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Is Tetrasilatetrahedrane Kinetically Stable?†
Prof. Dr. Shigeru Nagase,
Mari Nakano,
Corresponding Author
Prof. Dr. Shigeru Nagase
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)Search for more papers by this authorMari Nakano
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)
Search for more papers by this authorProf. Dr. Shigeru Nagase,
Mari Nakano,
Corresponding Author
Prof. Dr. Shigeru Nagase
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)Search for more papers by this authorMari Nakano
Department of Chemistry, Faculty of Education, Yokohama National University, Yokohama 240 (Japan)
Search for more papers by this author†
This work was supported in part by a grant from the Ministry of Education, Science, and Culture in Japan. Calculations were carried out at the Computer Center of the Institute of Molecular Science and the Computer Room of the Faculty of Education of Yokohama National University.
Graphical Abstract
The answer is probably no, even though it violates common expectations. Calculations on 1–3, taking into consideration electron correlation, gave 1 as the highest-energy species at all levels of approximation. This reflects once again the fact that—in contrast to the carbon analogues—Si3 rings are more highly strained than Si4 rings.
References
- 1For reviews, see (a)
A. Greenberg,
J. F. Liebman:
Strained Organic Molecules,
Academic Press, New York
1978;
(b)
N. S. Zefirov,
A. S. Koz'min,
A. V. Abramenkov,
Russ. Chem. Rev. (Engl. Transl.)
47
(1978) 163;
10.1070/RC1978v047n02ABEH002209 Google Scholar(c) G. Maier, Angew. Chem. 100 (1988) 317; Angew. Chem. Int. Ed. Engl. 27 (1988) 309.
- 2For the synthesis and characterization of bicyclic silicon compounds, see S. Masamune, Y. Kabe, S. Collins, D. J. Williams, R. Jones, J. Am. Chem. Soc. 107 (1985) 5552; R. Jones, D. J. Williams, Y. Kabe, S. Masamune, Angew. Chem. 98 (1986) 176; Angew. Chem. Int. Ed. Engl. 25 (1986) 173; H. Matsumoto, H. Miyamoto, N. Kojima, Y. Nagai, J. Chem. Soc. Chem. Commun. 1987, 1316; H. Matsumoto, H. Miyamoto, N. Kojima, Y. Nagai, M. Goto, Chem. Lett. 1988, 629.
- 3 D. A. Clabo Jr., H. F. Schaefer III, J. Am. Chem. Soc. 108 (1986) 4344.
- 4 A. F. Sax, J. Kalcher, J. Chem. Soc. Chem. Commun. 1987, 809.
- 5 W. W. Shoeller, T. Dabisch, T. Busch, Inorg. Chem. 26 (1987) 4383; T. Dabisch, W. W. Schoeller, J. Chem. Soc. Chem. Commun. 1986, 896.
- 6(a) S. Nagase, M. Nakano, T. Kudo, J. Chem. Soc. Chem. Commun. 1987, 60; (b) S. Nagase, T. Kudo, Organometallics 6 (1987) 2456; (c) J. Chem. Soc. Chem. Commun. 1988, 54
- 7 The strain energy is as large as 141 kcal mol−1 in 1 [6a]. In constrast, silicon compounds consisting of four-membered rings possess considerably smaller strain energies: for example, octasilacubane (being 94 kcal mol−1 strained) is 65 kcal mol−1 less strained than cubane and forms an interesting synthetic target [6a].
- 8See also
P. von R. Schleyer,
A. F. Sax,
J. Kalcher,
R. Janoschek,
Angew. Chem.
99
(1987) 374;
10.1002/ange.19870990434 Google ScholarAngew. Chem. Int. Ed. Engl. 26 (1987) 364; P. von R. Schleyer, R. Janoschek, Angew. Chem. 99 (1987) 1312;10.1002/ange.19870991227 Google ScholarAngew. Chem. Int. Ed. Engl. 26 (1987) 1267; Ref. [5].
- 9Si-Si bonds are ca. 14 kcal mol−1 weaker than CC bonds: R. Walsh, Acc. Chem. Res. 14 (1981) 246.
- 10The program used is GAUSSIAN 82 developed by J. S. Binkley, M. J. Frisch, D. J. DeFrees, K. Rahgavachari, R. A. Whiteside, H. B. Schlegel, E. M. Fludre, J. A. Pople, Department of Chemistry, Carnegie-Mellon University, Pittsburgh, USA. For the basis sets employed, see M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. DeFrees, J. A. Pople, J. Chem. Phys. 77 (1982) 3654; M. J. Frisch, J. A. Pople, J. S. Binkley, J. Chem. Phys. 80 (1984) 3265.
- 11 For example, see p. 90 in Ref. [1a].
- 12 We also located a stationary point for a structure with D2d symmetry which corresponds to the simultaneous breaking of two Si-Si bonds. This stationary point (with two Si-Si bonds stretched to 2.612 Å) was only 3.7 kcal mol−1 less stable than 2 at the HF/6-31G(d) level but had two imaginary frequencies; one of these frequencies was associated with distortion to 2.
- 13 H. Kollmar, F. Carrion, M. J. S. Dewar, R. C. Bingham, J. Am. Chem. Soc. 103 (1981) 5292, and references cited therein.
- 14(a) R. Seeger, J. A. Pople, J. Chem. Phys. 66 (1977) 3045; (b) for the current topics of the HF instability problem, see J. Paldus, J. Cizek, Can. J. Chem. 63 (1985) 1803, and references cited therein.
- 15(a) For MP, see J. A. Pople, J. S. Binkley, R. Seeger, Int. J. Quantum Chem. Symp. 10 (1976) 1; (b) for CI, see J. A. Pople, R. Seeger, R. Krishnan, Int. J. Quantum Chem. Symp. 11 (1977) 149.
- 16 In order to check the effect of electron correlation on the geometry optimization, the structure of 1 was reoptimized at the MP2 level with the 6–31G(d) basis set. However, the resltant MP2 optimized structure (Si-Si = 2.316 and Si-H = 1.478 Å) differed little from the corresponding HF optimized structure (Si-Si = 2.314 and Si-H = 1.464 Å) and its MP2 energy (-1158.14842 au) was 2.1 kcal mol−1 higher than the MP2 energy of 2 calculated even on the HF/6–31G(d) optimized structure of 2.
- 17 An equatorial arrangement of the hydrogens results in a less stable minimum D2 structure which correlates in symmetry with 4 in Figure 2. On the other hand, a C2v transition structure results by arranging two hydrogens in equatorial positions and two other hydrogens in axial positions, which leads to a Cs structure as described in the text. However, it should be noted that the rearrangements of 3 to the D2 and C2v structures are both symmetry forbidden.
- 18The stability analyses of 3 and 4 show that the HF solutions (being singlet stable but non-singlet unstable [14b]) are unstable with respect to the spin density wave (SDW) solutions. This suggests that the four-membered rings of 3 and 4 have some tetraradical character (antiferromagnetic electron-spin localization onto each Si) and more sophisticated treatments of electron correlation may be essential for their relative energies. For some hexaradical character and puckering of the six-membered ring in hexasilabenzene, see S. Nagase, H. Teramae, T. Kudo, J. Chem. Phys. 86 (1987) 4513.
- 19 B. F. Yates, D. A. Clabo, H. F. Schaefer III, Chem. Phys. Lett. 143 (1988) 421.
