3551
Organometallics 1995, 14, 3551-3557
Thiadisilacyclopropanes: Stereospecific Formation from Disilenes and Solid State Structures John E. Mangette, Douglas R. Powell, and Robert West* Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706 Received May 9, 1995@ The reactions of (E)-1,2-bis(2,4,6-t~isopropylphenyl)-l,2-di-tert-butyldisilene, E-lc, (2)1,2-bis(2,4,6-triisopropylphenyl)-1,2~di-tert-butyldisilene, 2 - l c , and a n EIZ mixture of 1,2dimesityl-l,2-di-tert-butyldisilenes, lb, with elemental sulfur and either ethylene or propylene E-lb, with ethylene sulfide and the reaction of (E)-l,2-dimesityl-l,2-di-tert-butyldisilene, sulfide were found to be stereospecific with retention of the original disilene stereochemistry, giving thiadisilacyclopropanes, 2. X-ray crystal structures of cis- and trans-2,3-bis(2,4,6triisopropylphenyl)-2,3-di-tert-butyl-l-thia-2,3-disilacyclopropanes, 2c, and trans-2,3-dimesityl-2,3-di-tert-butyl-l-thia-2,3-disilacyclopropane, truns-2b, are reported and compared to the known structure of 2,2,3,3-tetramesityl-l-thia-2,3-disilacyclopropane, 2a. Compound cis-2c, C3gH&Si2, crystallized in the orthorhombic space group Pna21 with 2 = 8 and lattice constants a = 18.846(2) A, b = 9.555(2) A, and c = 42.236(4) A. Compound truns-2c, C38I-h' SSi2, crystallized in the monoclinic space group P21 with 2 = 2 and lattice constants a = 10.547(2) A, b = 16.096(2) A, c = 11.695(2) A, and B = 107.330(11)". Compound truns-2b, C26H&Si2, crystallized in the monoclinic space group C2/c with 2 = 4 and lattice constants a = 12.6447(5) A, b = 12.2663(5) A, c = 16.9828(9) A, and /I= 102.549(4)". The mechanistic consequences of stereospecific sulfur transfer are discussed.
Introduction The three-membered ring thiadisilacyclopropanes have been synthesized by the reaction of isolable disilenes with elemental sulfur' and, more recently, with episulfides.2 For example, tetramesitylthiadisilacyclopropane, 2a, as well as the 2,3-dimesityl-2,3-di-tert-butyl compound, 2b, have been made (eq 11.l The latter was R\ Mes'
Mes
si=(
s8
R
la, R = Mes b, R = tBu
?\
MesRSi-SiRMes
(1)
2
Mes = 2,4,6-trimethylphenyl
a single isomer produced from the reaction of Sg with the pure trans disilene, but its stereochemistry was not determined. The reaction of la with cyclohexene sulfide was shown by lH NMR to give exclusively 2a and cyclohexene. From a mechanistic viewpoint it is of great interest to determine if sulfur transfer to disilenes is stereospecific, stereoselective, or neither. However, this cannot easily and unequivocally be done with lb since only its E isomer can be isolated pure.3 Fortunately, efforts in this group to develop new disilenes have produced 1,2bis(2,4,6-triisopropylphenyl)-1,2-di-tert-butyldisiene, IC, a compound for which both geometrical isomers can be @Abstractpublished in Advance ACS Abstracts, June 15, 1995. (1)West, R.;DeYoung, D. J.; Haller, K. J. J.Am. Chem. SOC.1985, 107,4942. (2)Mangette, J. E.;Poyell, D. R.; West, R. J . Chem. SOC.,Chem. Commun. 1999,1348. (3)(a)Michalczyk, M. J.;West, R.; Michl, J. J.Am. Chem. Soc. 1984, 106,821. (b) Michalczyk, M. J.; West, R.; Michl, J. Organometallics 1985,4,826.(c)Murakami, S.;Collins, S.; Masamune, S. Tetruhedron Lett. 1984,25,2131.
isolated in pure Photolysis of the trisilane 3 (A = 254 nm) generates ICas an EIZ mixture (eq 2). The
hv
IstBuSi(SiMe3)2
pentane
3 Is = 2,4,6-triisopropylphenyl
tBu, /Si=Si sI' Is 'tBu
+
(Me3Si)2 (2)
IC
less soluble E isomer, the stereochemistry of which was determined by X-ray diffraction, precipitates cleanly from the reaction mixture. The Z isomer can be made on a small scale in '95% purity by complete photoisomerization (A = 350 nm) of the E isomer. Its identity was supported by its characteristic downfield 29Si chemical shift of +96.93 ppm and comparison of this value t o that of E-lc at f87.39 ppm. This report details stereospecific thiadisilacyclopropane syntheses by treatment of E-lc and 2 - l c with sulfur and propylene sulfide. X-ray structures of both isomeric three-membered rings were obtained. The sulfurization of E-lb with ethylene sulfide and EIZ mixtures of lb with both sulfur and ethylene sulfide is also described. An X-ray structure of tmns-2b was determined.
Results and Discussion Reactions of 1 with SSand Episulfides. Separate solutions of E- and 2-lc in benzene were treated with sulfur at room temperature. The reactions were complete within 1 min, as evidenced by the loss of the characteristic bright yellow or orange disilene color. For NMR-scale reactions, only one new 29Siresonance was (4)Archibald, R. S.;Van den Winkel, Y.;Millevolte, A. J.; Desper, J. M.; West, R. Organometallics 1992,11,3276.
