title: Generation, reactions, and kinetics of sterically congested triplet diphenylcarbenes. Effects of bromine groups.
abstract: A series of polybrominated diphenylcarbenes (DPCs) are generated by irradiation of the corresponding precursor diazomethanes, and their reactivities are investigated by means of low-temperature spectroscopies as well as laser flash photolysis. Triplet bis(2,4,6-tribromophenyl)carbene was shown to decay by undergoing dimerization and to have a half-life of 1 s in a degassed benzene solution at room temperature, some 6 orders of magnitude longer-lived than the parent DPC. Anomalous effects of para substituents on the stability of the triplet are noted. Thus, while the replacement of a 4-bromine group with a methyl group resulted in a sharp decrease in the lifetime, introduction of a tert-butyl group resulted in a dramatic increase in the lifetime; triplet bis(2,6-dibromo-4-tert-butylphenyl)carbene was shown to have a half-life of 16 s in solution at room temperature. Attempts to increase the stability of these polybrominated DPCs by buttressing effects of a m-bromine group and by the synergetic effect of bromine and methyl groups are also described.
authors.affiliation: Chemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Tomioka
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Watanabe
authors.forename: Makoto
authors.initials: M
authors.lastname: Hattori
authors.forename: Naoki
authors.initials: N
authors.lastname: Nomura
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Hirai