title: Structure, strain, and degenerate rearrangement of tricyclo[2.1.0.0 1,3]pentasilane and related molecules.
abstract: We theoretically investigate a highly strained tricyclic silane (tricyclo[2.1.0.0 1,3]pentasilane (4b), an isomer of pentasila[1.1.1]propellane (3b)) composed of three fused three-membered rings. The central ring is distorted. One of the fusion bonds in the central ring is shorter than the normal Si-Si single bond (2.350 A) whereas the other is as long as the fusion bonds in bicyclo[1.1.0]tetrasilane (2b) (2.860 A) and 3b (2.778 A). The tricyclic silane is less strained than the carbon congener and more strained than the isomer 3b. The electron delocalization between one of the fusion bonds and the geminal Si-Si ring bonds elongates the fusion bond and stabilizes the molecules to reduce the strain. The silanes composed of the fused three-membered rings are less strained than the carbon congener. A degenerate rearrangement of a three-membered ring is predicted. The enthalpy of activation of the rearrangement of the distorted central ring is low (7.2 kcal/mol) for 4b, but appreciable (22.3 kcal/mol) for the germanium congener, tricyclo[2.1.0.0(1,3)]pentagermane (4c). We investigate the effects of the substituents on the distortion of the central three-membered ring and the degenerate rearrangement.
authors.affiliation: Department of Chemistry, Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Takeuchi
authors.forename: Daijiro
authors.initials: D
authors.lastname: Uemura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Inagaki
mesh_terms: D005857:Germanium / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D017646:Organosilicon Compounds / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D017646:Organosilicon Compounds; D011083:Polycyclic Compounds; D012821:Silanes; C521890:tricyclo(2.1.0.0 1,3)pentasilane; C521891:tricyclo(2.1.0.0(1,3))pentagermane; D005857:Germanium