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

作者：Liu Yizhu; Kjaer Kasper S; Fredin Lisa A; Chabera Pavel; Harlang Tobias; Canton Sophie E; Lidin Sven; Zhang Jianxin; Lomoth Reiner; Bergquist Karl Erik; Persson Petter; Warnmark Kenneth^*; Sundstrom Villy

来源：Chemistry - A European Journal, 2015, 21(9): 3628-3639.

DOI：10.1002/chem.201405184

• iron
• femtosecond spectroscopy
• N ligands
• metal-to-ligand charge transfer
• N-heterocyclic carbenes

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.

• 出版日期2015-2-23