Organometallics 1995, 14, 5695-5699
5695
Reactions of a Disilene and a Silylene with Cyclopentadiene, Furan, and Thiophene: [2 41-Cycloadditions versus Chalcogen Abstraction1
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Edwin Kroke, Manfred Weidenbruch," Wolfgang Saak, and Siegfried Pohl Fachbereich Chemie der Universitat Oldenburg, Carl-von-Ossietzky-Strasse 9-11, 0-26111 Oldenburg, Germany
Heinrich Marsmann Fachbereich Chemie der Universitat-Gesamthochschule Paderborn, Warburger Strasse 100, 0-33095 Paderborn, Germany Received June 19, 1995@
Tetra-tert-butyldisilene (2) and di-tert-butylsilylene (31, generated by photolysis of hexatert-butylcyclotrisilane (11, react with the double bonds of cyclopentadiene (4) to provide the [2 43- and [1 21-cycloadditionproducts 2,2,3,3-tetra-tert-butyl-2,3-disilabicyclo[2.2.13cyclohept-5-ene (5) and 6,6-di-tert-butyl-6-silabicyclo[3.l.0lhex-2-ene (6), which are isolated together with two rearranged ene reaction products of 4 with 2. Photolysis of 1 in the presence of furan yields e~o-3,3,6,6,7,7-hexa-tert-butyl-3,6,7-trisila-8-oxat~cyclo[3.2.l.Oz~4loctane (9) in addition to l,l-di-tert-butyl-2,2-dimethyl-l-silacyclopropane (10) and trans1,1,2,3,3,4-hexa-tert-butylcyclotetrasilane. Reaction of 2 and 3 with thiophene gives the sulfur abstraction product 1,1,2,2-tetra-tert-butyl-1,2-disilathiirane (13) together with 2,2,6,6-tetratert-butyl-2,6-disilabicyclo[3.l.0lhex-3-ene, 1,1,2,2-tetra-tert-butyl-1,2-disilacyclohexa-3,5diene, and 10. The structures of 5, 9, and 13 were determined by X-ray crystallography.
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Introduction Similar to the C-C double bonds of alkenes, the Si-Si double bonds of disilenes participate in a wide variety of addition and cycloaddition reactions; this behavior has been summarized in several review articles.2 The differences between the two types of double bonds arise first from the higher lying 3pn level of the disilenes in comparison to the 2pn level of the alkenes and second from the appreciably smaller HOMO-LUMO separation in molecules containing the Si-Si structural unit.2aThe stable or marginally stable disilenes thus behave like highly strained, electron-rich olefins and accordingly should preferentially react with electron-poor reaction partner^.^,^ This hypothesis is supported by their smooth additions to a-diketones, 1,4-diazabutadienes, and a-ketoimines, which can all be considered DielsAlder reactions with inverse electron demand.6 On the 41-cycloadditions of the stable tetother hand, [2 raaryldisilenes t o the double bonds of conjugated 1,3dienes as well as [2 21-cycloadditionsto alkenes are
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Abstract published in Advance ACS Abstracts, October 15, 1995.
(1)Silicon Compounds with Strong Intramolecular Steric Interactions. 58. Part 57: Weidenbruch, M.; Pellmann, A.; Pohl, S.; Saak,
W.; Marsmann, H. Chem. Ber. 1995,128,935. (2)Reviews: (a) West, R. Angew. Chem. 1987,99, 1231;Angew. Chem., Int. Ed. Engl. 1987,26,1202;(b) Raabe, G.;Michl, J. In The Chemistry of Organic Silicon Compounds Part 2;Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, UK, 1989;p 1015; (c) Tsumuraya, T.; Batcheller, S. A.; Masamune, S.Angew. Chem. 1991,103,916;Angew. Chem., Int. Ed. Engl. 1991,30,902; (d)Weidenbruch, M. Coord. Chem. Rev. 1994,130,275. (3) Boger, D.L.;Weinreb, S. M. Hetero Diels-Alder Methodology; Academic Press: San Diego, 1987. (4) Scholler, W. W. J. Chem. SOC.,Chem. Commun. 1985,334. ( 5 ) For example: (a) Boudjouk, P.; Han, B.-H.;Anderson, K. R. J. Am. Chem. SOC.1982, 104,4992;(b) Weidenbruch, M.; Schafer, A,; Thom, K.-L. Z. Naturforsch. 1983,38B, 1695;(c) Weidenbruch, M.; Lesch, A,;Peters, K.; von Schnering, H. G. J.Organomet. Chem. 1991, 407, 31; (d) Weidenbruch, M.; Piel, H.; Lesch, A.; Peters, K.; von Schnering, H. G. J. Organomet. Chem. 1993,454,35.
