Rate expressions for abstraction of hydrogen atom from a molybdenum hydride by alkyl radicals
Rate expressions were determined for the abstraction of hydrogen atom from pentamethylcyclopentadienyltricarbonyl-molybdenum hydride (Me/sub 5/CpMo(CO)/sub 3/H). The radical clocks hept-6-en-2-yl, produced from bromine atom abstraction from 7-bromoheptene, and hex-5-enyl, produced from bromine atom abstraction from 6-bromohexene, were utilized to compete intramolecular cyclization (kcyc) with bimolecular abstraction (kabs) from Me/sub 5/CpMo(CO)/sub 3/H in n-octane. Using known rate expressions for the cyclization of the primary clock, and separate rate expressions for cyclization of the secondary clock to give cis- and trans-cyclized products, rate expressions for abstraction were developed from ratios of unrearranged and rearranged hydrocarbon products. For the primary clock, log(kabs/M/sup 1/s/sup -1/) = 9.0 +/- 0.3 - (0.93 +/- 0.2)/theta, theta = 2.3RT kcal/mole, kabs = 2.1 x 10/sup 8/ M/sup -1/s/sup -1/. For the secondary clock, log(kabs/M/sup -1/s/sup -1/) = 8.6 +/- 0.3 -(0.81 +/- 0.1)/theta, and kabs = 1.0 x 10/sup 8/ M/sup -1/s/sup -1/. The bimolecular rates are slower by a factor of ten than expected for diffusion control. The activation barriers are lower than activation barriers expected for diffusion-controlled hydrogen abstraction by ca. 1.5 kcal/mole. The results are discussed in terms of the thermochemistry of the reactions and in terms of rates of biomolecular reactions approaching diffusion control. The synthetic utility of the reduction reaction is discussed.
- Research Organization:
- Pacific Northwest Lab., Richland, WA (USA)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 7200482
- Report Number(s):
- PNL-SA-15499; CONF-880604-11; ON: DE88011897
- Resource Relation:
- Conference: Joint meeting of the 195th national meeting of the American Chemical Society and the 3rd Chemical Congress of North America, Toronto, Canada, 5 Jun 1988; Other Information: Portions are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALKYL RADICALS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
RESEARCH PROGRAMS
MOLYBDENUM HYDRIDES
REDUCTION
ORGANOMETALLIC COMPOUNDS
BATTELLE PACIFIC NORTHWEST LABORATORIES
DIFFUSION
EXPERIMENTAL DATA
HYDROGEN
DATA
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
KINETICS
MOLYBDENUM COMPOUNDS
NATIONAL ORGANIZATIONS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
RADICALS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
US DOE
US ERDA
US ORGANIZATIONS
400201* - Chemical & Physicochemical Properties