Acceptor strengths of some Group IV Lewis acids by electron paramagnetic resonance studies of their complexes with aliphatic nitroxides
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Molecular complexes have been formed between two aliphatic nitroxides, di-tert-butyl nitroxide and 2,2,6,6-tetramethylpiperidine-N-oxyl, and group IV Lewis acids. Analysis of the epr spectra shows that in all cases 1:1 complexes are formed. The π-electron spin density of a nitroxide complex can be analyzed from its epr spectrum and changes in the nitroxide 14N hfs upon complexation are a measure of the acceptor strength of the Lewis acid. For the acids studied here the order of acceptor strength is TiCl4 > SnCl4 > SnBr4 > SiF4 ≳ Sn(t-Bu)2Cr(CO)5 ≈ SiCl4 ≳ GeCl4 ≈ Ti(OPh)4. In some cases epr spectra show the nitroxide and its complex to be in equilibrium and thermodynamic constants for complex formation are obtained. © 1974, American Chemical Society. All rights reserved.
author list (cited authors)
Cohen, A. H., & Hoffman, B. M.