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Diiron oxo reactivity in a weak-field environment

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Abstract

Concomitant deprotonation and metalation of a dinucleating cofacial Pacman dipyrrin ligand platform tBudmxH2 with Fe2(Mes)4 results in formation of a diiron complex (tBudmx)Fe2(Mes)2. Treatment of (tBudmx)Fe2(Mes)2 with one equivalent of water yields the diiron μ-oxo complex (tBudmx)Fe2(μ-O) and free mesitylene. A two-electron oxidation of (tBudmx)Fe2(μ-O) gives rise to the diferric complex (tBudmx)Fe2(μ-O)Cl2, and one-electron reduction from this FeIIIFeIII state allows for isolation of a mixed-valent species [Cp2Co][(tBudmx)Fe2(μ-O)Cl2]. Both (tBudmx)Fe2(μ-O) and [Cp2Co][(tBudmx)Fe2(μ-O)Cl2] exhibit basic character at the bridging oxygen atom and can be protonated using weak acids to form bridging diferrous hydroxide species. The basicity of the diferrous oxo (tBudmx)Fe2(μ-O) is quantified through studies of the pKa of its conjugate acid, [(tBudmx)Fe2(μ-OH)]+, which is determined to be 15.3(6); interestingly, upon coordination of neutral solvent ligands to yield (tBudmx)Fe2(μ-O)(thf)2, the basicity is increased as observed through an increase in the pKa of the conjugate acid [(tBudmx)Fe2(μ-OH)(thf)2]+ to 26.8(6). In contrast, attempts to synthesize a diferric bridging hydroxide by two-electron oxidation of [(tBudmx)Fe2(μ-OH)(thf)2]+ resulted in isolation of (tBudmx)Fe2(μ-O)Cl2 with concomitant loss of a proton, consistent with the pKa of the conjugate acid [(tBudmx)Fe2(μ-OH)Cl2]+ determined computationally to be −1.8(6). The foregoing results highlight the intricate interplay between oxidation state and reactivity in diiron μ-oxo units.

Graphical abstract: Diiron oxo reactivity in a weak-field environment

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Publication details

The article was received on 02 Feb 2019, accepted on 08 May 2019 and first published on 09 May 2019


Article type: Edge Article
DOI: 10.1039/C9SC00605B
Chem. Sci., 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Diiron oxo reactivity in a weak-field environment

    E. J. Johnson, C. Kleinlein, R. A. Musgrave and T. A. Betley, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C9SC00605B

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