Organometallics 1994,13, 795-801
795
Synthesis and Structure of all-trans-1,2,3,4-Tetra-tert-butyl-1,2,3,4-tetrachlorocyclotetrasilane Soichiro Kyushin, Motoo Kawabata, Haruaki Sakurai, Hideyuki Matsumoto,' Michihiro Miyake, and Mitsuo Sat0 Department of Applied Chemistry, Faculty of Engineering, Gunma University, Kiryu, Gunma 376,Japan
Midori Goto National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305,Japan Received September 14, 1995 The synthesis of all-trans-[(t-Bu)ClSi14 (1) via chlorodephenylation of [(t-Bu)PhSi], with HCl/AlCl3 is described. Three isomers of [(t-Bu)PhSi]d (cis-cis-trans-2, cis-trans-cis-2, and all-trans-2) were separated, and each of them was subjected to chlorodephenylation. The X-ray structures are reported for cis-cis-trans-%and cis-trans-cis-2. Crystal data for cis-cis-trans-2: monoclinic, R 1 / c , a = 20.924(10) A, b = 10.813(5) A, c = 19.443(11) A, j3 = 117.57(3)", V = 3900(3) A3,Z = 4, R = 0.047, R, = 0.047 for 2572 reflections. Crystal data for cis-trans-cis-2: monoclinic, R 1 / n , a = 15.407(4)A,b = 23.798(6) A,c = 10.852(2)A,j3 = 94.93(2)', V = 3964(2) A3,Z = 4, R = 0.043,R, = 0.046 for 2905 reflections. The chlorodephenylation of cis-cis-trans-2, cis-trans-cis-2, and all-trans-2 gave 1 exclusively. The structure of 1 was established by X-ray crystallography. Crystal data for 1: orthorhombic, Pca21, a = 14.848(2) A, b = 13.719(1) A,c = 13.074(4)A, V = 2663(1) A3, 2 = 4, R = 0.052, R, = 0.077 for 1992 reflections. 1 has a folded structure, the dihedral angle being 26.6",which accommodates the chlorine atoms in pseudoaxial positions and the tert-butyl groups in less hindered pseudoequatorial positions. The principal average bond distances are Si-Si 2.375 A, Si-C 1.905 A, and Si-C12.086 A. The Si-C1 bond distances are somewhat longer than usual.
Introduction
X-ray structure of 1 was not de~cribed.~ In an attempt to prepare 1, we studied the replacement of phenyl groups As part of an ongoing investigation of the chemistry of by chlorine atoms in the cyclotetrasilane [(t-Bu)PhSiIr polycyclopolysilanes,l we have attempted to develop a (2). The earlier paper from our laboratory reported the convenient method for the synthesis of sila-functional synthesis of 2 by reductive coupling of (t-Bu)PhSiClzwith cyclotetrasilanes of the type [R(Cl)SiId,which would serve lithium.6 However, compound 2 was identified as a mixture of the four possible isomers by spectroscopy, and as building blocks in the preparation of octasilacubanes the mixture was not separated into individual isomers by and ladder polysilanes. Although a variety of alkyl- and chromatography? In this work, three isomers of 2, cisaryl-substituted cyclotetrasilanes have been synthesized cis-tram-2, cis-tram-cis-2,and all-trans-2, were separated because of interest in their structures and properties,2the and each of them was subjected to chlorodephenylation cyclotetrasilane [R(Cl)Si14 has not yet been reported with HC1/A1C13.6 We found that the chlorodephenylation except for one case. Thus, Masamune and co-workers reported that the reaction of 1,2-di-tert-butyl-l,1,2,2- proceeded smoothly to give 1 in high yield. In this paper, we present the following new information: (1)the X-ray tetrachlorodisilanewith lithium naphthalenide had given structures of cis-cis-trans-2 and cis-tram-cis-2; (2)sterall-tram-[(t-Bu)ClSi]4 (1) in 8-20% yields as well as tricyclo[2.2.0.02~slhexasilane and tetracyclo[3.3.0.02~7.03~61- eochemistry of the chlorodephenylation of cis-cis-trans2, cis-trans-cis-2,and all-tram-2; (3)the X-ray structure ~ctasilane.