Reaction of the CoI complex (TIMMNmes)CoI(PF6) (1) (TIMMNmes=tris‐2‐(3‐mesityl‐imidazolin‐2‐ylidene)‐methylamine) with mesityl azide yields the CoIII imide (TIMMNmes)CoIII(NMes)(PF6) (2). Oxidation ...of 2 with FeCp2(PF6) provides access to a rare CoIII imidyl (TIMMNmes)Co(NMes)(PF6)2 (3). Single‐crystal X‐ray diffractometry and EPR spectroscopy confirm the molecular structure of 3 and its S=1/2
ground state. ENDOR, X‐ray absorption spectroscopy and computational analyses indicate a ligand‐based oxidation; thus, an imidyl‐radical electronic structure for 3. Migratory insertion of one ancillary NHC to the imido ligand in 2 gives the CoI N‐heterocyclic imine (4) within 12 h. Conversely, it takes merely 0.5 h for 3 to transform to the CoII congener (5). The migratory insertion in 2 occurs via a nucleophilic attack of the imido ligand at the NHC to give 4, whereas in 3, a nucleophilic attack of the NHC at the electrophilic imidyl ligand yields 5. The reactivity shunt upon oxidation of 2 to 3 confirms an umpolung of the imido ligand.
Straightforward access to a CoIII terminal imidyl radical complex was provided by one‐electron oxidation of a CoIII terminal imido precursor. Oxidation of the CoIII terminal imido to its imidyl redox isomer facilitates intramolecular migratory insertion reactions of the imido with an NHC ligand by a switch of mechanism through umpolung of the imido ligand.
A novel covalent post-translational modification (lysine-NOS-cysteine) was discovered in proteins, initially in the enzyme transaldolase of
(
TAL)
,
, 460-464, acting as a redox switch. The ...identification of this novel linkage in solution was unprecedented until now. We present detection of the NOS redox switch in solution using sulfur K-edge X-ray absorption spectroscopy (XAS). The oxidized
TAL spectrum shows a distinct shoulder on the low-energy side of the rising edge, corresponding to a dipole-allowed transition from the sulfur 1s core to the unoccupied σ* orbital of the S-O group in the NOS bridge. This feature is absent in the XAS spectrum of reduced
TAL, where Lys-NOS-Cys is absent. Our experimental and calculated XAS data support the presence of a NOS bridge in solution, thus potentially facilitating future studies on enzyme activity regulation mediated by the NOS redox switches, drug discovery, biocatalytic applications, and protein design.
We disclose a new reactivity mode for electrophilic cyano λ3‐iodanes as group transfer one‐electron oxidants to synthesize FeIII and FeIV cyanide complexes. The inherent thermal instability of ...high‐valent FeIV compounds without π‐donor ligands (such as oxido (O2−), imido (RN2−) or nitrido (N3−)) makes their isolation and structural characterization a very challenging task. We report the synthesis of an FeIV cyanide complex (N3N′)FeCN (4) by two consecutive single electron transfer (SET) processes from FeII precursor (N3N′)FeLi(THF) (1) with cyanobenziodoxolone (CBX). The FeIV complex can also be prepared by reaction of (N3N′)FeIII (3) with CBX. In contrast, the oxidation of FeII with 1‐cyano‐3,3‐dimethyl‐3‐(1H)‐1,2‐benziodoxole (CDBX) enables the preparation of FeIII cyanide complex (N3N′)FeIII(CN)(Li)(THF)3 (2‐LiTHF). Complexes 4 and 2‐LiTHF have been structurally characterized by single crystal X‐ray diffraction and their electronic structure has been examined by Mössbauer, EPR spectroscopy, and computational analyses.
Cyano λ3‐iodanes react with iron(II) and iron(III) complexes as cyano‐transfer one‐electron oxidants. This approach enables the straightforward synthesis of iron(III) and iron(IV) cyanide complexes, which have been thoroughly characterized by spectroscopic methods, including X‐ray diffraction, EPR, Mössbauer and NMR spectroscopies and computational methods.
We disclose a new reactivity mode for electrophilic cyano λ
-iodanes as group transfer one-electron oxidants to synthesize Fe
and Fe
cyanide complexes. The inherent thermal instability of high-valent ...Fe
compounds without π-donor ligands (such as oxido (O
), imido (RN
) or nitrido (N
)) makes their isolation and structural characterization a very challenging task. We report the synthesis of an Fe
cyanide complex (N
N')FeCN (4) by two consecutive single electron transfer (SET) processes from Fe
precursor (N
N')FeLi(THF) (1) with cyanobenziodoxolone (CBX). The Fe
complex can also be prepared by reaction of (N
N')Fe
(3) with CBX. In contrast, the oxidation of Fe
with 1-cyano-3,3-dimethyl-3-(1H)-1,2-benziodoxole (CDBX) enables the preparation of Fe
cyanide complex (N
N')Fe
(CN)(Li)(THF)
(2-Li
). Complexes 4 and 2-Li
have been structurally characterized by single crystal X-ray diffraction and their electronic structure has been examined by Mössbauer, EPR spectroscopy, and computational analyses.
