title: Metalla-cope rearrangements: bridging organic and inorganic chemistry.
abstract: Density functional theory calculations are performed to explore both concerted chairlike and boatlike as well as stepwise mechanisms of the Cope rearrangement of two hypothetical metalladienes. An osma-1,5-hexadiene is designed by substituting CH(2) in 1,5-hexadiene by its isolobal analogue, 16-electron Os(PH(3))(4). The energy of activation corresponding to the rearrangement of osma-1,5-hexadiene involving the chairlike saddle point is computed as 37.4 kcal/mol, 3.9 kcal/mol above the energy barrier of the parent 1,5-hexadiene calculated with the same method and basis set, and is 4.5 kcal/mol below that of the boatlike pathway. In another isolobal replacement, the CH in 1,5-hexadiene is substituted by a 15-electron Re(PH(3))(3) fragment. Now the chairlike rearrangement of the rhenia-1,5-hexadiene has an E(a) value of 23.0 kcal/mol, 10.8 kcal/mol less than the energy barrier of the parent 1,5-hexadiene calculated at the same level of theory. The ring inversion of the chair and osma-chair diradical intermediates of the stepwise reaction pathway is also examined and is found in both cases to proceed through a very flat potential energy surface involving twist intermediates.
authors.affiliation: Department of Natural Sciences, Baruch College, the City University of New York, 17 Lexington Avenue, New York, New York 10010, USA.
authors.forename: Edyta M
authors.initials: EM
authors.lastname: Greer
authors.forename: Roald
authors.initials: R
authors.lastname: Hoffmann