~ However, even in this single example, the of 1. .Abstract published in Advance ACS Abstracts, January 15, 1994. (1) Nagai, Y.;Watanabe, H.; Mataumoto, H. Synthesis and Properties of Strained Cyclopolysilanes. In Silicon Chemistry;Corey, J. Y., Corey, E. R., Gaspar, P. P., Ede.; Ellis Horwood: Chichester, 1988; Chapter 24 and references therein. (2) (a) Hurt, C. J.; Calabrese, J. C.; West, R. J. Organomet. Chem. 1975,91,273. (b) Biernbaum, M.; West, R. J. Organomet. Chem. 1977, 131,179. (c) Biembaum, M.; West, R. J . Organomet. Chem. 1977,131, 189. (d) Parkanyi, L.; Sasvari, K.; Barta, I. Acta Crystallogr. 1978, B34, 883. (e) Chen, Y.-S.; Gaspar, P. P. Organometallics 1982, I, 1410. (f) Helmer, B.J.; West, R. Organometallics 1982,1,1458. (g) Mataumoto, H.; Minemura, M.; Takatauna, K.; Nagai, Y.; Goto, M. Chem.Lett. 1985, 1006. (h) Mataumoto,H.; Takateuna, K.; Minemura,M.; Nagai, Y.; Goto, M. J . Chem. SOC.,Chem. Commun. 1985,1366. (i) Watanabe, H.; Kato, M.; Okawa, T.;Kougo, Y.; Nagai, Y.; Goto, M. Appl. Organomet. Chem. 1987,1, 157. (j)Weidenbruch, M.; Thom, K.-L.; Pohl,S.;Saak, W. J. Organomet. Chem. 1987,329,151. (k) Chrusciel,J.; Cypryk,M.; Fossum, E.; Matyjaszewski, K. Organometallics 1992,11,3257. (3) Kabe, Y.; Kuroda, M.; Honda, Y.; Yamashita, 0.;Kawase, T.; Masamune, S.Angew. Chem., Znt. Ed. Engl. 1988,27, 1725.
Results and Discussion Crystal Structures of cis-cis-trans-[(t-Bu)PhSi]4 and cis-trans-cis-[(t-Bu)PhSi]d. Cyclization of (t-Bu)PhSiCla with an excessof lithium metal in tetrahydrofuran (THF) at -10 "C gave a 50% yield of [(t-Bu)PhSi], (2). This represents a substantial improvement over the 32% (4) Masamune et al. attempted X-ray structure determination for 1 and noted that, although strong diffractions of heavy atom (Si, C1) produced a satisfactory solution of the Si framework, severe dieordering of tert-butyl groups had resulted in a moderate quality of the refinement (Rvalue was not described).a (5) Mataumoto, H.;Sakamoto, A.; Minemura, M.; Sugaya, K.; Nagai, Y. Bull. Chem. SOC.Jpn. 1986,59,3314. (6)Tamao, K.; Kumada, M. J. Organomet. Chem. 1971, 30, 339.
0276-733319412313-0795$04.50/0 0 1994 American Chemical Society
Kyushin et al.
796 Organometallics, Vol. 13, No. 3, 1994
Scheme 1
1
cis-cis-trans-2 (16%)
I
cis-trans-cis-2 ( 2 % )
I I
1
all-frans-2 ( 3 3 % )
yield previously reportedS6 Three of the four possible isomers, cis-cis-trans-2, cis-trans-cis-2, and all-trans-2, could easily be separated by reverse-phase recycle-type HPLC; yields of 16% (cis-cis-trans-2), 2 % (cis-trans-cis2), and 33% (all-trans-2) were obtained (Scheme 1). The structures of cis-cis-trans-2and cis-trans-cis-2 were confirmed by X-ray crystallography.7-8 In Figures 1 and 2, the structures of cis-cis-trans-2 and cis-trans-cis-2 are shown. Crystallographic data, positional parameters, and selected bond distances and angles are given in Tables 1-5. Both molecules adopt folded conformations, the dihedral angles being 27.7O in cis-cis-trans-2 and 32.8' in cis-trans-cis-2. By comparison, the corresponding angles and 12.8O in (Phzare 36.8O in all-tran~-[(t-Bu)MeSi]4~~ Si)4.2d The Si-Si bond distances range from 2.419(2) to 2.432(2) A in cis-cis-trans-2 with an average of 2.423 A, and in cis-trans-cis-2 they range from 2.421(2) to 2.429(2) A with an average of 2.424 A. These values fall into the longer range of the reported values for cyclotetrasilanes, e.g., 2.377 A in all-trans-[(t-B~)MeSi14~~ and 2.445 A in cis-cis-trans- [ (t-Bu)(c-CaHn)Si]4.2j In cis-cis-trans-t , the molecule exists in a relatively stable conformation, in which three tert-butyl groups occupy pseudoequatorial positions and one tert-butyl group occupies a pseudoaxial position, in order to minimize steric repulsion among the tert-butyl groups. In cis-trans-cis-2, two neighboring tert-butyl groups occupy pseudoequatorial positions and the remaining two tert-butyl groups occupy pseudoaxial positions. In Figure 3, UV spectra of cis-cis-trans-2, cis-transcis-2, and all-trans-2 are shown. Although absorption spectra of the stereoisomers of 2 are rather different, absorption bands extend to the wavelength region of ca. 350 nm in every case. The lowest energy transitions occur at 318 nm (e 500) in cis-cis-trans-2,319 nm (e 650) in cistrans-cis-2, and 319 nm (e 1500) in all-trans-2. The wavelength may be compared with that of all-trans-[(tBu)MeSiIr (Amm 300 nm, t 290).2b Probably, increasing strain in the silicon framework in [(t-Bu)PhSi], or the (7) The structure of all-trans-2 is assigned by NMR spectroscopy (ExperimentalSection). 