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An Arsanylidensilane (УArsasileneФ) and its Derivatization with Tellurium and Benzophenone.

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Table 1. Bond angles a ( & C-C-X, X = main-group element) determined by
X-ray crystallography for compounds with the structure element Et-X.
X
n la1
1
Be
Mg
B
Al
C
Si
N
P
0
S
2
7
88
51
3431
24
3105
1410
1751
245
115.35 f 0.95
120.73 f 6.98
115.50 k 3.38
116.82 f 4.78
113.50 5 4.53
116.69 f 3.88
118.60 f 3.41
115.64 f 3.89
110.01 5.44
112.69 f 3.99
[a] n
= Number
*.I"]
*
a,,,["I
a,,,l"I
114.67
111.65
100.08
105.59
74.88
112.87
75.42
95.85
83.96
88.83
116.02
129.58
128.07
133.74
159.66
132.03
145.88
137.47
164.32
139.53
+
of structures examined [9].
gation effects. Specifically, in the perpendicular conformation o f CH,CH,-BH,, the empty boron p orbital lies in the
C-C-B plane (perp. in Fig. 3). Thus the resulting hyperconjugation with the C-C bond results in a considerable reduction
in the C-C-B angle to 105.3".
In the eclipsed conformation, in which the empty boron p
orbital is perpendicular to the C-C-B plane, the C-C-B angle
is influenced indirectly. Hyperconjugation with the vacant p
orbital now involves the two equivalent c( CH bonds (which
have roughly 30" dihedral angles). Electrons are withdrawn
from the CH, orbital with n symmetry. Hence, the antibonding interactions between the hydrogen atoms are reduced
and the orbital which has H . .. H character has a greater
influence. The result is that the H-C-H angle decreases to
103.1' in Et,B (MP2/6-31G'). The C-C-B angle expands (to
137.4") as a consequence (the Thorpe-Ingold hypothesis).['31
When the X group is a n-donor rather than a n-acceptor,
negative hyperconjugation with a lone pair results in a wider
C-C-X angle. For example, for X = NH, in the staggered
conformation with the N lone pair anti to the C-C bond the
C-C-X angle is 115.5'. In the trans conformations of
C,H,OH and C,H,SH, for example, the smaller C-C-X angles (ca. 107.2") arise indirectly as summarized in Scheme 1.
A
B
Scheme 1. Orientations of the ethyl group relative to the p orbital of the maingroup element X. Left, perpendicular conformation A; right, eclipsed conformation B. When the p orbital in A is empty, the C-C-X angle decreases; when
occupied, the angle increases. When the p orbital in B is empty, the H-C-H angle
decreases and the C-C-X angle increases; when occupied, the H-C-H angle
increases and the C-C-X angle decreases.
Idealized "sp3" bond angles of 109.47" require tetrahedral
symmetry and thus cannot be expected generally. "The regular tetrahedral angle is the exception rather than the rule in
3 and Table 1 emphasize the
organic ~ h e m i s t r y . " ~Figure
'~]
variety of molecular geometries and that many bond angles
in simple organic compounds do not fit the widely accepted
generalizations.
Received: October 14, 1991 [Z 4968 IE]
German version: Angew. Chem. 1992, 104, 356
CAS Registry numbers:
2, 97-94-9; 3, 15523-24-7; 3 ' 3 dioxane, 138785-29-2; EtBeH, 6917-51-3;
EtMgH, 63533-53-9; EtBH,, 25070-50-2; EtAIH,, 14914-86-4; EtCH,, 7498-6; EtSiH,, 2814-79-1; EtNH,, 75-04-7; EtPH,, 593-68-0; EtOH, 64-17-5;
EtSH, 75-OX-1.
31 6
0 VCH
Verlagsgesellschaft mbH. W-6940 Weinheim, 1992
[I] R. Koster, G. Seidel, R. Boese, B. Wrackmeyer, Chem. Ber. 1988, 121.
597-615.
[21 R. Koster, G. Seidel. R. Boese, Chem. Ber. 1990, 123, 1013-1028.
