2H1C Mimicry: Bioinspired Iron and Zinc Complexes Supported by N,N,O Phenolate Ligands

Abstract

In pursuit of mimicking the ubiquitous 2H1C motif in mononuclear non‐heme iron enzymes, two new bioinspired N,N,O phenolate ligands, BenzImNNO and ImPh2NNO, are synthesised and their coordination chemistry with zinc(II) and iron(II) is explored. BenzImNNO coordinates by means of an anionic κ3‐N,N,O donor set and readily forms homoleptic bisligated complexes, also in the presence of equimolar amounts of metal salt. In contrast, the increased steric bulk of ImPh2NNO promotes the formation of dinuclear complexes, [M2(ImPh2NNO)2(OTf)2] (M=Fe, Zn), with facially opposing metal sites, as a result of its unique bridging μ2:κ2‐N,N:κ1‐O coordination mode. We investigate the robustness of the ligand's dinucleating coordination mode during oxidative transformations and demonstrate that its coordination mode is retained upon triflate substitution for a biorelevant thiophenolate co‐ligand.

Synthesis, Structure and Reactivity of a Mononuclear N,N,O‐Bound Fe(II) α‐Keto‐Acid Complex

“…We attribute this to the more localised negative charge of the Im Ph2 NNO tBu ligand, which quenches the Lewis acidity of the iron centre. The Fe−N bond lengths are characteristic of a high‐spin iron(II) centre bound to an imidazole‐containing N,N,O ligand [84,85,88,89] …”

“…The FeÀ N bond lengths are characteristic of a high- spin iron(II) centre bound to an imidazole-containing N,N,O ligand. [84,85,88,89]…”

“…[84][85][86][87] Typically, problems are encountered through the formation of homoleptic bis-ligand complexes, the formation of polynuclear complexes due to bridging O-donor coordination modes, or disruption of the N,N,O triad due to labile N-or O-donors. [88,89] To the best of our knowledge, the dinuclear complex [Fe 2 (μ 2 -Me 2 HDP) 2 (μ 2 -BF)], reported by the group of Que (Figure 2), is the only structurally characterised iron(II) benzoylformato complex to date that features a mixed N,O-donor ligand. [90] Burzlaff and co-workers have since reported a mononuclear Ru(II) complex, [Ru(bdmpza)(k 2 -BF)(PPh 3 )], which features a bis(pyrazolyl)-acetate ligand (Figure 2).…”

“…This is largely due to the fact that very few tridentate N,N,O ligands have been reported that support the formation of mononuclear, monoligated iron complexes [84–87] . Typically, problems are encountered through the formation of homoleptic bis‐ligand complexes, the formation of polynuclear complexes due to bridging O‐donor coordination modes, or disruption of the N,N,O triad due to labile N‐ or O‐donors [88,89] . To the best of our knowledge, the dinuclear complex [Fe 2 (μ 2 ‐Me 2 HDP) 2 (μ 2 ‐BF)], reported by the group of Que (Figure 2), is the only structurally characterised iron(II) benzoylformato complex to date that features a mixed N , O ‐donor ligand [90] .…”