Molybdenum(0) catalysis of (1,5)sigmatropic carbon migration in unsaturated (4. 4. 2)propellanes. Deuterium isotope effects, kinetics, and mechanism

Journal Article · Tue Nov 22 23:00:00 EST 1977 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00466a025· OSTI ID:5183363

Paquette, L A; Micheli, R P; Photis, J M

Through assessment of the Mo(CO)/sub 6/-promoted isomerizations of the 2,5- and 11,12-d/sub 2/ (4.4.2)propella-2,4,11-trienes, it could be unequivocally established that C/sub 11/ of the cyclobutene ring and not C/sub 7/ of the cyclohexane moiety is directly involved in formal (1,5)sigmatropic migration. The kinetic behavior of the tetrahapto complexes revealed several additional mechanistic features: (a) the presence of deuterium atoms at C/sub 2/ and C/sub 5/ has little impact on the rate-determining step; (b) the 11,12-dideuterio derivative exhibits, in contrast, an appreciable intermolecular isotope effect (k/sub H//k/sub D/ = 0.92 at 80.6/sup 0/C); and (c) a 2-methyl substituent accelerates rearrangement by a factor of 2. The level of isotopic discrimination realizable during intramolecular competition was shown to be entirely comparable (k/sub H//k/sub D/ = 0.93 at 80/sup 0/C) by making recourse to a monodeuterated propellatriene. The magnitude and inverse nature of these secondary isotope effects has been interpreted to be incompatible with two mechanistic alternatives involving ''top-side'' complexation of the propellatriene (i.e., syn to the cyclobutene bridge). Rather, a transition state model involving modified (1,5)sigmatropic migration on that molecular face opposite to the site of molybdenum coordination is shown to account best for the experimentally determined Arrhenius parameters, deuterium fractionation factors, regioselectivity, and circumambulation (the latter operative only when both C/sub 11/ and C/sub 12/ carry methyl groups).

• Research Organization: Ohio State Univ., Columbus
• OSTI ID: 5183363
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 99:24; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALKENES
CARBONYLS
CATALYSIS
CHEMICAL REACTIONS
CYCLOALKENES
DEUTERIUM
HYDROCARBONS
HYDROGEN ISOTOPES
ISOMERIZATION
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MOLYBDENUM COMPOUNDS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS