Highly asymmetric coordination in alkenes: Gas-phase structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene

Lorna J. McLachlan, Sarah L. Hinchley, David W.H. Rankin, Carole A. Morrison, Heather E. Robertson, Norbert W. Mitzel, Christoph RUdinger, Hubert Schmidbaur

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Abstract

The molecular structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene have been determined by gas-phase electron diffraction (GED) and ab initio molecular orbital calculations (MP2/6-311G*). Both compounds were found to have highly asymmetric coordination around the carbon atoms with [ab initio (re)/GED (ra)] C=C-Cl [117.0/117.0(2)°] and C=C-Si [126.2/128.1(1)°] in the C2h structure of trans-1,2-dichloro-1,2-disilylethene and C=C-Br [119.2/120.7(4)°] and C=C-Si [125.0/125.0(4)°] in the Cs structure of 1-bromo-1-silylethene. Other important structural parameters for trans-1,2-dichloro-1,2-disilylethene are C=C [135.2/134.5(3) pm], C-Si [189.4/ 187.9(2) pm], and C-Cl [175.1/174.9(1) pm], and C=C [134.2/133.4(2) pm], C-Si [187.8/187.2(3) pm], and C-Br [191.3/191.0(3) pm] for 1-bromo-1-silylethene. Further ab initio calculations were carried out on CH2CRX and trans-(CRX)2 (R = SiH3, CH3, or H; X = H, F, Cl, or Br) to gauge the effects of electron-withdrawing and electron-donating groups on the structures. They reveal some even more distorted structures. The asymmetric appearance of these molecules can largely be accounted for by valence shell electron pair repulsion theory.

Original languageEnglish
Pages (from-to)6539-6544
Number of pages6
JournalInorganic Chemistry
Volume42
Issue number20
DOIs
StatePublished - 6 Oct 2003
Externally publishedYes

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