0276-7333I95/2314-5695$09.00l0
Scheme 1 R,
1
2
3
aR = CMe, a
R = CMe3.
still ~ n k n o w n . ~ Indications that such systems are indeed able to react with disilenes were provided by the recently reported isolation of a [4 21-cycloadductfrom the reaction of 3,4,5-trimethoxybenzoyl chloride with tetramesityldisilene in which the oxygen atom and a ring carbon atom reacted with the Si-Si double bond.6 The marginally stable tetraalkyldisilene 2 is somewhat more reactive than the stable tetraaryldisilenes. Previously the only known example of a [2 41-cycloaddition to a diene was the reaction of 2 with 2,3dimethylbutadiene,from which the correspondingDielsAlder adduct was isolated in 4% yield together with the ene adduct and an additional ~ompound.~ Very recently, the [2 21-cycloaddition of a disilene to an alkene was achieved for the first time by the reaction of 2 with o-methylstyrene.8 Currently, the best approach to 2 is the photolysis of the cyclotrisilane 2, which gives the desired species together with the silylene 3 (Scheme 1).l0We now
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(6)Fanta, A. D.;Belzner, J.; Powell, J. R.; West, R. Organometallics 1993,12,2177. (7)Masamune, S.; Murakami, S.;Tobita, H. Organometallics 1983, 2, 1464. (8)Weidenbruch, M.;Kroke, E.; Marsmann, H.; Pohl, S.; Saak, W. J.Chem. SOC., Chem. Commun. 1994,1233. (9)Jutzi, P. Chem. Rev. 1986,86,983. (10)Weidenbruch, M. Chem. Rev. 1995,95,1479.
0 1995 American Chemical Society
Kroke et al.
5696 Organometallics, Vol. 14,No. 12, 1995
Scheme 2 a
4
7a,b
6
9
8
12
11
10
13
14
Cl31
15
R = CMe3.
report on the photolysis of 1 in the presence of the fivemembered-ring compounds cyclopentadiene, furan, and thiophene. All three reactions give rise to a different spectrum of products. Results and Discussion
A solution of 1 was irradiated in the presence of an excess of cyclopentadiene (4) until the pale yellow color of 1 had disappeared. Subsequent short-path distillation first resulted in the isolation of the bicyclic compound 6 in high yield. This product is formed by the [2 11-cycloaddition of 3 to one of the double bonds in 4; its constitution was confirmed by a complete NMR analysis as well as mass and IR spectral data. Of particular diagnostic value is the position of the 29Si NMR signal at -55.99 ppm in the region typical for siliranes (Scheme 2). Whereas the reaction of 3 with 4 gave rise to a major product, the reaction of the disilene 2 with 4 furnished a mixture of products that were difficult to separate. After various methods such as fractional crystallization or HPLC separation had failed, we finally obtained gas chromatographic evidence for the presence of a t least three products in an approximate ratio of 2 5 3 in the distillation residue. Three fractions were then separated by preparative GC; of these, only the smallest mass fration (no. 1ca. 20%) has not yet been identified unequivocally. The main fraction (no. 2, ca. 50%) was shown t o be a 1:l mixture of the positionally isomeric cyclopentadienyldisilanes7 4 b by complete N M R analysis, including the two-dimensional techniques 'H,lHCOSY, lH,13C-COLOC (correlation spectroscopy for long-range couplings), and 1H,29Si-INEPT. Although conclusive evidence for the mechanism of formation of 7a,b is still lacking, the most plausible explanation involves a primary ene reaction between 2 and 4 and subsequent 1,n-sigmatropic hydrogen shifts within the cyclopentadienyl ring, which finally lead t o the constitutionally isomeric compounds 7a,b. Silatropic rearrangements are also possible, but would appear to be improbable on account of the bulkiness of the tetra-tertbutyldisilanyl group. The spatial requirements of this group are also held t o be responsible for the fact that the disilanyl group undergoes bonding exclusively t o the olefinic carbon atoms of the cyclopentadienyl ring.g The last fraction was found t o be the [4 + 21-cycloadduct of 4 to 2. Since the preparative GC separation furnished only small amounts of 5 , the structural
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Figure 1. ORTEP drawing and labeling scheme for 5 (hydrogen atoms omitted). Ellipsoids are drawn at 30% probability. Table 1. Atomic Parameters ( x lo4) and Equivalent Isotropic Displacement Coefficients (pm2x 10-l)for 5 Y
X
Si C(2) '(') C(3) c(4) C(5) C(6) C(7) c(8) ('C(10) )
C(11) C(12) C(13)
695(1) 48(8) 607(10) 226(9) -472(5) -726(12) 1082(2) 552(2) 1826(2) 1213(2) 1365(1) 1370(2) 2206(2) 1120(2)
2
1935(1) -802(19) -554(12) -1197(15) -1168(10) -345(25) 2679(4) 2323(5) 1766(5) 4557(4) 2801(3) 1707(4) 2882(4) 4563(3)
2363(1) 3174(10) 2483(12) 1718(11) 1852(6) 2722(14) 1251(2) 491(2) 1031(2) 1244(2) 3260(2) 4071(2) 2986(2) 3505(2)
ue, 40(1) 63(4) 39(4) 66(3) 57(2) 47(4) 58(1)
80(1) 93(1) 77(1) 53(1) 73(1) 75(1) 68(1)
Table 2. Selected Bond Lengths (pm) and Angles (deal for 5 Si(l)-Si(la) Si(l)-C(lO) C(6)-Si(l)-C(lO) C(5)-si(l)-si(la)
248.49(14) 195.9(3)
Si(l)-C(6)
108.05(12) C(7)-Si(l)-Si(la) 92.4(5) C(2)-C(l)-C(5)
195.5(3) 84.8(5) 102.7(14)
elucidation is based on an X-ray crystallographic analysis of the colorless crystals of 5 (Figure 1,Tables 1and 2). The most conspicuous feature of this, the first X-ray crystallographic characterization of a Diels- Alder product from a stable or marginally stable disilene, is the Si-Si bond length of 248.5 pm; this is markedly longer than the normal single bond length of 234 pm and also exceeds the bond lengths in other tetra-tert-butyldisilanes.1° However, the Si-Si bond lengths in 1 (251.1 pm)ll and in hexa-tert-butyldisilane (269.7 pm)12 are appreciably longer; the latter being the longest Si-Si bond length measured to date in a discrete molecule. The reaction of furan (8) with 2 generated by photolysis of 1 is also presumably initiated by a [4 + 21-cycloaddition. In contrast to the corresponding reaction of 2 with 4, however, the newly formed double bond in the present case is so activated that an additional [2 11-addition of 3 follows to furnish the tricyclic compound 9 as the final product (Scheme 2). The 29Si
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(11)Schafer, A.; Weidenbruch,M.; Peters, K.; von Schnering, H. G. Angew. Chem. 1984,96,311; Angew. Chem., Int. Ed. Engl. 1984,23, 302. (12)Wiberg, N.; Schuster, H.; Simon, A.; Peters, K. Angew. Chem. 1986,98,100;Angew. Chem., Int. Ed. Engl. 1986,25, 79.
Reactions of Disilene and Silylene
Organometallics, Vol. 14, No. 12, 1995 5697 Sill
Figure 3. ORTEP drawing and labeling scheme for 13 (hydrogen atoms omitted). Ellipsoids are drawn at 30% probability. Figure 2. ORTEP drawing and labeling scheme for 9 (hydrogen atoms omitted). Ellipsoids are drawn at 30% probability. Table 3. Atomic Parameters ( x 104) and Equivalent Isotropic Displacement Coefficients (Dm2 x 10-l) for 9 X
-2306(1) -3149( 1) 429(1) -1437(1) -1836(2) -990(2) -433(2) -1037(2) -2289(3) -3436(3) -1893(4) -1621(3) -2569(3) -1632(3) -3560(3) -2687(3) -4152(2) -5000(3) -4707(3) -3606(3) -3630(2) -4774(3) -3497(3) -3017(3) 1229(2) 74x31 2352(3) 1253(4) 963(2) 156(4) 1946(4) 1111(5)
Y
z
652(1) 2239(1) 2899(1) 1179(2) 2422(3) 311l(3) 2110(3) 968(3) 941(3) 1192(4) -95(5) 2028(4) -1078(3) -1831(3) -1528(4) -1367(4) 1693(3) 923(4) 2718(4) 940(4) 3766(3) 3699(4) 4768(3) 4230(4) 4143(3) 4489(4) 3743(5) 5275(4) 2165(3) 2304(5) 2756(5) 827(4)
696(1) 1286(1) 1614(1) 1765(1) 1726(1) 1429(1) 1050(1) 1169(1) - 162(1) -378(2) -537(2) -318(2) 832(2) 642(2) 494(2) 1491(2) 1857(1) 1535(2) 2193(2) 2360(2) 930(2) 709(2) 1413(2) 406(2) 1251(1) 641(2) 1150(2) 1640(2) 2341(1) 2823(2) 2600(2) 2249(2)
246.97(11) Si(l)-C(9) 195.1(3) Si(l)-C(4) 192.7(3) Si(3)-C(2) C(2)-C(3) 186.1(3) 50.25(12) C(2)-C(3)-Si(3) 64.74(14) C(l)-O-C(4)
X
5000 5052(1) 4095(1) 3525(2) 3641(2) 4289(2) 6053(1) 6749(2) 5863(2) 6355(2)
Y
z
633(1) -2324(1) -3108(4) -4447(5) -1124(6) -4558(7) -2218(5) -1001(7) -916(6) -4465(6)
2500 3090(1) 3376(1) 2797(2) 3498(2) 4017(2) 3871(1) 3692(2) 4460(1) 4137(2)
sponds well with the angles observed at the silicon atoms in other siliranes substituted by both sterically unpretenti~us'~ and sterically demanding groups.14 The low yield of 9 indicates that the [4 21-cycloaddition of 2 to 8 proceeds only very slowly. This assumption is in harmony with the concomitant formation of the cyclotetrasilane 11, which is often observed when suitable reaction partners are available for 3 but not for 2.1° Compound 11 was first detected in the ultrasound-induced dehalogenation of di-tert-butyldichlorosilane.15 The formation of the silirane 10 also supports the impeded reaction between 2 and 8 since irradiation of 1 in the presence of less reactive trapping agents does lead to partial elimination of isobutene,16which would then experience a [2 13-cycloadditionof 3 to its double bond to furnish the isolated product 10. The constitution of this silirane has again been confirmed by a complete NMR analysis. In comparison to the photolysis of 1 in the presence of 4 or 8, the corresponding reaction with thiophene (12) follows a completely different course. Here, the disilene 2 abstracts the sulfur atom from 12 to furnish the 1,2disilathiirane 13 as the major product (Scheme 2). Since the structure of only one tetraaryl-substituted disilathiirane had been reported previously,l' we have also characterized 13 by X-ray crystallography (Figure 3, Tables 5 and 6). The Si-Si bond in 13 is extraordinarily short (230.5 pm) and remains under those of the corresponding
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Table 4. Selected Bond Lengths (pm) and Angles (deg) for 9 Si(l)-Si(2) Si(2)-C(13) Si(2)-C( 1) Si(3)-C(3) C(2)-Si(3)-C(3) C(3)-C(2)-Si(3)
Table 5. Atomic Parameters ( x lo4)and Equivalent Isotropic Displacement Coefficients for 13
196.2(3) 193.8(3) 186.5(3) 158.2(4) 65.01(14) 103.3(2)
NMR spectrum of 9 shows two signals of differing intensities a t 14.65 and -46.67 ppm; the upfield signal again being in the region typical for siliranes. The structure of this double cycloaddition product has been confirmed by an X-ray crystallographic analysis of the colorless crystals of 9 (Figure 2, Tables 3 and 4). Similar to 5, the Si-Si bond is markedly stretched (247.0 pm), as are the Si-C bonds, in comparison to normal single bond lengths. On the other hand, the acute C-Si-C angle in the silirane part of 9 corre-
(13)For example: Delker, G. L.; Wang, Y.; Stucky, G . D.; Lambert, R. L.; Haas, C. K.; Seyferth, D. J . Am. Chem. SOC.1976,98,1779. (14)For example: (a)Ando, W.; Fujita, M.; Yoshida, H.; Sekiguchi, A. J . A m . Chem. Soc. 1988,110,3310; (b)Pae, D. H.; Xiao, M.; Chiang, M. Y.; Gaspar, P. P. J. Am. Chem. SOC.1991,113,1281. (15)Boudjouk, P.; Samaraweera, K.; Sooriyakumaran,R.; Chrisciel, K.; Anderson, K. R. Angew. Chem. 1988;100, 1406;Angew. Chem.,
Int. Ed. Enggl. 1988,27,1355. (16)Weidenbruch, M.;Brand-Roth, B.; Pohl, S.; Saak, W. J . Organomet. Chem. 1989,379,217. (17) West, R.; DeYoung, D. J.;Haller, K. J. J . Am. Chem. Soc. 1985, 107,4942.
