title: Diphenylcarbene Protected by Four ortho-Iodine Groups: An Unusually Persistent Triplet Carbene.
abstract: Diphenyldiazomethane with four iodine groups at theorthopositions and twotert-butyl groups at theparapositions, i.e., bis(4-tert-butyl-2,6-diiodophenyl)diazomethane (1a-N₂), was synthesized as a sterically hindered triplet carbene precursor. Irradiation of1a-N₂ in solution effectively generated the corresponding triplet diphenylcarbene ³1a, which was characterized by UV-vis spectroscopy at low temperature, along with laser flash photolysis techniques at room temperature. The UV-vis spectrum of ³1awas obtained by irradiating1a-N₂ in a 2-methyltetrahydrofuran matrix at 77 K. The ESR spectrum showed no triplet carbene signals, while a radical species was observed at the anticipated temperature of the decomposition of triplet carbene ³1a. Transient absorption bands ascribable to ³1awere observed by laser flash photolysis of1a-N₂ in a degassed benzene solution and decayed very slowly with a second-order rate constant (2k/εl) of 5.5 × 10-³·s-¹. Steady-state irradiation of1a-N₂ in degassed benzene afforded 9,10-diarylphenanthrene derivative2ain a 31% yield. Triplet carbene ³1awas also trapped by either oxygen (kO2= 6.5 × 10⁵ M-¹·s-¹) or 1,4-cyclohexadiene (kCHD= 1.5 M-¹·s-¹) to afford the corresponding ketone1a-O or the diarylmethane1a-H₂. The carbene was shown to be much less reactive than the triplet diphenylcarbene that is protected by twoortho-iodo and twoortho-bromo groups, ³1b.
authors.affiliation: Community-University Research Cooperation Center, Mie University, Tsu, Mie 514-8507, Japan. hirai@chem.mie-u.ac.jp.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Hirai
authors.affiliation: Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan. kinou@chem.mie-u.ac.jp.
authors.forename: Kana
authors.initials: K
authors.lastname: Bessho
authors.affiliation: Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan. cultivation_eigode@i.softbank.jp.
authors.forename: Kosaku
authors.initials: K
authors.lastname: Tsujita
authors.affiliation: Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan. kitagawa@chem.mie-u.ac.jp.
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Kitagawa
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry*; D007455:Iodine / Q000737:chemistry*; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D015394:Molecular Structure; D010782:Photolysis; D013057:Spectrum Analysis / Q000379:methods; D013696:Temperature
chemical_list: D001713:Biphenyl Compounds; D007455:Iodine; D008697:Methane; C030011:carbene; C010574:biphenyl
keywords: diazo compound; photolysis; steric hindrance; substituent effect; triplet carbene