0276-733319512314-3551$09.00/00 1995 American Chemical Society
3552 Organometallics, Vol. 14,No. 7,1995 c220
9
Mangette et al.
0 C13
c12 QC40
Figure 2. Thermal ellipsoid drawing of trans-2c at the 50% probability level. Hydrogens omitted for clarity. Figure 1. Thermal ellipsoid drawing of cis-2~) molecule A, at the 50% probability level. Hydrogens omitted for clarity. observed for each isomer: -33.71 ppm from E-lc, assigned as trans-2c, and -28.91 ppm from 2-lc, assigned as cis-2c. The lH NMR spectra showed no contamination of either product with its diastereomer, implying stereospecific sulfur transfer. Similar results were obtained with propylene sulfide, although reactions were much slower. Standard NMRscale reactions (20mg of disilene) were complete after 4 days at room temperature using ca. 1.5 equiv of episulfide. Several complex peaks at 6 5.0 and 5.7 in the lH NMR were assigned as p r ~ p y l e n e .Again ~ the E disilene gave only a trans three-membered ring. The Z isomer gave nearly complete retention with a cisltrans ratio of 24:l. Preparative- or semipreparative-scale reactions were also conducted. Products were purified by preparative thin layer chromatography or crystallization. Isolated yields of cis- and trans-2c, respectively, were 47 and 75% using elemental sulfur and 50 and 57% using propylene sulfide. Disilene E-lb was treated with ethylene sulfide, giving 'H and 29Si(-35.96ppm) NMR data consistent with 2b as previously isolated.' EIZ mixtures [(3-3.5): 11 of lb, generated by photolysis of the E i ~ o m e rwere ,~ treated separately with sulfur and ethylene sulfide. Two 29Sipeaks were observed for each reaction; a large signal was seen at -35.96 ppm and a smaller one at -29.63 ppm. The minor product was not isolated but, based on the results from IC, was assumed to be the other diastereomer of 2b. Integration of product peaks in the lH spectra gave ratios roughly equal t o those of the disilene precursors. Solid State Structures of cis- and tram-2c and trans-2b. Structural analyses of the three compounds listed above were undertaken to unequivocally establish the stereochemical course of sulfur transfer and for comparison to the known structure of 2a.l Crystals of cis-ac, trans-2c, and trans-2b were isolated from preparative-scale reactions of 2-lc, E-lc, and E-lb, respectively, with sulfur. Thermal ellipsoid diagrams are given in Figures 1-3, and Tables 1-4 present X-ray acquisition data. Selected structural parameters are given in Table 5 . (5)The vinylic region of the spectrum agreed with an authentic sample of propylene generated by reaction of propylene sulfide with triphenylphosphine.
(5
b
Figure 3. Thermal ellipsoid drawing for transdb at the 50% probability level.
-
Scheme 1 Sg or
tBu \ / ~r ,Si=Si Ar 'tBu E-lb, Ar = Mes c, Ar = Is
Z-lb, Ar = Mes c, Ar = Is
episulfide
S / \
tBu,"jSi-Si
*-llAr t'Bu trans-2b,c
Ar
&-2b,c
Clearly, from the X-ray data, sulfur transfer occurs with either exclusive (Sa) or predominant (episulfides) retention of the silicon-silicon double bond configuration (Scheme 1). As mentioned earlier, it is also evident that the unisolated product from sulfurization of EIZl b is cis-2b. Mechanistic ramifications are discussed in the next section. As can be seen from Table 5 , the structural parameters of 2b,c are similar to those for 2a. The exceptionally short silicon-silicon bond distances (versus the normal silicon-silicon single bond distance of 2.34-2.35 A) and the near 360" summations of the CtB,-Si-Ck, CtB,-Si-Si, and Ck-Si-Si angles about each silicon (CO(Si))are characteristic of reported structures of other disilacyclopropane derivatives. For instance 1,1,2,2tetramesityl-3-oxa-l,2-disilacy~lopropane~ and 1,1,2,2tetrakis(2,6-dimethylphenyl)-l,2disilacyclopropane7 have silicon-silicon bond distances of 2.227(2)and 2.272(2)
Organometallics,Vol.14,No.7, 1995 3553
Thiadisilacyclopropanes
Table 1. Experimental Crystallographic Data for 2c and trane-2b cis-2c
empirical formula fw cryst syst space group a, A b, A C,
A
a,deg
/A deg
d(calcd), g/cm3 cryst size, mm abs coeff, mm-l F(OO0) T, "C 28 range, deg scan type scan speed, deg/min scan range ( w ) , deg index ranges no. of reflns collcd no. of ind reflns final R indices (obs data), % goodness of fit largest and mean N u data-to-param ratio largest diff peakhol, e A-3
transdc
trans-2b
C38H&Si2 609.13 orthorhombic PnaQl 18.846(2) 9.555(2) 42.236(4) 90 90 90 7606(2) 8 1.064 0.40 x 0.30 x 0.10 1.511 2688 -160(2) 4.0-114.0
C38H&Si2 609.13 monoclinic p2 1 10.547(2) 16.096(2) 11.695(2) 90 107.330(11) 90 1859.3(5) 2 1.067 0.30 x 0.20 x 0.20 1.516 672 -160(2) 4.0-114.0
12.6447(5) 12.2663(5) 16.9828(9) 90 102.549(4) 90 2571.2(2) 4 1.139 0.30 x 0.15 x 0.05 2.065 960 -160(2) 4.0-114.0
w
w
w
2.00-40.00 0.70 Ochc20,Ockc10, 0 5 1 5 45 Friedel 10 442 10 274 (Rint = 3.37%) R = 5.39, R , = 14.27 1.036 0.00410.000 13.9 0.4291-0.421
2.00-40.00 1.42 0 5 h 5 11,0 5 k 5 17, -12 c 1 c 12 Friedel 5607 5098 (Ri,t = 8.93%) R = 6.53, R, = 16.92 1.074 -0.003/0.000 13.7 0.705f-0.423
2.00-40.00 0.72 O5hc13,Ock~13, 0 5 1 5 18 Friedel 3574 1744 (Rint = 4.87%) R = 3.90, R , = 10.10 1.085 0.015/0.000 12.8 0.3451-0.470
+
A,respectively, while, in the former compound, the s u m of the angles about the silicons was reported to be 360".s Experimentalists and theoreticians have attributed these structural characteristics to a certain amount of x-bonding between the silicons.lr6J0 Thus the overall bonding is related to that in olefin-transition metal complexes where, according t o the Dewar-ChattDuncanson model,12a o bond is created by donation of x electron density from the olefin to the metal and an interaction of iz symmetry allows back-donation of electron density from a d-orbital of the metal to the x*orbital of the olefin. Note that for 2 and similar compounds a filled p-orbital on the heteroatom would have the proper symmetry for back-donation to the x*orbital of the disilene-like unit. Besides the basic similarities between the structures of 2, several differences are also evident. The siliconsilicon bond distances, although all unusually short, show a steady increase following the order trans-2b 2a = trans-2c cis-2c. It is difficult to correlate this trend with the silicon-silicon double bond lengths of the parent disilenes since crystal packing forces and (6)Yokelson, H. B.;Millevolte,A. J.; Gillette, G. R.; West, R. J.Am. Chem. Soc. 1987,109,6865. (7)Masamune, S.;Murakami, S.; Tobita, H. J.Am. Chem. Soc. 1983, 105,7776. (8)For comparison cyclotrisilaneshave been shown by X-ray studiesg
to have longer than normal silicon-silicon bond lengths (2.375-2.511 In agreement with calculational work,lOJ1and in contrast to the three-membered rings mentioned in the present discussion, several exhibit three equivalent silicon-silicon bond lengths. (9)(a)Masamune, S.;Hanzawa, Y.; Murakami, S.; Bally, T.; Blount, J. F.J.Am. Chem. Soc. 1982,104,1150.(b)Schafer, A.;Weidenbruch, M.; Peters, K.; von Schnering, H.-G. Angew.Chem.,Int. Ed. Engl. 1984, 23, 302. (c) Dewan, J. C.; Murakami, S.; Snow, J. T.; Collins, S.; Masamune, S. J. Chem. Soc., Chem. Commun. 1988,892.(d)Weidenbruch, M.; Pohl, S.; Saak, W.; Thom, K. L. J. Organomet. Chem. 1987, 329,151. (10)(a) Grev, R. S.; Schaefer, H. F.,111. J. Am. Chem. SOC.1987, 109, 6577. (b) Cremer, D.; Gauss, J.; Cremer, E. J. Mol. Struct.-
A).
Theochem. 1988,169,531. (11)Boatz, J. A.; Gordon, M. S. J. Phys. Chem. 1989,93,3025. (12)(a)Dewar, M. J. S. Bull. SOC.Chim. Fr. 1951,18,C71. (b) Chatt, J.; Duncanson, L. A. J. Chem. SOC.1963,2939.
monoclinic CWC
+
+
crystallization conditions apparently afFect the observed Si=& distances. This fact is most evident with l a for which two significant1 different double bond lengths, 2.143(2) and 2.160(1) , were reported.13 Perhaps a better correlation is with the degree of twisting of the bulky groups about the silicon-silicon single bond of 2, as depicted in Figures 4 and 5 for the newly reported structures. The twist angle, 4, is defined as the average of the torsional angles between cis carbon atoms directly bonded to silicon, e.g. for cis.2c, 4 = [e(C(5)-Si(l)-Si(2)-C(24) e(C(l)-Si(l)-Si(2)-C(2O)Y 2. As shown in Table 5, in general, as 4 increases so does the silicon-silicon bond distance. The two extremes are represented by trans-2b with a 4 of nearly 0" (Figure 5) and the shortest silicon-silicon bond length of the series and cis-2c with 4 = 27.5" (Figure 4, bottom) and a relatively long silicon-silicon bond. Compounds 2a and trans-2c (Figure 4, top) show comparatively modest twist angles with intermediate bond distances. Steric effects alone should influence the silicon-silicon bond lengths and could cause significant twisting. This is best illustrated for the most highly distorted structure, &-2c, which has the bulkiest combination of substituents, foremost being the cis tertbutyl groups. However, a greater degree of twisting could, in and of itself, lead to longer Si-Si bonds considering the bonding model discussed above. The twisting distortion would decrease the n overlap between the silicons, thus reducing the bond order and increasing the bond length. A second likely result of the combination of steric hindrance and large 4 is the 0.02 A difference in the silicon-sulfur bond lengths within a molecule for cis2c (Table 5). In contrast, the structures of 2a and trans-2b exhibit equal Si-S distances, while trans-2c
w
+
(13)(a)Fink, M. J.;Michalczyk,M. J.;Haller, K.J.;West, R.; Michl, J. Organometallics 1984,3, 793. (b) Shepherd, B. D.; Campana, C. F.; West, R. Heteroatom Chem. 1990,1, 1.
Mangette et al.
