Tetraasterane. Assignment DaMocles Supervising tutor: Prof. Dr. Fessner. Marvin Bergmann. Fabian Bär. Thomas Heydt.

Transcription

1 Assignment DaMocles Tetraasterane Supervising tutor: Prof. Dr. Fessner Marvin Bergmann Fabian Bär Thomas Heydt Ben Kühne Assignment DaMocles Tetraasterane 1

2 1. Introduction In context of the assignment DaMocles in the summer term of 2010 at Technische Universität Darmstadt under direction of Prof. Dr. Fessner of the Department of Organic Chemistry and Biochemistry we present the molecule tetraasterane. The molecule can be considered as cubane which is linked by one methylene bridge or as two cyclohexane molecules in boat conformation, attached via four C-C-bonds. 2. History Tetraasterane appeared the first time in 1965 in a paper by Hans Musso about asteranes in general. The name asterane is derived from the latin astrum which means star due to its characteristic star-like structure. After a guest professorship at the Department of Chemistry, at the University of Wisconsin, Madison, U.S.A. Musso established a new field of research by synthesizing highly symmetric cyclic hydrocarbons with Hans-Martin Hutmacher at the Department of Organic Chemistry at Universität Karlsruhe. The synthesis of tetraasterane however did not succeed until Other asteranes, such as triasterane were already synthesized in 1967 by Musso and Hutmacher. A silicon analogue of tetraasterane was already made and isolated in 1968 by Prof. Dr. G. Fritz, Dr. R. Haase and Dr. H. Scheer of the Department of Inorganic Chemistry at Universität Karlsruhe. The present interest in tetraasterane is in terms of quantum chemistry as there are short bond angles and consequently high strain energies within the molecule. Assignment DaMocles Tetraasterane 2

3 Silicon analogue by Prof. Dr. G Fritz, Dr. R. Haase and Dr. H Scheer 1968 [4] 3. Data The 13 C-NMR shows two peaks. The first one with a chemical shift of 27.5 ppm is a result of the four carbon atoms outside of the cubane while the second peak with a chemical shift of 41 ppm is an outcome of the eight carbon atoms of the cubane. The integrals correspond in the same way as there is a proportion of 1:2. 13 C-NMR of tetraasterane The 1 H-NMR shows two multiplets. One is generated by the protons of the methylene bridges that link the cubane while the other one is the result of the hydrogen nuclei within the cubane. The multiplets are created by the interconnection of the hydrogen Assignment DaMocles Tetraasterane 3

4 nuclei of the cubane and the methylene bridges. The methylene bridges do not interconnect with each other as the distance over three C-C-bonds is too far and the protons within the cubane do not interlink because of the equivalence in symmetry. 1 H-NMR of tetraasterane Point Group: D 4h Symmetry elements: 4 C 2 ; 1 C 4 ; i ; 1σ h ; 4 σ v ; 1 S 4 Physical data: Molecular formula: C 12 H 16 IUPAC-Name: Pentacyclo-[ ,7.0 4,11.0 5,10 ]dodecane CAS: Molar mass: g/mol Melting point: theoretical: C C experimental: C Density (calculated): 1.7 g/cm g/cm3 Vaporization enthalpy (calculated): kj/mol Theoretical data was calculated with Advanced Chemistry Development Software V9.04 ( ACD/Labs) and the NMR-spectra with Version Advanced Chemistry Development Software V9.07 ( ACD/Labs). Assignment DaMocles Tetraasterane 4

5 4. Synthesis [2] 1.Step: [2+2] Cycloaddition in ether, acetone and dioxane 3,6-Benzenedicarboxylic anhydride Tetraasteranecarboxylic anhydride 2.Step: Saponification Tetraasteranecarboxylic anhydride Tetraasterane-1,4,5,8-tetracarboxylic acid 3.Step: Grob-Decomposition [5] Tetraasterane-1,4,5,8-tetracarboxylic acid Tetraasterane tetrachloride 4.Step: Dehalogenation Tetraasterane tetrachloride Tetraasterane Assignment DaMocles Tetraasterane 5

6 5. Quantum Mechanics [6] Interaction of atoms in a molecule can be calculated if the three dimensional structure is known. In tetraasterane the quantum mechanical parameters are MM3 calculations. This method uses the characteristic force field of every atom which is interacting with the other atoms around resulting in specific parameters such as bond length, bond angle or strain energy and van der Waals forces. Some parameters are shown in the following table: Bond length [Ȧ] Bond angle Strain energy [kj/mol] r (C-C) ring C r -C r -CH E Strain. (total) r (C-CH 2 ) M-C r -CH E Compr r (C br C br ) 2.82 C-CH 2 -C E Bend r (H br H br ) 2.49 H-C-H E Tors Flip E vdw.(1,4) The increased torsional energy is caused by the bonds in the four-membered rings with an orthogonal angle. The two rings can be contemplated as two cyclobutane molecules which are structurally forced to be planer and that is the main reason for the high strain energy in tetraasterane. The form of the six-membered rings reminds of cyclohexane in a free boat conformation. The flip angle is almost the same and the methylene bridges in tetraasterane have got an ideal tetrahedron angle which results in minor steric and van der Waals repulsion. 6. Works Cited [1] ASTERANE, U. Biethan, U.V. Glzyoki and H. Musso Tetrahedron Letters, No.20, p , Pergamon Press Ltd [2] Tetraasteran,Hans-Martin Hutmacher, Hans-Günter Fritz and Hans Musso, AngewandteChemie, 87. Jahrg. 1975, Nr. 5 [3] Dictionary of organiccompounds: Phl-Z, P Z , Band 6, S.5766 [4] Ein Carbosilan mit Asteran-Struktur, G. Fritz, R. Haase and H. Scheer, Angewandte Chemie, 80. Jahrgang 1968, Nr. 10 S. 397 [5] Synthesis 1973 s.493 von K.B. Becker, M. Geisel, C.A. Grob and F. Kuhnen [6] TheMolecularStructure of Triasterane: An Experimental and TheoreticalStudy,B. Ahlquist, A. Almenningen, B. Benterud, M. Trztteberg, P. Bakken, W. Luttke, Chem. Ber. 1992, 125, VCH Verlagsgesellschaft mbh, D-6940 Weinheim, 1992 Assignment DaMocles Tetraasterane 6