Organometallics 1994, 13, 3715-3727
3715
Syntheses, Structures, and Reactions of Sulfur and Selenium Insertion Products of 1,l-Di-tert-butylsiliranes Philip Boudjouk,*l+Eric Black,? Rajkumar Kumarathasan,? Upasiri Samaraweera,? Stephen Castellino,*??John P. Oliver,*?$and Jeff W. KampP Departments of Chemistry, North Dakota State University, Fargo, North Dakota 58105,and Wayne State University, Detroit, Michigan 48202 Received June 24, 1994@ One-atom and two-atom sulfur and selenium ring expansion products of trans-1,l-di-tert-
butyl-2,3-dimethylsilirane(l),6,6-di-tert-butyl-6-silabicyclo[3.l.0lhexane (41, and 7,7-di-tertbutyl-7-silabicyclo[4.l.0lheptane (7)are prepared by stirring the silirane and the chalcogen in the presence of tetrabutylammonium halide salts and/or alkali-metal halide salts with crown ethers. Potassium fluoride, 18-crown-6,and selenium in benzene react with 1 to give (17)in 85%yield. the novel ring system truns-2,2-di-tert-butyl-3,4-dimethyl-l,2-selenasiletane When tetrabutylammonium chloride (TBAC) is stirred with selenium and 1 or 17 in benzene, truns-3,3-di-tert-butyl-4,5-dimethyl-1,2-diselena-3-silacyclopentane (18)is formed in 87% and 82% yields, respectively. Similar results are observed for analogous reactions with sulfur. The mechanism responsible for the differences in product distributions seems to involve chalcogen activation by salts and crown ethers. Control of chalcogen insertions is demonstrated by reaction of 17 and sulfur in the presence of TBAC, which results in a new ring system, trans-3,3-di-tert-butyl-4,5-dimethyl-l-thia-2-selena-3-silacyclopentane (21)in (2)and cis-7,7-di-tert-butyl64% yield. truns-2,2-Di-tert-butyl-3,4-dimethyl-1,2-thiasiletane 6-thia-7-silabicyclo[3.2.0lheptane(5), prepared from reactions of sulfur with 1 and 4, respectively, are thermolyzed and photolyzed. Products consistent with the generation of a di-tert-butylsilathione fragment are observed, but bimolecular processes are not excluded. Three-dimensional structures of the bicyclic insertion products 7-9,15,and 27 are elucidated using 1D and 2D NMR techniques. Experimental data are correlated with geometries calculated by molecular mechanics methods. The stereochemistries of 4,4-di-tert-butyl-2,3dithia-4-silabicyclo[4.3.0lnonane ( 8 )and of 4,4-di-tert-butyl-2,3-diselena-4-silabicyclo[4.3.01nonane (15),prepared from reactions with 7 and sulfur and selenium, respectively, are further confirmed by single-crystal X-ray crystallography.
Introduction Insertion of sulfur into cyclic carbosilanes is a wellknown and useful method of preparing sulfur-containing heterocyc1es.l With the exception of cis- and trans-1,ldi-tert-butyl-2,3-dimethylsilacyclopropane,2 all known siliranes react with sulfur to give products resulting from insertion of two atoms of sulfur into the Si-C bond without forming a 1,2-thia~iletane.~ In this paper we report the details of the synthesis and characterization of several new compounds resulting from inserting sulfur and selenium atoms into siliranes. The effects of salts on these insertion reactions are also presented, as are detailed structural analyses in the form of two-dimensional NMR studies of 7-9, 16,and 27 in solution and the molecular structures of 8 and 15 using X-ray crystallography. Mechanistic pathways for ring expansion of siliranes, as well as for the thermolytic and photolytic decompositions of some of these ring systems, are discussed. 'North Dakota State University. *Wayne State University. *Abstract published in Advance ACS Abstracts, August 15, 1994. (1)(a) Weidenbruch, M.; Scht8er, A. J . Organomet. Chem. 1964,269, 231. (b) West, R.;Carlson, C. W. Organometallics 1985,2,1798. (c) Dubac, J.;Mazerolles, P. C. R . Seances Acad. Sci., Ser. C 1968,267, 411.
(2)Boudjouk, P.;Samaraweera, U.; Sooriyakumaran, R.; Chrusciel, J.;Anderson, K. R. Angew. Chem., Znt. Ed. Engl. 1988,27,1355. (3)Seyferth, D.; Duncan, D. P.; Haas, C. K. J. Orugnomet. Chem. 1979,164,305.
