Understanding ring strain and ring flexibility in six- and eight-membered cyclic organometallic group 14 oxides

被引:16
作者
Beckmann, J
Dakternieks, D
Lim, AEK
Lim, KF
Jurkschat, K
机构
[1] Deakin Univ, Ctr Chiral & Mol Technol, Geelong, Vic 3217, Australia
[2] Univ Dortmund, Fachbereich Chem, Lehrstuhl Anorgan Chem 2, D-44221 Dortmund, Germany
来源
JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM | 2006年 / 761卷 / 1-3期
基金
澳大利亚研究理事会;
关键词
cyclo-siloxanes; cyclo-germoxanes; cyclo-stannoxanes; cyclo-stannasiloxanes; DFT-calculations; ring strain;
D O I
10.1016/j.theochem.2006.01.003
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
A simple model was developed for the approximation of ring strain energies of homo- and heterometallic, six- and eight-membered cyclic organometallic group 14 oxides and the degree of puckering of their ring conformations. The conformational energy of a ring is modelled as the sum of its angular strain components. The bending potential energy functions for the various endocyclic M-O-M' and O-M-O linkages (M, M' = Si, Ge, Sn) were calculated at the B3LYP/(v)TZ level of theory using H3MOM'H-3 and HZM(OH)(2) as model compounds. For the six-membered rings, the minimum total angular contribution to ring strain, E-RSGmin was calculated to decrease in the order: cyclo-(H2SiO)(3) (13.0 kJ mol-(1))> cyclo-H2Sn(OSiH2)(2)O (7.0 kJ mol-(1))> cyclo-H2Ge(OSiH2)(2)O (4.9 kJ mol-(1))> cyclo-H2Si(OSnH2)(2)O (3.4 kJ mol(-1))> cyclo-(H2SnO)(3) (1.7 kJ mol(-1))> cyclo-H2Si(OGeH2)(2)O (0.8 kJ mol(-1))=cyclo-H2Ge(OSnH2)(2)O (0.7 kJ mol(-1))> cyclo-H2Sn(OGeH2)(2)O (0.1 kJ mol(-1))approximate to cyclo-(H2GeO)(3) (0 kJ mol(-1)). All of the six-membered rings were predicted to adopt (nearly) planar conformations (a=0.996 < a < 1). By contrast, all eight-membered rings were predicted to adopt strainless, but puckered conformations. The degree of puckering was predicted to increase in the order: cyclo-(H2SiO)(4) (a=0.983)< cyclo-H2Sn(OSiH2O)(2)SiH2 (a=0.959)< cyclo-(H2SiO)(2)(H2SnO)(2) (a=0.942)< cyclo-H2Si(OSnH2O)(2)SiH2 (a=0.935)< cyclo-(H2SnO)(4) (a=0.916)< cyclo-(H2GeO)(4) (a=0.885). The differences in ring strain and the degree of puckering were linked to the different electronegativities of Si, Ge and Sn. The results obtained are consistent with experimental ring strain energies; reactivities towards ring opening polymerizations or ring expansion reactions and observed ring conformations of cyclic organometallic group 14 oxides. (c) 2006 Elsevier B.V. All rights reserved.
引用
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页码:177 / 193
页数:17
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