Tuning the Bergman cyclization by introduction of metal fragments at various positions of the enediyne. Metalla-Bergman cyclizations.
We expand the scope of the Bergman cyclization by exploring computationally the rearrangement of two osmaenediynes and one rhodaenediyne. The three hypothetical metallaenediynes are constructed by substituting the 14-electron Os(PH3)3 fragment for the C fragment, or the 15-electron Os(PH3)3H or Rh(PH3)3 fragments for the sp2 CH fragment, of 3-ene-1,5-diyne. This replacement is guided by the isolobal analogy and previous metallabenzene chemistry. The rearrangement of osmaenediyne with an Os(PH3)3 fragment in place of C is exothermic by 3 kcal/mol (the parent Bergman reaction is computed to be endothermic by 5 kcal/mol) and associated with a significant decrease in the barrier to rearrangement to 13 kcal/mol (the Ea of the parent reaction computed at the same level of theory is 33 kcal/mol). The replacement of a CH by the isolobal analogue Os(PH3)3H reduces the energy of activation for the rearrangement to 23 kcal/mol and produces a corresponding metalladiradical that is 8 kcal/mol less stable that the corresponding osmaenediyne. The activation energy corresponding to the rearrangement of the rhodaenediyne is the same as that of the organic parent enediyne. Interesting polytopal rearrangements of metallaenediynes and the diradical nature of the resulting intermediates are also explored.
Brzostowska
Edyta M
EM
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA.
Hoffmann
Roald
R
Parish
Carol A
CA
D003198:Computer Simulation; D003500:Cyclization; D053281:Enediynes / Q000737:chemistry*; D007536:Isomerism; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure
D053281:Enediynes; D008670:Metals