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TRIPLET CARBENE HAS LONG LIFE
Serendipitous discovery may lead to organic ferromagnetic materials
A carbene derivative in the triplet state that is significantly more stable than previously observed triplet carbenes has been serendipitously discovered by chemists in Japan.
Chemistry professor Hideo Tomioka, graduate student Eri Iwamoto, and coworkers at Mie University, Tsu, generated triplet bis(9-anthryl)carbene by photolysis of a precursor diazomethane. The half-life of the carbene is 19 minutes in solution at room temperature, they report [Nature, 412, 626 (2001)].
Carbenes in the electronic triplet state have two nonbonding electrons that occupy different orbitals. Unlike their sister singlet carbenes, which have two nonbonding electrons paired in the same orbital, triplet carbenes are organic radicals. And because their two unpaired electrons have parallel spins, triplet carbenes are potentially useful as building blocks for organic ferromagnetic materials.
Triplet carbenes are notoriously transient and highly reactive species, however. The one prepared by Tomioka's team is stabilized by delocalization of the unpaired electrons onto the anthryl substituents of the carbene.
"We have generated the longest-lived triplet carbene," Tomioka tells C&EN. "The previous most stable one, which we reported in 1999, has a half-life of about nine minutes."
The latest discovery was made while the group was preparing a series of carbene precursor diazo compounds with anthryl groups as substituents.
"We asked Iwamoto, a student who had just joined our group, to prepare di(9-anthryl)diazomethane," Tomioka says. "She prepared it in about two months. Much to our surprise, the carbene generated from the diazo compound was fairly stable."
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Copyright © 2001 American Chemical Society