764

Chem. Ber. 118, 764-773 (1985)

W. Bauer, T. Laube, and D. Seebach

Crystal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer

Walter Bauer'), Thomas Lathe2), and Dieter Seebach *

Laboratorium fur Organische Chemie der Eidgenossischen Technischen Hochschule, ETH-Zentrum, Universitatstrde 16, CH-8092 Zurich (Schweiz)

Received February 10, 1984

The structure of a crystalline complex with the composition [lithium 8-(dimethylamino)-E-hepta- fulvenolate], . (THF), has been determined by X-ray analysis at - 115°C ( R = 0.048). The lith- ium atoms form a four-membered ring with the two oxygen atoms of the enolates and are solvated by two THF oxygens each. The n-system and the dimethylamino group are not involved in complexing the metal. The geometry of and the bonding in the nearly planar heptafulvene moiety of the enolate are discussed.

Kristall- und Molekiilstruktur eines mit THF solvatisierten dimeren Lithiumenolats eines Carbonsiureamids

Die Struktur eines kristallinen Komplexes der Zusammensetzung [Lithium-S-(dimethylamin0)-8- heptafulvenolat], . (THV4 wurde durch Rhtgen-Strukturanalyse bei - 115 "C mit einem R-Wert von 0.048 bestimmt. Die Lithium-Atome bilden rnit den beiden Enolat-Sauerstoffen einen Vier- ring und tragen als weitere Liganden je zwei THF-Sauerstoffe. Weder das x-System noch die Dimethylamino-Gruppe sind an der Komplexierung beteiligt. Die Geornetrie und die Bindung im fast planaren Heptafulven-Teil des Enolates werden diskutiert.

In view of the importance of lithium enolates in modern synthetic organic chemistry, two years ago we started a project for determining the structure o f some representative reagents of this type by X-ray crystal structure analysis. We found two tetrameric ketone enolates3*') as well as dimeric and tetrameric aggregates o f ester enolates9. So far, n o structure of a lithium enolate of a N,N-dialkylcarboxamide has been elucidated. An interesting example of this class o f compounds is lithium 8-(dimethylamino)-& heptafulvenolate (1) which is at the same time an amide enolate and a heptafulvene with inverse polarization6.').

1V.. THF THF 2_0!

1 I", - 108

(simplified numbering of the atoms of the enolate molecule used in the discussion)

(numbering of the atoms of the enolate molecules in the dimer as chosen in the X-ray

structure determination)

0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1985 0009 - 2940/85/0202 - 0764 $ 02.50/0

Crystal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer 165

For the X-ray structure analysis, the enolate 1 was generated from N,N-dimethyl- 1,3,5-cycloheptatriene-7-carboxamide (IUPAC name) with lithium diisopropylamide (LDA) and recrystallized from tetrahydrofuran (THF)/hexane. Both the solution and the crystals of 1 are deep violets-"). Although "potentially antiaromatic", 1 is remark- ably stable even at room temperature"). From the 'H and.13C NMR spectra of 1 there is evidence for an oxygen-bound lithium atom, as concluded from the facile rotation around the C(3) - N bond, and from a high barrier to rotation around the exocyclic C(3) - C(4) bond: there are signals due to anisochronous pairs of ring carbons in the l3C spectrum, and there is only one signal from the methyl groups on nitrogen7). The same conclusion was drawn by Woodbury and Rathke from the NMR spectrum of the lithium enolate of N,N-dimethyl acetamidel9.

It was of interest to find out whether 1 is aggregated in the solid state as are other lithium enolates2-5), whether the lone pair on nitrogen takes part in conjugation and/or in lithium complexation, and to what extent the ring geometry is determined by antiaromaticity.

A. Results The lithium enolate 1 crystallized with two equivalents of tetrahydrofuran (THF)

solvent. The crystal structure contains dimeric aggregates with approximate C,-sym- metry13), see Figures 1 and 2. The enolate oxygen atoms and the lithium atoms form a nearly planar central four-membered ring. The heptafulvene rings in each dimer take a cis-position on the Li,O, ring. Every lithium atom is coordinated by two THF mole- cules, thus achieving a tetrahedral environment of oxygen atoms. Neither the nitrogen atoms nor the x-systems are involved in Li-coordination.

C217

Fig. 1. Stereoscopic ORTEP Representation of 1 (Hydrogen Atoms Omitted, Thermal Ellipsoids are Drawn on the 50% Propability Level)

Like the ketone enolates, the amide enolate has a short olefinic double bond [C(3) - C(4)] and a long C- 0 single bond [C(3) - OLi] compared to the non-lithiated precursor. The C- N bond [C(3)- N] in the enolate moiety of 1 is significantly longer than the corresponding bond of carboxamides.

Chem. Ber. 118(1985)

766 W. Bauer. T. Laube, and D. Seebach

Table 1. Geometrical Dataa) of the Enolate Fragments in 1 and of Comparable Fragments in Topologically Similar Molecules. (The Letters on the Bonds Refer to the Corresponding Bonds in

Molecules with Comparable Fragments. The Numbers at the Atoms Refer to 1)

8 Pinacolone Enaminesb) Carbox- 1 (i = 1) 1 (i = 2) Li-Enolate amides

a 1.301 (5) 1.303 (6) 1.347 (3) - 1.228 (9) 1.378 b 1.385 (7)C) 1.381 (7)c) 1.338 (4) 1.334-1.366 1.533 (14) 1.332 C 1.435 (7) 1.427 (5) - 1.380-1.426 1.346 (10) 1.409 ab 125.0 (5) 125.1 (4) 122.3 (2) - 119.2 (12) 118.9 bc 117.8 (4) 118.1 (4) - 121.6-124.8 118.7 (12) 127.2 ac 117.3 (4) 116.9 (4) - - 122.0 (6) 113.8 cd 114.0 (4) 116.1 (4) - 113-126.0 117.7 (14) 112.4 ce 113.6 (4) 116.4 (4) - 115.7-122.1 124.4(15) 115.1 de 111.0 (4) 111.6 (4) - 108-111.9 117.5 (13) 112.0 bed + 159.5 ( 5 ) + 164.1 (5) - 119-180 - 126 bee - 72.0 (6) - 61.5 (6) - -8- +I1 - - 3 A 0.393 0.338 - 0.013 - 0.402 - 0.386 ref. this work this work 3, 1 4) 15) 22)

a) Bond lengths and A in A, angles and torsion angles in degrees. - b) Ranges. - C) Bond b inter- acts with the heptafulvene ring.

/ \ 104s

Fig. 2. Newman Projections Along the C(103)-C(104) Bond (Left Side) and Along the N(l) - C(103) Bond (Right Side) (The Corresponding Newman Projections of the Second Enolate

Molecule are Similar)

The nitrogen atom of the dimethylamino group in 1 is pyramidal. The distance Ai4) of the nitrogen above the plane formed by its bonding partners has an average value of 0.365 A. This value is within the range of pyramidalities A found in enarnine~'~) in

2 a 2 b

Chem. Ber. 118 (1985)

Crvstal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer 767

which the structure 2a is favoured. A Newman projection along the N- C(3) bond of 1 reveals, however, that one of the methyl groups is fully eclipsed with the C - 0 bond, see 2b, rather than with the C = C bond, see 2a, Figure 2, and Table 1.

As in other complexes of lithium with ethers15) the OTHP - Li bond in 1 coincides with the bisector of the C - 0 - C angle of the THF molecules.

Table 2. Bond Lengths and Folding Angles of Heptafulvenesd)

,boLi i@ ih@CN im k I - NMe2 -7 I k y m .

- m CN

1 2 3

% 4

5 6

b') f g h k 1

7

rn ah) 6 ref

l ( 1 . 1 ) 1.385 1.461 1.340 1.456 1.331 1.460 1.338 1.451 14.8 12.6 t h i s

l [ i = 2 ) 1.381 1.458 1.342 1.463 1 3 3 1 1.447 1.336 1.461 20 .8 17.9 work

0 16)

1 1.422 1.425 1.353 1.448 1.311 1 .448 1 .353 1.425 7.6 1 . 8 1 7 )

1.373 1.454 1.341 1.430 1.332 1.427 1.343 1.459 24.7 15.7 18)

1.350 1,450 1.365 1.470 1.334 1.470 1.365 1.450 0 2

4

6 7 1.361 1.465 1.339 1.415 1.338 1.415 1.339 1.465 45.3 20.1 21)

I 1.426 1.427 1.362 1.409 1.349 1.403 1.266 1.425 -'I --- 19)

1.329 1.472 1.336 1.434 1.337 1.441 1.332 1.473 41.4 23.6 20)

a) Bond lengths in A. - b) Folding angles in '. - C) Not stated and not calculable due to missing atom coordinates in ref. 19). - d) Data from X-ray structure (1 ,3 - 7) or microwave spectral ana- lysis (2).