3554 Organometallics, Vol. 14, No. 7, 1995
R
R
S
, \
Figure 6. Visual description of the torsional angle, a. along the silicon-silicon axis away from the larger g r 0 ~ p . lThe ~ longer Si(2a)-S bond, under this premise, would correspond t o the tert-butyl group of the pair of closer substituents exerting a greater steric influence. This should be expected considering the known steric dominance of the tert-butyl group. Furthermore, the dihedral angle, a,which the Si(1a) 2,4,6-triisopropylphenyl ring makes with the Si-Si-C plane (Figure 6) is -115.5(4)", a value which should correspond to a less than maximum steric influence. In addition to the twisting distortion, the 86.0(4)" a SHal angle of the Si(2a) 2,4,6-triisopropylphenylring should result in a further steric encumbrance at Si(2a). Eclipsing interactions between sulfur and the ortho aromatic carbon which bears an isopropyl group would be expected. Using this type of analysis the silicon-sulfur bond length difference in trans-2c should be small in comparison. Both tert-butyl groups are bent toward sulfur and have very similar conformations. The torsional angles between sulfur and the tert-butyl methyl groups L Uta1 are -60.8(4), 58.6(4),and -179.1(3)" for C(1)and -67.6(4), 50.3(4), and 174.6(4)" for C(20). Also, there would C124al likely be no difference in the steric influence of the 2,4,6triisopropylphenyl groups since their a values differ by Figure 4. End-on views of the silicon-silicon bonds of cisless than 2". 2c (bottom) and tmns-2c (top). A similar situation exists for 2a. The two closer groups are both mesityl, and their effective bulk should be nearly equal since their a angles are comparable, 133 and 128". The a angles of the two distant mesityl groups are somewhat different from each other, 85 and 73", but due to the Si-Si twisting distortion they would be expected to have less influence on the orientation of sulfur than would the other rings. The equality of the silicon-sulfur bonds in truns-2b is a consequence of CZsite symmetry. Mechanistic Considerations. Certainly more experimentation must be done to establish mechanistic details with any confidence. But the present stereochemical results may suggest that a concerted mechanism is a dominant pathway for both sulfur transfer Figure 5. End-on view of the silicon-silicon bond of agents. tmne-2b. An attractive mechanism involving elemental sulfur is presented in A, Scheme 2. Steudel has proposed has a comparatively small asymmetry with a bond sulfuranes as possible intermediates in the well-known length difference of less than 0.01 A. interconversion reactions of sulfur allotropes at elevated The twisting distortion in molecule A of c i s - 2 ~ ' ~ temperatures (Scheme 3),16 and t o explain kinetic causes the C(20a) tert-butyl group and the C(5a) 2,4,6results of the redistribution reaction of R& and R'2S3 triisopropylphenyl group to be closer to sulfur compared to give RR'S3.l6" Becker and Wojnowski have subseto the C(la) tert-butyl group and the C(24a) 2,4,6quently used this mechanism to rationalize the insertion triisopropylphenyl group (Figure 4, bottom). The nonof sulfur into a silicon-silicon bond of (Me~E4i)s.l~ bonded distances in Table 6 demonstrate this. A significant difference in the steric requirements of the (15) Complexes of transition metals to monosubstituted olefins exhibit a longer distance between the metal and the substitutedcarbon, two closer groups could cause sulfur to be displaced
4'""'
~~
~~~~
~~
attributed, at least in part, to sterics. Herberhold, M. Metal n-Com-
(14)Molecule B in the crystal structure ofcie-2c exhibits structural features similar to those of molecule A. The general description also applies to it.
plexes; Elsevier: New York, 1974; Vol. 2, Part 2, p 183.
(16)(a) Steudel, R. Top. Curr. Chem. 1982,102, 149. (b) Laitinen,
R.S.; Pakkanen, T. A,; Steudel, R. J.Am. Chem. SOC.1987, 109, 710. (17) Becker,B.;Wojnowski, W. J.Orgunomet. Chem. 1988,346,287.
Organometallics, Vol.14,No. 7, 1995 3555
Thiadisilacyclopropanes
Table 2. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters ( x 109) for cis-2c S(1A)
a
6002(1) 6617(1) 6482(1) 7527(3) 8103(3) 7595(3) 7629(4) 5977(3) 5822(3) 5279(3) 4876(3) 5052(3) 5589(3) 6754(4) 6228(4) 5747(3) 4173(3) 4221(3) 3552(3) 5969(5) 5726(4) 5076(3) 6948(3) 6335(4) 7401(5) 7367(5) 5955(3) 6321(3) 5951(3) 5209(3) 4860(3) 5198(3) 7414(3) 7132(3) 7434(3) 4302(3) 4825(3) 4474(4) 4244(3) 4749(3) 4352(3)
7258(1) 5744(1) 5660(1) 6248(6) 5599(8) 5624(8) 7833(8) 4900(6) 3471(5) 2943(6) 3802(6) 5228(6) 5791(5) 1595(7) 2436(5) 1426(6) 1716(7) 3308(7) 3855(8) 7726(7) 7352(5) 8208(6) 6707(5) 7383(9) 7890(9) 5874(7) 4151(6) 2890(7) 1709(6) 1683(6) 2899(7) 4144(5) 2313(6) 2791(6) 1847(6) 465(6) 318(6) -260(8) 5698(6) 5432(6) 5349(6)
7771(1) 8025(1) 7480(1) 8200(1) 7991(2) 8533(2) 8221(2) 8322(1) 8322(1) 8517(1) 8706(1) 8717(1) 8533(1) 8334(2) 8131(2) 7943(1) 8923(2) 8888(2) 8722(2) 8907(2) 8568(2) 8477(2) 7149(1) 6966(3) 7276(2) 6910(2) 7316(1) 7236(1) 7150(1) 7134(1) 7199(1) 7284(1) 6917(2) 7237(2) 7499(2 6794(1) 7063(1) 7364(2) 7064(1) 7343(1) 7655(1)
S(1B) Si(1B) Si(2B) CUB) C(2B) C(3B) C(4B) C(5B) C(6B) C(7B) C(8B) C(9B) C(1OB) C(11B) C(12B) C(13B) C(14B) C(15B) C(16B) C(17B) C(18B) C(19B) C(20B) C(21B) C(22B) C(23B) C(24B) C(25B) C(26B) C(27B) C(28B) C(29B) C(30B) C(31B) C(32B) C(33B) C(34B) C(35B) C(36B) C(37B) C(38B)
6446(1) 5964(1) 5848(1) 5496(3) 6105(4) 5106(4) 4994(4) 6494(2) 6124(3) 6497(3) 7235(3) 7594(3) 7246(3) 5036(3) 5308(3) 5015(3) 7981(4) 7622(3) 8160(3) 8203(3) 7696(3) 8096(3) 4957(3) 4361(3) 4907(3) 4826(4) 6498(3) 6635(3) 7175(3) 7585(3) 7424(3) 6898(3) 5694(4) 6213(3) 6682(3) 8159(3) 8206(3) 8903(3) 6563(4) 6785(4) 7444(4)
2774(1) 4398(1) 4335(1) 3351(5) 2575(7) 4187(7) 2257(8) 5901(6) 7152(7) 8349(6) 8386(6) 7142(7) 5920(6) 7746(6) 7247(6) 8209(7) 10282(8) 9723(6) 9566(6) 4347(6) 4608(6) 4691(7) 3852(6) 4532(8) 4453(7) 2280(7) 5175(6) 6624(6) 7161(6) 6309(6) 4900(6) 4310(5) 8463(7) 7652(6) 8664(7) 8392(7) 6863(7) 6571t8) 2352(7) 2744(6) 1926(7)
5397(1) 5687(1) 5141(1) 6017(1) 6178(2) 6265(2) 5882(2) 5858(1) 5931(1) 6021(1) 603U1) 5964(2) 5886(1) 6255(2) 5929(2) 5674(2) 5814(2) 6108(1) 6375(1) 6109(2) 5834(1) 5517(1) 4954(1) 5152(2) 4616(2) 4944(2) 4851(1) 4847(1) 4654(2) 4461(1) 4458(1) 4644( 1) 4832(2) 5042(2) 5227(2) 4186(2) 4268(2) 4448(2) 4274(2) 4611(2) 4711(2)
Equivalent isotropic U defined as one-third of the trace of the orthogonalized U" tensor.
transition states. This comparison implies an electrophilic nature of the episulfide sulfur such as in the stereospecific concerted desulfurizations with phosphines,21 organolithium reagents,21i22and catalytic thi~phenoxide.~~ More probable, though, is an initial nucleophilic attack by sulfur on the disilene which, if concerted, would be more like the concerted episulfide desulfurizations on metal surfaces.24 For episulfides a nonconcerted mechanism deserves some consideration, though, since the reaction of 2-lc
Scheme 2
Scheme 3
S".I
S"+I
A concerted sulfur transfer from episuliides, B, Scheme 2, might be analogous to the concerted alkene epoxida-
tions with peroxy acids,18 oxaziridines,lg and dioxiranes20 which are thought to involve similar butterfly
(18)For reviews see: (a) Rebek, J., Jr. Heterocycles 1981, 15, 517. (b)Dryuk, V. G. Tetrahedron 1976,32,2855. (c) Swern, D. Chem.Rev. 1949,45, 1. For more recent work see: (d) Beak, P.; Woods, K.W. J. Am. Chem. SOC.1991. 113. 6281. (e) Bach. R. D.: Owensby, A. L.; Gonzalez, C.; Schlegel, H. B.; McDouall, J. J. W. J. Am. Chim. Soc. 1991,113, 2338. (19)(a) Davis, F. A.; Billmers, J. M.; Gosciniak, D. J.; Towson, J. C.; Bach, R. D. J. Org. Chem. 1988,51,4240. (b)Bach, R. D.; Wolber, G. J. J.Am. Chem. SOC.1984,106,1410. (c)Bach, R. D.; Coddens, B. A.; McDouall, J. J. W.; Schlegel, H. B.; Davis, F. A. J.Org. Chem. 1990, 55, 3325. (20)(a)Baumstark, A. L.; McCloskey, C. J. Tetrahedron Lett. 1987, 28, 3311. (b) Baumstark, A. L.; Vasquez, P. C. J. Org. Chem. 1988, 53, 3437. (c) Murray, R. W.; Shiang, D. L. J. Chem. Soc., Perkins Trans. 2 1990, 349. (d) Bach, R. D.; AndrBs, J. L.; Owensby, A. L.; Schlegel, H. B.; McDouall, J. J. W. J.Am. Chem. Soc. 1992,114,7207. (21) (a)Bordwell, F. G.; Andersen, H. M.; F'itt, B. M. J. Am. Chem. Soc. 1984, 76,1082. (b)Neureiter, N. P.; Bordwell, F. G. J.Am. Chem. SOC.1959,81,578. (c) Boskin, M. J.; Denney, D. B. Chem. Ind. 1959, 330. (d) Boskin, M. J.; Denney, D. B. J. Am. Chem. Soc. 1980, 82, 4736. (22)(a)Trost, B. M.; Ziman, S. D. J. Org. Chem. 1973,38,932. (b) Bonini, B. F.; Maccagnani, G.; Mazzanti, G.; Zani, P. h z . Chim. Ital. 1990,120, 115. (23)Huisgen, R. Phosphorus Sulfur 1989, 43, 63.
Mangette et al.
3556 Organometallics, Vol. 14,No. 7, 1995
Table 3. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters ( x 10s) for tram-2c X
400(1) 808(1) 1675(1) 1756(5) 3049(5) 2055(6) 861(6) -680(5) -1981(5) -3042(5) -2867(6) -1581(6) -493(5) -2294(5) -2891(7) -3185(6) -4007(7) -5210(6) -4271(8) 881(6) 1120(6) 1112(7) 871(5) -5736) 1656(6) 860(6) 3463(5) 3828(5) 5175(5) 6164(5) 5807(5) 4478(5) 2857(6) 3152(6) 2823(8) 7603(6) 8179(6) 8376(8) 8206(20) 4179(5) 4568(6) 4838(6)
Y
7436(1) 6914(1) 6347(1) 7724(3) 7968(3) 7399(4) 8485(4) 6428(3) 6738(3) 6270(4) 5491(4) 5219(4) 5680(3) 7580(3) 8165(5) 7506(4) 4926(5) 5044(5) 4995(7) 5332(3) 5288(5) 4484(4) 5460(3) 5326(4) 4660(3) 5721(4) 6542(3) 7153(3) 7349(4) 6972(4) 6351(4) 6132(3) 7597(3) 7448(5) 8537(4) 7244(5) 7552(4) 6658(5) 7264(13) 5435(3) 5663(4) 4615(4)
z
U(eq),A2
4635(1) 3074(1) 4944(1) 2434(5) 3380(5) 1316(5) 2082(6) 1932(4) 1711(4) 1034(5) 556(6) 727(5) 1390(5) 2153(5) 1102(7) 2961(6) -110(6) 289(7) -1405(6) 1492(5) 261(6) 2101(7) 5572(5) 4800(6) 5693(5) 6839(5) 5836(4) 6749(5) 7243(5) 6894(5) 6024(5) 5504(4) 7251(5) 8607(5) 6991(6) 7423(6) 6495(5) 8273(8) 8642(18) 4566(5) 3446(5) 5089(6)
Table 4. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters ( x 10s) for tram-2ba 5000 5064(1) 3841(2) 2773(2) 3871(2) 3881(2) 6402(2) 6921(2) 7956(2) 8509(2) 7988(2) 6953(2) 6387(2) 9648(2) 6475(2)
2214(1) 3718(1) 3960(2) 3788(2) 3184(2) 5141(2) 3940(2) 4967(2) 5100(2) 4249(2) 3256(2) 308112) 5945(2) 4411(2) 1954(2)
7500 6844(1) 5988(1) 6263(2) 5286(1) 5689(2) 6550(1) 6682(1) 6543(1) 6269(2) 6122(2) 6256(1) 6971(2) 6143(2) 6080(2)
The compound sits on a 2-fold rotation axis in the crystal structure.
with propylene sulfide was not completely stereospecific. In fact, with neither sulfurization agent is it possible to dismiss stepwise mechanisms since it is not clear how (24) (a) Thomas, T. M.; Grimm, F. A.; Carlson, T. A.; Apron, P. A. J . Electron Spectrosc. Relat. Phenom. 1982, 25, 159. (b) Friend, C. M.; Roberts, J. T. J.Am. Chem. SOC.1987, 109, 7899. (c) Friend, C. M.; Roberts, J. T. ACC.Chem. Res. 1988,21, 394. (d) Calhorda, M. J.; Hoffmann, R.; Friend, C. M. J . Am. Chem. SOC.1990, 112, 50. (e) Wiegand, B. C.; Friend, C. M. Chem. Reu. 1992, 92, 491.
rapid silicon-silicon bond rotation would be in intermediates such as *S-S,-S-SiRR-Si*RR and *CH2CHz-S-SiRR-Si*RR (* = 0 , f,or -1 relative to threemembered ring formation.
Conclusions The present work has expanded upon the earlier thiadisilacyclopropane syntheses to show that sulfur transfer occurs with either exclusive (with sulfur) or predominant (with episulfides) retention of the disilene stereochemistry and that the newly reported structures possess features characteristic of other disilacyclopropane derivatives. Very few studies have been dedicated to disilene reaction mechanisms. However, this work can now serve as a starting point for further mechanistic study which will focus on the reactions of cis- and transl,2-disubstituted episulfides with disilenes.
