A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3-triazol-5-ylidene) Ligands: Taming the MLCT Excited State of Iron(II)

Yizhu Liu, Kasper Skov Kjær, Lisa A. Fredin, Pavel Chabera, Tobias C. B. Harlang, Sophie E. Canton, Sven Lidin, Jianxin Zhang, Reiner Lomoth, Karl-Erik Bergquist, Petter Persson, Kenneth Wärnmark, Villy Sundström

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Strongly sigma-donating N-heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic Fe-II complex (1) was synthesized based on sequentially furnishing the Fe-II center with the benchmark 2,2-bipyridine (bpy) ligand and the more strongly sigma-donating mesoionic ligand, 4,4-bis(1,2,3-triazol-5-ylidene) (btz). Complex1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)(3)](PF6)(2) and (TBA)(2)[Fe(bpy)(CN)(4)]. Heteroleptic complex1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic Fe-II NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal-centered (MC) states relative to the triplet metal-to-ligand charge transfer ((MLCT)-M-3) state in 1, rendering it a lifetime of 13ps, the longest to date of a photochemically stable Fe-II complex. Deactivation of the (MLCT)-M-3 state is proposed to proceed via the (MC)-M-3 state that strongly couples with the singlet ground state.
Original languageEnglish
JournalChemistry: A European Journal
Volume21
Issue number9
Pages (from-to)3628-3639
Number of pages12
ISSN0947-6539
DOIs
Publication statusPublished - 2015

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