Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

Brusar, Vedran; Forjan, Mateo; Ljubić, Ivan; Alešković, Marija; Becker, Kristin; Vdović, Silvije (2023) Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction. The Journal of Organic Chemistry, 88 (7). pp. 4286-4300. ISSN 0022-3263

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Abstract

The photochemical reactivity of diphenyldiazomethane 1 and phenyl 1- and 2 adamantyl diazomethanes 2 and 3, respectively, was investigated by transient absorption spectroscopy (TA). Photoelimination of N2 upon UV excitation takes place in the anti-Kasha ultrafast photochemical reaction from the upper excited singlet states to deliver singlet carbenes, which were, in the case of 1 and 2, detected by fs-TA. The reactivity of the carbenes differs with respect to the substituent at the carbene center. The singlet car-1 in a nonpolar solvent delivers the triplet carbene by intersystem crossing (ISC). Singlet car-2 does not undergo ISC but reacts in the intermolecular insertion reactions into C–H bonds. Car-3 has an α-C–H bond next to the carbene center and reacts rapidly in the intramolecular C– H insertion reaction to deliver alkene, precluding its detection by fs-TA. However, the isolation of ketone photoproducts from 3 is highly indicative of triplet car-3’s intermediate formation. The TA spectra from the S1–S3 states of 1–3 were computed using time-dependent density functional theory, while the multiconfigurational perturbation theory to the second order was used for the absorption spectra of the corresponding singlet and triplet carbenes. The modeled and measured spectra are in good agreement, and the computations corroborate the assignments of the key short-lived intermediates.

Item Type:	Article
Additional Information:	This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in The Journal of Organic Chemistry, Copyright © 2023 American Chemical Society after peer review. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.joc.2c02875
Uncontrolled Keywords:	absorption ; carbene compounds ; excited states ; hydrocarbons ; time-dependent density functional theory
Subjects:	NATURAL SCIENCES > Chemistry > Physical Chemistry NATURAL SCIENCES > Chemistry > Theoretical Chemistry NATURAL SCIENCES > Chemistry > Analytic Chemistry NATURAL SCIENCES > Chemistry > Organic Chemistry
Divisions:	Division of Organic Chemistry and Biochemistry Division of Physical Chemistry
Projects:	Project title Project leader Project code Project type Efekt kvantnog tuneliranja: dinamika molekula s kvantnim jezgrama-QuanTunMol Marko Tomislav Cvitaš IP-2020-02-9932 HRZZ Supramolekulska kontrola fotokemijskih reakcija eliminacije-SupraPhotoE Nikola Basarić IP-2014-09-6312 HRZZ Fotokemija: Reakcijski mehanizmi i primjene u organskoj sintezi i biologiji-PhotoApp Nikola Basarić; Irena Škorić; Dragana Vuk IP-2019-04-8008 HRZZ Grupa za primijenjenu ultrabrzu spektroskopiju i fotokemijsku identifikaciju-GASPI Silvije Vdović UIP-2017-05-5831 HRZZ
Depositing User:	Ivan Ljubić
Date Deposited:	08 Jan 2025 10:00
URI:	http://fulir.irb.hr/id/eprint/9349
DOI:	10.1021/acs.joc.2c02875

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