Reactions of Radicals with Stable Metallylenes
Written by Dennis Sheberla
Dennis Sheberla, Boris Tumanskii, Robert West, and Yitzhak Apeloig
Schulich Faculty of Chemistry and the Lise Meitner Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
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Metallylenes and radicals are among the most important reactive intermediates. However, very little is known about their cross-reaction − the addition of a radical to a carbene to yield a new radical. Only recently have several radical adducts of unsaturated metallylenes 1–3 with free radicals of different chemical nature (O-, P-, Re-, Mn-, etc) been studied in our group by EPR and DFT calculations and were reported recently (Eq. 1).1
In present work we study computationally the geometry and the electronic structure of these radical adducts. In phosphoryl radical adducts, the spin density on the central atoms decreases in the order C (53%) >> Si (14%) > Ge (3%). The degree of spin delocalization into the five member ring follows the order: Ge > Si > C. This can be explained by a contribution of a zwitterionic structure (Figure 1). Which dominates for E=Si and Ge as the thermodynamic stability of ER3(+) follows the order Ge > Si > C.
Figure 1. a) Zwitterionic resonance structure; b) Calculated (DFT B3LYP/6-31G*) NBO charges (in parenthesis) and spin density at central atoms in the products of phosphoryl radical addition to metallylenes.
1. B. Tumanskii, P. Pine, Y. Apeloig, N. J. Hill, R. West, J. Am. Chem. Soc. 2004, 126, 7786; B. Tumanskii, P. Pine, Y. Apeloig, N. J. Hill, R. West, J. Am. Chem. Soc. 2005, 127, 8248; B. Tumanskii, D. Sheberla, G. Molev, Y. Apeloig, Angew. Chem. Int. Ed. 2007, 46, 7408.