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Issue 2, 2010
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Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

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Abstract

Stable N-heterocyclic carbenes and germylenes were allowed to react with a phosphonyl radical, (i-PrO)2(O)P˙ (7), generated by photolysis of [(i-PrO)2(O)P]2Hg. The products were identified by EPR spectroscopy. An unsaturated carbene (1) and germylene (3) react with 7 at the divalent atom to give unstable radical products (τ½ = 0.2 s). A benzo-annulated carbene (4) and a saturated germylene (6) react with 7 to give more active radicals. An unsaturated (2) and a saturated silylene (5) undergo rapid reaction (in the dark) with [(i-PrO)2(O)P]2Hg to yield unusual silyl phosphites. In these cases only secondary radicals were observed. DFT (PBE0/TZVP//B3LYP/6-31+G(d)) calculations of the radical adducts of the different (C, Si, Ge) unsaturated N-heterocyclic divalent species with the phosphonyl radical show that the unpaired electron is delocalized over the five-membered ring; the spin density on the central atoms decreases in the order C, 39% > Si, 14% > Ge, 2%. These trends can be understood in terms of a zwitterionic structure of the radical adducts. The calculations of the radical adducts of 4, 5 and 6 with 7 indicate larger spin density on the central atom, 47%, 58% and 42% on C, Si, Ge, respectively.

Graphical abstract: Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

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Article information


Submitted
21 Jan 2010
Accepted
18 Mar 2010
First published
26 May 2010

Chem. Sci., 2010,1, 234-241
Article type
Edge Article

Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

D. Sheberla, B. Tumanskii, A. C. Tomasik, A. Mitra, N. J. Hill, R. West and Y. Apeloig, Chem. Sci., 2010, 1, 234
DOI: 10.1039/C0SC00143K

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