Diphenyldiazomethane with four iodine groups at the
ortho positions and two
tert-butyl groups at the
para positions, i.e., bis(4-
tert-butyl-2,6-diiodophenyl)diazomethane (
1a-N
2), was synthesized as a sterically hindered triplet carbene precursor. Irradiation of
1a-N
2 in solution
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Diphenyldiazomethane with four iodine groups at the
ortho positions and two
tert-butyl groups at the
para positions, i.e., bis(4-
tert-butyl-2,6-diiodophenyl)diazomethane (
1a-N
2), was synthesized as a sterically hindered triplet carbene precursor. Irradiation of
1a-N
2 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
31a was obtained by irradiating
1a-N
2 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
31a were observed by laser flash photolysis of
1a-N
2 in a degassed benzene solution and decayed very slowly with a second-order rate constant (2
k/ε
l) of 5.5 × 10
−3·s
−1. Steady-state irradiation of
1a-N
2 in degassed benzene afforded 9,10-diarylphenanthrene derivative
2a in a 31% yield. Triplet carbene
31a was also trapped by either oxygen (
kO2 = 6.5 × 10
5 M
−1·s
−1) or 1,4-cyclohexadiene (
kCHD = 1.5 M
−1·s
−1) to afford the corresponding ketone
1a-O or the diarylmethane
1a-H
2. The carbene was shown to be much less reactive than the triplet diphenylcarbene that is protected by two
ortho-iodo and two
ortho-bromo groups,
31b.
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