[3] R. Boese, M. Polk. D. Bliser, Angew. Chem. 1987, 99, 239-241; Anger?.
Chem. I n f . Ed. Engl. 1987, 26, 245-247.
[4] 2 (m.p. = 182.3 K) was crystallized in a capillary by means of a computercontrolled miniature zone-melting procedure [5] at 161 K, the data were
collected at 350 K. Nicolet R3/mV diffractometer with a low temperature
device of our own construction, Mo,, radiation, program used:
SHELXTL-Plus (Version 4.11). Crystal size: 0.3 mm diameter (cylindric).
Triclinic, u = 4.172(1), 6 =7.803(1), c = 11.727(2)A, a =100.23(1).
p = 96.35(1). y = 94.60'(1), V = 368.3(1)A', Z = 2. Space group P T.
P'~,=
~ . 0.884 Mgm-', 28,,, = 60". 2133 independent intensities, 1815 observed (Fo 2 4o(F)), 124 parameters, hydrogen atoms refined without
constraints and individual isotropic DPs, all other atoms with ADPs.
R = 0.048, R, = 0.058, K,-' = a2(Fo) 6.63 x lo-' Fi), maximum
residual electron density 0.28 e k ' .
[5] D. Brodalla, D. Mootz, R. Boese, W. Osswald. J. Appl. Crysfallogr.1985,
18, 316-319.
[6] Structure determination of3, crystallized with three molecules of dioxane:
The crystal had to be kept with the mother liquor and transferred below
270K; cooling below 250 K damages the crystal. Crystal size:
0.33 x 0.27 x 0.18 mm3. Monoclinic, a = 18.071(3), b = 10.916(2), c =
15.453(3)A, J
! = 125.31(1)". V = 2487.4(8) A'; Z = 4, T = 250 K, space
= 45", 2212independent intensigroup C2/c,p,,,, = 1.283 Mgm-',28,,,.
ties. 1193 observed (Fot 4u(fl), 141 parameters, hydrogen atoms refined
as rigid groups with isotropic DPs for each group, all other atoms were
refined with ADPs. R = 0.056, R, = 0.051, r v F 1 = u2(Fo)+1.7 x
F:, maximum residual electron density 0.26 e k 3 . Other data are the same
as for 1. Further details of the crystal structure investigations are available
on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur
wissenschaftlich-technische Information mbH, D-W-7514 EggensteinLeopoldshafen 2, on quoting the depository number CSD-320332 for 2,
CSD-320331 for 3. the authors' names, and the full journal citation.
[7] W. J. Hehre, L. Radom, P. von R. Schleyer, J. A. Pople, Ah Initio Molecufur
Orhitul Theory, Wiley, New York, 1986.
[8] a) R. Koster, G. Seidel, R. Boese. Cheni. Ber. 1990, 123,2109-2116; b) M.
Yalpani, R. Boese. R. Koster, ibid. 1990. 123, 713-718; c) R . Koster, G.
Seidel, G. Miiller, R. Boese, B. Wrackmeyer, ibid. 1988, 121, 1381-1392;
d) R. Koster. G. Seidel, R. Boese, B. Wrackmeyer, ;bid. 1988, 121, 597615; e) M. Ydpani, R. Boese. R. Koster, ibid. 1990, 123. 707-712.
[9] The data were obtained from the Cambridge Structural Database (CSD),
Version from 8.5.1991 with 90296 entries, using the Cambridge Structural
Database System (CSDS) Version 4.40. [I01 Only crystal structures containing the structure element X-Et (X = second- or third-period element)
with R values between 0.001 -0.08 were considered. The valencies of the
specified elements have not been taken into account. Despite the relatively
high standard deviations, the t-test [I 11 shows that most of the comparisons among the angles involving the various elements are significantly
different (except for Be and Si).
[lo] E H. Allen, 0. Kennard, R. Taylor, Acr. Chem. Res. 1983, 16, 146.
[ l l ] R. Kaiser, G. Gottschalk, Elernenlure Tests zur Beurteilung von Mepdafen,
B. I.-Wissenschaftsverlag, Mannheim. 1972, p. 25.
[12] a) T. Clark, G. W. Spitznagel, R. Klose, P. von R. Schleyer, J. Am. Chem.
Sor. 1984,106,4412-4419; b) P. von R. Schleyer, Pure Appl. Chem. 1987,
59, 1647-1660.
1131 See P. von R. Schleyer: J. Am. Chem. SOC.1961, 83, 1368-1373.
[14] K. Mislow, Introduction to Stereochernrsrry, Benjamin, New York, 1966,
p. 13.
An Arsanylidensilane ("Arsasilene") and its
Derivatization with Tellurium and Benzophenone""
By Mutthius Driess* and Huns Pritzkow
Organosilicon compounds with low-coordinated Si atoms
and multiple bonds to silicon were of great importance for
the recent development of silicon chemistry. In the last ten
years the use of, for example, disilenes, silaalkenes, and
[*I Dr. M. Driess, Dr. H. Pritzkow
Anorganisch-chemisches Institut der Universitdt
Im Neuenheimer Feld 270, D-W-6900 Heidelberg (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie and the
Deutsche Forschungsgemeinschaft (SFB 247). We thank Messer-Griesheim GmbH, Duisburg, for chemicals, and Prof. Dr. W Siebert Heidelberg
for his support.
0570-0X33/92/0303-0316$3.50f.25/0
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 3
silanimines for the preparation of new classes of organosilicon compounds have proved to be extremely profitable.“]
For investigations into the structure and reactivity of compounds with low-coordinated Si atoms, the synthesis of unsaturated Si compounds of the type R,Si=E with new combinations of element-silicon (p-p), bonds and h4, o3
coordinated Si atoms plays a key role. Therefore, we search
for efficient ways to isolate compounds with TI bonds between silicon and the heavy homologues of Group 15, i.e.
phosphorus, arsenic, antimony, and bismuth. Whereas compounds with a P-Si x bond (“phosphasilenes”) A[21 are
already known, there are so far no examples for the homologous systems B-D.
Fig. 1. Molecular structure ofd. Selected bond lengths [A] and angles [“I: AslSil 2.296(4), Asl-Si2 2.320(4), Sil-Fl 1.631(8), Li-As1 2.46(3), Li-01 1.91(3),
Li-02 1.92(4); Sil-Asl-Si2 106.4(1), Sil-Asl-Li 110.2(7), Si2-Asl-Li 109.5(7).
Asl-Li-01 143.9(16), Asl-Li-02 114.0(15), 01-Li-02 101.9(16).
Recently we have achieved, starting from Is,SiF, (Is =
2,4,6-iPr3C,H,) and LiPH, . DME (DME = dimethoxyethane), in a multiple-step reaction, a simple synthesis of
thermally stable and at the same time activated phosphanylidensilanes (“phospha~ilenes”).[~~
It has been shown that this
simple synthetic route surprisingly is also suitable for the
preparation of 1, the first arsasilene. Thus, the reaction of
Is,SiF, with two equivalents of LiAsH, . DME in T H F at
20 “C leads quantitatively to the lithiated coupling product 2,
which is stable in T H F for several days.
-ASH,
-
‘2
BuLilTHF
:.SI
- BuH
3
2
Li(thf),
BOOC
- LiF, THF
__+c
F
Is = 2.4.6-iPr,C6H2
1%
Jsi=Y
‘a.
IS
4
Sii Pr,
1
Compound 2, which is not isolated, can be directly transformed into the disilylarsane 3 (Table 1) with triisopropylsilyl trifluoromethanesulfonate. Lithiation of 3 with one
equivalent of nBuLi in a hexane/THF mixture leads to the
lithoarsane 4 (Table I), which is isolated in the form of colorless, extremely air- and moisture-sensitive crystals. The ‘H
NMR spectrum and an elemental analysis prove that the Li
atom in 4, solvated with two T H F molecules, is only threefold coordinated. This result was confirmed by a crystal
structure analysis of 4 (Fig. l).[41
In contrast to LiAs(SiMe,), DME,151which up to now is
the only lithium disilylarsane complex structurally confirmed,
and which both in solution and also in the solid state is
dimeric, 4 is monomeric in the solid state. The Li atom is
distorted trigonal planar, the As atom pyramidal, and the
fluoro-substituted Si atom as a result of steric overloading
has a highly distorted tetrahedral coordination. In contrast
to that, the iPr substituted Si atom is tetrahedrally surrounded. Noteworthy is the short Li-As bond (2.46A)* The
As-Si bond lengths of 2.29A (FSi-As) and 2.328,
(iPrSi-As) are shorter than As-Si single bonds (2.332.40 A) and not significantly different from the value in the
dimeric LiAs(SiMe,), . DME (2.30 A).[’]
The thermal elimination of LiF and THF from 4 in
toluene at ca. 90 “C leads to an intensely red solution of 1,
Angel?. Chcm In!. Ed. Engl. 31 11992) No. 3
which can be isolated as a spectroscopically pure ( ‘H NMR
and mass spectra), deep-red oil (Table 1). In the 29Si NMR
spectrum, for the h4, o3coordinated Si atom, similar to the
analogous ph~sphasilene,[~]
a signal at very low field
(6 = 179.1) is observed. The 29Si nuclei of the SiiPr, group
result in a singlet at 6 = 28.0. The 29Si chemical shifts of I ,
as with the analogous ph~sphasilene[~]
and other compounds of this type,[’] are noticeably temperature dependent
[6(29Si) for Si=As at 80°C: 177.2, for As-SiiPr,: 27.91;
however, they are only slightly influenced by the donor ability of the solvent in contrast to silanimines. Therefore, the
Table 1. NMR spectroscopic and selected mass spectrometric data of 1 and
3-6.
1: ‘ H N MR (200 MHz, C,D,, 300 K): 6 = 1.35 (br.d, 54H, SiCHMe,, o-,
p-CHMe,, J=7.0Hz). 1.50(br.m,3H,SiCHMe,),2.92(br.m,2H,p-CHMe2),
4.00 (br., 2H, o-CHMe,), 4.16 (br., 2H, o-CHMe,), 7.16 (s, 4H, arom. H);
”SiNMR (INEPT): 6 = 28.0 (s, SiiPr), 179.0 (s, SiAs); MS (El, 70 eV): m/r
666 ( Mt . 71%), 623 ( M - C,H,)+, 8), 509 ( ( M - SiiPr3)+, 7). 451
((A4 - Sir’Pr, - C,H, - Me)+, S), 433 ((Is,Si -1 H ) + , 100).
3: ‘ H N MR (200 MHz, C,D,, 300 K): 6 = 1.02 (br., 18H, SiCHMe,), 1.11 (d,
12H, p-CHMe,, J = 6.9 Hz), 1.19 (br., 24H, o-CHMe,), 2.73 (sept. 2H, pCHMe,, J = 6.9 Hz), 3.59 (br.sept 4H,p-CHMe2), 7.04 (s, 4H, arom. H) [a];
” FN MR (standard CFCI,): 6 = -125.6 (s, J(F-Si) = 356 Hz); 29SiNMR
(INEPT): 6 = 13.5 (d, SiF,J(Si-F) = 355.6 Hz), 14.4 (s. SiiPr); MS (El. 70 eV):
m / i 686 (Mt, 10%). 453 (Is,SiF+, 100).
4: ‘HNMR(200 MHz, [D,]toluene, 300 K): 6 = 1.20-1.46(br.m, 65H, SiiPr,
CHMeZand 8 H von THF), 2.77 (sept, 2H. p-CHMe,, J = 6.9 Hz), 3.38 (m,
8H, THF), 3.65 (br., 4H, o-CHMe,), 7.09 (s, 4H, arom. H); 19FNMR (standard CFCI,): 6 = -1 18.3 (s, J(F-Si) = 320 Hz); ”Si NMR (INEPT): 6 = 24.4
(d, SiF, J(Si-F) = 320.8 Hz), 26.7 (d. SiiPr, J(Si-F) = 3.6 Hz). Correct C,Hanalysis.
5 : ‘HNMR (200 MHz, C,D,, 300 K): 6 = 0.45-1.64 (br.m, 57H, SiiPr and
CHMe,), 2.75 (sept, 1H, J = 6.9 Hz, p-CHMe,), 2.78 (sept, 1H, J = 6.9 Hz,
p-CHMe,), 3.87 (br., 4H, o-CHMe,), 7.11 (s, 2H, arom. H), 7.19 ( s , 2H, arom.
H); ”SiNMR (INEPT): 6 = 18.5 (s, SiiPr), -44.5 (s, SiTe); lZ5TeNMR
(C,D,, standard Me,Te): S = -1 157.5 (s); MS (El, 70eV): mjr 796 ( M + ,
21 %), 666 ( ( M - Te)’, 9), 435 (Is,SiH+, 100).
6: ‘HNMR (200MHz, C,D6, 340K): 6 = 1.10 (d, IEH, SiCHMe,,
J=7.2Hz), 1.18 (d, 36H, o-,p-CHMe,, J = 6.8Hz), 1.42 (sept, 3H, SiCHMe,, J = 7 . 2 Hz), 2.78 (sept, 2H, p-CHMe,, J = 6.8Hz), 4.05 (br.. 4H,
o-CHMe,), 6.83-7.06(m, lOH, Ph), 7.62(s, 2H, arom. H), 7.66(s, 2H, arom.
H); 13CNMR (50 MHz, C,D,, 340 K): 6 = 15.428 (s, SiCHMe,), 20.224 (s,
CHMe,), 23.731 (s, CHMe,), 24.901 (br., CHMe,), 34.273 (s, CHMe,), 86.872
(s, AsC), 122.536 (br.), 126.649 (s), 134.713 ( s ) , 150.860 (br.), 151.156 (s).
154.807 (br.); “SiNMR (INEPT, C,D,): 6 = -3.24 (s, Si-0), 23.00 (s, SiiPr);
MS (El. 70eV): m/r 848 (M’, 2.5%). 666 ((M-Ph,CO)+. 40). 433
((ls,Si - 1 H)‘, 100); correct C,H-analysis.
[a] ASH signal not found. Below 278K two anisochronic methyl groups of the
SiPr group are observed.
8 VCH Verlagsgerellschafi mbH, W-6940 Weinheim, 1992
0570-0833/92/0303-0317$3.50+ .2S/0
317
29SiNMR spectrum proves that in 1 there is a As-Si TI bond
with similar polarity relations as is in the P-Si x system.
The high kinetic stability of 1 allowed investigations into
the reactivity of this compound. Thus, the oxidation of 1
with elemental tellurium (toluene, 2 5 T , Id) leads to the
yellow, crystalline three-membered ring compound 5. The
structure of the AsSiTe three-membered ring is confirmed by
mass spectrometry and 29Si as well as lz5Te NMR spectra
(Table I), especially since the 29Si and "'Te chemical shifts
are very similar to those of the homologous PSiTe threemembered ring.t61
arsaalkenes['O1via arsasilenes by means of a pseudo Wittig
reaction.
-
,
Ph,C=O
I$
Is-Si-As
=
-
SiiPr,
I
'O-CPhp
I
iPr,Si-As=CPh,
8
~0"c
Ph-As=C(Sii Pr,)Ph
6
7
5
Since kinetically stabilized silanimines react with ketones
in a metathetical process to give azomethine derivatives
(R,C=NR) and trimeric cyclosilanones (R,SiO), ,[71 we investigated whether analogous methylenarsanes "arsaalkenes" are obtained from 1 and ketones R,C=O (R = Ph,
tBu). Whereas benzophenone reacts with 1 to give 6 already
at 0 "C, with tBu,C=O even at 90 "C for 8 h no reaction is
achieved. The composition and structure of 6 are confirmed
by mass spectrometry, and NMR spectroscopy, respectively
(Table 1). In the mass spectrometer, as a retro reaction of 6
only the fragmentation to I f and Ph,C=O is observed.
The crystal structure analysis[*]of 6 shows that as a result
of the bulky substituents unusual bonding situations exist
(Fig. 2). The SiOCAs four-membered ring is slightly bent
Experimental Procedure
4 : A solution of Is,SiF, (5.4 g, 11.44 mmol) in THF (40 mL) was added to
LiAsHl . DME (3.98 g, 22.88 mmol) and was stirred for 3 h at 0 "C then 16h at
25 "C. To the orange-yellow solution of 2, Pr,SiOSO,CF, (3.5 g, 11.44 mmol)
was added at - 50°C and then this was stirred for 30 min at 25 "C.Finally, all
volatiles were removed at
Torr and the dark brown crude product was
taken up in hexane (50 mL) and filtered over a G3 frit. Compound 3 could be
crystallized from a concentrated solution. For the further processing to 4 this
was not absolutely necessary. Therefore, the filtrate was diluted with THF
(10 mL), cooled to -78 "C, and treated with nBuLi (11.44 mmol, 2 . 5 solution
~
in hexane, Aldrich). The clear orange solution was slowly warmed to 25 "C, the
solvent removed in vacuum, and the solid residue recrystallized twice from
hexane at -30°C. Yield: 5.13g (6.13mmo1, 53.7%), colorless crystals.
1: 4 (912 mg, 1.09 mmol) was dissolved in toluene (5 mL) and heated to 8090°C for 14h. The red solution was completely evaporated and taken up in
hexane (5 mL). Me,SiCI (1 mL) was added and the solution was stirred for 1d
at 25°C to separate the LiE The LiCl was filtered off and the filtrate was
concentrated in vacuum to give 1 as a deep-red, viscous oil. Yield: 660 mg
(0.99 mmol, 91 YO).
5: 1 (420 mg, 0.63 mmol) was dissolved in toluene (10 mL) and stirred with Te
powder (excess) for 1 d at 25 "C. The excess Te was filtered off and the red
filtrate was concentrated to ca. 2 mL and left at 10 "C so that after two crystallizations yellow crystals of 5 precipitated. Yield: 199 mg (0.25 mmol, 39.8%),
mp = 164 "C.
6: 1 (583 mg, 0.88 mmol) was dissolved in toluene (10 mL) and added to benzophenone (160 mg) dissolved in toluene (5 mL) at ca. 0 "C. The initial deep red
color of the solution disappeared immediately. All volatiles were removed at
l o - * Torr, and the residue was recrystallized twice from hexane (2 mL) at 25".
Yield: 621 mg (0.73 mmol, 83.3%), colorless crystals, mp = 135°C.
Received: October 24, 1991 [Z4985IE]
German version: Angew. Chem. 1992,104, 350
Fig. 2. Molecular structure of 6. Selected averaged bond lengths [A] and angles
f"]:Asl-Sil 2.382(2), Asl-Si2 2.393(2), Asl-Cl 2.057(7), Sil-01 1.688(4), C10 1 1.450(8);Sil-Asl-C1 68.6(2), Asl-Sil-01 82.5(1), Sil-01-C1 105.8(3), 01Cl-As1 101.0(4).
(along the As-0 axis 11.7" and relative to Sil-C1 16.2"),
the Si-As, Si-0, and C-0 bond lengths correspond to
extended single bonds, and the As atom is tetrahedrally coordinated (sum of angles 299.4"). Of particular note is the
long As-C distance (2.060(7) A), which is 0.1 8, longer than
the average single bond (ca. 1.95 A); this is probably caused
by the bulky substituents. The inert behavior of tBu,C=O
towards 1 is probably due to steric hindrance.
