Niobium complexes adducts

The use of both 8(CH3) values and iftM- H) magnitudes does, however, allow determination of the coordination mode in many instances (e.g., 462). Problems due to ligand dissociation are frequently evident in H-NMR studies of sulfoxide complexes. Thus the dimethyl sulfoxide adduct of niobium oxychloride (409) undergoes solvolysis in acetoni-... 

Reactions of Tantalum(V) and Niobium(V) Iodides with Pyridine. Both niobium(V) and tantalum(V) iodide were reduced in pyridine. In each case the di-adduct of pyridine with the metal tetraiodide was produced, along with elemental iodine as its pyridine complex. The two reduction products were identified by analysis after washing with chloroform to remove the iodine liberated in the reaction. Further identification of the tantalum product was provided by x-ray diffraction data, which compared favorably to those obtained for samples of the tetraiododi(pyridine)niobium (IV) as shown in Table V. 

Numerous adducts of MX4 with nitrogen, phosphorus, arsenic, oxygen and sulfur donors have been obtained, mainly for niobium with X = CI or Br7 (Tables 29-33). The absence of MF4 adducts, except for [NbF4(py)2],511 may be due less to their instability than to a lack of investigations. An ill-defined fluoro trichloride complex, [NbCl3F(MeCN)2.65], has also been reported.512... 

The latter deep-purple THF adducts of niobium and tantalum have been prepared independently by the photolysis of the corresponding [M(CO)6] " in tetrahydrofuran at — 70°C (54). They are even more reactive than the corresponding ammine complexes (vide infra) with respect to ligand substitution reactions. 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

No dioxygen adducts of vanadium porphyrins have been reported. However, a niobium(IV) porphyrin, NbBr2TPP, has recently been reported to react with dioxygen. Characterization was based upon ESR data. A 10-line signal g — 2.002), due to weak coupling to the Nb nucleus (/ = f), was seen. This implied a superoxo-type complex. IR data are consistent with the superoxo formalism showing Vo o = 1220cm". ... 

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