Ligand Redox Non-Innocence in [Coᴵᴵᴵ(TAML)]0/‒ Complexes Affects Nitrene Formation

The redox non-innocence of the TAML scaffold in cobalt-TAML (Tetra-Amido Macrocyclic Ligand) complexes has been under debate since 2006. In this work we demonstrate with a variety of spectroscopic measurements that the TAML backbone in the anionic complex [CoIII(TAMLred)]- is truly redox non-innocent, and that one-electron oxidation affords [CoIII(TAMLsq)]. Multi-reference (CASSCF) calculations show that the electronic structure of [CoIII(TAMLsq)] is best described as an intermediate spin (S = 1) cobalt(III) center that is antiferromagnetically coupled to a ligand-centered radical, affording an overall doublet (S = ½) ground-state. Reaction of the cobalt(III)-TAML complexes with PhINNs as a nitrene precursor leads to TAML-centered oxidation, and produces nitrene radical complexes without oxidation of the metal ion. The ligand redox state (TAMLred or TAMLsq) determines whether mono- or bis-nitrene radical complexes are formed. Reaction of [CoIII(TAMLsq)] or [CoIII(TAMLred)]- with PhINNs results in formation of [CoIII(TAMLq)(N•Ns)] and [CoIII(TAMLq)(N•Ns)2]-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron reduced Fischer-type nitrene radicals (N•Ns-) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV-Vis spectroscopy, high resolution mass spectrometry, magnetic moment measurements and supporting CASSCF calculations.

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Electronically Asynchronous Transition States for C-N Bond Formation by Electrophilic [Coᴵᴵᴵ(TAML)]-Nitrene Radical Complexes Involving Substrate-to-Ligand Single-Electron Transfer and a Cobalt-Centered Spin Shuttle

10.26434/chemrxiv.11472627 ◽

2019 ◽

Author(s):

Nicolaas P. van Leest ◽

Martijn A. Tepaske ◽

Jarl Ivar van der Vlugt ◽

Bas de Bruin

Keyword(s):

Electron Transfer ◽

Bond Formation ◽

Macrocyclic Ligand ◽

Transition States ◽

Lone Pair ◽

Single Electron ◽

Nucleophilic Attack ◽

Single Electron Transfer ◽

Radical Species ◽

Nitrene Transfer

The oxidation state of the redox non-innocent TAML (Tetra-Amido Macrocyclic Ligand) scaffold was recently shown to affect the formation of nitrene radical species on cobalt(III) upon reaction with PhI=NNs [J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.9b11715]. For the neutral [CoIII(TAMLsq)] complex this leads to the doublet (S = ½) mono-nitrene radical species [CoIII(TAMLq)(N•Ns)], while a triplet (S = 1) bis-nitrene radical species [CoIII(TAMLq)(N•Ns)2]‒ is generated from the anionic [CoIII(TAMLred)]‒ complex. The one-electron reduced Fischer-type nitrene radicals (N•Ns‒) are formed through single (mono-nitrene) or double (bis-nitrene) ligand-to-substrate single-electron transfer (SET). In this work we describe the reactivity and mechanisms of these nitrene radical complexes in catalytic aziridination. We report that [CoIII(TAMLsq)] and [CoIII(TAMLred)]‒ are both effective catalysts for chemoselective (C=C versus C‒H bonds) and diastereoselective aziridination of styrene derivatives, cyclohexene and 1-hexene under mild and even aerobic (for [CoIII(TAMLred)]‒) conditions. Experimental (Hammett plots, radical inhibition, catalyst decomposition tests) and computational (DFT, CASSCF) studies reveal that [CoIII(TAMLq)(N•Ns)], [CoIII(TAMLq)(N•Ns)2]‒ and [CoIII(TAMLsq)(N•Ns)]– are key electrophilic intermediates in the aziridination reactions. Surprisingly, the electrophilic one-electron reduced Fischer-type nitrene radicals do not react as would be expected for nitrene radicals (i.e. via radical addition and radical rebound). Instead, nitrene transfer proceeds through unusual electronically asynchronous transition states, in which (partial) styrene substrate to TAML ligand (single) electron transfer precedes C-N coupling. The actual C-N bond formation processes are best described as involving a nucleophilic attack of the nitrene (radical) lone pair at the thus (partially) formed styrene radical cation. These processes are coupled to TAML-to-cobalt and cobalt-to-nitrene single-electron transfer, effectively leading to formation of an amido-[gamma]-benzyl radical (Ns–N–CH2–•CH–Ph) bound to an intermediate spin (S = 1) cobalt(III) center. Hence, the TAML moiety can be regarded to act as a transient electron acceptor, the cobalt center behaves as a spin shuttle and the nitrene radical acts as a nucleophile. Such a mechanism for (cobalt catalyzed) nitrene transfer was hitherto unknown and complements the known concerted and stepwise mechanisms for N-group transfer.