Under drastic conditions (160 "C, 10 h) 6 actually decomposes into Is,Si=O, which immediately dimerizes to 7 (in
contrast to less bulky silanones, which usually trimerize),
and the arsaalkenes 8 and 9.[91This presents a new way to
31 8
0 VCH
Verlagsgesel/schaft mbH, W-6940 Weinheim, 1992
CAS Registry numbers:
1.138435-76-4; 2,138435-77-5; 3,138435-78-6; 4,138435-84-4; 5,338435-79-7;
6, 138435-80-0; 7, 138435-81-1; 8, 138435-82-2; 9, 138435-83-3; Is,SiF,,
108202-50-2; LiAsH,. DME, 138435-85-5; Pr,SiOSO,CF,, 80522-42-5;
Ph,CO, 119-61-9; Te, 13494-80-9.
[l] Reviews: Disilenes: R. West, Angew. Chem. 1987, 99,1231; Angew. Chem.
I n l . Ed. Engl. 1987, 26, 1201; Silaalkenes: G. Raabe, J. Michl (Multipk
bonds to silicon) in The Chemistry of Organic Silicon Compounds, Purl 2
(Eds.: S. Patai, 2. Rappaport), Wiley, New York, 1987, p. 1044;
Silanimines: ibid., p. 1108.
[2] C. N. Smit, F. Bickelhaupt, Organomerullics 1987,6, 1156; H. M. M. Bastiaans, E Bickelhaupt, Y. van den Winkel, Phosphorus Sulfur Silicon Relur.
Elem. 1990,49/50, 333; Y. van den Winkel, H. M. M. Bastiaans, F. Bickelhaupt, L Organomel. Chem. 1991, 405, 183; see also (31.
[3] M. Driess, Angew. Chem. 1991, 103, 979; Angew. Chem. I n t . Ed. Engl.
1991, 31, 102.
141 Crystal structure analysis of 4: Monoclinic, P2,/n, a = 18.933(10),
b =12.053(6), c = 24.306(12) A, fl =111.30(6)', V = 5168 A3, 2 = 4;
2667 reflections (1>2u(I), four-circle diffractometer, Mo,, radiation, w
scan), R = 0.091, R, = 0.097 (As, Si, F, 0 anisotropic, C isotropic, H in
calculated positions, methyl groups as rigid groups, 332 parameters). A
THF molecule and p-positioned isopropyl groups are disordered." l 1
[5] G. + c . C. Witthauer, Z . Anorg. Allg. Chem. 1982, 492, 28.
[6] Is,Si-Te-P(SiiPr,):
= - 66.5 (d); 6('25Te) = -1124.8 (d). M.
Driess, unpublished.
0570-0833/92/0303-0318 8 3.50+.25/0
Angew. Chem. In?. Ed. Engl. 31 (1992) No. 3
[7] N. Wiberg, J. Organomer. Chem. 1984,273,141; S . Vollbrecht, U. Klingebiel, D. Schmidt-Base, Z. Naturforsch. B 1991, 46, 709.
[8] Crystal structure analysis of 6 : monoclinic. P2,/a, a = 17.919(18). b =
16.238(16), c = 34.53(3) A, j3 = 90.83(6)”, V = 10047 A3, Z = 8; 7501 reflections ( I > 2 4 four-circle diffractometer, Mo,, radiation, w scan),
R = 0.065, R, = 0.059 (As, Si, 0, C anisotropic, H in calculated positions,
isotropic temperature factors, phenyl rings as rigid groups, 921 parameters).‘”’
[9] The arsaalkenes 8 and 9 were characterized by ‘H NMR as well as ” C
NMR spectroscopy and also mass spectrometry. The 1,3,2,4-dioxadisilethane 7 [a(’%) = - 6.38; MS (EI, 70 eV): m/z 900 ( M i , 84(%), 435
(Is,SiH+, IOO)] is identical with the product from the oxidation of
Is,Si=SiIs, with 0,: R. West, A. Millevolte, 24th Organosilicon Symposium, April 12-13 1991, El Paso, USA.
