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Diiron oxo reactivity in a weak-field environment† †Electronic supplementary information (ESI) available. CCDC 1554783–1554789. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9sc00605b ‡ ‡Authors contributed equally.


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.

SUBMITTER: Johnson EJ 

PROVIDER: S-EPMC6598509 | BioStudies | 2019-01-01

REPOSITORIES: biostudies

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Diiron oxo reactivity in a weak-field environment.

Johnson Elizabeth J EJ   Kleinlein Claudia C   Musgrave Rebecca A RA   Betley Theodore A TA  

Chemical science 20190509 25


Concomitant deprotonation and metalation of a dinucleating cofacial Pacman dipyrrin ligand platform <sup><i>t</i>Bu</sup>dmxH<sub>2</sub> with Fe<sub>2</sub>(Mes)<sub>4</sub> results in formation of a diiron complex ( <sup><i>t</i>Bu</sup>dmx)Fe<sub>2</sub>(Mes)<sub>2</sub>. Treatment of ( <sup><i>t</i>Bu</sup>dmx)Fe<sub>2</sub>(Mes)<sub>2</sub> with one equivalent of water yields the diiron μ-oxo complex ( <sup><i>t</i>Bu</sup>dmx)Fe<sub>2</sub>(μ-O) and free mesitylene. A two-electron oxidatio  ...[more]

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