The heptafulvene unit in 1 has a shallow boat conformation. At the same time a clear-cut single bond/double bond alternation is present. The values of the bond lengths and the folding angles C C , ~ are shown in Table 2 together with those of the other heptafulvenes. The seven-membered ring in 1 is surprisingly flat when compared to the other structures. The bond length alternation in 1 is more pronounced than in the di- cyanoheptafulvene 3 but still lies within the range found in the other heptafulvenes. Of the double bonds in 1, C(7) - C(8) (= bond i) is the shortest one as is the rule for most compounds shown in Table 2.

Chem. Ber. l la(1985)

768 W. Bauer. T. Laube. and D. Seebach

B. Discussion Considering the bond lengths, the enolate unit in 1 can be classified as an amino sub-

stituted lithium enolate. This classification also holds if 1 is compared with enamines'", and even better with the ketene N,Oacetal aZ): the nitrogen is pyramidalized (sp3- hybridized). This effect indicate^^^.^^) a low degree of p,n-overlap between the lone- pair on nitrogen and the double bond.

&b H

8

If the two-ring model description of double bonds is ~ s e d ' ~ , ~ ~ ) , enamines can in prin- ciple occur in two staggered and two eclipsed conformations 9a, b and 10a, b, respec- tively. For simple enamines which have an H atom in the cis-position with respect to the dialkylamino group, the conformation 9a has been found by X-ray crystal structure

In molecules with a potential leaving group such as CI on the carbon bearing the nitrogen atom, conformation 9b is favoured by an anomeric effect? the lone pair on nitrogen is antiperiplanar to the geminal electronegative substituent.

analysis 1422.23).

9 a 9 b 10 a 10 b

Enamines with the eclipsed conformation 10a have not yet been observed. For con- formation 10b the amide enolate 1 is the first example.

We assume that the eclipsed conformation of the C(3) - N bond in our structure is a compromise between two factors:

a) Minimun van der Waals interaction of the N-methyl [C(2)] and the neighboring methine groups [C(S)] (the shortest Hcc9-Hqs) distance is 2.27(6) A), i.e., steric repul- sion disfavors conformation 9a and 10a.

b) Maximum deviation from a conformation with antiperiplanar arrangement of the virtual N-lone pair and the C(3)- 0 bond, i.e., conformation 9b should be disfavored by two opposing anomeric effects.

The ring geometry in heptafulvenes is governed by steric and electronic factorsz6).

11 a 11 b 11 c

Chem. Ber. ll8(1985)

Crystal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer 769

Heptafulvenes 11 with normal polarization (X,Y = acceptors) tend to be flat due to the contribution of resonance structure l l b (cf. 3 in Table 2). Due to the canonical form l l c heptafulvenes with inverse polarization (X,Y = donors) might be expected to adopt a boat shape to avoid “antiaromaticity” in the cycloheptatrienyl anion moiety. MND0/3 calculations, however, predict energy minima for planar structures of the un- substituted cycloheptatrienyl anion with charge and electron distributions as indicated in the formulae 12 and 1327).

12 13 14

For the anion of methyl 1,3,5-cycloheptatriene-7-carboxylate (IUPAC name) such a calculation2*) produced an energy minimum with a planar seven-membered ring, alternating bond lengths, the ester group twisted around 60” with respect to the ring plane, and a charge and electron distribution as indicated by the formula 14.

We believe that the experimentally found flat boat conformation of the seven-mem- bered ring in 1 is controlled by two effects:

a) Inverse polarization in 1 favors reduced K-orbital overlap in the ring which is achieved by deviation of the folding angles a$ from zero.

b) Folding causes reduction of the C(5) - C(4) - C(10) angle in heptafulvenes 11. Since the corresponding angle in 1 already has the ideal sp2 value of 120”, increasing ci would produce strain.

Because of the tight bond of lithium to oxygen and due to the high C(7)-C(8) double bond character”) we prefer the description of 1 as a “cross conjugated lithium enolate” with an electron distribution as indicated in formula 15.

15

W. B. thanks the Deutsche Forschungsgerneinschaft for a grant. We thank Prof. J. D. Dunitz and his coworkers W. B. Schweizer and P. Seller for many discussions and practical help.

Experimental Part Preparation ofl: To a solution of 0.35 ml(2.50 mmol) of diisopropylamine in 2 ml of THF was

added at 0°C 1.46 ml(2.45 mmol) of 1.68 M n-butyllithium in hexane. After stirring at room tem- perature for 10 min and subsequently cooling to -5O“C, a solution of 400 mg (2.45 mmol) of N,N-dimethyl-I ,3,5-cycloheptatriene7-carboxamide30) in 2 ml of THF was added dropwise. The deep violet solution was stirred for 1 h and warmed to room temperature. After addition of 8 ml of hexane the solution was rapidly cooled to - 78”C, warmed again to 0°C and slowly cooled to

Chem. Ber. lla(1985)

770 W. Bauer, T. Laube. and D. Seebach

- 27°C (2 h). Crystals of appropriate size grew under these conditions, were separated from the mother liquor, washed with small portions of hexane and dried in vacuo.

Table 3. Atomic Coordinates and Thermal Parameters of 1 (2 1 . 4 C,H,O) THE TEMPERATURE FACTOR HAS THE FORM OF E X P I - T I YHERE

T ~ ~ 8 ~ l P I i ~ 2 l ~ U i l S I N l T H E T A l ILAMBOAI**Z FOR I S O T R O P I C A10115 T a 2 ~ O I I I 2 I ~ S U I I J l H 1 I I * H l J l 8 U l I ~ J l 8 A S T A R l I l * ~ ~ T A R l J l I t FOR

A N I S O T R O P I C ATOMS. ASTAR111 ARE RECIPROCAL A X I A L LEYCTHS A N 0

THE E.S.O. OF THE L A S T S I G N I F I C A N T O I S I T I S G I V E N I N PARENTHESES. H I 1 1 A R E H I L L E R I N D I C E S .

ATOM X Y 1 U11lOR Ul U 2 Z u33 u12 U13 U23

01 1 N 1 ClOl ClOZ Cl03 ClOk C105 ClOh C107 Cl08 c109 t110 L I 1 012 Clll tllt t113 Cllk 013 Cll5 C116 c117 Cll8

N2 CZOl CZOZ C203 C204 C205 C206 t207 C208 C209 CZlO L I Z 022 c211 CZIZ C213

a2 1

0.7010111 -0.001801 0.35Ok12I 0.034121 0.031121 0.5965121 0.073701 0.3k39121 0.038121 0.038131 0.619kl31 0.0334161 0.2b9801 0.05b131 O.Ob9lkl 0.5384121 -0~0105161 0.3805131 0.035131 0.0k801 0.b479121 0.074001 0~3190121 0.033131 0.027131 0.6370121 0.1539151 0.4407121 0.03k131 0.030131 0.580k121 0.2512151 O.kb34121 0 . 0 2 9 0 ) 0.034131 0.5545121 0.318bOl 0.5250131 0.035131 0.032131 0.5730131 0.3058161 U.5907131 0.052131 0.038131 0.6292131 0~2502161 0.5980131 0.070141 0.012131 0.6852IZI 0.18921bl 0.S4k301 O.Okb131 0.012131 0.6875121 0.1402151 0.4106131 0.037131 0.030131 0.7939141 0.0180191 0.3159141 0.Ok2151 0.037151 0.8385121 0.18mio O.I~OZIZI O.OWIZ I O.O~OIZI 0.8077131 0.3317171 0.34411il 0.0b0Ikl 0.03714) 0.82P4131 0.4126Ibl 0.3996131 0.080151 0.038141 0.8965131 0.3495i7) 0e39kb131 0.060Ikl 0.053lkl Oa8870121 0.191616) 0.3791(31 0.052131 0,036131 0.0241121 0~03611kl 0.2116421 0.06blZl 0.0b1131 0.8009131 -0.0491101 0.1627131 0.061Ikl 0.061151 0.8145131 0.0359171 0.0963131 0.094151 0.061141 0.8699151 0.132111 0.1005141 0.21111 0.148181 0.869501 0.137111 O.ll2lIkl 0.24111 0.182191 O.LI122111 -0.1571131 0.3b01121 0.029121 0.035121 0~9194121 -0.2499l41 0.3196121 0.037l21 0.014131 0.9027131 -0.2917161 0.2558131 0.060111 0.0651b1 0~9809121 -0.1680171 0.3038(31 0.037131 0;08415l 0.8660121 -0.1911151 0.3759121 0.036131 0.018131 0.8749121 -0.1890151 0.k425121 0.030131 0.024131 0.9303121 -0.2659151 0.k576121 0.039131 0.031131 0.9579121 -0.Zkb7Ibl 0.510201 0.015131 0.064Ikl 0.9k38131 -0.1342(71 0.5631131 0.055141 0.076151 0.8877131 -0.0581161 0.5859131 0.081141 0.052C41 0.8283121 -0~0677l61 0.5612131 0.059131 0.044131 0.8240121 -0~1200111 0.4992121 0.037131 0.037131 0.7205141 -0.1924101 0.38101k1 0.039141 0.030151 0.669bllI -0.253b141 0.47b7121 0.041121 0.039121 0.6935131 -0.3600161 0.5127131 0.047141 0.035141 0.66k3131 -0.3372181 0.5903131 0.067141 0.0571+1 0.5975131 -0.2713181 0.5917131 0.080141 0.123161 0.6078121 -0.19861bl 0.522801 0.036131 0.052141 0.69k0121 -0.3586lkl 0.3tb8121 0.054121 0.042121 0.6355131 -0.k452191 0.3570131 0.063141 0.070151 0.6166131 -0.5135181 0.2956131 0.078151 0.096151 0.6782141 -0.5103191 0.2385131 O.lOBIb1 0.128171 0.7163141 -0.3827181 0.252bl3l 0.070151 0.071151 0.b59131 0.089161 0.2k5131 0.08121 0.62k121 -0.073lbl O~Lb0131 0.0712)

0.045121 0.033121 0.038131 0.061141 0.0k2131 0.032131 0.039131 0.05501 0.047131 0.042 131 0.052131 0.04801 0.028141 0.053121 0.07801 0.0 68 I 41 0.0551bI 0.055131 0.03212) 0.041131 0.0571k1 0.059151 0.05201 0.03912l 0.031121 0.046131 0.0471 31 0.039131 0.032131 0.011131 0.016131 0.041131 0.033131 0.038131 0.037131 0.033141 0.033121 0.048141 0.039131 0~041l31 0~04b131 0.036121 0.049141 0.053141 O.Ok9141 0.039131

0.006121 -0.009121 -0.001121 -0.014121 -0.005131 -0.019131 -0.005131 -0.018131 -0.004121 -0.015121 0.001121 -0.000121

-0.005131 -0.008121 0.00001 -0.009131

-0.004131 -0.008131 -0.008131 -0.023131 -0.002131 -0.027131 0.001121 -0~014121

-0.OOlIk1 -0~OO8Ikl O.OOOl2I -0.024121 0.00301 -0.03bOl

-0.004l31 -0.011131 -0.013131 -0.019131 -0.00313) -0.025131 -0.031121 -0.011121 -0.020141 -0.018l31 -0.014lk1 -0.0291k1 -0.130181 -0.04OIbl -0.181191 -0.022161 0.003121 -0.015111 0.007121 -0.011121 0.021131 -0.021131 0.004131 -0.001131

-0.003121 -0.010121 -0.001121 -0.001121 0.010131 -0.013l21 0.010131 -0.02101

-0.001lkl -0.023131 -0.003141 -0.022131 0.005131 -0.009131

-0.001121 -0.011121 -0.006141 -0.009141 0.001121 -0.OO9IZI 0 . 0 0 4 0 1 -0.015131 0.00k141 -0.017131 0~050151 Oa003131 0 . 0 0 3 0 1 -0.004121

-0.02OlZI -0.OOb121 - 0 . O 4 O O I -0.OO4131 -0.04501 -0~011141 -0.058151 -0.01blkl -0.030141 -0.010131

0.00212) 0 ~ 0 0 6 1 2 1 0.0011 31 0 .00101 0 . 0 1 2 0 1 0.0061 2 I 0~009131 0 ~ 0 0 3 1 3 1 0. 00213 I 0.000131 0 .00301 0.0031 31 O.OO2141

-0~005121 0.007141

-0.009131 0.001131 0.007i21 0.000( 31 0.014131 0+037151 O+Otllb) 0.004111

-O.O09121 -0.017111 -0~010131 0.000l2 I

-0.OQ313 I 0.0011 3 I -0.001131 -0.006131

0.003(31 0.001(31 0.0021 41 0.0081t1 O~OO7131 0.01701 0.011111 0.001131

-0.OO2121 -0.00214I -0.001 I 41 -0.016141

0.000111

-o.oitoi

0.0031 t I

Chem. Ber. Zl8(1985)

Crystal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer 771

Table 4. Bond Lengths (A) and Angles (Degrees) in 1 (2 1 . 4 C4H80) with Standard Deviations in Parentheses

C l n l -N1 l s k 5 5 l b l C l O Z - N 1 1.4531bl C l 0 3 -ClOk 1.38Yl7l C 1 0 3 - N l 1.435171

C103 -011 1.301151 C l O I -Cloy 1.451161 ClO4 4 1 1 0 l . Ib110 l C105 4 1 0 6 1.331171

ClOb -C107 l .4tC181 C107 - C l O R 1.331181 C l O B -C100 1+43017I ClOP -C110 1.3k0171

C l l l 4 1 1 2 1.50111 C 1 1 1 -012 1 . 4 4 9 0 1 C l l 2 -e l ls 1.900191 c113 -c111 1.501in1

C 1 1 6 -012 1.439111 C115 4 1 1 6 1.484191 (115 -013 1.k30101 C l l b - C l l ? 1.48111

C117 - t i i n i . 4 i t i i e l l 8 -013 1.40111 C Z O l -N2 1.552171 C202 -N2 1.649171

C203 -CSO4 1.38117) (203 -N2 1.+27151 C203 -021 1.303lb) C204 -C205 l . k b l 1 7 l

C204 -CZlO 1.k58Ihl C2d5 - C N b 1.336181 C20b -C207 1.447181 C207 - C Z O I I 1.33118)

c m -czo9 i . 4 t 3 1 ~ 1 c m 4 2 1 0 i . w t i 7 1 c211 -cz iz 1.5111ni c z i l -w 1.k40171

C212 -CZ13 1.52111 C213 -C2 l I 1.I15181 C21k -022 l.kkV151 C215 -CZlb 1.5111l

CZ15 -023 1.46kI81 C 2 l b -C217 1.4S9181 C217 -C218 1.59111 C Z l 8 -023 1.427171

