A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3‐triazol‐5‐ylidene) Ligands: Taming the MLCT Excited State of Iron(II) |
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| Authors: | Dr Yizhu Liu Dr Kasper S Kjær Dr Lisa A Fredin Dr Pavel Chábera Tobias Harlang Dr Sophie E Canton Prof Sven Lidin Dr Jianxin Zhang Prof Reiner Lomoth Dr Karl‐Erik Bergquist Prof Petter Persson Prof Kenneth Wärnmark Prof Villy Sundström |
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| Institution: | 1. Department of Chemical Physics, Lund University, P.O. Box?124, 22100 Lund (Sweden);2. Centre for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box?124, 22100 Lund (Sweden);3. Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby (Denmark);4. Theoretical Chemistry Division, Lund University, P.O. Box?124, 22100 Lund (Sweden);5. Department of Synchrotron Instrumentation, Lund University, P.O. Box?124, 22100 Lund (Sweden);6. Current address: School of Environment and Chemical Engineering, Tianjin Polytechnic University, Tianjin, 300087 (China);7. Department of Chemistry—?ngstr?m Laboratory, Uppsala University, P.O. Box?523, 75120 Uppsala (Sweden) |
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| Abstract: | Strongly σ‐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 FeII complex ( 1 ) was synthesized based on sequentially furnishing the FeII center with the benchmark 2,2′‐bipyridine (bpy) ligand and the more strongly σ‐donating mesoionic ligand, 4,4′‐bis(1,2,3‐triazol‐5‐ylidene) (btz). Complex 1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to Fe(bpy)3](PF6)2 and (TBA)2Fe(bpy)(CN)4]. Heteroleptic complex 1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic FeII 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 (3MLCT) state in 1 , rendering it a lifetime of 13 ps, the longest to date of a photochemically stable FeII complex. Deactivation of the 3MLCT state is proposed to proceed via the 3MC state that strongly couples with the singlet ground state. |
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| Keywords: | iron femtosecond spectroscopy N ligands metal‐to‐ligand charge transfer N‐heterocyclic carbenes |
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