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Adducts of Niobium (V) and Tantalum (V) Halides. XV. Ligand Exchange of the Adducts with Some Phosphoryl Compounds

✍ Scribed by Christian M. P. Favez; André E. Merbach

Publisher
John Wiley and Sons
Year
1977
Tongue
German
Weight
414 KB
Volume
60
Category
Article
ISSN
0018-019X

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✦ Synopsis

The ligand exchange MX5 . L + *L 8 MX, . *L + L for the octahedral adducts MX, . L, in an inert solvent (CH2CI2 or CHCI,) with neutral ligands, proceeds via a dissociative D mechanism when M = Nb, X = C1 and L= phosphoryl compound. A dissociative interchange Id mechanism is suggested when M = N b or Ta, and X = F. A first order rate law and positive values for AS* ( + 4 to + 14 cal K-' mol-') are observed for the exchanges on the pentachloride adducts. However, a second order rate law and large negative values for AS* (-15 to -24 cal K-' mol-I) are found for the intermolecular neutral ligand exchange (measured by 'H-NMR.) and for the intramolecular fluorine exchange (measured by I9F-NMR.) reactions on the pentafluoride adducts. The fluorine exchange is 2 to 5 times faster than the ligand exchange. The exchanges, on the pentachloride and on the pentafluoride adducts, are slowed down with increasing donor strength of the phosphoryl compound.

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