Kroke et al.
5698 Organometallics, Vol. 14, No. 12, 1995 Table 6. Selected B o n d Lengths (pm) and Angles (deg)for 13 Si(1)-S 217.13(9) Si(1)-Si(1a) 230.49(11) Si(l)-C(5) 194.4(2) Si(l)-C(l) 194.1(2) 112.84(10) 64.11(4) C(l)-Si(l)-C(5) Si(1)-S-Si(1a) C(1)-Si(l)-Si(la) 118.71(8) C(5)-Si(l)-Si(la) 127.12(8)
compounds 5 and 9 by about 17 pm. Although the bond length in tetramesityldisilathiirane is even shorter (228.9 pm),17it must be remembered that the lengths of the Si-Si bonds in tetra-tert-butyldisilanes are, on average, 10 pm greater than those in tetramesityldisilanes; hence, the compression of this bond in 13 is even more pronounced than that in the tetramesityl derivative. Compound 13 thus can be considered to provide further support for the assumption that the disiliranes occupy a position in the continuum between the classical three-membered ring structure and that of a n-complex of the respective disilene with the heteroatoma2 A further indication of the predominance of the n-complex form is given by the almost planar orientation about each silicon atom of the quaternary carbon atoms and the respective other silicon atoms (angular sum = 358.7'). The first 1,2-disilathiiranes were obtained by the addition of sulfur to tetramesityl- and 1,2-di-tert-butyldime~ityldisi1enes.l~It was recently demonstrated that the reaction of cyclohexene sulfide with tetramesityldisilene also gave rise to the disilathiirane.18 Although this reaction does have a formal similarity to the sulfur abstraction reaction described in the present work, the differences are, in fact, considerable: in the case of cyclohexene sulfide, a thermally stable olefin is formed, whereas in the present case cyclobutadienewhich is not known in the free form-would be the corresponding product. As illustrated by the isolation of the bicyclic compound 14 and the 1,2-disilacyclohexadiene 15, sulfur abstraction from 12 is only possible when the simultaneous insertion of the silylene 3 or the disilene 2 into the hole resulting from the sulfur elimination occurs. It is interesting to note, however, that not the silole expected from silylene insertion but rather the bicyclic product 14 is isolated; compound 14 presumably arises from an additional [2 + ll-cycloaddition of a further silylene molecule to the double bond of the si10le.l~The constitutions of both products 14 and 15 were elucidated by comprehensive spectroscopic analyses. Thus, the 29SiNMR spectrum of 15 reveals only one signal at 22.44 ppm, whereas that of 14 contains a singlet for the silicon atom in the fivemembered ring (34.38 ppm), as well as a singlet for the silicon atom in the three-membered ring (-36.32 ppm). The results of the present work are worthy of note in that the replacement of the CH2 group in 4 by an oxygen or a sulfur atom gives rise t o widely different product patterns. It thus will be of interest to subject other fivemembered heterocyclic compounds of this type to photolysis in the presence of 1. Experimental Section General Procedures. All reactions were carried out in oven-dried glassware under an atmosphere of dry argon. (18)Mangette, J. E.; Powell, D. R.; West, R. J. Chem. SOC., Chem. Commun. 1993,1384. (19)One referee pointed out that compound 13 may also arise from a [2 + 41-cycloaddition of 2 to 12 followed by sulfur abstraction and that compound 14 is formed by photochemically induced rearrangementZ1of 15. In fact, these possibilities cannot be excluded.
