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Molecules 2016, 21(11), 1545; doi:10.3390/molecules21111545

Diphenylcarbene Protected by Four ortho-Iodine Groups: An Unusually Persistent Triplet Carbene

1
Community-University Research Cooperation Center, Mie University, Tsu, Mie 514-8507, Japan
2
Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Shunichi Fukuzumi
Received: 20 October 2016 / Revised: 8 November 2016 / Accepted: 11 November 2016 / Published: 15 November 2016
(This article belongs to the Special Issue Cutting-Edge Organic Chemistry in Japan)
View Full-Text   |   Download PDF [2595 KB, uploaded 15 November 2016]   |  

Abstract

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-N2), was synthesized as a sterically hindered triplet carbene precursor. Irradiation of 1a-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 31a was obtained by irradiating 1a-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 31a were observed by laser flash photolysis of 1a-N2 in a degassed benzene solution and decayed very slowly with a second-order rate constant (2k/εl) of 5.5 × 103·s1. Steady-state irradiation of 1a-N2 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 × 105 M1·s1) or 1,4-cyclohexadiene (kCHD = 1.5 M1·s1) to afford the corresponding ketone 1a-O or the diarylmethane 1a-H2. 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. View Full-Text
Keywords: triplet carbene; diazo compound; photolysis; steric hindrance; substituent effect triplet carbene; diazo compound; photolysis; steric hindrance; substituent effect
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MDPI and ACS Style

Hirai, K.; Bessho, K.; Tsujita, K.; Kitagawa, T. Diphenylcarbene Protected by Four ortho-Iodine Groups: An Unusually Persistent Triplet Carbene. Molecules 2016, 21, 1545.

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