Neocuproine as a Redox-Active Ligand Platform on Iron and Cobalt

Abstract

A family of bis(neocuproine) complexes of Fe 2+ and Co 2+ have been investigated for neocuproine redox noninnocence. A series of redox isomers of M(neocuproine) 2 n+ (where n = 2, 1, 0 for Co and n = 2, 0 for Fe) have been synthesized and thoroughly characterized. The electronic structure of these complexes has been rigorously investigated using a variety of techniques, including X-ray absorption spectroscopy, Mossbauer spectroscopy, X-ray diffraction, electron paramagnetic resonance spectroscopy, and magnetic measurements. All of these techniques are consistent with ligand-based reduction events to generate radical neocuproine complexes. Thus, neocuproine adds to a growing family of chelating N-donor type ligands that participate in redox noninnocence and may be useful for future catalyst and reaction design.

Halogen Transfer to Carbon Radicals by High-Valent Iron Chloride and Iron Fluoride Corroles

“…The 1 H NMR spectrum of 2 in C 6 D 5 CD 3 reveals 6 paramagnetic peaks from δ = 0 to −60 ppm that are in the same region as peaks seen for Fe­(Cl)­(ttppc) and Fe­(OH)­(ttppc) (Figure ) and the related Fe­(Cl)­(tpc) (tpc = triphenylcorrolato 3– ). , These resonances have been assigned to the β-CH pyrrole protons for iron triphenylcorrole complexes. ,− The 19 F { 1 H} NMR spectrum of 2 in C 6 D 5 CD 3 has a broad peak at δ = −76.4 ppm (full width at half-maximum (fwhm) = 692 Hz), which can be compared to the sharp resonance for AgOTf in the same solvent at −76.5 ppm (fwhm = 2.82 Hz) (Figure S4). The broad line in C 6 D 5 CD 3 is consistent with coordination of the triflate ligand to the paramagnetic iron center, although tight binding of OTf – is expected to give a larger downfield shift for the OTf – peak. , In contrast, the 1 H NMR spectrum of 2 in the presence of CD 3 CN (CD 3 CN/C 6 D 5 CD 3 (1/1 v/v) exhibits paramagnetic peaks between 0 and −50 ppm that are shifted from neat C 6 D 5 CD 3 (Figure S5). The corresponding 19 F { 1 H} NMR spectrum exhibits a much sharper peak at δ = −77.73 ppm (fwhm = 127 Hz), consistent with displacement of the OTf – axial ligand by CH 3 CN, as indicated by the UV–vis spectra in the same solvent (Figure S3).…”

“…The broad line in C 6 D 5 CD 3 is consistent with coordination of the triflate ligand to the paramagnetic iron center, although tight binding of OTf − is expected to give a larger downfield shift for the OTf − peak. 64,65 In contrast, the 1 H NMR spectrum of 2 in the presence of CD 3 CN (CD 3 CN/C 6 D 5 CD 3 (1/1 v/v) exhibits paramagnetic peaks between 0 and −50 ppm that are shifted from neat C 6 D 5 CD 3 (Figure S5). The corresponding 19 F { 1 H} NMR spectrum exhibits a much sharper peak at δ = −77.73 ppm (fwhm = 127 Hz), consistent with displacement of the OTf − axial ligand by CH 3 CN, as indicated by the UV−vis spectra in the same solvent (Figure S3).…”

Photocatalytic CO2 Reduction Using Mixed Catalytic Systems Comprising an Iron Cation with Bulky Phenanthroline Ligands

“…Note that in the absence of TEOA, the system with Fe II ( MeHp )­Cl 2 did not induce CO 2 reduction. This indicates that a singly reduced Fe II ( MeHp )­Cl 2 , in which the added electron was localized on the MeHp ligands, i.e., Fe II ( MeHp •– )­Cl 2 , could not induce CO 2 reduction. Thus, the production of MeHp H • and its interaction with the Fe ion are essential for the CO 2 reduction.…”

Thermally Stable Redox Noninnocent Bathocuproine-Iron Complex for Cycloaddition Reactions

“…In the latter case, standard glovebox conditions are usually mandatory, which can preclude a routine use of such species in organic synthetic chemistry. Therefore, the compared stabilities of reduced complex 2 and of its neocuproine analogue 2′ utilized by Anderson were investigated after in situ generation using a Grignard reagent on one hand and after synthesis and purification on the other hand.…”

“…Great care must thus be taken regarding the control of the metal-to-ligand charge transfer induced by this noninnocent behavior, since it can have a dramatic impact on the stability of the complex. Recently, Anderson and co-workers systematically explored 2,9-dimethyl-1,10-phenanthroline, more commonly referred to as neocuproine (L′ herein), as a potentially redox noninnocent ligand to iron and cobalt . Thorough characterization of the 2:1 neocuproine/metal neutral L′ 2 M (M = Co, Fe) complexes revealed them to be Fe 2+ and Co 2+ with two ligand-based radicals.…”