Photolyses were carried out at -25 "C by using a high-pressure mercury immersion lamp (Heraeus TQ 150). The lH and 13C NMR spectra were obtained on a Bruker AM 300 spectrometer using CsDs as solvent. The 29Siand twodimensional NMR spectra were recorded on a Bruker AMX 300 spectrometer. IR spectra were taken on a Bio-Rad FTS-7 spectrometer. Mass spectra were recorded on a Varian-MAT 212 or Finnigan-MAT 95 instrument. Elemental analyses were performed by Analytische Laboratorien (D-51647 Gummersbach, Germany). The cyclotrisilane 1was prepared according to the literature procedure.'l Photolysis of 1 in the Presence of Cyclopentadiene (4). A solution of 1 (0.505 g, 1.18 mmol) and 4 (0.802 g, 12.1 mmol) in n-hexane (100 mL) was irradiated for 2 h. After this time, the reaction was shown to be complete by the disappearance of the pale yellow color of 1. The solvent was removed by vacuum destillation and the residue was transfered to a molecular still. Distillation at 60-70 "Cll mbar yielded 0.206 g (84%) of 6. The distillation residue (0.6 g) was redissolved in n-hexane (15 mL) and filtered through a 2 cm layer of silica gel. According to GC analysis, the residue contained three fractions in a ratio of 20:50:30%. A part of the residue was separated by preparative GC. While the minor fraction 1 (20%)could not be identified unambiguously, the main fraction 2 (50%) was shown to consist of a 1:l n$xture of the cyclopentadienyldisilanes 7a,b. Fraction 3 (30%) was identified as the [4 + 21-cycloadduct 5.
2,2,3,3-Tetra-tert-butyl-2,3-disilabicyclo[2.2.11 hept-5ene (5): colorless crystals; mp 200-204 "C; lH NMR 6 1.18 (s, 18H), 1.25 (s, 18H), 2.05-2.14, 2.20-2.28 (m, 4H, 2 x CH, CHZ), 5.91 (s, 2H, HC=C); 13CNMR 6 22.77 (Cq), 31.45 (CH21, 32.77 (C,), 33.20 (C,), 42.33 (CHI, 133.16 (C=C) (C, and C, refer to primary and quaternary carbon atoms); mass spectrum (CI, isobutane) m l z 350 (M+, 17); HRMS calcd for C21H42Si2 350.2825, found 350.2826.
6,6-Di-tert-butyl-6-silabicyclo[3.l.0]hex-2-ene (6):colorless liquid; 'H NMR 6 0.99 (s, 9H), 1.12 (s, 9H), 1.58 (pseudo-t of d, l H , 35= 19 Hz, 35= 2 Hz, CH2CH), 2.15 (m, lH), 2.77 (m, 1H), 3.07 (m, lH), 5.38 (m, lH), 6.88 (m, 1H); NMR 6 17.32 (CH), 18.99 (C,), 22.25 (C,), 29.88 (C,), 30.03 (CHI, 31.48 (C,), 35.39 (CHz), 127.67 (C=C), 131.59 (C=C); 29SiNMR 6 -55.99; IR (KBr) v 1653, 1597 (C=C) cm-'; mass spectrum (EI, 70 eV) m l z 208 (M+,121,151 (M+ - tBu, 88); HRMS calcd for C13H24Si 208.1647, found 208.1632. 