Results and Discussion Reactions with Sulfur. When sulfur is stirred with approximately 1 equiv of trans-l,l-di-tert-butyl-2,3dimethylsilirane (1) is degassed hexane at room temperature, the sulfur dissolves t o produce a colorless solution. Removal of solvent followed by preparative gas chromatography leads to the isolation of trans-2,2di-tert-butyl-3,4-dimethyl-l,2-thiasiletane (2) and trans3,3-di-tert-butyl-4,5-dimethyl-l,2-dithia-3-silacyclopentane (3)in 60% and 19% yields, respectively (eq l L 4
1
2
3
GC-MS analysis detected a minor product (12%) of slightly longer retention time than 3 with the same molecular weight. Presumably, this is the cis isomer of 3. When thiasiletane 2 is treated with sulfur, 3 is not produced, implying that 3 arises from the direct reaction of 1 and sulfur. When the cis isomer of 1 is used, identical results are obtained, suggesting a stepwise radical mechanism (Scheme l).4 (4) Boudjouk, P.; Samaraweera, U. Organometallics 1990,9,2205.
0276-733319412313-3715$04.50/0 0 1994 American Chemical Society
3716 Organometallics, Vol. 13, No. 9, 1994
Boudjouk et al. Table 1. Effect of Salts on the Insertion of Sulfur into 6,6-Di-tert-butyl-6-silabicyclo[4.l.0]heptane(7)
Scheme 1
salts none KFb
LiCl LiBr LiI NaI NaC104
time, min
yield of 8, %
yield of 9, %
30 30 10 45 45 60 10
120 55 72 68 40
33 9 0 3 5 5 47
44 21
All yields reported are GC yields. 10 mol %; all other salts at approximately 2: 1 mole ratio to silirane.
Fused-ring siliranes follow similar chemistry. For .Olhexane (4) example, 6,6-di-tert-butyl-6-silabicyclo[3.1 Table 2. Effect of Salts and Crown Ethers on the Insertion of Sulfur into l , l - D I - t e r t - b u t y l - 2 9 - d i e ~ y ~ ~(1) r~e reacts with sulfur t o give the thiasiletane, 7,7-di-tertbutylS-thia-7-silabicyclo[3.2.Olheptane ( 5 ) and a twoencry time, yieldof yieldof conditions min 2,% 3, % atom insertion product, cis-8,8-di-tert-butyl-6,7-dithia- no. 8-silabicyclo[3.3.0loctane (61, in 44% and 20% yields, 1 10% KF, 10% 18-crown-6 e1 1W 0 respectively (eq 2). The cis geometries of 5 and 6 were 2 10% LiF, 10% 12-crown-4 1 55 21 3 4 5 6 7 8
\I/
5
4
deduced from 2D NMR experiments (see below). The products of the reaction of sulfur with cis-7,7-di-tertbutyl-7-silabicyclo[4.l.0lheptane(7)differ slightly from those with 4 in that, in spite of repeated attempts to detect one, a monosulfur insertion product was not observed. The products were the disulfur cis (8) and trans (9) isomers (eq 3). Isomer 8 does not convert to 9 under the conditions of the reaction, i.e., stirring of the reagents at room temperature, but will form 9 in 17% yield, at 350 "C.
7
8
9
Effects of Added Salts. Silirane 7 is prepared by the reaction of lithium with di-tert-butyldichlorosilane in the presence of excess cy~lohexene.~ When this product mixture is treated with sulfur, only the cisdisulfur addition product 8 is obtained in 46% yield. This is in sharp contrast to the isomer mixture obtained when sulfur is added to purified 7 (eq 3). Product distributions were monitored for sulfur insertions into samples of 7 that were first distilled, doped with salts, and then treated with sulfur. The results of these studies are summarized in Table 1. Similar observations were recorded for 4. For example, in the absence of a salt, silirane 4 gives 5 and 6, as indicated in Scheme 2. However, if alkali-metal halide is present when sulfur is added, only the monoinsertion product 5 is obtained, The efficiency with which nucleophilic anions suppress 9 suggests that attack by the halide leading to a (5) Boudjouk, P.; Black, E.; Kumarathasan, R. Organometallics 1991, 10, 2095.
9 10 11 12
10% LiCl, 10% 12-crown-4 1O%KF 10%LiF lO%LiCl 10%TBAFb 10%TBAC lO%TBAB lO%TBAP crown, no salt no crown, no salt
10 15 10 15