As key intermediates in metal-catalyzed nitrogen-transfer chemistry, terminal imido complexes of iron have attracted significant attention for a long time. In search of versatile model compounds, the ...recently developed second-generation
-anchored
-NHC chelating ligand
-2-(3-mesityl-
idazole-2-ylidene)-
ethylami
e (TIMMN
) was utilized to synthesize and compare two series of mid- to high-valent iron alkyl imido complexes, including a reactive Fe(V) adamantyl imido intermediate en route to an isolable Fe(V) nitrido complex. The chemistry toward the iron adamantyl imides was achieved by reacting the Fe(I) precursor (TIMMN
)Fe
(N
)
(
) with 1-adamantyl azide to yield the corresponding trivalent iron imide. Stepwise chemical reduction and oxidation lead to the isostructural series of low-spin (TIMMN
)Fe(NAd)
(
-
) in oxidation states II to V. The Fe(V) imide (TIMMN
)Fe(NAd)
(
) is unstable under ambient conditions and converts to the air-stable nitride (TIMMN
)Fe
(N)
(
) via N-C bond cleavage. The stability of the pentavalent imide can be increased by derivatizing the nitride (TIMMN
)Fe
(N)
(
) with an ethyl group using the triethyloxonium salt Et
OPF
. This gives access to the analogous series of ethyl imides (TIMMN
)Fe(NEt)
(
-
), including the stable Fe(V) ethyl imide. Iron imido complexes exist in a manifold of different electronic structures, ultimately controlling their diverse reactivities. Accordingly, these complexes were characterized by single-crystal X-ray diffraction analyses, SQUID magnetization, and electrochemical methods, as well as
Fe Mössbauer, IR vibrational, UV/vis electronic absorption, multinuclear NMR, X-band EPR, and X-ray absorption spectroscopy. Our studies are complemented with quantum chemical calculations, thus providing further insight into the electronic structures of all complexes.
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•Electrochemical studies of hybrid system formed by gold nanoparticles and manganese porphyrin.•Surface modification of FTO electrodes by gold nanoparticles and manganese ...porphyrin.•Amperometric sensor to detection of cysteine.
Monitoring of biomarkers can be used to early diagnosis of diseases. Changes in levels of cysteine can indicate several disorders, because of this, development of suitable sensors are essential to welfare of people. Herein it was described the electrochemical response of a hybrid system modified electrode composed by gold nanoparticles and manganese meso-tetra(pentafluorophenyl) porphyrin for the sensing of cysteine. For this purpose, fluorine tin oxide-coated glass (FTO) electrodes were chosen as substrate due to their low cost and easily modifying surface. The hybrid system was deposited on the FTO surface using a self-assembly strategy and all experiments were performed at pH 7.0. The obtained modified electrode has shown good response for cysteine oxidation in amperometric studies with figures of merit comparable to other sensors described in literature.
Cobalt complexes with multiproton- and multielectron-responsive ligands are of interest for challenging catalytic transformations. The chemical and redox noninnocence of pentane-2,4-dione ...bis(S-methylisothiosemicarbazone) (PBIT) in a series of cobalt complexes has been studied by a range of methods, including spectroscopy UV–vis, NMR, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), cyclic voltammetry, X-ray diffraction, and density functional theory (DFT) calculations. Two complexes CoIII(H2LSMe)II and CoIII(LSMe )I2 were found to act as precatalysts in a Wacker-type oxidation of olefins using phenylsilane, the role of which was elucidated through isotopic labeling. Insights into the mechanism of the catalytic transformation as well as the substrate scope of this selective reaction are described, and the essential role of phenylsilane and the noninnocence of PBIT are disclosed. Among the several relevant species characterized was an unprecedented Co(III) complex with a dianionic diradical PBIT ligand (CoIII(LSMe••)I).
We disclose a new reactivity mode for electrophilic cyano λ3‐iodanes as group transfer one‐electron oxidants to synthesize FeIII and FeIV cyanide complexes. The inherent thermal instability of ...high‐valent FeIV compounds without π‐donor ligands (such as oxido (O2−), imido (RN2−) or nitrido (N3−)) makes their isolation and structural characterization a very challenging task. We report the synthesis of an FeIV cyanide complex (N3N′)FeCN (4) by two consecutive single electron transfer (SET) processes from FeII precursor (N3N′)FeLi(THF) (1) with cyanobenziodoxolone (CBX). The FeIV complex can also be prepared by reaction of (N3N′)FeIII (3) with CBX. In contrast, the oxidation of FeII with 1‐cyano‐3,3‐dimethyl‐3‐(1H)‐1,2‐benziodoxole (CDBX) enables the preparation of FeIII cyanide complex (N3N′)FeIII(CN)(Li)(THF)3 (2‐LiTHF). Complexes 4 and 2‐LiTHF have been structurally characterized by single crystal X‐ray diffraction and their electronic structure has been examined by Mössbauer, EPR spectroscopy, and computational analyses.
Cyano λ3‐iodanes react with iron(II) and iron(III) complexes as cyano‐transfer one‐electron oxidants. This approach enables the straightforward synthesis of iron(III) and iron(IV) cyanide complexes, which have been thoroughly characterized by spectroscopic methods, including X‐ray diffraction, EPR, Mössbauer and NMR spectroscopies and computational methods.