1,1,2,2-Tetra-tert-butyl-l-(cyclopenta1,3-dienyl)disilane and 1,1,2,2-tetra-tert-butyl-1-(cyclopenta-2,4-dienyl)disilane (7a,b): colorless oil; 'H NMR (CsDs, 500 MHZ) 6 1.17 (s, 9H), 1.211 (s, 9H), 1.214 (s, 9H), 1.26 (s, 9H), 2.75 (pseudo-q, 2H, 35= 45= 1.5 Hz, CH2), 3.12 (2H, AB system, CH2), 4.03 (s, l H , S a ) , 4.10 (s, l H , SiH), 6.32 (dq, l H , 35= 5.1 Hz, 45= 1.5 Hz, CH=C), 6.54 (2H, AB system, CH=C), 6.77 (pseudo-quint, l H , 35= 4J = 1.5 Hz, CH=C), 6.92 (dq, l H , 35= 5.1 Hz, 45= 1.5 Hz, CH=C), 7.07 (quint, l H , 35= 4J = 1.5 Hz, CH=C); 13CNMR 6 21.71 (Cq),21.80 (Cq),22.14 (Cq), 31.45 (C,), 32.68 (C,), 32.74 (C,), 43.40 (CH21, 48.88 (CH21, 131.34 (=CH), 132.99 (=CHI, 137.35 (=CHI, 138.94 (=CH), 144.02 (C,), 144.09 (C,), 144.17 (=CHI, 144.95 (=CH); 29Si NMR 6 -0.50 (s, SIH), -1.03 (s), -1.22 (s, SiH), -2.01 (s);IR (KBr) v 2070 (m, SiH), 1765,1719 (C=C) cm-'; mass spectrum (CI, isobutane) m l z 351 (MH+, 100);HRMS calcd for C21H42Si2 350.2825, found 350.2732. Photolysis of 1 in the Presence of Furan (8).A solution of 1 (0.608 g, 1.42 mmol) and 8 (0.832 g, 13.7 mmol) in n-hexane (80 mL) was irradiated at -25 "C for 4 h. After this time, the pale yellow color of 1 had disappeared. The solvent was removed by evaporation and the residue was transferred to a molecular still. Distillation at 36 "Cl1.5 mbar yielded 0.082 g (29%) of 10 as a colorless liquid. At 50-70 "Cl0.01 mbar, 0.070 g of a second colorless fraction was obtained. It consisted of several compounds that could not be identified.
Organometallics, Vol. 14,No. 12, 1995 5699
Reactions of Disilene and Silylene
Table 7. Crystallographic Data 5 9 empirical formula fw a (pm)
b (pm) (pm) p (de& V (pm3) c
Z
D(ca1cd)(g ~ m - ~ ) cryst syst space group cryst size (mm) data collection mode 28,,, (deg) no. of rfls measd no. of unique r f l s no. of rfls [I > 2dZ)I GOF (F) R , Rwz [I > 2 d ) I residual electron density e nm-3
CzlH42Si2 350.73 1762.4(4) 809.2(2) 1555.3(2) 2281(9) x lo6 4 1.050 orthorhombic Pbcn 0.46 x 0.38 x 0.30 0-28 scan 50 1956 1956 1287 1.003 0.048, 0.107 267 -169
CzsHssOSia 495.01 1284.1(1) 1102.4(1) 2243.2(1) 92.43(1) 3127.6(4) x lo6 4 1.036 monoclinic P21ln 0.61 x 0.45 x 0.45 o scan 50 5843 5575 3749 1.039 0.056, 0.128 354 -201
13
C16H36SSi2 316.69 1703.2(3) 622.3(1) 1992.8(4) 107.03(3) 2019.6(6) x 4
lo6
1.042
monoclinic c21c
1.15 x 0.49 x 0.49 0-28 scan 50 1848 1784 1437 1.034 0.043, 0.107 311 -156
The solid distillation residue was dissolved in n-hexane, filtered, and concentrated to 5 mL. Cooling a t -25 "C for 1 week afforded 0.068 g (10%)of colorless crystals of 9. Crystallization of the residue (from the mother liquor after the separation of 9 ) from a minimum amount of n-hexane a t -50 "C provided 0.064 g (20%)of colorless crystals of 11.
153.14 (=C); 29SiNMR 6 -36.32 (SI, 34.38 (s); mass spectrum (CI, isobutane) m l z 337 (MH+, 100); HRMS calcd for C20H40Si2 336.2669, found 336.2672.
(100). Anal. Calcd for CzsHs80Si3: C, 67.94; H, 11.81. Found: C, 67.71; H, 11.74. l,l-Di-tert-butyl-2,2-dimethyl-l-silacyclopropane (10): IH NMR 6 0.54 (s, 2H, CHz), 1.08 (s, impurity,