LIl - L I Z 2.58111 L I 1 411 1.88kIOI 111 -012 1.05b19l 111 -013 1.901181

111 -021 1.91719I L I Z -011 1.931(91 L I Z -021 1 . ~ 7 8 1 8 1 L I Z - n u 1 . ~ 7 3 1 7 1

L I ~ 4 2 3 Z . O Z ( I ~ P I

C104 -C103 - N 1

(103 - c io4 -cia(

c i o 4 - n o s - c l o t

c107 - C l O R -El09

A 1 2 -c111 -012

~ 1 1 6 - c i i 7 - c i i o C113 - C l l I - n l2

C?O4 -CL03 -021

~ 2 0 3 -c204 -c210

CZ05 -CLJb -C207

C20R -c709 -c210

C Z l l -CZ12 -C213

CZlh -C215 -023

c z i t - t z i 8 -023

I I ? -111 -013

I l l1 -LI1 -013

012 -LI1 -021

L I 1 - L I Z -021

n i l -LIZ -021

021 -LIZ -022

c i n i -NI - c ioz cmi - N Z -mi cioa - n u -LII

tiii - n i z - t i 1 4

c i i 5 -n i3 - c i i n C203 -021 -111

C Z l l -022 -c214

117.011.1

121.0151

130.81 5 1

i ~ n . ' 1 1 5 1

105.ZlhI

iOb.1151

107.01 71

125.1141

i10.1141

128.2151

127.4141

101.71 5 I

lOb.3151

10b.1151

iZ3.5141

112.215I

113.0191

k 7 . 9 1 3 1

VI.0141

120.3151

111.0141

111 sb14 I

l I1 .2141

109 * 3 1 1 1

107.115 1

129.414l

108. b 1 3 l

C l O I -C103 -011

c103 -c104 -c110

C105 -ClOb -C107

c lan - c lop -c110

C l l l -C112 -C113

C11b 4 1 1 5 -013

c t i 7 - c n a -013

N2 'CZ03 -021

(205 -C20+ - C L l O

CZOb - C Z O 7 S 2 0 8

C204 - C L l O -C209

C Z l 2 -CZ13 -C214

C215 -C21b -C217

LI2 -LI1 -011

LIZ - L I l -021

011 - L l l -021

013 -111 -021

111 - L I Z 4 2 2

n i l -112 -022

02: -LIZ -023

C l O l - N t -C103

C2Ol -NZ -C203

C103 -011 - L I Z

C l l l -012 -111

E l l 5 -013 -LI1

c z o i -mi -LIZ

C Z l l 4 2 2 - L I Z

125.015l

117.91 4 1

129.1151

128.1 15 I

183.6151

1c7.0151

110.3181

l lb .914I

120.3(41

126.31bl

12P.bI5I

105.91kI

103,7101

kR.3131

4 h . b O l

94.2131

119,8141

lk1.114 I

116.91+I

115.4141

114.01*1

116.1141

125.k131

120.0141

125.9141

153.5141

120.8131

w i - c i a 3 -011

C105 - C l O k -Cl10

r i m - t i c 7 -CIOR

C l 0 4 -C110 -C109

C l l 2 -C113 -C114

C l l 5 - C l l b -C117

C?O5 -C703 -92

C?03 -C?O* -C205

C204 -C205 -CZOb

czo7 -czm -c209

c212 - C ? l l 4 2 2

C213 -C214 -022

C21b -C?17 -C218

LIZ -111 -012

011 -111 - m i n i z -111 -013

L I 1 -LIZ -011

111 - L I Z -nz,

011 -LIZ -023

022 -LIZ -023

C l O Z - N 1 -ClO3

C Z O Z -NZ -C20'4

L I l -011 - L I Z

c114 -012 411

C l l O -013 -111

111 -021 -LIZ

c214 -022 - L I Z

111.21bI

120.9141

126.51LI

130.7141

102.1151

lOZ.9lbl

i i n . i i 4 i

120.1 I k l

11P.ll5l

128.2151

105. 2 1 41

107.2141

10b.1101

137.71kI

120.5151

08.8141

Ib.81 31

l?O.P141

113 .b I I l

97.0 13 I

113.0141

l l b .1151

84.9161

127.01II

127.01 51

3 5 . 5 1 4 1

130. b l 4 l

Crystol Structure Analysisji): 2 CloH12LiNO~ 4 C4H80, M = 626.74. A single crystal (approximated size 0.3 mm x 0.3 mm x 0.6 mm) was mounted in a Lindeman glass tube under Ar with hexadecane as adhesive. The unit cell has been determined after a search run with 15 reflections. Monoclinic, space group P2,/c, a = 20.987 (17), b = 9.170 (3), c = 19.761 (9) A, p = 73.65 ( 5 ) " , V = 3649.2 A3, at - 115"C, 2 = 4, d, = 1.14 g . cm-j. Intensitymeasurements were carried out at - 115°C with an Enraf Nonius CAD 4 diffractometer, equipped with graphite

Chem. Ber. I18(1985)

52

772 W. Bauer, T. Laube, and D. Seebach

monochromator and cooling device (Mo-K, radiation, h = 0.7107 A, 4468 independent reflex- ions with @ < 22“, 2574 with I > 30(1)). The structure was solved by MULTAN 8032) and refined by bloc full-matrix analysis using SHELX33). All hydrogen positions have been found, but those at C(112), C(114), C(116), C(117), C(118), C(213), C(214), C(216), C(217) were substi- tuted by calculated positions. After anisotropic refinement of the non-hydrogen atoms, isotropic refinement of H atoms (with ride-mode for the calculated H atoms) in the SHELX system and anisotropic refinement of the non-hydrogen atoms and isotropic refinement of the experimentally found H atoms in the X-ray34) system, the final R value was 0.048 (R, = 0.050). Some large vibrational parameters in the THF molecules point to a certain amount of orientational disorder in the crystal structure. Atomic coordinates and thermal parameters are listed in Table 3, bond lengths and angles in Table 4.

l ) Postdoctoral Fellow, ETH Zurich, 1983/84. 2, The results described here will be part of the dissertation of Th. Laube, ETH Zurich 1984. 3, R. Amstutz, W. B. Schweizer. D. Seebach, and J. D. Dunitz, Helv. Chim. Acta 64, 2617

4, D. Seebach, R. Arnstutz, and J. D. Dunitz, Helv. Chim. Acta 64, 2622 (1981). 5, Th. Laube and W. B. Schweizer, unpublished results, ETH Zurich, 1983.

(1981).

W. Bauer, I . Betz, J. Daub, L . Jakob, W. Pickl, and K. M. Rapp, Chem. Ber. 116, 1154 (19 83).

7, K. M. Rapp, Th. Burgemekter. and J. Daub, Tetrahedron Lett. 1978, 2685. 8, The UV/VIS spectrum of 19) in pure THF and in the absence of excess butyllithium has a

h,,, = 551 nm ( E = 14O)ln). The bathochromic shift in the spectrum of 1 as compared with heptafulvenes of normal polarization indicates a HOMO/LUMO-gap narrowing%.

