Trends in Sc[sup +]-alkyl bond strengths
Journal Article
·
· Journal of the American Chemical Society; (United States)
- California Inst. of Technology, Pasadena, CA (United States)
Recent Fourier transform ion cyclotron resonance (FTICR) studies of the gas-phase [sigma]-bond metathesis reactions of Sc(CH[sub 3])[sub 2][sup +] with alkanes (C[sub 2]H[sub 6], C[sub 3]H[sub 8]. and n-C[sub 4]H[sub 10]) demonstrate a preference for attack at primary rather than secondary C-H bonds, reaction 1a rather than 1b. This occurs even though the substrate primary bond is about 2.4 kcal/mol stronger than the secondary bond. In addition, the efficiencies of the reactions are observed to increase with the size of the alkane ([le] 0.02, 0.17, and 0.37 for C[sub 2]H[sub 6], C[sub 3]H[sub 8], and n-C[sub 4]H[sub 10], respectively). Ab initio calculations on the analogous reaction with CH[sub 4] indicate that the reaction proceeds via a four-center transition state. Consequently, the variations in the observed reactivities should be largely attributable to the differences in the corresponding metal-alkyl and alkyl-H bond strengths. In order to verify that this is the case, we examined the Sc[sup +]-R bond strengths, where R=CH[sub 3], C[sub 2]H[sub 5], n-C[sub 3]H[sub 7]. i-C[sub 3]H[sub 7], and t-C[sub 4]H[sub 9]. Our results indicate that the observed selectivity has a clear thermodynamic origin and the Sc[sup +]-R bond strengths are consistent with two sometimes conflicting trends. 14 refs., 1 fig., 2 tabs.
- OSTI ID:
- 7019409
- Journal Information:
- Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 116:11; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
661300 -- Other Aspects of Physical Science-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKANES
CATIONS
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL REACTIONS
DATA
HYDROCARBONS
INFORMATION
ION CYCLOTRON RESONANCE SPECTROSCOPY
ION SPECTROSCOPY
IONS
LIGANDS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
SCANDIUM COMPOUNDS
SPECTROSCOPY
THEORETICAL DATA
THERMODYNAMICS
TRANSITION ELEMENT COMPOUNDS
400201* -- Chemical & Physicochemical Properties
661300 -- Other Aspects of Physical Science-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKANES
CATIONS
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL REACTIONS
DATA
HYDROCARBONS
INFORMATION
ION CYCLOTRON RESONANCE SPECTROSCOPY
ION SPECTROSCOPY
IONS
LIGANDS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
SCANDIUM COMPOUNDS
SPECTROSCOPY
THEORETICAL DATA
THERMODYNAMICS
TRANSITION ELEMENT COMPOUNDS