Reactions of a Cyclotrisilane with Olefins and Dienes: Evidence for an

Dec 1, 1994 - Evidence for an Equilibrium between Silylenes and a ... indicated these compounds to be in a thermal equilibrium with cyclotrisilane la ...
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Organometallics 1995, 14, 305-311

305

Reactions of a Cyclotrisilane with Olefins and Dienes: Evidence for an Equilibrium between Silylenes and a Cyclotrisilanet Johannes Belzner,*lS Heiko Ihmels,S Boris 0. Kneisel,§ Robert 0. Gould,§Jland Regine Herbst-IrmerE Institut fur Organische Chemie der Georg-August-Universitat Gottingen, Tammannstrasse 2, 0-37077 Giittingen, Germany, and Institut fur Anorganische Chemie der Georg-August-Universitat Giittingen, Tammannstrasse 4, 0-37077 Gottingen, Germany Received May 17, 1994@ Various new siliranes were synthesized by reaction of the cyclotrisilane cycZo-(Ar2Si)~(Ar = 2-(MezNCH2)CsH4; la) with terminal and strained internal olefins under mild thermal

n

conditions. The thermolysis of siliranes Ar2SiCH2CHR (3a,R = n-propyl; 3b,R = n-butyl) indicated these compounds to be in a thermal equilibrium with cyclotrisilane la and the corresponding alkene; this observation provides evidence for a n equilibrium between the silylene Ar2Si: (Sa) and cyclotrisilane la and, moreover, proves that free silylenes are involved in silylene transfer reactions of la. Reaction of la with conjugated dienes resulted, presumably via vinylsiliranes, in the formation of the expected 1,4-cycloaddition products in high yield. The solid-state structures of silaindane 14 and silanorbornene 17a were b= determined by single-crystal X-ray diffraction (14,monoclinic, C2/c, a = 36.255(7) 8.877(2) c = 14.966(2) fi = 109.60(1)", 2 = 8; 17a,monoclinic, C2/c, a = 14.155(5) b = 13.336(4) c = 23.339(8) p = 107.16(2)", 2 = 8).

A,

A,

A,

A, A,

A,

Introduction In 1972, Lambert and Seyferthl reported the first isolation of stable siliranes (silacyclopropanes), which were synthesized by intramolecular closure of a C-C bond of acyclic precursors. Later it was demonstrated that siliranes also are formed by addition of thermally or photolytically generated silylenes to substituted olefins2 and even ethene.3 A major drawback of this method is the low stability of the siliranes under the conditions employed for silylene generation, which frequently gives rise to the isolation of isomerized compounds. This is especially true for the addition of silylenes t o conjugated dienes: initially formed vinylsiliranes almost inevitably undergo subsequent rearr a n g e m e n t ~ .A~ third synthetically useful approach to

stable siliranes makes use of the reductive dehalogenation of dihalosilanes by lithium metal in the presence of 0lefins.2~J15 We have recently shown that cyclotrisilane la6serves as an effective synthetic equivalent for silylene 2a: it transfers all three of its silylene subunits to various unsaturated substrates such as ketones6 or alkynes7 under mild thermal conditions. It remained uncertain whether free silylenes are involved in these reactions. We now have investigated the reactivity of la toward olefins, both to examine the aptitude of la as a precursor for new siliranes and to obtain some insight into possible mechanisms of the unusual silylene transfer reactions of this cyclotrisilane.

Results and Discussion Dedicated to Prof. Dr. Wolfgang Luttke on the occasion of his 75th birthday. Institut fur Organische Chemie der Georg-August Universitlit Gttingen. 0 Institut fiir Anorganische Chemie der Georg-August Universitat Gttingen. Permanent address: Department of Chemistry, West Mains Road, Edinburgh EH9 355, Scotland. Abstract published in Advance ACS Abstracts, December 1,1994. (1)Lambert, R. L., Jr.; Seyferth, D. J. Am. Chem. SOC.1972,94, 9246. (2)(a) Ishikawa, M.;Nakagawa, K.-I.; Kumada, M. J. Organomet. Chem. 1979,178,105.(b) Tortorelli, V.J.; Jones, M., Jr. J.Am. Chem. SOC.1980,102,1425.(c) Seyferth, D.; Annarelli, D. C.; Duncan, D. P. Organometallics 1982,1,1288.(d) Tortorelli, V.J.; Jones, M., Jr.; Wu, S.-H.; Li, Z.-H. Orgunometallics 1983,2,759. (e) Ando, W.;Fujita, M.; Yoshida, H.; Sekiguchi, A. J.Am. Chem. SOC.1988,110,3310. (0 Pae, D.H.; Xiao, M.; Chiang, M. Y.; Gaspar, P. P. J.Am. Chem. SOC. 1991,113,1281. (3)Boudjouk, P.; Black, E.; Kumarathasan, R. Organometallics 1991,10,2095. (4)For recent studies on the reactivity of silylenes with conjugated dienes, see: (a) Lei, D.; Hwang, R.J.; Gaspar, P. P. J. Orgunomet. Chem. 1984,271,1. (b) Gaspar, P. P.; Lei, D. Organometallics 1986, 5 , 1276. (c) Clarke, M.P.; Davidson, I. M. T. J. Chem. Soc., Chem. Commun. 1988,241. (d) Zhang, S.; Conlin, R. T. J. Am. Chem. Soc. 1991,113,4272. +

*

@

When l a was heated a t 40 "C for 12 h with 1-pentene in C&, silirane 3a was formed quantitatively, as shown by lH NMR spectroscopy using poly(dimethylsi1oxane) as the internal integration standard. A large excess of olefin (> 10 equiv per silylene unit of la) was necessary in order to drive the reaction to completion. Furthermore, it was essential to perform this reaction in quite concentrated solution (>0.1 mofi); otherwise, appreciable amounts of unidentified byproducts were formed. Even under these conditions, isolation of analytically pure silirane 3a from the reaction mixture was impossible due to its thermal instability. Spectroscopically pure samples8 of 3a could be obtained by rapid removal of excess olefin and solvent in vacuo at room tempera( 5 ) Boudjouk, P.; Samaraweera, U.; Sooriyakumaran, R.; Chrisciel, Angew. Chem., Int. J.; Anderson, K. R. Angew. Chem. 1988,100,1406; Ed. Engl. 1988,27,1355. (6)Belzner, J. J. Organomet. Chem. 1992,430,C51. (7) Belzner, J.; Ihmels, H.Tetrahedron Lett. 1993,6541.