Experimental Section General Procedures. Reactions and manipulations of disilenes were conducted under a nitrogen atmosphere using standard Schlenk techniques. Solvents were dried over sodium benzophenone ketyl, distilled, and degassed prior to use. Disilenes lb,c were prepared as described in the l i t e r a t ~ r e . ~ ~ ~ ~ J ~ * Commercial episulfides were distilled and degassed prior to use, while the sulfur was purified by sublimation. Chromatography was performed on 20 x 20 cm commercial preparative silica gel plates (Whatman, 60 A, 1000 ,um thickness). Reported melting points are uncorrected. 'H NMR spectra were referenced to residual solvent resonances which were calibrated against tetramethylsilane. 29SiNMR spectra were obtained using INEPT pulse sequences and were referenced t o external tetramethylsilane. NMR-Scale Sulfurization Reactions of IC. A solution of 20 mg (0.035 mmol) of isomerically pure IC(trans as isolated from the original trisilane photolysis, cis from photolysis of pure trans) in ca. 0.75 mL O f benzene& was mixed with either 2 mgatoms of sulfur or 4 mg of propylene sulfide (0.05 mmol, 1.5 equiv) in an NMR tube. The sulfur reaction was complete within minutes, while the episulfide reaction required 4 days. 'H NMR showed isomerically pure products for the reactions of E-lc with both reagents and of 2-lc with sulfur. The reaction ofZ-lc with propylene sulfide gave a cis- and trans2c ratio of 96:4. Characteristic spectra are given below. NMR-Scale Sulfurization Reactions of trans-lb. To 12 mg (0.03 mmol) of pure trans-lb was added 1.0 mL of a 0.05 M solution of ethylene sulfide in benzene-& (0.05 mmol of episulfide, 1.7 equiv). After 2 h, the following NMR spectra, which correspond t o those reported for 2b,l were observed: 'H NMR (C6D6, 200 MHz) 6 6.78, 6.76 (2 9, Mes H), 2.82, 2.77 (2 s, o-Me), 2.08 (s, p-Me), 1.00 (s, t-Bu); 29SiNMR (CsDs, 99.36 MHz) 6 -35.94. NMR-Scale Sulfurization Reactions of EIZ Mixtures of lb. Two solutions of 15 mg of E-lb (0.037 mmol) in 0.75 mL of benzene-& were photolyzed with light of 2. = 350 nm until the E to 2 ratios were (3-3.5):l. One solution with an E to 2 ratio of 3.6:l was treated with 10 mg of sulfur to give a mixture of two compounds assigned as trans- and cis-2b. 'H NMR gave a trans t o cis ratio of 4 . 1 : ~The other solution, containing a 3:l E to 2 ratio was treated with 0.5 mL of a 0.13 M solution of ethylene sulfide (0.065 mmol of ethylene sulfide, 1.8 equiv) in benzene-ds. After several hours the reaction was complete. 'H NMR gave a trans to cis ratio of 3 5 1 . NMR data for cis-2b: 'H NMR (C6D6,200MHz) 6 6.56, 6.46 (2 s, Mes H), 2.69, 2.59 (2 s, o-Me), 1.87 (s,p-Me), 1.25 (s, tBu groups); 29SiNMR (C6D6, 53.67 MHz) 6 -29.63. Preparative Synthesis of cis-2c with Sulfur. Two NMR-scale reactions (40 mg of 2-lc, 0.07 mmol) were combined and concentrated in vacuo. The residue was chromatographed on silica gel in hexanes, giving a central major band
Thiadisilacyclopropanes
Organometallics,
Vol.14, No. 7, 1995 3557
Table 6. Selected Structural Data for 2 2ac trans-2b cis-2cd
dsi-si) (A) 2.289(2) 2.2697(12) 2.318(2) 2.317(2)
trans-2c
2.294(2)
r(S-Si)
(A)
2.161(2) 2.1655(8) 2.159(2) 2.176(2) 2.158(2) 2.178(2) 2.166(2) 2.173(2)
B(Si-S-Si) (deg) 64.0(1) 63.21(4) 64.64(6)
@(Si-Si-S) (deg) 58-00) 58.39(2) 58.03(7) 57.33(7) 58.11(7) 57.27(7) 58.23(6) 57.93(6)
64.62(6) 63.84(6)
D ( S i p (deg) 357.3(2) 357.13(8) 358.0(3) 359.2(3) 358.1(3) 359.2(3) 358.4(3) 358.4(3)
QP(deg) 12.7(3) 0.42(8) 27.5(3) 27.6(3) 8.7(3)
EO(Si) = O(CtBu-Si-CA -+ O(CtB,-Si-Si) + B(Ch-Si-Si). The twist angle, 4, is defined as the average of the torsional angles between cis carbon atoms directly bonded to silicon. Reference 1. There are two molecules per asymmetric unit. Data for molecule A are given first.
Table 6. Selected Sulfur-Carbon Nonbonded Distances (A>in Molecule A of cia-2c S(la)-C(l) S(1a)-C(5a)
3.538(5) 3.259(5)
S(la)-C(2Oa) S(la)-C(24a)
3.222(5) 3.560(5)
which provided 20 mg (47.0%)of cis-2c. Somewhat larger quantities of cis-2c (ca. 50 mg) were obtained by adding an excess of sulfur to the filtrate from the original synthesis/ isolation of E-lc. After 3 h of stirring, the colorless solution was concentrated in vacuo, and the residue was dissolved in boiling diethyl ether. Elemental sulfur crystallized after 24 h a t -25 "C. The mother liquor was removed, and crystals of cis& were isolated after 2 weeks at -25 "C. Analytical data: 'H NMR (C6D.5, 300 MHz) 6 7.03,6.98 ( 2 d, J = 1.8 Hz, 4 H, aromatic H), 4.04 (sept, J = 6.6 Hz, 2 H, ortho isopropyl methine H), 3.34 (sept, J = 6.6 Hz, 2 H, ortho isopropyl methine H), 2.67 (sept, J = 7.0 Hz, 2 H,para isopropyl methine H), 1.32, 1.32, 1.29, 1.29 (s, tBu, 3 d, J = 6.6 Hz, six ortho isopropyl methyl groups, 36 HI, 1.12 (d, J = 7 Hz, 12 H, four para isopropyl methyl groups), 0.96 (d, J = 6.6 Hz, 6 H, two ortho isopropyl methyl groups); 29SiNMR (CsD6, 99.36 MHz) 6 -28.91; exact mass for C38H&Si2 calcd mle 608.4267, found 608.4260; mp 158-161 "C. Preparative Synthesis of trans-2c with Sulfur. An excess of elemental sulfur was added to a solution of E-lc (50 mg, 0.087 mmol) in 15 mL of hexanes, and the mixture was swirled for ca. 1 min. The resulting colorless suspension was concentrated in vacuo, and the residue chromatographed on silica gel in hexanes. The band with the second highest Rf provided 39.7 mg (75.2%) of trans-2c. Analytical data: 'H NMR (C6D6, 300 MHz) d 7.17, 7.12 (2 d, J = 1.5 Hz, 4 H, aromatic H), 4.17 (sept, J = 6.6 Hz, 2 H, ortho isopropyl methine H), 3.76 (sept, J = 6.6 Hz, 2 H, ortho isopropyl methine H), 2.76 (sept, J = 6.9 Hz, 2 H,para isopropyl methine H), 1.60 (d, J = 6.6 Hz, 6 H, two ortho isopropyl methyl groups), 1.52 (d, J = 6.6 Hz, 6 H, two ortho isopropyl methyl groups), 1.39, 1.37 ( 2 d, J = 6.6 Hz, 12 H, four ortho isopropyl methyl groups), 1.19 (d, J = 6.6 Hz, 12 H, four para isopropyl methyl groups), 1.04 (s, 18 H, tBu); 29Si NMR (C6D6, 99.36 MHz) 6 -33.71; exact mass for C38H&Siz calcd mle 608.4267, found 608.4260; mp 231-233 "C.
