Gas-phase chemistry of Sc(CH{sub 3}){sub 2}{sup +} with alkenes: Activation of allylic C-H bonds by a d{sup 0} system and the migratory insertion of C=C bonds into Sc{sup +}-CH{sub 3} bonds

Journal Article · Wed Nov 04 04:00:00 EST 1992 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00049a050· OSTI ID:569224

Huang, Yongqing; Hill, Y D; Freiser, B S ^[1]

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1. Purdue Univ., West Lafayette, IN (United States); and others

The gas-phase chemistry of Sc(CH{sub 3}){sub 2}{sup +} with alkenes was studied by Fourier transform mass spectrometry. The metal center on Sc(CH{sub 3}){sub 2}{sup +} is d{sup 0}, providing an opportunity to study alternative mechanisms of C-C or C-H activation other than the most common one involving oxidative addition. The elimination of H{sub 2} is observed in the reaction of Sc(CH{sub 3}){sub 2}{sup +} with ethylene, and the product ScC{sub 4}H{sub 8}{sup +} and ScC{sub 6}H{sub 10}{sup +} ions have a metal(methyl)(allyl) and metal-bisallyl structure, respectively, consistent with a proposed reaction mechanism involving the consecutive migratory insertion of ethylenes into the scandium-methyl bonds. In addition, theoretical calculations indicate that the metal(methyl)(allyl) structure is between 10 and 20 kcal/mol more stable than the metal(1-butene) isomer. Sc(CH{sub 3}){sub 2}{sup +} reacts with propene to form predominantly ScC{sub 4}H{sub 8}{sup +} by loss of CH{sub 4}, with minor amounts of ScC{sub 3}H{sub 4}{sup +} and ScC{sub 4}H{sub 6}{sup +} also observed. ScC{sub 4}H{sub 6}{sup +} is formed as either the exclusive or the predominant product ion in the reactions of Sc(CH{sub 3}){sub 2}{sup +} with butenes. Sc(CH{sub 3}){sub 2} reacts with cyclopentene to form predominantly ScC{sub 6}H{sub 8}{sup +} by losing CH{sub 4} and H{sub 2}. Isotope labeling studies with Sc(CD{sub 3}){sub 2}{sup +} and other structure studies indicate that all of the alkenes studied, with the exception of ethylene, react with Sc(CH{sub 3}){sub 2}{sup +} via a multicentered {sigma}-bond metathesis mechanism to activate allylic C-H bonds. Finally, the dehydrogenation reactions of Sc{sup +} with n-butane and neopentane were revisited, and a new mechanism is proposed for such chemistry in light of the new results from this study. 34 refs., 5 figs., 2 tabs.

• DOE Contract Number: FG02-87ER13766
• OSTI ID: 569224
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 23 Vol. 114; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ALKENES
CARBON
CHEMICAL ACTIVATION
CHEMICAL BONDS
CHEMICAL PROPERTIES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CYCLOHEXANE
DEHYDROGENATION
ELECTROCHEMISTRY
ELECTRON TRANSFER
ETHYLENE
GAS ANALYSIS
HYDROCARBONS
HYDROGEN
MASS SPECTROMETERS
MOLECULAR STRUCTURE
POLYMERIZATION
SCANDIUM COMPOUNDS
TRANSITION ELEMENTS
ZIEGLER CATALYST