0276-7333/95/2314-0305$09.Q0/0 0 1995 American Chemical Society

Belzner et al.

306 Organometallics, Vol. 14, No. 1, 1995 R

R\

\

F:

Scheme 1

R

Si=Si,

R'

R

2

1

/

R R

7

b 3a,b

la

la, 2a, 7a: R = 2-(Me2NCH2)C6H4( EAr) lb, 2b, 7b: R = r-Bu IC,ZC, 7c: R = H AI 'si: / AI

AMe Me2

Ar2

/'\

Ar2Sq

3a, 6a: R = n-Pr 3b, 6b: R ~ - B u 3c,6c: R = P h

R 3

Me,,""' Me

"W

+ ArzSi:

AI,

AI si=(

AI'

Ar

Me

4

AI* Si-Si

I I

Ar2

/!\

F R

'

6a,b

Pr

5

ture. Heating a concentrated solution of Sa, which was prepared as described above, in C6D6 for 5.5 h a t 40 "C resulted in a mixture Of 3a, la, and 1-pentene in a 1:1:3 ratio; this mixture could be converted back to 3a by addition of excess olefin. Silirane 3b, which was similarly prepared by reaction of l a with an excess of 1-hexene, exhibited an analogous partial retro reaction to cyclotrisilane la and olefin. Both siliranes were obtained as highly air- and moisture-sensitive oils, which were identified mainly by their NMR spectra, especially the 29Si NMR shift values, which fell into the high-field region typical for siliranesg (3a,6 -76.6; 3b, 6 -76.8) and proved the proposed cyclic structure unambiguously. The thermal retro reaction of siliranes 3a and 3b, respectively, to cyclotrisilane l a and the corresponding olefin indicates an equilibrium that does not have any precedent in the chemistry of siliranes. A possible mechanistic pathway for this reversible reaction is represented in Scheme 1: the first step of the sequence is the extrusion of silylene 2a, which could be trapped by addition to 1-pentyne, yielding quantitatively the known silirene 5.7 An analogous retro cleavage of a silirane is well-known from the pioneering studies on the reactivity of siliranes by Seyferth,2cJ0which have unequivocally established an equilibrium between hexamethylsilirane (4) and dimethylsilylene: thermolysis of 4 resulted in formation of tetramethylethylene and dimethylsilylene, which polymerized, inserted into a Si-C bond of the starting silirane 4, or could be intercepted by various trapping agents such as siloxanes, organosilicon hydrides, 2,3-dimethylbuta-1,3-diene, and alkynes. But whereas dimethylsilylene polymerizes in the absence of a trapping agent, 2a trimerizes, presumably via disilene 7a as intermediate, eventually (8)The content of l a in such samples was shown by lH NMR spectroscopy to be less than 1%. ( 9 )Williams, E. A. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, U.K.,1989; p 511. (10)(a) Seyferth, D.; Annarelli, D. C.; Vick, S. C.; Duncan, D. P. J. Organomet. Chem. 1980,201, 179. (b) Seyferth, D.; Annarelli, D. C. J . Am. Chem. Soc. 1976,97, 7162. (c) Seyferth, D.; Annarelli, D. C.; Vick, S. C. J. Organomet. Chem. 1984,272, 123.

Ar2

yielding cyclotrisilane 1a.l1 A n alternative, albeit less probable, mechanism cannot totally be ruled out: initially formed silylene 2a could insert into a Si-C bond of the starting material to form 1,2-disilacyclobutane 6; [2 21 cycloreversion of the four-membered ring again would lead to disilene 7a as a precursor of la. Both of the proposed mechanisms proceed through silylene 2a as an intermediate. Because of the reversibility of the cyclotrisilane formation from 3a and 3b, the principle of microscopic reversibility applies to these reactions and we must conclude that in the reverse reaction, i.e., that of l a with olefins to form siliranes, silylene 2a is involved as well. This is the first time that an equilibrium between a cyclotrisilane, a disilene, and a silylene has been established, thus adding a third reaction mode to the known decomposition pathways of cyclotrisilanes.12 In organotin chemistry, an analogous thermal equilibrium between cyclotristannane, distannene, and stannylene is ~ell-known,'~ whereas in organosilicon chemistry it had been sought without success.14 Only a few observations reported in the last number of years have given hints of the possibility of such an equilibrium. First, reductive dehalogenation of 1,2-dibromo-1,1,2,2-tetratert-butyldisilane led, depending on the reaction conditions, to the corresponding disilene 7b,cyclotrisilane lb, or silylene 2b, which was trapped by subsequent cycloaddition rea~ti0ns.l~ The formation of compounds containing monosila or trisila units starting from a disilane may be due to silylene intermediates in these reactions but does not necessarily require the involvement of these species: it cannot be excluded that the initially formed disilene 7b undergoes metal-mediated redistribution reactions via metal silyl compounds as

+

(11)Formation of a cyclotrisilane by addition af a silylene to a disilene was recently suggested by West: Gillette, G. R.; Noren, G.; West, R. Organometallics 1990,9 , 2925. (12)Weidenbruch, M. Comments Inorg. Chem. 1986,5, 247. (13)(a) Masamune, S.; S i b , L. R. J . h . Chem. SOC.1985,107,6390. (b) Weidenbruch, M.; Schiifer, A.; Kilian, H.; Pohl, S.; Sa&, W.; Marsmann, H. Chem. Ber. 1992,125,563. (14)See,e.g.: Masamune, S.; Eriyama, Y.; Kawase, T.Angew.Chem. 1987,99, 601;Angew. Chem., Int. Ed. Engl. 1987,26, 584. (15)(a)Weidenbruch, M.; Schiifer, A.; m o m , K. L. Z . Naturforsch. 1983, 38B, 1695. (b) Schiifer, A.; Weidenbruch, M.; Peters, K.; von Schnering, H. G. Angew. Chem. 1984,96,31l;Angew.Chem., Int. Ed. Engl. 1984,23, 302.

Equilibrium between Silylenes and a Cyclotrisilane observed for various cyclic oligosilanes.l6 Second, an extremely bulky substituted disilene recently was reported to undergo silylene-like rea~ti0ns.l~ Presumably the extreme steric bulk of the organic substituents in this disilene reduces the strength of the Si-Si double bond substantially. Finally, the ability of the 2-((dimethy1amino)methyl)phenyl substituent to induce SiSi bond cleavage in disilene 7a by intramolecular coordination of the amino group to silicon finds support in ab initio calculations by Apeloig for the H2Si=SiHd H2O interaction.ls On the basis of these computational results, an equilibrium between disilene 7a,which bears four potentially intramolecularly coordinating substituents, and the silylene 2a,stabilized by intramolecular coordination, seems reasonable. It might be expected that such intramolecular coordination will substantially lower the activation energy for the formation of 2a from la and 7a,respe~tive1y.l~ la did not react with unstrained internal olefins. Addition of 2a to the C=C bond of trans-3-hexene, transstilbene, cyclooctene, cyclohexene, or cyclopentene was not observed. However, when the cyclopentene ring was part of a strained system as in norbornene, clean formation of tricyclic silirane 8 occurred. On the basis

$MeMe

8

9

Me 10

12

Me

11

13

Ar = ~ - ( M c ~ N C H ~ ) C ~ H ~

of the lH and 13C NMR data we assume the silirane ring in 8 adopts the ex0 configuration, which is in good agreement with the ex0 selectivity found for carbene attack on norbornene.20 The same strategy that worked (16) Brough, L. F.; West, R. J. Organomet. Chem. 1980, 194, 139 and references cited therein. (17) Tokitoh, N.; Suzuki, H.; Okazaki, R.; Ogawa, K. J.Am. Chem. SOC.1993,115, 10428. (18)Apeloig, Y. In Heteroatom Chemistry;Block, E., Ed.; VCH New York, 1990; p 27. For related calculations on silylenes, see: Gano, D. R.; Gordon, M. S.; Boatz, J. A. J. Am. Chem. SOC.1991, 113, 6711. (19) (a) Corriu, R.; Lanneau, G.; Priou, C.; Soulairol, F.; Auner, N.; Probst, R.; Conlin, R.; Tan, C. J. Organomet. Chem. 1994,466,55. (b) Conlin, R. T.; Laakso, D.; Marshall, P. Organometallics 1994,13,838. (20) See for example: (a)Kropp, P. J.; Pienta, N. J.; Sawyer, J. A.; Polniaszek, R. P. Tetrahedron 1981, 37, 3229. (b) Jefford, C. W.; Mahajan, S.; Waslyn, J.; Waegell, B. J.Am. Chem. SOC.1965,87,2183. (c) Sauers, R. R.; Sonnet, P. E. Tetrahedron 1965, 20, 1029. (d) Simmons, H. E.; Smith, R. D. J.Am. Chem. SOC.1959, 81, 4256. (e) Moore, W. R.; Moser, W. R.; LaPrade, J. E. J. Org. Chem. 1983, 28, 2200.

Organometallics, Vol. 14,No. 1, 1995 307

C181

ww Figure 1. Crystal structure of 14. Hydrogen atoms are omitted for clarity; displacement ellipsoids are at the 50% probability level. for norbornene, i.e., to increase the reactivity of the olefinic double bond by introduction of strain, was successful also with geminally disubstituted olefins. Whereas 9 did not form a silirane with la,the methylenecyclopropane 10,which is formally the ring-closure product of 9,reacted with la to give spiro[2.2lpentane 11. Extending this methodology to bicyclopropylidene, whose enhanced reactivity toward carbenes is known as allowed the synthesis of dispiro[2.0.2.1]heptane 12 in quantitative yield. Decrease of strain, as realized in tetramethylethylene, resulted in complete suppression of the cycloaddition. In contrast to 3a and 3b,8 as well as 11 and 12 were thermally stable; no retro reaction to la was observed a t room temperature. Only at temperatures above 110 "C did 8 transfer its silylene unit to 2,2'-bipyridyl a t a reasonable rate, giving the known6 tricyclic system 13.22 Presumably the high strain energy of norbornene, which is formed in the course of the cleavage reaction, compared with that of normal olefins is responsible for the decreased silylene transfer reactivity of 8. The addition reaction of 2a with styrene was more complex: stirring la for 12 h at 40 "Cwith an excess of styrene led to quantitative formation of silaindane 14, whose structure was confirmed by X-ray analysis (Figure 1). When the reaction was monitored by means of lH NMR spectroscopy,the formation of an intermediate, 3c,was observed, which was converted subsequently to 14. So far, it has not been possible t o find reaction conditions which allow the exclusive formation of 3c.23 On the basis of the characteristic 29Si NMR shift 6 -82.5, as well as examination of lH NMR spectra of the reaction mixture, the structure of silirane 3c was ascribed to this intermediate, which is formed by initial addition of 2a to the olefinic double bond of styrene. It has been assumed that silylene cycloaddition to conjugated dienes proceeds by a stepwise mechanism, (21) See for example: (a)Fitjer, L.; Conia, J. M. Angew. Chem. 1973, 8 5 , 3 4 9 Angew. Chem., Znt. Ed. Engl. 1973,12,334. (b) Lukin, K. A.; Kuznetsova, T. S.; Kozhushkov, S. I.; Piven, V. A.; Zefirov, N. S. Zh. Org.Khim. 1988,24, 1644. (22) Similar compounds were shown by Weidenbruch to be the reaction products of photochemically generated 2b with 2,2'-bipyridyl: (a)Weidenbruch, M.; Schtifer, A.; Marsmann, H. J. Organomet. Chem. 1988, 354, C12. (b) Weidenbruch, M.; Lesch, A.; Marsmann, H. J . Organomet. Chem. 1990,385, C47. (23) Very recently an analogous but stable phenyl-substituted silirane was obtained by cophotolysis of l b and 2-methylstyrene: Weidenbruch, M.; Kroke; E.; Marsmann, H.; Pohl, S.; Saak, W. J. Chem. SOC.,Chem. Commun. 1994, 1233.

Belzner et al.

