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Crystal structure of 2-Lithio-2-phenyl-1 3-dithiane-Tetrahydrofuran-Tetramethylethylenediamine (111); Electron-Density Difference Maps for Lithio-methyl- and Lithio-phenyl-dithiane.

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Crystal Structure of 2-Lithio-2-phenyl-l,3-dithianeTetrahydrofuran-Tetramethylethylenediamine (l/l/l);
Electron-Density Difference Maps for Lithio-methyland Lithio-phenyl-dithiane
By Rene Arnstutz, Jack D. Dunitz, and Dieter Seebach"]
Dedicated to Professor Edgar Heilbronner on the occasion
of his 60th birthday
The nature of the Li-C bond and of the stabilization of
carbanionoid centers by adjacent third- and higher-row
atoms are both still matters of debate"]. ". .., the mechanism of anion stabilization by third and higher row elements remains an unsettled and important problem. Operational criteria to distinguish charge transfer from polarization effects are difficult to devise, particularly with the
limitations of working with real compoundsl'"]". The main
features of electron-density difference maps obtained by
X-ray analysis are often identifiable, at least qualitatively,
with concepts (bonding density, lone-pair electrons, nbonds) that chemists use in discussing the electronic structure of moleculesfz1.In this paper we describe evidence
from such mapsLz1for the existence of two different types
of Li-C bond in closely related sulfur-a-substituted organolithium compounds, namely dimeric 2-lithio-2-methyl1,3-dithianetetramethylethylenediamine (TMEDA)
and the title compound (2)14].
carbon C1 and the two nitrogen atoms of TMEDA; thus,
in contrast to (I), the complex (2) is monomeric. The phenyl group in unmetalated 2-phenyldithiane is equatorial[61
but in (2) is axial"] and its plane is rotated by 90" with respect to the unmetalated compound to achieve an orientation that allows conjugative stabilization. Although the
C1-C5 bond length of 147 pm indicates considerable
double-bond character, the carbanionoid CI is still far
Fig. I . Structure of complex (2) with H-atoms excluded (drawn by Program PLUTO, Cambridge Crystallographic Data Centre). Crystal data: Space group Pi;
2 = 2 , a=900.56, 6-980.32. c= 1295.55 pm, a=96.28, 8-97.15,
y= 101.55",
p..,.= 1.178 g/cm3. Bond lengths [pm, uSO.5 pm] Lil-01 197.0, LiI-NI
105.8, 01-LiI-NZ
Lil-N2 211.0; angle I", uCO.10"] 01-Lil-Nl
117.2, CI-LiI-NI
119.8. CI-LiI-N2
114.1, NIL-Lil-N2 86.9.
Crystalline (2) was obtained by deprotonation of phenyldithiane [0.25 M solution in hexaneltetrahydrofuran (THF)
3 : I ] with butyllithium in the presence of TMEDA (0.33 M)
at - 15 "C, followed by cooling to - 78 "C. X-ray analysis's] of (2) led to the structure depicted in Figure 1. The
surroundings of the carbanionoid centers in (I) and (2) are
shown in (3) and (4). respectively.
from planar (see Fig. 1). On passing from (I) to (2), the
Li-C bond length increases by 10 pm and the angle between this bond and the Sl-Cl-S2
bisector decreases
from 121" to 96" [cf. (3) and (4J. While these changes indicate a shift towards a n-complex type of structure in (2) (cf.
the structure of benzyllithium-TMEDA[81), they may appear small when considerd against the differences in reactivity between the two compounds, for example, with aJ3unsaturated carbonyl compounds191,or against the difference of 8 units between the pK,'s of the conjugate
- ApCa,J
Electron-density difference maps (Ap= Apexp
calculated for (I) and (2) show, on the whole, similar bonding density for corresponding C-C,
and C-S
bonds in the two structures together with lone-pair peaks
in the expected directions, close to the N, 0 and S atoms.
