Selective Photo-Induced Oxidation with O
2 of a Non-Heme Iron(III) Complex to a Bis(imine-pyridyl)iron(II) Complex.
Inorg Chem 2018;
57:4510-4515. [PMID:
29601196 PMCID:
PMC5906753 DOI:
10.1021/acs.inorgchem.8b00187]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Non-heme iron(II)
complexes of pentadentate N4Py (N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine)
type ligands undergo visible light-driven oxidation to their iron(III)
state in the presence of O2 without ligand degradation.
Under mildly basic conditions, however, highly selective base catalyzed
ligand degradation with O2, to form a well-defined pyridyl-imine
iron(II) complex and an iron(III) picolinate complex, is accelerated
photochemically. Specifically, a pyridyl-CH2 moiety is
lost from the ligand, yielding a potentially N4 coordinating ligand
containing an imine motif. The involvement of reactive oxygen species
other than O2 is excluded; instead, deprotonation at the
benzylic positions to generate an amine radical is proposed as the
rate determining step. The selective nature of the transformation
holds implications for efforts to increase catalyst robustness through
ligand design.
Photoaccelerated oxidation
of an aminopyridyl ligand bound
to an Fe(III) ion to a well-defined imine-based Fe(II) complex involves
initial alkyl C−H deprotonation followed by reaction with O2 to form an alkyl peroxyl radical. Intramolecular C−H
abstraction followed by C−N bond cleavage yields picoline aldehyde
and a pyridyl-imine complex. The selectivity of the reaction prevents
further oxidation and holds implications for ligand degradation under
conditions used in oxidation catalysis with peroxides.
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