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Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a...

We report high‐valent iron complexes supported by N‐heterocyclic carbene (NHC)‐anchored, bis‐phenolate pincer ligands that undergo ligand‐to‐metal charge transfer (LMCT) upon photoexcitation. The resulting excited states – with a lifetime in the picosecond range – feature a ligand‐based, mixed‐valence system and intense intervalence charge transfer bands in the near‐infrared region. Upon oxidation of the complex, corresponding intervalence charge transfer absorptions are also observed in the ground state. We suggest that the spectroscopic hallmarks of such LMCT states provide useful tools to decipher excited‐state decay mechanisms in high‐valent NHC complexes. Our observations further indicate that NHC‐anchored, bis‐phenolate pincer ligands are not sufficiently strong donors to prevent the population of excited metal‐centered states in high‐valent iron complexes.

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)2C2P2 (1) (IPr=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe2CO9] gives the neutral iron tricarbonyl complex [Fe(CO)3-η3-{(IPr)2C2P2}] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2](BArF24), affords the dicationic tricarbonyl complex [Fe(CO)3-η4-{(IPr)2C2P2}](BArF24)2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2-η4-{(IPr)2C2P2}](BArF24) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2-η4-{(IPr)2C2P2}] (6). An analysis by various spectroscopic techniques (57Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade–Mingos clusters., Angewandte Chemie. International Edition, 61 (43), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)

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The synthesis and characterization of a series of homoleptic iron complexes [Fe(benzNHCOCO)2]2–/1–/0/1+ supported by the tridentate bis-aryloxide benzimidazolin-2-ylidene pincer ligand benzNHCOCO2–...