The almost bottleable triplet carbene

2,6-Dibromo-4-tert-butyl-2′,6′-bis (trifiuoromethyl)-4′-isopropyldiphenylcarbene

H. L. Woodcock, D. Moran, P. Von Ragué Schleyer, H. F. Schaefer*

*Corresponding author for this work

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Computations on 2,6-dibromo-4-tert-butyl-2′,6′-bis(trifluoromethyl) -4′-isopropyldiphenylcarbene (1) using ab initio and density functional theory methods underscore the unusual stability of the triplet over the singlet state. At the B3LYP/6-311G(d,p) level, the triplet state had a slightly bent central C-C-C bond angle of 167°, whereas this angle in the singlet was 134°. The B3LYP singlet-triplet splitting (12.2 kcal/mol) was larger than that of the parent molecule (5.8 kcal/mol), diphenylcarbene (2), which also has a triplet ground state. The energy of a suitable isodesmic reaction showed the triplet and singlet states of 1 to be destabilized, by 6.3 and 12.5 kcal/mol, respectively, due to the combined effects of the CF3, Br, and alkyl substituents. The linear-coplanar form of 31, which might facilitate dimerization or electrophilic attack at the more exposed diradical center, was prohibitively (35.9 kcal/mol) higher in energy. Our results confirm Tomioka's conclusion that the triplet diarylcarbene, ortho-substituted with bulky CF3 and Br substituents, is persistent due to steric protection of the diradical center. Dimerization and other possible reaction pathways are inhibited, not only by the bulky ortho substituents but also by the para alkyl groups. The increase in stability of the triplet (31) state relative to the singlet (11) state does not influence the reactivity directly.

Original languageEnglish
Pages (from-to)4331-4335
Number of pages5
JournalJournal of the American Chemical Society
Volume123
Issue number18
DOIs
Publication statusPublished - 2001
Externally publishedYes

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