A density functional study on the activation of hydrogen-hydrogen and hydrogen-carbon bonds by Cp[sub 2]Sc-H and Cp[sub 2]Sc-CH[sub 3]

Journal Article · Wed Jan 27 04:00:00 EST 1993 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00055a037· OSTI ID:6539212

Ziegler, T; Folga, E; Berces, A ^[1]

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1. Univ. of Calgary, Alberta (Canada)

Density functional calculations have been carried out on Cp[sub 2]Sc-R (R = H, methyl, ethyl, propyl, vinyl, and acetylide). Geometry optimizations reveal an agostic interaction for R = ethyl, whereas methyl and propyl are bound to the metal center without agostic interactions. The Sc-R bond energies are calculated as D[sub e](Sc-acetylide) = 540 kJ mol[sup [minus]1] > D[sub e](Sc-H) = 340 > D[sub e](Sc-vinyl) = 338 > D[sub e](Sc-methyl) = 295 > D[sub e](Sc-ethyl) = 283 > D[sub e](Sc-propyl) = 240. A study on the [sigma]-bond metathesis reaction (I) (Cp[sub 2]Sc-R + H-R[prime] [yields] Cp[sub 2]Sc-R[prime] + H-R) reveals the following reaction enthalpies [[Delta]H[sub 1](R,R[prime]), in kJ mol[sup [minus]1]]: [Delta]H[sub 1](CH[sub 3], acetylide) = [minus]128 < [Delta]H[sub 1](H, acetylide) = [minus]86 < [Delta]H[sub 1](CH[sub 3], H) = [minus]28 < [Delta]H[sub 1](CH[sub 3], vinyl) = [minus]26 < [Delta]H[sub 1](H, vinyl) = 16. The activation energies increase with the number of vinyl and methyl groups in the Sc-R-H-R[prime] core as the directional [sigma]-orbitals on these groups are unable to maintain optimal interactions with both neighbors in the Sc-R-H-R[prime] core. The transition states for reactions with negative activation energies are below the reactants in energy but still above the adduct (a). The formally forbidden [2[sub [sigma]] + 2[sub [sigma]]] reaction is facilitated by a pool of s-, p-, and d-type orbitals on scandium which maintain optimal interactions with the neighboring groups throughout the reaction. 44 refs., 3 figs., 2 tabs.

• OSTI ID: 6539212
• Journal Information: Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 115:2; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ACTIVATION ENERGY
ALKANES
ALKENES
ALKYNES
CHEMICAL ACTIVATION
CHEMICAL REACTIONS
CYCLOALKENES
CYCLOPENTADIENE
DIENES
ELEMENTS
ENERGY
ENTHALPY
HYDROCARBONS
HYDROGEN
MATHEMATICAL MODELS
NONMETALS
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PHYSICAL PROPERTIES
POLYENES
REACTION HEAT
SCANDIUM COMPOUNDS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS