Triplet Di(9-anthryl)carbene Undergoes Trimerization

Takahashi, Yasutake; Tomura, Masaaki; Yoshida, Kenzo; Murata, Shigeru; Tomioka, Hideo

doi:10.1002/1521-3757(20001002)112:19<3620::aid-ange3620>3.0.co;2-b

Cited by 5 publications

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“…24 Structure of triplet bis(9-anthryl)carbene ( 3 2b), generated by photolysis of the precursor diazomethane (1b), and the corresponding carbene dimer (4). The phenyl groups in 3 2b are not expected to be in the same plane as the anthryl rings owing to the repulsion between ortho-and peri-hydrogens.…”

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Generation and characterization of a fairly stable triplet carbene

Tomioka

Iwamoto

Itakura

et al. 2001

Nature

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Most molecules are held together by covalent bonds-electron pairs jointly shared by the two atoms that are linked by the bond. Free radicals, in contrast, have at least one unpaired electron. In the case of carbon-based radicals, the carbon atom at the radical centre no longer makes four bonds with other atoms as it would do in its normal, tetravalent state. The presence of unpaired electrons renders such radicals highly reactive, so they normally occur only as transient intermediates during chemical reactions. But the discovery by Gomberg in 1900 of triphenylmethyl, the first relatively stable free radical containing a central trivalent carbon atom, illustrated that radicals with suitable geometrical and electronic structures can be stable. Compounds containing a divalent carbon atom that uses only two of its four valence electrons for bonding are usually less stable than Gomberg-type radicals with trivalent carbon. Although the role of these so-called carbenes in chemical reactions has long been postulated, they were unambiguously identified only in the 1950s. More recently, stable carbenes have been prepared, but the singlet state of these molecules, with the two nonbonding valence electrons paired, means that they are not radicals. Carbenes in the second possible electronic state, the triplet state, are radicals: the two nonbonding electrons have parallel spins and occupy different orbitals. Here we report the preparation and characterization of a triplet carbene, whose half-life of 19 minutes at room temperature shows it to be significantly more stable than previously observed triplet carbenes.

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confidence: 99%

Generation and characterization of a fairly stable triplet carbene

Tomioka

Iwamoto

Itakura

et al. 2001

Nature

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“…[8] A dramatic change is brought about by phenyl substituents in these positions: carbene 9 has a half-life of 19 min at 20 8C and is the most persistent diarylcarbene known to date. In fact, the major product obtained from 7 is the trimer 8 arising by linking of the 10,10'-positions.…”

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confidence: 99%