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Composés d'addition des halogénures de niobium(V) et de tantale(V). V. Stabilité relative des composés des chlorures avec quelques oxydes et sulfures organiques
Author(s) -
Merbach A.,
Bünzli J. C.
Publication year - 1972
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19720550231
Subject(s) - chemistry , adduct , medicinal chemistry , steric effects , lewis acids and bases , ligand (biochemistry) , sulfide , stereochemistry , organic chemistry , catalysis , biochemistry , receptor
The adducts of niobium(V) and tantalum(V) chlorides with some aliphatic and cyclic oxides and sulfides, studied by NMR. spectroscopy in CHCl 3 , are found to have 1:1 stoechiometry, at room temperature and lower. In the thioxane complex TaCl 5 · C 4 H 8 OS two species are present with the ligand coordinated by the sulfur atom or by the oxygen atom, respectively, in a proportion which has been determined. The thioxane adduct of niobium(V) chloride, however, is preferentially coordinated by the sulfur atom. There is also evidence for the species 2MCl 5 · C 4 H 8 OS. The relative basicity of each donor atom in dioxane, thioxane and dithiane is calculated and discussed. In contrast to the nitrile adducts, whose stability was found earlier to be controlled by inductive factors, the steric factors are more important for the ether and sulfide adducts: MCl 5 · Me 2 X is more stable than the corresponding MCl 5 · Et 2 X (M = Nb, Ta; X = O, S). Both niobium(V) and tantalum(V) chlorides have a soft behaviour, but NbCl 5 is a weaker Lewis acid than TaCl 5 and shows also a softer behaviour.