i i ( ' h l V 7 i .
1995. 107. 2861: A y i u C/iwi. /n/ Ed Gig/ 1995. 34.1 S h l
[lo] N. Risch. A. Esser. Liehi,?.! hii.C 7 i e i i i . 1992. 73.3
[ I 11 D. A E ~ a n s .J. V Nelson. T. R. Taber. Zip S i i v w d i u i r . 1982. 13. I . T
Mukaiqama. Org. Riwr. 1982. 3X. 203: C. H . Heathcocl, in l \ v / i i m , i r i < .S! 11i/ic,.\i\, Lid 3 (Ed : J. D. Morrison). Academic P r c s . Orlando. FL. USA. 1984.
p I I I : S. Miasaniune. W. Choy. F A. J. Kerdrsky. B . Iiiipcriali. ,4ij,qmi. C/wiii.
1985. Y7. I. Aiipeii. C h i ? ./!I/ E d Eii,?/ 1985. 24. I : M I ~ I M L I Iihid
~ . 1987. YY.
24 o r 1987. -76. 24.
[I?] D Enders. B B Lohray. Aiigeii < ' h i . 1987. YY. 359: ,4iity11 ( ' / i w i . / t i / CI.
€jig/ 1987.26.351: D Enders. S. Nakai. C/it,ni. Bidr 1991. 124. 219: D. Ender,.
8. B. Lohraq. F. Burkamp. V. Bushiin. R Hett. L i c h w lwi . i n pi-e\s
[l3] R. E. Ireland. R H Mueller. A K . Willard. J h i . C/iiwi. .Sm 1976. 98. 2X6X.
[ 141 A. Ho!,om!. S lijiina. H. Sakurai. Ti,/ro/iidriin LA,// 1982. -7.3, 547. H . Heme).
G Papageoigiou. R. F Wilkins. J. C/iiw S o i . U i w i Comiiiiii 1988.
1161
[I51 Prepared bq reaction 01' dihcnzylamine with par;iforiii.ildch\de .ind solid
K,CO, in methanol at room temperature Workup coiisi~tcdof filtration o f t h e
solids and t'rraclional distillation (b.p. 116- 118 C 0 1 l o r r ) : T D. Stewart.
W E Bradley. J A m Ciirri? So<..1932. 54. 4172.
[I61 D. Endcrs. D Ward. unpublished result\
COMMUNICATIONS
1 171 Suiiahlc s i n ~ . l ccrystals \VCI-C ohiained by crystallization from methanol at room
teiiipci-atui-e The ~cihstan rystallizes i i i the monoclinic space group PZ, (no.
4) ~ i t l (iI = h 644(6). h = 24 243(2). c’ = 10 68X(1) A and /I = 104 O(2). With ii
cell \oiimicof 1670.5
= ? a n d .M,.,,L, = 592.8, thcdensiry is 1 178 gcm-’.
Totd number ofelectrons per unit cell is 632. Enraf-Nonius CAD4-four-circle
diffi-:ictoineter. Mo,, radiaiion (graphite inonochroinator. i = 0 71069 A )
The sti-uctut-ewas solved by using SHELXSXh [ I X ] and relined ujith XTAL3.2
[19]. The positions of the hydrogen atoms were calculated. 3248 observed
reflections [ f > b ( f ) J . 343 parameters i-efined against F. R = 0.061 (Rw =
0.035). Maximum residual electron density k0.6 e A-’. The Libsolute configuration of the newly formed stereogenic center in the r-position was deteriiiined
on thc basis of the known configuration in the Lposition. Crystallographic
data (excluding structure factors) for the structures reported in this paper have
been deposited with the Cambridge Ci ystallogi-aphic Data Centre as supplementary publication no CCDC-179-1 I Coptes ofthe data can be obtained free
ofcharge on application to The Director. CCDC. 1 2 Union Road. Cambridge.
CBZ 1EZ. U K (fax: int. code +( 1223)3360?3: e-mail. techedro chemcrys
caii1.x u k )
[IS] G. M . Sheldrick i n C‘,:i..stii//~~~’.~i~/ir~.
Compi/i~i.~
3 (Eds : G . M. Sheldrick. C.
Kruger. R. Goodard). University Pi-ess. Oxford. 1985. p. 175.
[I91 S. R. Hall. H. D. Flack. J M. Stewart. XTAL3.2 R ~ / m w c cM w i i d Universities of Western Australia. Geneva. and Maryland. Perth. 1992.
[20] H. E Zimmeriiiaii. M . D. Traxler. J. Am CIIPIII.Sor 1957. 7Y. 1920: D Enders. B. B. Lohray, A!i,qw CJwii 1988. l00. 594: A n p r C/IEIII.
fm.€(I. €q/
1988. 27. 581
[ Z l ] I Flemming. Piire A p p / . C/wii. 1988. 60. 71; B. B. Lohray. D. Enders. H r h
Chiiii Acto 1989. 72. 9x0.
[32] J. Adam. planned Dissertation. RWTH Aachen.
Huckel Arenes with Ten n Electrons:
Cyclic Zintl Anions Sito- and Geto-,
Isosteric to PZ- and As%Hans Georg von Schnering,* Urs Bolle, Jan Curda,
Karl Peters, Wilder Carrillo-Cabrera, Mehmet Somer,
Martin Schultheiss, and Ulrich Wedig
Our investigations on the completely intercalated heterographite LiBC ( G Li’ +(BC)-)[’] have revealed that very
few compounds of this structure type and its derivatives do not
meet the valence electron concentration (VEC) of 4 for the
heterographite nets I(BC)-. A striking example is BaLiSi
(g Ba” +(LiSi)’-) with a VEC of 3.5.[’] Initially, this phase
was described by Gladi~hevskij[~’
as a hexagonal modification
of BaSi,, which with a VEC of 5 would fit even less in this family
of structures. However, Axel et al.[’I showed later that this modification cannot be prepared from the elements barium and silicon, but that the compound BaLiSi is formed instead by reaction with molten LiCI. It is even more amazing that the recent
edition o f “Pearson’s Handbook”I4I only mentions hexagonal
BaSi,! In the present communication we will show that the
actual composition of the ternary silicide is Ba,Li,Si, and that
an isotypic germanide, Ba,Li,Ge,, exists as
61 Both compounds form a stuffed derivative of the orthorhombic /?-K,P,
s t r ~ c t u r e ’ ~(Fig.
]
1, top) with complete and ordered heterographite nets 3(Li,Si,)8- and 2(Li,Ge,)8-. respectively. but
with a VEC of 4.25. The atoms of these nets center the trigonal
Ba, prisms. The most remarkable structural features are isometric Siio- and GeAo- rings with 34 valence electrons, isosteric to
[*] Prof Dr. H . G. von Schnering. Dr U. Bolle. Dipl.-Ing. J. Curdii
Dr. K. Peters, Dr. W. C a r r t b c a b r e r a . Dr. M Somer.
Dip1 -Chem. M. Schultheiss, Dr. U. Wedig
Max-Planck-Institut fiir Festkorperforschung
Heisenbergstrasse I . D-70569 Stuttgart (Germany)
Fax: Int code +(711)6891-562
984
cJ VCH Ver.lu~s~esell.~~/iiifi
mhH. 0-69451 Wrinhcoti,I996
Fig. 1 Top. Crystal structure of Ba,Li,Si, with the weakly twisted Si, rings in the
heterographite net j(Li2Sih)*- The Ba atoms form slightly distorted trigonal
prisms. Ba,Li,Ge, also crystallizes in this structure. Bottom. Projection of the
Ba,,,Ge-0, crystal structure on its hexagonal base In this structure. the GeAoanion is planar. The position Ge2 (Ge4-) is statistically only half-filled; thus the 0
atonis are placed on either one of the two alternative positions (open circles)
P2- and As:-,[’. ‘I, respectively. Both compounds are narrowband semiconductors ( E , % 80 meV) and reveal a weak van
Vleck paramagnetism.
Systematic investigations into the formation of clathrates in
the Na/Ba/Ge ternary system led to the discovery of the new,
unusual germanium oxide Ba,,Ge,O,, which formally can be
considered as an oxidation product of a barium germanide. This
compound was initially discovered as a byproduct in reaction
mixtures accidently contaminated with traces of oxygen o r
moisture. However, it can be prepared in bulk by thermal decomposition of NaGe in the presence of the required amounts of
BaO and Ba.19] In the hexagonal crystal structure (Fig. 1, bottom) Ba atoms form a framework of linked monocapped trigonal prisms and tetragonal bipyramids. These polyhedra are centered either with isolated G e atoms, with 0 atoms, o r with G e
atoms that belong to six-membered G e
The electron
count fulfills the Zintl-Klemm concept with the formal charge
distribution according to BaZ+,0 ’ - , Ge4-, Geio--the latter
again reveals a cyclic system with 34 electrons.
0570-0~33/Y6~350Y-OY84
S IS 00
+ .25/0
AnRex Cliem Int. Ed. Engl. 1996, 35, No. Y
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