308 Organometallics, Vol. 14,No. 1, 1995

Scheme 2

Table 1. Selected Bond Lengths (A), Nonbonding Distances (A), and Bond Angles (deg) in Silaindane 14 Si(l)-C(l) Si(l)-C(21) C(3)-C(4)

3c

Si(1). -.N( 11)

3.259(3) 90.6(2) 109.9(2) 114.6(2)

C(l)-Si(l)-C(4) C(4)-Si(l)-C(ll) C(4)-Si(l)-C(21)

Ar

‘si:

AI

1.888(3) Si(l)-C(4) 1.877(3) C(l)-C(2) 1.533(5)

1.881(4) Si(l)-C(ll) 1.3920) C(2)-C(3) Si(1). eN(21) C(1)-Si(1)-C(l1) C(l)-Si(l)-C(21) C(ll)-Si(l)-C(21)

1.888(3) 1.508(5) 3.060(3) 112.8(1) 110.8(1) 115.6(2)

When la was stirred with 3 equiv of 2,3-dimethyl1,3-butadiene a t 40 “C for 12 h, silacyclopentene M 3 0 was formed quantitatively. In this case, the assumed

/

15

16

17

17% R = 2-(Me2NCH2)C6H4( 3Ar) starting with 1,2-addition of the silylene to the C-C 17b: R = M e double bond, followed by subsequent rearrangement.z4 The transient existence of the initially formed vinylsilirane was proved indirectly by trapping experiments. Only recently, Conlin4 has succeeded in stabilizing such intermediates by reacting photolytically generated, bulky substituted silylenes with conjugated dienes. The 18 resulting vinylsiliranes, which were contaminated with vinylsilirane intermediate could not be detected in the isomeric products, were identified unambiguously by course of this cycloaddition. In comparison with the means of NMR spectroscopy. Initial formation of the reluctance of the olefin 9 (vide supra) to react with la, silirane 3c also was observed in the reaction of l a with the activating influence of a conjugated double bond styrene, thus suggesting two different mechanistic becomes rather evident. This seems to be true for pathways to 14 (Scheme 2). The silaindane either may cyclohexene and 1,3-cyclohexadieneas well: 2a did not be the product of a [1,3]-silylmigrationz5 from initially add to the isolated internal double bond of cyclohexene, formed 3c, followed by irreversible rearomatization of whereas 7-silanorbornene 17a was formed by reaction intermediate 15, which is the formal lP-addition prodof la with 1,3-cyclohexadienewithout any side products. uct of 2a, to the conjugated system, or it may be the Comparison of this result with the outcome of the result of a possibly reversiblez6 1,4-~ycloadditionof 2a, interaction of thermally generated dimethylsilylene with which originates from cycloreversion of silirane 3c or 1,3-cyclohexadiene,which resulted in a 1:l mixture of directly from la, t o styrene, again yielding 15 as the corresponding silanorbornene 17b and the acyclic precursor of 14. The second possibility appears to be triene 18 in 20% yield,31 once more points out the less probable. Styrene is well-known to react with advantage of having precursors from which silylenes 2a electron-deficient olefins as a 1,3-diene,z7but this reaccan be generated under mild conditions. tion mode was never observed for additions of carbenesz8 or other group 14 homologues to styrene or substituted Crystal Structures styrenes. However, germylenes have been reported t o Crystals of 14 suitable for X-ray structural analysis undergo concerted 1,4-~ycloadditionswith “normal” were obtained by crystallization from diethyl ether/ conjugated olefins such as 1,4-diphenyl-1,3-b~tadiene.~~pentane. Figure 1 shows the structure of 14; selected interatomic distances and angles are listed in Table 1. (24) Gaspar, P. P. In Reactive Intermediates; Jones, M., Jr., Moss, Whereas atoms Si(l), C(l), C(2), and C(3) form an R. A., Eds.; Wiley: New York, 1985; Vol. 3, p 333 and references cited therein. almost perfect plane (mean deviation 0.012 A),C(4) is (25) This shift may proceed in a concerted& or s t e p w i ~ fashion e~~ located 0.517 A above this plane. Thus, the silacyclovia diradical intermediates. pentene ring in 14 adopts an envelope conformation, (26) Compare, e. g.: Lei, D.; Gaspar, P. P. Organometallics 1986, 4, 1471. which is more strongly developed than that in a similar (27) Fringuelli, F.; Taticchi, A. Dienes in the Diek-Alder Reaction; silaindane whose structure was reported recently by Wiley: New York, 1990; and references cited therein. (28) Compare, e.g.: Hoffmann, R. W.; Lilienblum, W.; Dittrich, B. Brook.3z The bonding geometry around silicon is that Chem. Ber. 1974,107,3395. of distorted tetrahedron: the small endocyclic C(1)(29) (a) Schriewer, M.; Neumann, W. P. Angew. Chem. 1981, 93, Si(l)-C(4) angle (90.6(2)”) is in contrast with the 1089; Angew. Chem., Int. Ed. Engl. 1981,20, 1019. (b) Ma, E. C.-L.; Kobayashi, K.; Barzilai, M. W.; Gaspar, P. P. J . Orgummet. Chem. widened exocyclic C(2l)-Si(l)-C( 11)angle (115.6(2)”). 1982,224, C13. The Si(l>**N(11)and Si(1).**N(21)distances (3.259(3) (30) Recently, rather incomplete NMR data for 16 were reported.l9a and 3.060(3) A, respectively) are shorter than the sum The lH NMR shift values differ considerably from values found by us; we consider our data reported here to be correct. of the van der Waals radii of both elements (3.65 (31) Hwang, R.-J.; Conlin, R. T.; Gaspar, P. P. J. Orgummet. Chem. but significantly longer than the usual distance between 1975. - - .-, 94. - -, C.78. - - -. (32) Brook, A. G.; Baumegger, A.; Lough, A. J. Organometallics 1992, 11, 310. (33) Bondi, A. J. Phys. Chem. 1964, 68, 441.

~~

(34) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. Rev. 1993,93, 1371.

Organometallics, Vol. 14, No. 1, 1995 309

Equilibrium between Silylenes and a Cyclotrisilane

Table 2. Selected Bond Lengths (A), Nonbonding Distances (A), and Bond Angles (deg) in Silanorbornene 17a Si(l)-C(l) Si(l)-C(21)

1.917(3) Si(1)-C(4) 1.883(2) Si(1). .*N(11)

C(l)-Si(l)-C(4) C(4)-Si(l)-C(ll) C(4)-Si(l)-C(21)

Figure 2. Crystal structure of 17a. Hydrogen atoms are omitted for clarity; displacement ellipsoids are at the 50% probability level. silicon and nitrogen in hypercoordinated silicon compounds (ca. 2-3 A).34 This could indicate a weak coordination of nitrogen t o silicon. However, this conclusion is questioned by the observation that the lone pairs of the amino groups are not oriented exactly toward the silicon center. The structure of 17a is shown in Figure 2; selected structural parameters are summarized in Table 2. The double bond is disordered over two positions (C(2)= C(3) and C(5)=C(6) bonds, respectively, resulting in bond lengths between single and double bonds. The occupation ratio refined to 7:3. Again, severe distortion of the tetrahedral geometry around the silicon center is obvious: the endocyclic C(l)-S(l)-C(4) bond angle is reduced t o 80.5(1)", a phenomenon which finds its parallel in the structure of some 7-silan0rbornadienes.~~ On the other hand, the exocyclic angles around silicon are significantly enlarged (up to 123.6(1)' for C(11)Si(l)-C(4)). The widening of these angles allows one dimethylamino group to approach the silicon center, resulting in a S i ( l ) . - * N ( l l ) distance of 2.918(2) A. However, as in 14, the missing exact orientation of the amino lone pair toward silicon argues against a significant Si** .N interaction.

Experimental Section IH NMR and 13C NMR spectra were recorded on a Bruker AM 250 ('H NMR, 250 MHz; 13CNMR, 62.9 MHz). lH,IH and lH,13C COSY spectra were recorded on a Varian VXR-200 (200 MHz). C,, CH, CHz, and CH3 were determined using the D E R pulse sequence. 29Si NMR spectra were recorded on a Bruker AMX 300 (59.6 MHz) using a refocused INEPT pulse s Mass spectra were sequence. Chemical shifts refer to 6 ~0.0. recorded on a Varian MAT CH7 and MAT 731; HRMS data were determined with a Varian MAT 311 A, using preselected ion peak matching at R =S 10 000 to be within f 2 ppm of the exact mass. Because of the high sensitivity of siliranes toward moisture and air, satisfactory mass spectra or elemental analyses could not be obtained in most cases. Mass spectra always showed, besides M+, the silirane contamination with hydrolysis product and corresponding fragments. Melting points are uncorrected. Elemental analyses were performed at Mikroanalytisches Labor der Georg-August-Universitat Gottingen. All manipulations were carried out under an inert argon atmosphere using carefully dried glassware. Solvents used were dried by refluxing over sodium and distilled immediately before use. (35) F'reut, H.; Mayer, B.; Neumann, W. P. Acta Crystallogr. 1983, C39,1118.

80.5(1) 123.6(1) 114.8(1)

1.908(2) Si(1)-C(l1)

1.886(3)

2.918(2) C(1)-Si(1)-C(l1) C(l)-Si(l)-C(21) C(l l)--Si(l)-C(21)

109.7(1) 114.5(1) 110.3(1)

l,l-Bis[B-( (dimethylamino)methyl)phenyll-2-n-propyll-silirane (3a). To a solution of 45 mg (0.06 mmol) of la in 0.4 mL Of C6D6 was added a 10-fold excess (about 0.07 mL) of l-pentene. The solution was heated at 40 "C for 12 h. After the reaction was completed, solvent and excess alkene were removed in vacuo at room temperature. The remaining pale green oil was redissolved in C6Ds t o yield a solution of spectroscopicallypure 3a. The NMR spectra were determined = 7 Hz, 2J within 30 min. 'H NMR (C&): 6 0.60 (dd, 'JtranS = 11 Hz; 1 H, 3-&ie), 1.01 (t, ' J = 7 Hz, 3 H, CH3), 1.18 (dd, 'Jck = 11 Hz, 2J = 11 Hz, 1 H, 3-Htrans),1.31-2.02 (m, 5 H, 2H-, propyl CHd, 1.80 (s, 6 H, NMez), 1.83 (s, 6 H, NMez), 3.18, 3.40 (AB system, 2J = 13 Hz, 2 H, CHZN),3.27 (s, 2 H, CHzN), 7.10-7.19 (m, 6 H, ar HI, 7.92-7.98 (m; 2 H, ar H). 13CNMR (C6D6): 6 5.3 (C-3), 14.4, 14.6 (CH3, C-2), 24.6, 35.7 (propyl CHz), 45.0, 45.1 (2 x NMez), 64.6, 64.8 (2 x CHZN), 126.3 (ar CH), 126.6 (ar CHI, 127.8 (ar CH), 128.0 (ar CH), 129.1 (ar CH), 129.2 (arCHI, 133.6 (ar C,), 135.7 (ar Cq),136.6 (ar CH), 137.4 (ar CH), 145.9 (ar CJ, 146.7 (ar C,). 29SiNMR (C6D6): 6 -76.8. Thermolysis of 3a. With 45 mg (0.05 mmol) of la and 0.07 mL of 1-pentene in 0.4 mL of C6Ds as starting materials, a solution of 3a was prepared as described above. After rapid removal of solvent and excess alkene in vacuo at room temperature, 0.4 mL of CsD6 was added to the residue; the content of starting materials la and l-pentene in this sample of 3a was shown t o be less than 1%by means of IH NMR spectroscopy. After poly(dimethylsi1oxane) was added as internal integration standard, the solution was heated t o 40 "C for 1 h. l a as well as l-pentene were formed; the ratio 3a:la:l-pentene was spectroscopically determined t o be 5:l: 3. When the solution was heated to 40 "C for another 4.5 h, the ratio changed t o 1:1:3. l,l-Bis[2-( (dimethylamino)methyl)phenyll-2-n-butyll-silirane (3b). To a solution of 60 mg (0.07 mmol) of la in 0.4 mL of C6D6 was added 0.1 mL of l-hexene. After the solution was heated for 3 h at 40 "C, the solvent and excess alkene were removed in vacuo at room temperature. The remaining oil was redissolved in C6D6 to yield a solution of 3b (97%, contaminated with 3% la). lH NMR (CsD6): 6 0.62 (dd, 3Jtra, = 7 Hz, '5 = 10 Hz, 1H, 3-&js), 0.95 (t, ' J = 7 Hz, 3 H, CH3), 1.12 (dd, 'JcLs= 12 Hz, '5 = 10 Hz, 1H, 3-Htr,ns), 1.222.03 (m, 7 H, 2-H, butyl CHz), 1.81 (8, 6 H, NMez), 1.83 (s, 6 H, NMez), 3.20, 3.41 (AB system, zJ = 13 Hz, 2 H, CHZN), 3.27 (9, 2 H, CHZN),7.09-7.25 (m, 6 H, ar H), 7.94-7.98 (m, 2 H, ar H). 13CNMR (C&): 6 5.4 (c-31, 14.5, 15.0 (CH3, c-2), 23.1, 33.2, 33.8 (butyl CHz), 45.0, 45.1 (2 x NMez), 64.7, 64.9 (2 x CHzN), 126.2 (ar CH), 126.6 (ar CH), 127.8 (ar CH), 129.1 (ar CH), 129.2 (ar CHI, 129.9 (ar CHI, 133.6 (ar Cq), 135.8 (ar CJ, 136.6 (ar CHI, 137.4 (ar CHI, 145.9 (ar Cq),146.7 (ar Cq). "si NMR (CsD6): -76.6. Thermolysis of ab. With 60 mg (0.07 mmol) of l a and 0.1 mL of l-hexene in 0.4 mL of CsDs as starting materials, a solution of 3b was prepared as described above. After rapid removal of the solvent and the alkene in vacuo at room temperature, CsD6 was added and the content of l a relative t o 3b was determined by IH NMR to be less than 3%. The solution was heated to 40 "C for 2 h, and the content of 3b was found to be 15%. When the solution was left at room temperature for 12 h, the content of la increased to 21%. 1,l-Bis[2-( (dimethylamino)methyl)phenyll-2-phenyl-lsilirane (3c) and 2,3-Benzo-l,l-bis[2-((dimethylamino)-

310 Organometallics, Vol. 14, No. 1, 1995

Belzner et al.

Table 3. Summary of Crystal Data, Details of the Intensity methyl)phenyl]-l-silacyclopent-2-ene (14).To a solution Collection, and Least-Squares Refinement Parameters for of 63 mg (0.07 mmol) of la in 4 mL of toluene was added 0.2 Silaindane 14 and Silanorbornene 17a mL of styrene, The solution was stirred at 40 "C for 1h; 3c could be identified in this reaction mixture in addition to 14 179 starting materials and 14 by means of NMR spectroscopy.The empirical formula C24H32NzSi CzaHdzSi solution was heated for another 11h t o 40 "C. After solvent 376.61 400.63 MI and excess styrene were removed in vacuo, 85 mg of a 0.7 x 0.7 x 0.5 0.7 x 0.6 x 0.3 cryst size (mm) spectroscopically pure, white solid wa8 obtained. Recrystalmonoclinic monoclinic cryst syst aic lization from ethedpentane (2:l) gave 44 mg (52%)of analytispace group ale 14.155(5) 36.255(7) a (A) cally pure 14. 3c (data incomplete due to partial signal overlap 13.336(4) 8.877(2) b (A) with starting materials and 14). lH NMR (C6Ds): 6 1.39 (dd, 23.339(8) 14.966(2) 3Jt,,, = 9 Hz, 25 = 12 Hz, 1H, 3-&& 2.63 (dd, V t , , = 9 Hz, 107.16(2) 1O9.60(1) 3J,i, = 11Hz, 2 H, 2-H), 1.66 (s,6 H, NMez), 1.90 (s,6 H, NMe2), 4120(2) 4537(2) 2.94 (B moiety of AB system, 25= 14 Hz). 29SiNMR (CsDs): 6 8 8 Z -82.5. 14: mp 114-115 "C. 'H NMR (CDC13): 6 1.54 (dd, 3J 1.188 1.173 D, (g = 7 and 8 Hz, 2 H, 5-H), 1.83 (s, 12 H, NMez), 3.20 (m,6 H, 0.123 0.118 P( "-9 1632 1728 CHzN, 4-H), 7.16-7.31 (m, 9 H, ar H), 7.69 (d, 35= 7 Hz, 2 H, F(000) 8 5 2e 5 45 8 5 2e 5 45 20 range (deg) ar H), 7.77 (d, 3 5 = 7 Hz, 1H, ar H). 13CNMR (CDC13): 6 12.9 -15 5 h 5 +15, -38 5 h 5 +38, range of hkl (C-5), 31.7 (C-41, 45.1 (NMeZ), 64.7 (CHZN),125.2 (ar CHI, -12 5 k 5 +14, 9 5 k 5 + 9 , 125.9 (ar CH), 126.4 (ar CH), 128.5 (ar CH), 128.8 (ar CH), -25 5 15 $25 -7 5 1 5 +16 128.9 (arCH), 134.6 (ar CHI, 135.9 (ar Cq),136.0 (arCHI, 139.3 4732 3565 no. of rflns coll (ar Cq),145.2 (ar Cq),154.0 (arCq). 29si (CsDs): 6 2.5. MS 2683 2881 no. of indep rflns (EI; 70 em: mlz (relative intensity) 400 (M+,l), 385 (M+ - Me, 0.0205 0.0437 R(int) l),297 (ArzSi+,21, 266 (M+ - 134, 34), 57 (CHNMeZ+, 100). 2876 2681 no. of data 249 266 no. of params ~ S77.95; ~: H, 8.05; N, 6.99. Anal. Calcd for C Z ~ H ~ Z NC, 1.131 1.103 S Found: C, 78.03; H, 8.03; N, 6.94. 0.0554 0.0249 gl 1,1-Bis-[2-((dimethylamino)methyl)phenyll-2-n-propyl13.5732 7.1883 gz 1-silirene(5).7 To a solution of 56 mg (0.15 mmol) of 3b in 0.0401 0.0515 R1 (F > 4u(F)) 0.5 mL of C& in the presence of 0.2 mL of 1-pentene (to 0.1552 0.0978 wR2 (all data) suppress retro reaction t o la)was added 0.2 mL of 1-pentyne, 0.0013(2) extinction coeff x 0.27 0.48 largest diff peak (e A-3) and the mixture was heated to 40 "C for 8 h. After evaporation -0.23 -0.48 largest diff hole (e A-3) of all volatile compounds in vacuo, silirene 5 remained as a lH NMR spectroscopically pure oil. Attempted further puril,l-Bis-[2-( (dimethylamino)methyl)phenyll-4,4-dification by distillation resulted in complete decomposition. 'H methyl-l-silaspiro[2.2lpentane(11). To a solution of 70 mg NMR (CsDs): 6 1.03 (t, 35= 7 Hz, 3 H, CH3), 1.75-2.04 (m, 2 of la (0.08 mmol) in 4 mL of toluene wa8 added 0.1 mL of 10. H, CH2), 1.94 (s, 12 H, NMez), 2.67 (dt, 35= 7 Hz, 45= 1Hz, The solution was stirred at 40 "C for 12 h. Solvent and alkene 2 H, CHz), 3.28 (s, 4 H, CHzN), 7.07-7.21 (m, 6 H, ar H), 7.71 were removed in vacuo to give 90 mg of 11 as a spectroscopi(dd, 35= 8 Hz, 45= 1Hz, 2 H, ar HI, 8.58 (t, 45= 1 Hz, 1H, cally pure, pale yellow oil. lH NMR (CsDs): 6 0.73, 1.13 (AX 3-H). 13C NMR (CsDs): 6 14.6 (CH3), 21.5 (CHz), 38.7 (CH2), system, 2 5 = 3 Hz, 2 H, 5-H), 0.88, 1.23 (AB system, 2J = 10 45.3 (NMeZ), 63.6 (CHzN), 126.8 (ar CH), 127.4 (ar CH), 128.9 Hz, 2 H, 2-H), 1.21 ( 8 , 3 H, CH3), 1.39 (s,3 H, CH3), 1.76 (8, 6 (ar CH), 136.4 (ar CH), 138.5 (ar CJ, 144.3 (ar Cq), 147.9 (CH, NMeZ), 1.80 (s, 6 H, NMeZ), 3.12, 3.27 (AB system, zJ = 13 2), 180.5 (C-3, JC-H = 166 Hz). 29SiNMR (CsDs): 6 -106.3. Hz, 2 H, C H a ) , 3.21,3.28 (AB system, 25= 13Hz, 2 H, C H a ) , MS (EI; 70 eV): mlz 364 (M+,1). Anal. Calcd for C23H32N~Si: 6.99-7.02 (m, 1H, ar H), 7.13-7.23 (m, 5 H, ar H), 7.85-7.88 C, 75.77; H, 8.85. Found: C, 74.55; H, 8.82. (m, 1 H, ar H), 8.09-8.13 (m, 1 H, ar HI. 13C NMR (CsDs): exo-3,3-Bis[2-((dimethylamino~methyl)phenyl)l-3-si- 8.1 (C-2), 20.2 (C-3,4), 23.4 (CH3),27.7 (CH3),28.3 (C-5), 45.1 latricycl0[3.2.1.0~~~]octane(8). To a solution of 80 mg (0.09 (NMez),45.4 (NMez),64.4 (CHZN),64.6 (CH2N), 126.5 (ar CHI, mmol) of la in 0.4 mL of CsDs was added 25 mg (0.27 mmol) 126.9 (ar CH), 127.2 (ar CH), 128.4 (ar CH), 128.7 (ar CH), of norbornene. The solution was heated for 4.5 h to 50 "C. 129.3 (arCH), 135.5 (ar CH), 135.9 (2 x ar Cq),137.1 (ar CH), After evaporation of solvent and remaining norbornene, 8 was 145.5 (ar cq),145.6 (ar cq)."Si NMR (CsDs): 6 -72.4. MS obtained as a spectroscopically pure colorless oil. lH NMR (EI; 70 em: mlz (relative intensity) 376 (Mf, 41, 363 (M+ (additional lH,lH and lH,13C COSY spectra; CsDs): 6 0.96Me, 16), 244 (M+ - 134, 17). Anal. Calcd for C24H382Si: C, 1.01 (m, 1 H, 8-Kyn),1.45-1.56 (m, 3 H, 8-%nti, 6,7-Endo), 76.13; H, 9.05. Found: C, 76.23; H, 9.25. 1.76-2.01 (m, 4 H, 6 , 7 - a 0 ,2,4-H), 1.86 (9, 6 H, NMez), 1.96 7,7-Bis-[2-((dimethylamino)methyl~phenyll-7-sila(s, 6 H, NMez), 2.65-2.90 (broad s, 2 H, 1,5-H), 3.17 (s, 2 H, dispiro[2.0.2.l]heptane (12). To a solution of 112 mg (0.13 CHzN), 3.40-3.50 (broadened AB system, 2 H, CHZN),6.95mmol) of la in 0.4 mL of CsDs was added 31 mg (0.39 mmol) 6.99 (m, 1 H, ar H), 7.10-7.20 (m, 5 H, a r HI, 7.81 (dd, 35= of bicyclopropylidene. The solution was heated t o 50 "C for 7 7 Hz, 4J = 1 Hz, 1 H, ar H), 8.16-8.20 (m, 1 H, ar H). 13C h to give 12 quantitatively. 'H NMR (CsDs): 6 0.67, 0.85 (m, NMR (125.7 MHz, CsDs): 6 26.3 (broad, C-2,4), 34.3 (C-6,7), AA'BB' system, 8 H, 1,2,5,6-H), 1.74 (a, 12 H, NMe2), 3.27 (s, 36.4 (C-81, 40.1 (broad, C-1,5), 45.1 (NMez),45.2 (NMez), 64.3 4 H, CHzN), 7.13-7.23 (m, 6 H, ar H), 8.07-8.11 (m, 2 H, ar (CHzN), 64.7 (CHz), 126.0 (ar CH), 126.9 (ar CH), 127.1 (ar H). l3C NMR (CsD6): 6 8.3 (C-1,2,5,6), 10.9 (c-3,4), 45.3 CHI, 128.6 (ar CHI, 128.9 (ar CHI, 129.8 (ar CHI, 134.7 (ar (NMe2), 64.7 (CHzN), 126.7 (ar CH), 127.3 (ar CHI, 129.0 (ar CJ, 135.4 (ar Cq),136.4 (ar CHI, 139.5 (ar CHI, 146.1 (ar Cq), CH), 136.4 (ar CJ, 136.6 (ar CH), 144.9 (ar Cq). 29SiNMR 146.4 (ar Cq). 29SiNMR (CsDs): 6 -77.3. HRMS: calcd for (CeDt3): 6 -75.6. C ~ 5 H d z S390.2491, i found 390.2491. Anal. Calcd for C2&4l,l-Bis-[2-((dimethylamino)methyl~phenyll-3,4-diNzSi: C, 76.87; H, 8.77. Found: C, 75.70; H, 8.92. methyl-1-silacyclopent-3-ene (16). To a solution of 51 mg Thermolysis of 8 in the Presence of 2,2-Bipyridyl.To (0.06 mmol) of la in 5 mL of toluene was added 0.2 mL of 2,3-dimethyl-1,3-butadiene. The solution was stirred at 40 "C a solution of 211 mg (0.54 mmol) of 8 in 10 mL of xylene was for 12 h. After removal of solvent and excess diene, 66 mg of added 84 mg (0.54 mmol) of 2,2'-bipyridyl. The solution was 16 as a colorless, spectroscopically pure oil was obtained. The stirred for 12 h at 120 "C. After evaporation of the solvent compound could be further purified by Kugelrohr distillation the crude product was recrystallized from ether to give 63 mg mmHg) t o yield 37 mg (57%) of 16 as a white (125 "C/5 x (21%) of 136(mp 60-62 "C dec).

