Dynamic Interligand Hydrogen Transfer in Some η5-Cyclopentadienylzirconium and -hafnium Tetrahydroborates

Tobin J. Marks; John R. Kolb

doi:10.1021/ja00845a020

Dynamic Interligand Hydrogen Transfer in Some η⁵-Cyclopentadienylzirconium and -hafnium Tetrahydroborates

Tobin J. Marks, John R. Kolb

Chemistry

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Abstract

The compounds (η⁵-C₅H₅)₂Zr(BH₄)₂, (η⁵-C₅H₅)₂Hf(BH₄)₂ and (η⁵-(C₅H₅)₂Zr(H)BH₄exhibit exchange of C₅H₅ and BH₄ hydrogens which is rapid on the proton NMR time scale at elevated temperatures. The process is found to be predominantly unimolecular, with free energies of activation (Δ Gt) for the above compounds of 21.3 ± 0.4, 19.4 ± 0.4, and 19.6 ± 0.4 kcal/mol (395°K), respectively. For (C₅H₅)₂Zr(H)BF₄, the hydrido hydrogen also appears to become involved in the exchange process at higher temperatures, with ηGt = 20.9 ± 0.5 kcal/mol (395°K). The interchange process also occurs for (C₅H₅)₂Zr(BD₄)₂ in the solid state, but more slowly. The possible mechanisms of this prototropic rearrangement are discussed, and the likely importance of η¹-C₅H₄M carbene-ylid complexes along the reaction coordinate is underscored.

Original language	English (US)
Pages (from-to)	3397-3401
Number of pages	5
Journal	Journal of the American Chemical Society
Volume	97
Issue number	12
DOIs	https://doi.org/10.1021/ja00845a020
State	Published - Jun 1 1975

ASJC Scopus subject areas

Catalysis
Chemistry(all)
Biochemistry
Colloid and Surface Chemistry

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title = "Dynamic Interligand Hydrogen Transfer in Some η5-Cyclopentadienylzirconium and -hafnium Tetrahydroborates",

abstract = "The compounds (η5-C5H5)2Zr(BH4)2, (η5-C5H5)2Hf(BH4)2 and (η5-(C5H5)2Zr(H)BH4exhibit exchange of C5H5 and BH4 hydrogens which is rapid on the proton NMR time scale at elevated temperatures. The process is found to be predominantly unimolecular, with free energies of activation (Δ Gt) for the above compounds of 21.3 ± 0.4, 19.4 ± 0.4, and 19.6 ± 0.4 kcal/mol (395°K), respectively. For (C5H5)2Zr(H)BF4, the hydrido hydrogen also appears to become involved in the exchange process at higher temperatures, with ηGt = 20.9 ± 0.5 kcal/mol (395°K). The interchange process also occurs for (C5H5)2Zr(BD4)2 in the solid state, but more slowly. The possible mechanisms of this prototropic rearrangement are discussed, and the likely importance of η1-C5H4M carbene-ylid complexes along the reaction coordinate is underscored.",

author = "Marks, {Tobin J.} and Kolb, {John R.}",

year = "1975",

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doi = "10.1021/ja00845a020",

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AU - Marks, Tobin J.

AU - Kolb, John R.

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Y1 - 1975/6/1

N2 - The compounds (η5-C5H5)2Zr(BH4)2, (η5-C5H5)2Hf(BH4)2 and (η5-(C5H5)2Zr(H)BH4exhibit exchange of C5H5 and BH4 hydrogens which is rapid on the proton NMR time scale at elevated temperatures. The process is found to be predominantly unimolecular, with free energies of activation (Δ Gt) for the above compounds of 21.3 ± 0.4, 19.4 ± 0.4, and 19.6 ± 0.4 kcal/mol (395°K), respectively. For (C5H5)2Zr(H)BF4, the hydrido hydrogen also appears to become involved in the exchange process at higher temperatures, with ηGt = 20.9 ± 0.5 kcal/mol (395°K). The interchange process also occurs for (C5H5)2Zr(BD4)2 in the solid state, but more slowly. The possible mechanisms of this prototropic rearrangement are discussed, and the likely importance of η1-C5H4M carbene-ylid complexes along the reaction coordinate is underscored.

AB - The compounds (η5-C5H5)2Zr(BH4)2, (η5-C5H5)2Hf(BH4)2 and (η5-(C5H5)2Zr(H)BH4exhibit exchange of C5H5 and BH4 hydrogens which is rapid on the proton NMR time scale at elevated temperatures. The process is found to be predominantly unimolecular, with free energies of activation (Δ Gt) for the above compounds of 21.3 ± 0.4, 19.4 ± 0.4, and 19.6 ± 0.4 kcal/mol (395°K), respectively. For (C5H5)2Zr(H)BF4, the hydrido hydrogen also appears to become involved in the exchange process at higher temperatures, with ηGt = 20.9 ± 0.5 kcal/mol (395°K). The interchange process also occurs for (C5H5)2Zr(BD4)2 in the solid state, but more slowly. The possible mechanisms of this prototropic rearrangement are discussed, and the likely importance of η1-C5H4M carbene-ylid complexes along the reaction coordinate is underscored.

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Dynamic Interligand Hydrogen Transfer in Some η⁵-Cyclopentadienylzirconium and -hafnium Tetrahydroborates

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