[lo] T. C . Klebach, H. van Dongen, F. Bickelhaupt, Angew. Chem. 1979, 91,
423; Angew. Chem. Int. Ed. Engl. 1979,18, 395; G. Becker, G. Gutekunst,
Z. Anorg. Allg. Chem. 1980, 470, 144.
1111 Further details of the crystal structure investigation may be obtained from
the Fachinformationszentrum Karlsruhe. Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2
(FRG) on quoting the depository number CSD-55937, the names of the
authors, and the journal citation.
pentyl)-P-CD (Lipodex D, 2).[41On capillary columns coated
with 2, the enantiomers of 1 are resolved with an unusually
large separation factor (c( = 2.02, on a 25 m “fused-silica
capillary” at 333 K AAG& = 2 kJmol-’).
The ‘HNMR spectrum of a solution of 1 and 2 in a nonpolar solvent ([D,,]cyclohexane, [D ‘Jhexane) shows significantly different signals for (R)-1 and (S)-1. All signals of the
( S ) enantiomer are shifted to lower field by up to A6 = 0.5
in comparison to the ( R ) enantiomer (Fig. 1). Futhermore,
Cyclodextrin Derivatives as Chiral SelectorsInvestigation of the Interaction with (&!?)-Methyl2-chloropropionate by Enantioselective Gas
Chromatography, NMR Spectroscopy, and
Molecular Dynamics Simulation**
By Jutta E. H . Kohler, Manfred ffohla,Martina Richters,
and Wilfried A . Konig*
Dedicated to Professor Ernst Bayer
on the occasion of his 65th birthday
Enantiomeric substrates form energetically and structurally distinguishable host-guest complexes with cyclodextrins and their derivatives. This is shown, for example, in the
investigation of chiral substrates in the presence of cyclodextrins by enantioselective chromatography,“] NMR spectroscopy,[’] and X-ray structure analysis.[31To understand
the host-guest interaction and thereby, the “chiral recognition” it would be very useful to obtain information concerning the spatial relationship between host and guest molecules
in molecular complexes.
The model we investigated involves (R,S)-methyl-2-chloropropionate 1 complexed with heptakis(3-O-acetyl-2,6-di-OOR6
2,R3= R6 = n-pentyl, R3 = acetyl
[*] Dr. J. E. H. Kohler. M. Hohla
Consortium fur Elekrochemische Industrie
Zielstattstrasse 20, D-W-8000 Munchen 70 (FRG)
Prof. Dr. W. A. Konig. M. Richters
Institut fur Organische Chemie der Universitat
Martin-Luther-King-Platz 6, D-W-2000 Hamburg 13 (FRG)
[*‘I This work was supported by the Deutscbe Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
Angew. Chem. Int. Ed. Engl. 31 (1992j No. 3
0 VCH
C
1
b
r
5
3
4
2
’
.
r
1
TMS
.
-
0
-8
Fig. 1. 400 MHz ‘H NMR spectra of (R,S)-1 (below) with the signals of the
methyl (a), methine (b), and methoxy groups (c), of (R,S)-1 and 2 in mol ratio
1:2.25 (middle; the resonance signals a, b, and c show different chemical shifts
for the enantiomers) and of 2 ( above). All spectra were recorded in [D,,]cyclohexane.
the methine proton of (S)-1does not show a quartet, but a
signal of higher order (Fig. 2). This could indicate a nonequivalence of the coupling CH, protons as a result of a
specific interaction with the chiral host molecule in the inclusion complex.
The differences in the chemical shift values decrease on
raising the temperature and also on increasing the hostguest ratio. Similar, though less pronounced effects appeared in the ‘H NMR spectra of solutions of 2 and either
(R,S)-methyl-2-bromopropionate, (R,S)-methyllactate, or
(R,S)-methylmandelate. In every case, the protons of the
enantiomer retained more strongly on the GC column also
absorb at lower field. Thus, in principle, cyclodextrin derivatives are suitable as chiral shift reagents. A similar example
of discrimination for the enantioselective inclusion of enantiomers was reported by A. Collet et al.”’ for bromochlorofluoromethane and a synthetic cryptophane.
Verlagsgeselischaf~mbH, W-6940 Weinheim, 1992
0570-0833/92/0303-0319$ 3 X t .2S/O
319
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