Organometallics, Vol.14,No. 1, 1995 311

Equilibrium between Silylenes and a Cyclotrisilane solid; mp 70 "C. lH NMR (CDC13):306 1.74 (broad s, 6 H, CH3), 1.84 (broad s, 16 H, NMe2, 2,5-H), 3.15 (s, 4 H, CHzN), 7.257.30 (m, 6 H, ar H), 7.69 (d, 3J= 7 Hz, 2 H, ar H). 'H NMR (CsD6): 6 1.76 (s, 12 H, NMez), 1.86 (s, 6 H, CH3), 1.99 (broad s, 4 H, 2,5-H), 3.12 (8,4 H, CH2N), 7.17-7.28 (m, 6 H, a r H), 7.82-7.88 (m; 2 H, a r H). 13C NMR (CDC4): 6 19.2 (CH3), 25.5 (CHz), 45.1 (NMeZ), 64.5 (CHzN), 126.1 (ar CHI, 128.3 (ar CH), 128.8 (ar CH), 130.4 (C-3,4), 135.7 (ar CH), 136.6 (ar Cq), 145.3 (ar Cq). 29Si NMR (C6De): 6 -2.3. MS (EI; 70 eV): mlz (relative intensity) 378 (M+, lo), 363 (M+ - Me, 4), 296 ( A r z Si+, 4), 281 (ArZSi+ - Me, loo), 244 (M+- 134, 40). Anal. Calcd for C24H3&Si: C, 76.13; H, 9.05; N, 7.40. Found: C, 76.26; H, 9.15; N, 7.39. 7,7-Bis-[2-((dimethylamino)methyI)pheny1]-7-~ilabicyclo[2.2.1]hept-2-ene (17). To a solution of 58 mg (0.07 mmol) of l a in 4 mL of toluene was added 0.2 mL of 1,3-cyclohexadiene. The solution was stirred at 40 "C for 12 h. Solvent and excess diene were removed in vacuo, and 13 mg (99%)of 17 was obtained as a white, analytically pure solid; mp 100 "C. lH NMR (250 MHz, C&; additional 'H,lH COSY): 6 1.57 (broad d, zJ= 7 Hz, 2 H, 5,6-Kn&),1.79 (s, 6 H, NMeZ), 1.88 ( 8 , 6 H, NMez), 2.17 (broad, zJ= 7 Hz, 2 H, 5,6-&), 2.45 (broad s, 2 H, 1,4-H), 3.09 (s, 2 H, CHzN), 3.13 (s, 2 H, CHzN), 6.45 (dd, 3J= 4 Hz, 4J= 3 Hz, 2 H, 2,3-H), 7.11-7.26(m,6H,arH),7.72-7.76(m, lH,arH),7.88-7.92 (m, 1H, ar H). l3C NMR (C6D6): 6 25.8 (C-5,6), 31.3 (C-1,4), 44.9 (NMeZ), 64.6, 65.0 (2 x CHzN), 125.6 (ar CH), 126.1 (ar CH), 128.3 (ar CH), 128.9 (ar CHI, 129.3 (ar CHI, 129.4 (ar CH), 133.8 (C-2,3), 134.6 (ar Cq), 137.1 (ar Cq), 137.7 (ar CHI, 140.1 (ar CH), 145.7 (ar Cq), 146.6 (ar Cq). 29SiNMR (CsDs): 6 19.0. MS (EI; 70 eV): m/z (relative intensity) 376 (M+, 5), 296 (ArzSi+, 7), 281 (ArzSi+ - Me, loo), 238 (ArzSi - 58, 33). Anal. Calcd for C24H3zNzSi: C, 76.54; H, 8.56. Found: C, 76.49; H, 8.70.

X-ray StructureDeterminationfor 14 and 17a. Crystal data, data collection, and least-squares parameters are summarized in Table 3. Data were collected at -120 "C on a STOE-Siemens-Huberfour-circle diffractometer using monochromated Mo Ka radiation (1 = 0.710 73 ), The structures were solved by direct methods.36 All non-hydrogen A riding model starting atoms were refined anisotropi~ally.~~ from calculated positions was employed for the hydrogen atoms. The structure was refined against F with the weight~ with P = (F2 2F,2)/ ing scheme w - l = u2(Fo2) ( ~ I P )gfl, 3. The R values were defined as R1 = CIIFol - IFcllEIFoI and wR2 = [Xw(Fo2 - F~)2EwFo4]uz. For 17a an extinction correction was applied: Fc* = kFJ1 0.001F>A3/(sin 2e)]-1/4.

YPfik-

+

+

+

+

Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft (financial support, fellowship to J.B.), the Fonds der Chemischen Industrie (financial support), the Friedrich-Ebert-Stiftung (fellowship to H.I.), and the Deutscher Akademischer Austauschdienst (fellowship to R.O.G.). We thank Dr. V. Belov, Dip1.-Chem. S. Brase, and Dip1.-Chem. Th. Spath for samples of 10 and bicyclopropylidene, and cand.-chem. B. Geers for recording lH,lH and lH,13C COSY spectra. Supplementary Material Available: For 14 and 17a, tables of crystal data and refinement details, atomic coordinates, bond lengths and angles, anisotropic displacement parameters, and hydrogen atom coordinates (10 pages). Ordering information is given on any current masthead page. OM9403765 (36)Sheldrick, G. M.Acta Crystallogr. 1990,A46, 467. (37)Sheldrick, G. M.SHELXL-93, Program for Crystal Structure Refinement; University of Gattingen: Gattingen, Germany, 1993.