Dataset Information

Selective Aromatic C-H Hydroxylation Enabled by ?6-Coordination to Iridium(III).

ABSTRACT: We report an aromatic C-H hydroxylation protocol in which the arene is activated through ?6-coordination to an iridium(III) complex. ?6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate ?5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene ?-activation into a catalytic cycle for C-H functionalization.

SUBMITTER: D'Amato EM

PROVIDER: S-EPMC4750501 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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Selective Aromatic C-H Hydroxylation Enabled by η6-Coordination to Iridium(III).

D'Amato Erica M EM Neumann Constanze N CN Ritter Tobias T

Organometallics 20150916 18

We report an aromatic C-H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into ...[more]

PMID: 26877574

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Project description:The factor inhibiting HIF (FIH) is a proximate oxygen sensor for human cells, hydroxylating Asn(803) within the ?-subunit of the hypoxia inducible factor (HIF). FIH is an ?-ketoglutatrate (?KG)-dependent, non-heme Fe(II) dioxygenase, in which Fe(II) is coordinated by a (His(2)Asp) facial triad, ?KG, and H(2)O. Hydrogen bonding among the facial triad, the HIF-Asn(803) side chain, and various second-sphere residues suggests a functional role for the second coordination sphere in tuning the chemistry of the Fe(II) center. Point mutants of FIH were prepared to test the functional role of the ?KG-centered (Asn(205) and Asn(294)) or HIF-Asn(803)-centered (Arg(238) and Gln(239)) second-sphere residues. The second sphere was tested for local effects on priming Fe(II) to react with O(2), oxidative decarboxylation, and substrate positioning. Steady-sate kinetics were used to test for overall catalytic effects; autohydroxylation rates were used to test for priming and positioning, and electronic spectroscopy was used to assess the primary coordination sphere and the electrophilicity of ?KG. Asn(205) ? Ala and Asn(294) ? Ala mutants exhibited diminished rates of steady-state turnover, while minimally affecting autohydroxylation, consistent with impaired oxidative decarboxylation. Blue-shifted metal to ligand charge transfer transitions for (Fe+?KG)FIH indicated that these point mutations destabilized the ?* orbitals of ?KG, further supporting a slowed rate of oxidative decarboxylation. The Arg(238) ? Met mutant exhibited steady-state rates too low to measure and diminished product yields, suggesting impaired substrate positioning or priming; the Arg(238) ? Met mutant was capable of O(2) activation for the autohydroxylation reaction. The Gln(239) ? Asn mutant exhibited significantly slowed steady-state kinetics and diminished product yields, suggesting impaired substrate positioning or priming. As HIF binding to the Gln(239) ? Asn mutant stimulated autohydroxylation, it is more likely that this point mutant simply mispositions the HIF-Asn(803) side chain. This work combines kinetics and spectroscopy to show that these second-sphere hydrogen bonds play roles in promoting oxidative decarboxylation, priming Fe(II) to bind O(2), and positioning HIF-Asn(803).

Dataset Information

Selective Aromatic C-H Hydroxylation Enabled by ?6-Coordination to Iridium(III).

Publications

Selective Aromatic C-H Hydroxylation Enabled by <i>η</i><sup>6</sup>-Coordination to Iridium(III).

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