9, W. Bauer, J. Daub, and K. M. Rapp, Chem. Ber. 116, 1777 (1983). In) W. Bauer and J. Daub, unpublished results, University Regensburg, 1983. 11) Some reactions of 1 have been described: silylation6) (see also K . M . Rapp and J. Daub, Tetra-

hedron Lett. 1977,227), deuterationg), oxidative dimerization [ W. Bauer, J. Daub, A . Hasen- htindl, K . M. Rapp, and P. Schmidt, Tetrahedron Lett. 22, 2977 (1981); W. Bauer, E. Eibler, J. Daub, V. Lamm, H. Lotter, and A . Gieren, Chem. Ber. 117, 809 (1984)l.

12) R. P. Woodbury andM. W. Rathke, J . Org. Chem. 42, 1688 (1977). 13) The monomeric units differ somewhat in all corresponding values. To simplify the discussion,

the gross structure of 1 is assumed to have C, symmetry. 14) K. L. Brown, L. Damm, J. D. Dunitz, A . Eschenmoser, R. Hobi, and C. Kratky, Helv. Chim.

Acta 61, 3108 (1978). P. Chakrabarti and J. D. Dunitz, Helv. Chim. Acta 65, 1482 (1982).

16) A. Bauder, C. Keller, and M. Neuenschwander, J. Mol. Spectrosc. 63, 281 (1976). 17) H. Shimanouchi, T. Ashida, Y. Sasada, and M. Kakudo, Bull. Chem. SOC. Jpn. 39, 2322

18) R. Thomas and P. Coppens, Acta Crystallogr., Sect. B 28, 1800 (1972). 19) C. Reichardt and K.-Y. Yun, Angew. Chem. 94,69 (1982); Angew. Chem. Supplement 1982,

2n) W. Henslee and R. E. Davis, Acta Crystallogr., Sect. B 30, 1267 (1974). 21) H. Shimanouchi, Y. Sasada, C. Kabuto, and Y. Kitahara, Acta Crystallogr., Sect. B 30, 1267

z2) A . Kiimin, E. Maverick, P. Seiler, N. Vanier, L . Darnm, R . Hobi, J. D. Dunitz, and

23) S. J. Blarer, W. B. Schweizer, and D. Seebach, Helv. Chim. Acta 65, 1637 (1982). 24) L. Pauling, Kkkulk and the Chemical Bond, IUPAC Symposium on Theoretical Chemistry,

Butterworths Sc. Publ., London 1958, p. 1; L. Pauling, The Nature of the Chemical Bond, 3rd Ed., Cornell University Press 1960, p. 136ff.; taken from ref.”) in ref.14).

25) P. Deslongcharnps, Stereoelectronic Effects in Organic Chemistry, Pergamon Press, Oxford 1983.

26) For x-SCF-force field calculations on heptafulvenes see H. J. Lindner, Tetrahedron 37, 535 (1981).

27) A . W. Zwaard, A. M. Brouwer, and J. J . C. Mulder, Rec. Trav. Chim. Pays-Bas 101, 137 (1982).

(1966).

113; Angew. Chem., Int. Ed. Engl. 21, 65 (1982).

(1974).

A . Eschenmoser, Helv. Chim. Acta 63, 1158 (1980).

Chem. Ber. 118(1985)

Crystal and Molecular Structure of a THF-solvated Lithium Amide Enolate Dimer

28) A. W. Zwaard, Ph. D. Thesis, University of Leiden, The Netherlands, 1983. 29) The chemical shifts of these two carbon atoms are nearly the same when switching from hepta-

30) W. Betz and J. Daub, Chem. Ber. 107, 2095 (1974). 3l) Further details and basic data concerning the X-ray analysis may be obtained from Fachinfor-

mationszentrum Energie Physik Mathematik, D-7514 Eggenstein-Leopoldshafen (W. Ger- many) by specifying registry number CSD 50763, author, and the reference to this publication.

32) P. Main, S. J . Fiske, S. E. Hull, L. Lessinger, G. Gerrnain, J.-P. Declerc. and M. M. WOOF son, MULTAN 80. A System of Computer Programs for the Automatic Solution of Crystal Structures from X-ray Diffraction Data, University of York, England, and Louvain-La Neuve, Belgium, 1980.

33) G. M. Sheldrick, SHELX 76. A Program for Crystal Structure Determination, University of Cambridge, England, 1976.

34) J. M. Stewart, G. J. Kruger, H. L . Ammann, C. Dickenson, and S. R . Hall, The X-Ray System, Version of June 1972, Technical Report 192, Computer Science Center, University of Maryland, MD, USA.

[ 5 1 /84]

773

fulvenes with normal to those with inverse polarization6).

Chem. Ber. 118(1985)

52.