NMR Investigations of the intra- and intermolecular exchange phenomena of the 3,5-dimethylpyrazolylsilane ClSi(pz*) and related compounds


NMR Investigations of the intra- and intermolecular exchange phenomena of the 3,5-dimethylpyrazolylsilane ClSi(pz*) and related compounds

Bitto, F.; Kretzschmar, J.; Brendler, E.; Kroke, E.

Chlorine substituted 3,5-dimethylpyrazolyl (pz*) silanes exhibit interesting inter- and intramolecular exchange phenomena. Intermolecular reactions involving Si-N vs. Si-Cl dismutation cause equilibria between the three species Cl2Si(pz*)2, ClSi(pz*)3 (main component) and Si(pz*)4. Intramolecular exchange is interpreted as a “dangling” of the pz*-moieties in every pyrazolyl silane molecule itself.[1] These phenomena were investigated with one and two dimensional NMR spectroscopic methods at variable temperatures. The “dangling” of the pz*-moieties is slowed down with decreasing temperature and are best visible in the spectra recorded at -40°C. The use of 1H-29Si-HMBC spectroscopy (heteronuclear multiple bond correlation) allows to assign the olefinic protons to the corresponding silicon species. In the EXSY (exchange spectroscopy) spectra the exchange between the pz*-methyl groups and the NOE (nuclear overhauser effect) correlation between the methyl groups and the olefinic protons are observed at the same time in one spectrum. The data obtained with EXSY and HMBC-spectroscopy in combination with variable temperature 1H NMR allows qualitative conclusions concerning the rate of exchange and the dependence on the silicon corresponding species.

[1] F. Bitto, J. Wagler, E. Kroke, Eur. J. Inorg. Chem. 2012, in press, doi:10.1002/ejic.201101409.

Keywords: NMR spectroscopy; H,Si-HMBC; H,H-NOESY, H,H-EXSY; 3,5-dimethylpyrazolyl silanes

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