Preparative Synthesis of cis-2c with Propylene Sulfide. Two NMR-scale reactions (40 mg of 2-lc, 0.07 mmol) were combined and concentrated in vacuo. The residue was chromatographed on silica gel in hexanes. The major band (second highest Rf) provided 21.3 mg (50.5%)of cis-2c.
Preparative Synthesis of trans-2c with Propylene Sulfide. A solution of 100 mg of propylene sulfide (1.35 mmol, 7.8 equiv) in 20 mL of benzene was added to 100 mg of E-lc (0.174 mmol). After stirring for 4 days at 25 "C, the colorless solution was concentrated in vacuo, and the residue was chromatographed on silica gel in hexanes. The fraction with the highest Rf gave 61 mg (57.8%)of trans-2c. X-ray Structure Determinations. X-ray crystallographic analyses were performed on a Siemens P4 diffractometer equipped with a graphite crystal monochromator. Cu K a radiation (A = 1.541 78 b;) was used for all three structures. Suitable crystals of trans-2cwere grown by slow evaporation from n-hexane a t 25 "C, while those of cis-2c were grown from
diethyl ether a t -25 "C, and of trans-2bby slow evaporation from benzene at 25 "C. The orientation matrices and unit cell parameters were determined by the least squares fitting of 36-38 centered reflections (10" 5 0 I27"). Intensities of three standard reflections were monitored evely 100 reflections with a maximum variation of 0.04-0.075. All structures were solved using the SHELXS-86 program.26 The non-hydrogen atoms were refined anisotropically using the SHELXL-93 programz6by full-matrix least squares analysis on F. The applied weighting scheme for all three structures was w-l = a2F02 (XP)~yP, wheren = 0.1014 and y = 2.7839 for tmm2c, x = 0.0870 and y = 6.1493 for cis-ac, and x = 0.0479 and y = 3.2056 for trans-2b and P = (Fo2 2Fc2)/3.z6Extinction corrections were applied with the form Fc* = KFJ1 0.001~F,2~3/sin(20)l-1~4 (ref 27) where x = 0.0024(5)for tram2c, x = 0.00020(3) for cisdc, and x = 0.0008(1) for tmm-2b. The positions of the hydrogen atoms were calculated by idealized geometry and refined using a riding model. Neutral atom scattering factors were taken from ref 28. Space groups Pnma and Pna21 were both possible for cis2c based on the systematic absences. With Z = 8, there would be either one or two molecules, respectively, in the asymmetric units of these space groups. Attempts to solve the structure in Pnma were not successful, whereas solution was readily accomplished in Pna21. Refinement in Pna2l produced correlations in a few of the atomic parameters in the two different molecules. An examination of the packing diagram revealed that no center of symmetry existed along the 21 axis which could relate the two independent molecules, as would be necessary if the space group were truly Pnma. The results on trans-2c revealed that atom C(35) occurred in a major location with a n occupancy of 0.72(2) and a minor location with an occupancy of 0.28(2). Both C(35) and C(35') were refined with isotropic thermal parameters.
+
+
+
+
Acknowledgment. This research was supportedby a grant from the National Science Foundation. Funding for X-ray instruments and computers was provided by the National Science Foundation (Grant CHE-9105497) and the University of Wisconsin. Supporting Information Available: Tables of all bond distances and angles, anisotropic displacement coefficients, and H-atom coordinates and isotropic displacement coefficients and packing diagrams (23 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information. OM9503353 (25) Sheldrick, G. M. Acta Crystallogr. 1990,A46, 467. (26) Sheldrick, G. M. J . Appl. Crystallogr., manuscript in preparation. (27) Larsen, A. C. In Crystallographic Computing; Ahmed, F. K., Ed.; Mundsgaard: Copenhagen, 1970; pp 291-294. (28) International Tables for X-ray Crystallography; Kynoch: Birmingham, U.K.,1992; Vol. C, Tables 6.1.1.4, 4.2.6.8, and 4.2.4.2
(Present distributors: Kluwer, Boston).
