Bis(η5-cyclopentadienyl)vanadium tetrahydroborate. A covalent organotransition metal borohydride with unusual spectroscopic and dynamic properties

Tobin J Marks, William J. Kennelly

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Abstract

The synthesis and spectroscopic (vibrational, nmr) characterization of (η5-C5H5)2VBH4 are described. In comparison to (η5-C5H5)2TiBH4, both (C5H5)2VBH4 and (C5H5)2NbBH4, which also have bidentate MH2BH2 ligation, appear to be more covalent and show considerable weakening of B-H bridging bonds and possibly some strengthening of M-H bonds in the vibrational spectra. In addition, the free energy barrier to bridge-terminal hydrogen interchange is surprisingly high for the vanadium compound (ΔG ≈ 7.6 ± 0.3 kcal/mol) and the fluxional behavior can be slowed on the nmr time scale. The permutation process is too rapid to slow in the niobium compound, and the reasons for the difference in rate are discussed in terms of the proposed rearrangement mechanism and the size of the metal ion.

Original languageEnglish
Pages (from-to)1439-1443
Number of pages5
JournalJournal of the American Chemical Society
Volume97
Issue number6
Publication statusPublished - 1975

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Niobium compounds
Vanadium Compounds
Vanadium compounds
Niobium
Borohydrides
Vanadium
Energy barriers
Interchanges
Vibrational spectra
Free energy
Metal ions
Ligation
Hydrogen
Metals
Ions
bis(cyclopentadienyl)vanadium(IV)

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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abstract = "The synthesis and spectroscopic (vibrational, nmr) characterization of (η5-C5H5)2VBH4 are described. In comparison to (η5-C5H5)2TiBH4, both (C5H5)2VBH4 and (C5H5)2NbBH4, which also have bidentate MH2BH2 ligation, appear to be more covalent and show considerable weakening of B-H bridging bonds and possibly some strengthening of M-H bonds in the vibrational spectra. In addition, the free energy barrier to bridge-terminal hydrogen interchange is surprisingly high for the vanadium compound (ΔG‡ ≈ 7.6 ± 0.3 kcal/mol) and the fluxional behavior can be slowed on the nmr time scale. The permutation process is too rapid to slow in the niobium compound, and the reasons for the difference in rate are discussed in terms of the proposed rearrangement mechanism and the size of the metal ion.",
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T1 - Bis(η5-cyclopentadienyl)vanadium tetrahydroborate. A covalent organotransition metal borohydride with unusual spectroscopic and dynamic properties

AU - Marks, Tobin J

AU - Kennelly, William J.

PY - 1975

Y1 - 1975

N2 - The synthesis and spectroscopic (vibrational, nmr) characterization of (η5-C5H5)2VBH4 are described. In comparison to (η5-C5H5)2TiBH4, both (C5H5)2VBH4 and (C5H5)2NbBH4, which also have bidentate MH2BH2 ligation, appear to be more covalent and show considerable weakening of B-H bridging bonds and possibly some strengthening of M-H bonds in the vibrational spectra. In addition, the free energy barrier to bridge-terminal hydrogen interchange is surprisingly high for the vanadium compound (ΔG‡ ≈ 7.6 ± 0.3 kcal/mol) and the fluxional behavior can be slowed on the nmr time scale. The permutation process is too rapid to slow in the niobium compound, and the reasons for the difference in rate are discussed in terms of the proposed rearrangement mechanism and the size of the metal ion.

AB - The synthesis and spectroscopic (vibrational, nmr) characterization of (η5-C5H5)2VBH4 are described. In comparison to (η5-C5H5)2TiBH4, both (C5H5)2VBH4 and (C5H5)2NbBH4, which also have bidentate MH2BH2 ligation, appear to be more covalent and show considerable weakening of B-H bridging bonds and possibly some strengthening of M-H bonds in the vibrational spectra. In addition, the free energy barrier to bridge-terminal hydrogen interchange is surprisingly high for the vanadium compound (ΔG‡ ≈ 7.6 ± 0.3 kcal/mol) and the fluxional behavior can be slowed on the nmr time scale. The permutation process is too rapid to slow in the niobium compound, and the reasons for the difference in rate are discussed in terms of the proposed rearrangement mechanism and the size of the metal ion.

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