By far the greatest difference between the two maps occurs
at the Li atoms. Figure 2 shows sections of Ap for (1) and
(2) in the plane of C1, Li and an N atom of TMEDA. The
diffuse peaks along the bond directions may be identified
as bonding or lone-pair density. At the Li atoms, Ap is
Several features of the structure of the metalated phenyldithiane (2) are noteworthy. In order to achieve its usual
coordination number 4, the lithium atom is bonded to the
oxygen atom of a THF molecule in addition to the dithiane
I*] Prof. Dr. D. Seebach, Dip1.-Chem. R. Amstutz, Prof. Dr. J. D. Dunitz
Laboratorium fiir Organische Chemie der Eidgenassischen Technischen Hochschule
ETH-Zentmm, Universitatstrasse 16, CH-8092 Zurich (Switzerland)
Angew. Chem.
Ed Engl. 20 (1981) No. 5
Fig. 2. Electron-density difference-maps in the planes: Nl-Li-NZ
of ( I ) and C1-Li-NZ
of (2). Contours at intervals of 0.05 eA-' (negative contours dotted).
0 Verlag Chemie GmbH. 6940 Weinheim, I981
057lW833/81/0505-465 .$ 02.50/0
close to zero in (1) but strongly negative in (2). By integration, the electron-density deficit on the Li atom in (2) is estimated to be about 0.5-0.6 electrons. Thus, from the
electron-density difference maps, 2-lithio-2-methyldithiane
would seem to have a covalent, at most polarized, Li-C
bond, whereas 2-lithio-2-phenyldithiane can be regarded
as an example of a contact ion-pair complex.
sults demonstrate for the first time that chains of cornerlinked tetrahedra, which are already known as basic structural units in the salts of isopolyacids of the main group elements, e. g. of silicon or phosphorus, can also occur in intermetallic compounds of the Zintl type.
Received: January 9, 1981 [Z 762 IE]
German version: Angew. Chem. 93,487 (1981)
111 a) E. Euncel, T. Dursrr Comprehensive Carhanion Chemistry, Elsevier, Amsterdam 1980; b) T. Clark, J. Chandrasekhar. P.v. R. Schleyer. J. Chem. Sac. Chem.
Commun. 1980,672; c) S. A. Srreirwieser Jr., E. Juarisri, L. L. Nebenmhl, in [la],
Chpt. 7.
I21 P. Coppens, Angew. Chem. 89, 33 (1977); Angew. Chem. Int. Ed. Engl. 16, 32
(1977); J. D. Dunirz: X-Ray Analysis and the Structure of Organic Molecules,
Chpt. 8, Comell University Press, 1979.
I31 R. Amstutz. D. Seebach. P. Seiler, E. Schweizer. J. D. Dunirz, Angew. Chem. 92,
59 (1980); Angew. Chem. Int. Ed. Engl. 19, 53 (1980).
141 D. Seebach, Synthesis 1969, 17; D. Seebach, E. J. Corey, J. Org. Chem. 40,231
(1975); E.-Th. Grobel, D. Seebach, Synthesis 1977, 357.
IS] A single crystal of (2) was enclosed in a thin-walled quartz capillary in a dry argon atmosphere using tetradecane as adhesive and transferred to a Enraf-Nanius-CAD4 diffractometer with graphite-monochromator (Moxa-radiation) and
low-temperature device. Data collection at - 180°C gave 3976 measured reflections (2314 with 1>3u,); out to b'=27'. Least-squares refinement with anisotropic vibration parameters for non-hydrogen atoms, isotropic for hydrogens
gave R- 0.038 ( R , = dIKI - IF,II/C dFor)= 0.045, w= u-*(F) exp(Asin2B /
h') with A=3.2
Cf. P. Seiler, J. D. Dunifz. Acta Cryst. B29, 589 (1973).
Similar refinement of (1) gave R,=0.033 with A=4.2 A2.Ap=p..,-p,.,.
were calculated with standard scattering factors for neutral atoms (International
Tables for X-Ray Crystallography, Val. 4, pp. 72-75.
16) M. T. Kalff: C . Romers, Acta Crystallogr. 20, 490 (1966).
171 In agreement with conclusions from captive experiments: A. G. Abatjoglou, E.
L. Elid. L. F. Kuyper, J. Am. Chem. Sac. 99, 8262 (1977).
I81 S. Parrermann. I . L. Krrrle. G. D. Stucky. J. Am. Chem. Sac. 92, llSO(1970).
191 P. C. Ostrowski. V. V. Kane, Tetrahedron Lett. 1977, 3549; A. Yamaichi. C. A.
Brown. J. Chem. Sac. Chem. Commun. 1979, 100; M. El-Eouz. L. Wartski. Tetrahedron Lett. 1980, 2897.
Fig. 1. Structure of CaAIAs,. Small open circles e C a atoms, large open circles c As atoms, small closed circles e A1 atoms [2].
Ca3A1As3-An Intermetallic Analogue of the Chain
Silicates 1"'
By Gerhard Cordier and Herbert Schayer[']
Dedicated to Professor Karl Heinrich Lieser on the
occasion of his 60th birthday
Salts with complex anions gain metallic bonding character if the nonmetallic components in their anionic moieties
are replaced by semimetals-there result Zintl phases with
complex anions. This transition in bond character was recently demonstrated for compounds having Ba$3(Ge)As4
structure, in which Si(Ge)As:--tetrahedra occur, corresponding to the isosteric Si(Ge)O:- tetrahedra in the orthesilicates and germanates"]. We have now succeeded in
preparing Ca,A1As3 having (AlAs,);--chain anions which
are isosterically and structurally completely analogous to
the poIysilicate(germanate) anions (SO,),' - and (GeO,),' -.
As shown in Figure lf2]the structure contains "Einereinfachketten" (nomenclature after Liebau) of A1As, tetrahedra. The Al-As atomic distances of 250.2, 250.3, 253.9
pm (2 x ) correspond to the sum of the covalent radii of
these elements as quoted by Pauling ( P 244 pm); they are
significantly shorter than the sum of the metal ( P 291 pm)
or ionic radii ( P 272 pm). The bond angles at the centraI A1
atom are 102.4, 112.4 (ZX), 108.8 (Zx), 111.6". These reAbteilung I1 ftir Anorganische Chemie im
Eduard-Zintl-Institut der Technischen Hochschule
Hochschulstr. 4, D-6100 Darmstadt (Germany)
['*I This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
0 Verlag Chemie GmbH. 6940 Weinheim. 1981
Received: October 31, 1980 [Z 760 IEI
German version: Angew. Chem. 93,474(1981)
I11 B. Eirenmann, H. Jordan. H Schayer, Angew. Chem. 93, 211 (1981): Angew.
Chem. Int. Ed. Engl. 20, 197 (1981); Z. Anorg. Allg. Chem., in press.
121 Ca,AIAs,, orthorhombic, space group Pnma, 2 = 4 , a = 1221.2(3), b-420.1(2),
c= 1343(4) pm, automatic two-circle diffractometer Stoe Stadi I1 (Ma,,, graphite monochromator, o-scan), R=0.093 (1074 independent reflections). Solution
of structure by statistical phase-determination methods; SHEL-X program system, G. M. Sheldrick, University of Cambridge, England (1976).
Macrotricyclic Quaternary Ammonium Salts:
Enzyme-Analogous Activity1**'
By Franz P. Schmidtchen"'
Natural enzymes achieve their extraordinary specificity
and catalytic activity by binding of the substrates in an en['I
[*] Prof. Dr. H. SchBfer, Dr. G. Cordier
Stoichiometric amounts of the elements were heated under argon at 1200 K in corrundum crucibles contained in
quartz bombs. After cooling, the reaction product was homogenized, re-heated to 1200 K, and annealed for 24 h at
900 K. The metallic-like regulus thus obtained was optically and X-ray crystallographically uniform. Ca3A1As, is
relatively stable, but shows distinct signs of decomposition
on exposure to moist atmosphere for a few days; the shiny
metallic-like surfaces become dull and covered with a gray
layer of unknown composition.
Dr. F. P. Schmidtchen
Lehrstuhl ftir Organische Chemie und Biochemie
der Technischen Universitst Miinchen
Lichtenbergstr. 4, D-8046 Garching (Germany)
Part 3: This work was supported by the Deutsche Fonchungsgemeinschaft.-Part 2: 141.
OS70-0833/8I/OSOS-466$ 02.50/0
Angew. Chem. inr. Ed Engl. 20 (1981) No. 5
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crystals, tetrahydrofuran, phenyl, 111, different, electro, density, dithiane, methyl, structure, maps, tetramethylethylenediamine, lithio
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