title: Triplet diphenylcarbenes protected by trifluoromethyl and bromine groups. A triplet carbene surviving a day in solution at room temperature.
abstract: Two types of diphenyldiazomethanes having two trifluoromethyl and two bromine groups at the ortho positions, either in unsymmetrical or in symmetrical fashion, that is, (2,6-dibromo-4-phenylphenyl)[4-phenyl-2,6-bis(trifluoromethyl)phenyl]diazomethane (U-1-N2) and bis(2-bromo-4-phenyl-6-trifluoromethylphenyl)diazomethane (S-1-N2), are prepared. Triplet diphenylcarbenes (U-(3)1 or S-(3)1) are generated from those precursors and are characterized by ESR, UV/vis spectroscopy at low temperature, as well as time-resolved UV/vis spectroscopy at room temperature. Those carbenes are shown to be at least 2 orders of magnitude less reactive than the most stable triplet diphenylcarbene thus far known, that is, bis(2,6-dibromo-4-phenylphenyl)carbene. It has been also shown that S-(3)1 is significantly more stable than U-(3)1 even though both have the same two kinds of substituents. It is suspected that the perpendicular alignment of the two most bulky groups is a more effective way to shield the carbenic center than the planar one. By this way, triplet substituted diphenylcarbene surviving nearly a day in solution at room temperature is realized for the first time.
authors.affiliation: Chemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan.
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Itoh
authors.forename: Yoshimaru
authors.initials: Y
authors.lastname: Nakata
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Hirai
authors.forename: Hideo
authors.initials: H
authors.lastname: Tomioka