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Characterization of Carbenes via Hydrogenation Energies, Stability, and Reactivity: What's in a Name?
Author(s) -
Vasiliu Monica,
Peterson Kirk A.,
Arduengo Anthony J.,
Dixon David A.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703539
Subject(s) - carbene , exothermic reaction , singlet state , chemistry , reactivity (psychology) , photochemistry , computational chemistry , ground state , medicinal chemistry , physics , atomic physics , organic chemistry , catalysis , medicine , alternative medicine , pathology , excited state
Abstract The hydrogenation energies and singlet–triplet (S–T) splittings at the G3MP2 level of theory have been calculated for a wide range of carbenes. The carbene, :CXY with different substituents (X, Y=H, CN, NC, F, Cl, OH, OCH 3 , CH 3 , CF 3 , SiH 3 , SiMe 3 , phenyl, CH=O, PH 2 , and NH 2 ) at the carbenic carbon center, immidazole‐based carbenes, Bertrand's carbenes, and Seppelt's CF 3 CSF 3 were studied. The stable carbenes are singlets with large S–T splittings and with the least exothermic hydrogenation energies. The singlet ground state immidazole‐based carbenes are calculated to have the least exothermic hydrogenation energies (−15 to −30 kcal mol −1 ) and the largest S–T gaps. The singlet ground states of the Bertrand carbenes have more exothermic hydrogenation (ca. −67 kcal mol −1 ) energies and much smaller S–T gaps. The more exothermic reaction energies arise due to the need to make the phosphorus planar in the carbene so that it can donate into the empty p‐orbital at the carbene carbon center. The bending potential at the carbene carbon center in the Bertrand compounds is very flat with a large XC:Y angle. Seppelt's CF 3 CSF 3 appears to be energetically similar to the Bertrand system, probably due to the required adjustments for geometric distortions at the sulfur center.