Syntheses and Properties of Homoleptic Carbonyl and Trifluorophosphane Niobates: [Nb(CO)6]-, [Nb(PF3)6]- and [Nb(CO)5]3-

Mikhail V. Barybin, John E. Ellis, Marie K. Pomije, Mary L. Tinkham, Carry F. Warnock

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Reductive carbonylations of NbCl4(THF)2, THF = tetrahydrofuran, mediated by sodium naphthalene in 1,2-dimethoxyethane, DME, or sodium anthracene in THF, provide [Nb(CO)6]- as the tetraethylammonium salt in 60% or 70% isolated yields, respectively, the highest known for atmospheric pressure syntheses of this metal carbonyl. Corresponding reductions involving PF3 give about 40% yields of [Et4N][Nb(PF3)6], which in the past was only accessible by a photochemical route. Electrochemical data for [Nb(CO)6]- and [Nb(PF3)6]- are compared and show that the PF3 complex is almost 1 V more difficult to oxidize than the CO analogue. Protonation of [Nb(PF3)6]- by concentrated sulfuric acid yields a volatile, thermally unstable species, which has been shown by 1H NMR and mass spectral studies to be the new niobium hydride, Nb(PF3)6H. Previously unpublished 93Nb and 13C NMR studies corroborate prior claims that the sodium metal reduction of [Nb(CO)6]- in liquid ammonia affords [Nb(CO)5]3-, the only known Nb(III-) species. The first details of this synthesis and those of [Nb(CO)5H]2-, [Nb(CO)5SnPh3]2-, [Nb(CO)5NH3]-, and [Nb(CO)5(CNtBu)- are presented.

Original languageEnglish (US)
Pages (from-to)6518-6527
Number of pages10
JournalInorganic chemistry
Issue number25
StatePublished - 1998


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