'H,W ,and "Si NMR indicate the presence of only one kind of tert-butyl group, one kind of phenyl group, and one kind of silicon atom, allowing the assignment to all-trans or all-cis structures. By considering the steric repulsion among tert-butyl groups, we assign the structureto all-trans. An X-ray structuredeterminationis underway, and the preliminary results indicate the all-trans structure. (8)A reviewer has commented that cis-trans-cis4 can be present in two different noneuperimposable (diastereomeric)Structures with equivalent energy because the flipping of the cyclotetrasilane ring should not occur in the solid state, and that reviewer has questioned why only one isomer appears to be present in crystalline cis-trans-cia-2. However, in actuality, we could not observe the formation of two kinds of crystals of cis-trans-cis-2,and only one kind of prism was obtained, the structure of which is discussed in the text.
cfi 3)
Figure 1. ORTEPII drawing of cis-cis-trans-2projected on the ab plane. Thermal ellipsoids are drawn at the 30% probability level. CI381
24)
:(23)
Figure 2. ORTEPII drawing of cis-trans-cis-2projected on the ab plane. Thermal ellipsoids are drawn at the 30% probability level. interaction between the silicon-silicon u bonds and the benzene rings is responsible for the shift of the absorption maxima to the longer wavelengths and the increase of the extinction coefficients. Synthesis and Structure of 1. Chlorodephenylation of cis-cis-trans-2, cis-trans-cis-2, and all-trans-2 could be effected by passing dry HC1 at room temperature through its solution in benzene containing AlC13. It is noted that catalytic amounts of AlC13 were ineffective and that more than 0.5 equiv facilitated the chlorodephenylation. When cis-cis-trans-2 was subjected to chlorodephenylation, the reaction reached completion in 2 h and all-trans-[(t-Bu)ClSi14 (1) was obtained in 83% yield as the sole product. Similarly, chlorodephenylation of cis-trans-cis-2 and alltrans-2 produced 1 in 74 and 89 % yields, respectively. We found that the stereochemical course of the reaction was unaffected by reaction times. For example, when the reaction was quenched before complete consumption of the starting material, 1 was observed as the single stereoisomer. The result suggests that the inversion on the silicon atoms occurred rapidly to reach equilibrium during chlorodephenylation, in which the all-trans isomer
Organometallics, Vol. 13,No.3,1994 797
All-Trans Substituted Cyclotetrasilane
Table 1. Summary of Crystal Data, Data Collection,and Refinement cis-cis-tram-2 formula mol wt cryst descr cryst size, mm cryst syst space group a, A
b, A c, A A deg
v,A3
Z Dmead, mg
IO^, mg m-3
diffractometer radiation (A, A) fi, mm-1 abs corr variation of stds 28 range, deg range of h range of k range of I scan type scan width, deg no. of rflns measd no. of indep rflns no. of obsd rflns (pol 2 3dFo))
CNHS~S~~ 649.23 colorless prisms 0.4 X 0.8 X 0.25 monoclinic n1/c 20.924( 10) 10.813(5) 19.443(11) 117.57(3) 3900(3) 4 1.101 1.106
cis-tram-cis-2 Crystal Data CoHssSi4 649.23 colorless prisms 0.4 X 0.5 X 0.7 monoclinic
1
CisHasC4S4 482.62 colorless prisms 0.6 X 0.6 X 0.8 orthorhombic Pca2l 14.848(2) 13.719(1) 13.074(4)
Rigaku AFC-6 Mo Ka (0.7107) 0.1724 none
