Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Photoredox catalysis via consecutive 2LMCT- and 3MLCT-excitation of an Fe(iii/ii)-N-heterocyclic carbene complex

Ilic, Aleksandra LU orcid ; Schwarz, Jesper LU ; Johnson, Catherine ; de Groot, Lisa H.M. LU ; Kaufhold, Simon LU orcid ; Lomoth, Reiner and Wärnmark, Kenneth LU (2022) In Chemical Science 13(32). p.9165-9175
Abstract

Fe-N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe-NHC complexes to date. Here, we have employed [Fe(iii)(btz)3]3+ (btz = (3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe-NHC complexes, [Fe(iii/ii)(btz)3]3+/2+ benefits from sizable charge transfer excited state lifetimes ≥0.1 ns in both oxidation... (More)

Fe-N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe-NHC complexes to date. Here, we have employed [Fe(iii)(btz)3]3+ (btz = (3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe-NHC complexes, [Fe(iii/ii)(btz)3]3+/2+ benefits from sizable charge transfer excited state lifetimes ≥0.1 ns in both oxidation states, and the Fe(iii) 2LMCT and Fe(ii) 3MLCT states are strong oxidants and reductants, respectively. The combined reactivity of both excited states enables efficient one-electron reduction of the alkyl halide substrate under green light irradiation. The two-photon mechanism proceeds via reductive quenching of the Fe(iii) 2LMCT state by a sacrificial electron donor and subsequent excitation of the Fe(ii) product to its highly reducing 3MLCT state. This route is shown to be more efficient than the alternative, where oxidative quenching of the less reducing Fe(iii) 2LMCT state by the alkyl halide drives the reaction, in the absence of a sacrificial electron donor.

(Less)
Please use this url to cite or link to this publication:
author
; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Chemical Science
volume
13
issue
32
pages
11 pages
publisher
Royal Society of Chemistry
external identifiers
  • pmid:36093023
  • scopus:85135573987
ISSN
2041-6520
DOI
10.1039/d2sc02122f
language
English
LU publication?
yes
id
60bf5f34-5bb9-4c4d-bb5b-a5105e8e2d29
date added to LUP
2022-10-18 15:18:03
date last changed
2024-03-21 08:59:51
@article{60bf5f34-5bb9-4c4d-bb5b-a5105e8e2d29,
  abstract     = {{<p>Fe-N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe-NHC complexes to date. Here, we have employed [Fe(iii)(btz)<sub>3</sub>]<sup>3+</sup> (btz = (3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe-NHC complexes, [Fe(iii/ii)(btz)<sub>3</sub>]<sup>3+/2+</sup> benefits from sizable charge transfer excited state lifetimes ≥0.1 ns in both oxidation states, and the Fe(iii) <sup>2</sup>LMCT and Fe(ii) <sup>3</sup>MLCT states are strong oxidants and reductants, respectively. The combined reactivity of both excited states enables efficient one-electron reduction of the alkyl halide substrate under green light irradiation. The two-photon mechanism proceeds via reductive quenching of the Fe(iii) <sup>2</sup>LMCT state by a sacrificial electron donor and subsequent excitation of the Fe(ii) product to its highly reducing <sup>3</sup>MLCT state. This route is shown to be more efficient than the alternative, where oxidative quenching of the less reducing Fe(iii) <sup>2</sup>LMCT state by the alkyl halide drives the reaction, in the absence of a sacrificial electron donor.</p>}},
  author       = {{Ilic, Aleksandra and Schwarz, Jesper and Johnson, Catherine and de Groot, Lisa H.M. and Kaufhold, Simon and Lomoth, Reiner and Wärnmark, Kenneth}},
  issn         = {{2041-6520}},
  language     = {{eng}},
  number       = {{32}},
  pages        = {{9165--9175}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{Chemical Science}},
  title        = {{Photoredox catalysis via consecutive <sup>2</sup>LMCT- and <sup>3</sup>MLCT-excitation of an Fe(iii/ii)-N-heterocyclic carbene complex}},
  url          = {{http://dx.doi.org/10.1039/d2sc02122f}},
  doi          = {{10.1039/d2sc02122f}},
  volume       = {{13}},
  year         = {{2022}},
}