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

Beckmann, Jens, Dakternieks, Dainis, Lim, Allan, Lim, Kieran and Jurkschat, Klaus 2006, Understanding ring strain and ring flexibility in six - and eight-membered cyclic organometallic group 14 oxides, Journal of molecular structure: THEOCHEM, vol. 761, no. 1-3, pp. 177-193.

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Title Understanding ring strain and ring flexibility in six - and eight-membered cyclic organometallic group 14 oxides
Author(s) Beckmann, Jens
Dakternieks, Dainis
Lim, Allan
Lim, Kieran
Jurkschat, Klaus
Journal name Journal of molecular structure: THEOCHEM
Volume number 761
Issue number 1-3
Start page 177
End page 193
Publisher Elsevier BV
Place of publication Amsterdam, The Netherlands
Publication date 2006-03-17
ISSN 1872-8014
0022-2860
0166-1280
Keyword(s) cyclo-Siloxanes
cyclo-Germoxanes
cyclo-Stannoxanes
cyclo-Stannasiloxanes
DFT-calculations
ring strain
Summary 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′H3 and H2M(OH)2 as model compounds. For the six-membered rings, the minimum total angular contribution to ring strain, ERSGmin was calculated to decrease in the order: cyclo-(H2SiO)3 (13.0 kJ mol−1)>cyclo-H2Sn(OSiH2)2O (7.0 kJ mol−1)>cyclo-H2Ge(OSiH2)2O (4.9 kJ mol−1)>cyclo-H2Si(OSnH2)2O (3.4 kJ mol−1)>cyclo-(H2SnO)3 (1.7 kJ mol−1)>cyclo-H2Si(OGeH2)2O (0.8 kJ mol−1)≈cyclo-H2Ge(OSnH2)2O (0.7 kJ mol−1)>cyclo-H2Sn(OGeH2)2O (0.1 kJ mol−1)≈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)2SiH2 (a=0.959)<cyclo-(H2SiO)2(H2SnO)2 (a=0.942)< cyclo-H2Si(OSnH2O)2SiH2 (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.
Language eng
Field of Research 039904 Organometallic Chemistry
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2006, Elsevier B.V.
Persistent URL http://hdl.handle.net/10536/DRO/DU:30003833

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