Ion beam studies of organometallic chemistry. High energy sampling of reaction intermediates involved in carbon-carbon bond cleavage by transition metals
Chemical transformation often involves reactive intermediates which correspond to local minima on a complex potential energy surface. In this study of the reactions of cobalt ions with alkanes, the intermediate is provided more energy than needed for reaction. The quantitative assessment of the fragmentation of reaction intermediates provided thermodynamic data. These investigations involved organo transition metal reactions using ion beam technqiues. Results for the reaction of Co/sup +/ with 2-methylpropane and 2,2-dimethylpropane are included. The observation that the cross section for production of CoCH/sub 3//sup +/ is always greater than that of C/sub 3/H/sub 7/+ implies that IP(C/sub 0/CH/sub 3/) < IP(iso-C/sub 3/H/sub 7/) = 7.36 eV. A similar analysis of the 2,2-dimethylpropane system establishes IP(CoCH/sub 3/) > IP(tert-C/sub 4/H/sub 9/) = 6.70 eV. Measurement of the thresholds for the endothermic processes observed at high energies provides band energies of the products. Preliminary data for the endothermic reactions of Co/sup +/ with hydrogen and ethane indicate that D/sup 0/(Co/sup +/-H) = 52 +- 4 and D/sup 0/(Co -- CH/sub 3/) = 61 +- 4 kcal/mol. Combined with the ionization potentials, IP(CoH) = 7.3 +- 0.1 and IP(CoCH/sub 3/) = 7.0 +- 0.3 EV; we find the neutral band dissociation energies, D/sup 0/(CoH) = 39 +- 6 and D/sup 0/(CoCH/sub 3/) = 41 +- 10 kcal/mol. The results provide substantial evidence for the viability of a mechanism for carbon-carbon bond cleavage of alkanes which involves direct insertion of a metal into the carbon-carbon band as a first step. Thermochemical data indicating strong metal-carbon bonds corroborate this hypothesis. 2 figures. (DP)
- Research Organization:
- California Inst. of Tech., Pasadena
- OSTI ID:
- 5345693
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:5; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Ion beam studies of the reactions of atomic cobalt ions with alkanes: determination of metal-hydrogen and metal-carbon bond energies and an examination of the mechanism by which transition metals cleave carbon-carbon bonds
Activation of alkanes by Cr{sup +}: Unique reactivity of ground-state Cr{sup +}({sup 6}S) and thermochemistry of neutral and ionic chromium-carbon bonds
Related Subjects
2-METHYLPROPANE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKANES
BEAMS
BINDING ENERGY
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CLEAVAGE
COBALT COMPOUNDS
CRYSTAL STRUCTURE
ELEMENTS
ENERGY
HYDROCARBONS
INTERMEDIATE STRUCTURE
ION BEAMS
IONS
METALS
MICROSTRUCTURE
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PHYSICAL PROPERTIES
REACTION INTERMEDIATES
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS