Abstract
The systematic high yield syntheses of a number of (h5-C5H5)3UR compounds from (A5-C5H5)3UC1 and the corresponding RLi or RMgX reagents are reported. The new compounds have been characterized by chemical and magnetochemical means and by vibrational and nmr spectroscopy. The allyl compound has a ground state monohaptoallyl geometry and is fluxional. In the isopropyl compound restricted rotation is observed about the U-R bond, indicating considerable crowding of ligands around the central metal. Analysis of the isotropic nmr chemical shifts indicates the contribution of large contact shifts; the mechanism of spin distribution involves negative spin density at the α-carbon atom of the alkyl or aryl group and is qualitatively in accord with SCF INDO molecular orbital calculations. The U-C bond is susceptible to attack by protonic solvents and, hence, is somewhat ionic. Most of the new compounds exhibit surprisingly high thermal stability, the general order of stability determined by kinetic studies in toluene solution being primary > secondary > tertiary. In the thermolysis, β elimination of olefin does not occur to any major extent, but intramolecular abstraction of hydrogen from a cyclopentadienyl ring occurs yielding RH; this takes place with essentially complete retention of stereochemical configuration at the α carbon atom of R. A homolytic U-C bond scission producing a highly constrained caged radical pair, or a concerted elimination of RH, explains these observations.
| Original language | English |
|---|---|
| Pages (from-to) | 5529-5539 |
| Number of pages | 11 |
| Journal | Journal of the American Chemical Society |
| Volume | 95 |
| Issue number | 17 |
| Publication status | Published - 1973 |
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Synthesis, chemistry, and spectroscopy of some tris(pentahaptocyclopentadienyl)uranium(IV) alkyl and aryl compounds. / Marks, Tobin J; Seyam, Afif M.; Kolb, John R.
In: Journal of the American Chemical Society, Vol. 95, No. 17, 1973, p. 5529-5539.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Synthesis, chemistry, and spectroscopy of some tris(pentahaptocyclopentadienyl)uranium(IV) alkyl and aryl compounds
AU - Marks, Tobin J
AU - Seyam, Afif M.
AU - Kolb, John R.
PY - 1973
Y1 - 1973
N2 - The systematic high yield syntheses of a number of (h5-C5H5)3UR compounds from (A5-C5H5)3UC1 and the corresponding RLi or RMgX reagents are reported. The new compounds have been characterized by chemical and magnetochemical means and by vibrational and nmr spectroscopy. The allyl compound has a ground state monohaptoallyl geometry and is fluxional. In the isopropyl compound restricted rotation is observed about the U-R bond, indicating considerable crowding of ligands around the central metal. Analysis of the isotropic nmr chemical shifts indicates the contribution of large contact shifts; the mechanism of spin distribution involves negative spin density at the α-carbon atom of the alkyl or aryl group and is qualitatively in accord with SCF INDO molecular orbital calculations. The U-C bond is susceptible to attack by protonic solvents and, hence, is somewhat ionic. Most of the new compounds exhibit surprisingly high thermal stability, the general order of stability determined by kinetic studies in toluene solution being primary > secondary > tertiary. In the thermolysis, β elimination of olefin does not occur to any major extent, but intramolecular abstraction of hydrogen from a cyclopentadienyl ring occurs yielding RH; this takes place with essentially complete retention of stereochemical configuration at the α carbon atom of R. A homolytic U-C bond scission producing a highly constrained caged radical pair, or a concerted elimination of RH, explains these observations.
AB - The systematic high yield syntheses of a number of (h5-C5H5)3UR compounds from (A5-C5H5)3UC1 and the corresponding RLi or RMgX reagents are reported. The new compounds have been characterized by chemical and magnetochemical means and by vibrational and nmr spectroscopy. The allyl compound has a ground state monohaptoallyl geometry and is fluxional. In the isopropyl compound restricted rotation is observed about the U-R bond, indicating considerable crowding of ligands around the central metal. Analysis of the isotropic nmr chemical shifts indicates the contribution of large contact shifts; the mechanism of spin distribution involves negative spin density at the α-carbon atom of the alkyl or aryl group and is qualitatively in accord with SCF INDO molecular orbital calculations. The U-C bond is susceptible to attack by protonic solvents and, hence, is somewhat ionic. Most of the new compounds exhibit surprisingly high thermal stability, the general order of stability determined by kinetic studies in toluene solution being primary > secondary > tertiary. In the thermolysis, β elimination of olefin does not occur to any major extent, but intramolecular abstraction of hydrogen from a cyclopentadienyl ring occurs yielding RH; this takes place with essentially complete retention of stereochemical configuration at the α carbon atom of R. A homolytic U-C bond scission producing a highly constrained caged radical pair, or a concerted elimination of RH, explains these observations.
UR - http://www.scopus.com/inward/record.url?scp=33947088034&partnerID=8YFLogxK
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M3 - Article
VL - 95
SP - 5529
EP - 5539
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 17
ER -