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
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKYL RADICALS
BATTELLE PACIFIC NORTHWEST LABORATORIES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DIFFUSION
ELEMENTS
EXPERIMENTAL DATA
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
INFORMATION
KINETICS
MOLYBDENUM COMPOUNDS
MOLYBDENUM HYDRIDES
NATIONAL ORGANIZATIONS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
RADICALS
REACTION KINETICS
REDUCTION
REFRACTORY METAL COMPOUNDS
RESEARCH PROGRAMS
TRANSITION ELEMENT COMPOUNDS
US DOE
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