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Electronically Asynchronous Transition States for C-N Bond Formation by Electrophilic [Coᴵᴵᴵ(TAML)]-Nitrene Radical Complexes Involving Substrate-to-Ligand Single-Electron Transfer and a Cobalt-Centered Spin Shuttle

10.26434/chemrxiv.11472627.v1 ◽

2019 ◽

Author(s):

Nicolaas P. van Leest ◽

Martijn A. Tepaske ◽

Jarl Ivar van der Vlugt ◽

Bas de Bruin

Keyword(s):

Electron Transfer ◽

Bond Formation ◽

Macrocyclic Ligand ◽

Transition States ◽

Lone Pair ◽

Single Electron ◽

Nucleophilic Attack ◽

Single Electron Transfer ◽

Radical Species ◽

Nitrene Transfer

The oxidation state of the redox non-innocent TAML (Tetra-Amido Macrocyclic Ligand) scaffold was recently shown to affect the formation of nitrene radical species on cobalt(III) upon reaction with PhI=NNs [J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.9b11715]. For the neutral [CoIII(TAMLsq)] complex this leads to the doublet (S = ½) mono-nitrene radical species [CoIII(TAMLq)(N•Ns)], while a triplet (S = 1) bis-nitrene radical species [CoIII(TAMLq)(N•Ns)2]‒ is generated from the anionic [CoIII(TAMLred)]‒ complex. The one-electron reduced Fischer-type nitrene radicals (N•Ns‒) are formed through single (mono-nitrene) or double (bis-nitrene) ligand-to-substrate single-electron transfer (SET). In this work we describe the reactivity and mechanisms of these nitrene radical complexes in catalytic aziridination. We report that [CoIII(TAMLsq)] and [CoIII(TAMLred)]‒ are both effective catalysts for chemoselective (C=C versus C‒H bonds) and diastereoselective aziridination of styrene derivatives, cyclohexene and 1-hexene under mild and even aerobic (for [CoIII(TAMLred)]‒) conditions. Experimental (Hammett plots, radical inhibition, catalyst decomposition tests) and computational (DFT, CASSCF) studies reveal that [CoIII(TAMLq)(N•Ns)], [CoIII(TAMLq)(N•Ns)2]‒ and [CoIII(TAMLsq)(N•Ns)]– are key electrophilic intermediates in the aziridination reactions. Surprisingly, the electrophilic one-electron reduced Fischer-type nitrene radicals do not react as would be expected for nitrene radicals (i.e. via radical addition and radical rebound). Instead, nitrene transfer proceeds through unusual electronically asynchronous transition states, in which (partial) styrene substrate to TAML ligand (single) electron transfer precedes C-N coupling. The actual C-N bond formation processes are best described as involving a nucleophilic attack of the nitrene (radical) lone pair at the thus (partially) formed styrene radical cation. These processes are coupled to TAML-to-cobalt and cobalt-to-nitrene single-electron transfer, effectively leading to formation of an amido-[gamma]-benzyl radical (Ns–N–CH2–•CH–Ph) bound to an intermediate spin (S = 1) cobalt(III) center. Hence, the TAML moiety can be regarded to act as a transient electron acceptor, the cobalt center behaves as a spin shuttle and the nitrene radical acts as a nucleophile. Such a mechanism for (cobalt catalyzed) nitrene transfer was hitherto unknown and complements the known concerted and stepwise mechanisms for N-group transfer.

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Acylated Anthocyanins from Red Cabbage and Purple Sweet Potato Can Bind Metal Ions and Produce Stable Blue Colors

International Journal of Molecular Sciences ◽

10.3390/ijms22094551 ◽

2021 ◽

Vol 22 (9) ◽

pp. 4551

Author(s):

Julie-Anne Fenger ◽

Gregory T. Sigurdson ◽

Rebecca J. Robbins ◽

Thomas M. Collins ◽

M. Mónica Giusti ◽

...

Keyword(s):

Metal Ions ◽

Sweet Potato ◽

Metal Binding ◽

Metal Ion ◽

High Resolution Mass Spectrometry ◽

Large Set ◽

Water Addition ◽

Red Cabbage ◽

Aluminum Ions ◽

Purple Sweet Potato

Red cabbage (RC) and purple sweet potato (PSP) are naturally rich in acylated cyanidin glycosides that can bind metal ions and develop intramolecular π-stacking interactions between the cyanidin chromophore and the phenolic acyl residues. In this work, a large set of RC and PSP anthocyanins was investigated for its coloring properties in the presence of iron and aluminum ions. Although relatively modest, the structural differences between RC and PSP anthocyanins, i.e., the acylation site at the external glucose of the sophorosyl moiety (C2-OH for RC vs. C6-OH for PSP) and the presence of coordinating acyl groups (caffeoyl) in PSP anthocyanins only, made a large difference in the color expressed by their metal complexes. For instance, the Al3+-induced bathochromic shifts for RC anthocyanins reached ca. 50 nm at pH 6 and pH 7, vs. at best ca. 20 nm for PSP anthocyanins. With Fe2+ (quickly oxidized to Fe3+ in the complexes), the bathochromic shifts for RC anthocyanins were higher, i.e., up to ca. 90 nm at pH 7 and 110 nm at pH 5.7. A kinetic analysis at different metal/ligand molar ratios combined with an investigation by high-resolution mass spectrometry suggested the formation of metal–anthocyanin complexes of 1:1, 1:2, and 1:3 stoichiometries. Contrary to predictions based on steric hindrance, acylation by noncoordinating acyl residues favored metal binding and resulted in complexes having much higher molar absorption coefficients. Moreover, the competition between metal binding and water addition to the free ligands (leading to colorless forms) was less severe, although very dependent on the acylation site(s). Overall, anthocyanins from purple sweet potato, and even more from red cabbage, have a strong potential for development as food colorants expressing red to blue hues depending on pH and metal ion.

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ChemInform Abstract: LIGAND DESIGN AND METAL-ION RECOGNITION. INTERACTION OF NICKEL(II) WITH 17- TO 19-MEMBERED MACROCYCLES CONTAINING O2N3 AND O3N2 DONOR SETS AND THE X-RAY STRUCTURE OF THE PARENT 17-MEMBERED MACROCYCLIC LIGAND

Chemischer Informationsdienst ◽

10.1002/chin.198344266 ◽

1983 ◽

Vol 14 (44) ◽

Author(s):

K. R. ADAM ◽

A. J. LEONG ◽

L. F. LINDOY ◽

H. C. LIP ◽

B. W. SKELTON ◽

...

Keyword(s):

Metal Ion ◽

Macrocyclic Ligand ◽

Ligand Design ◽

Ion Recognition ◽

X Ray

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Zn(II) and Ag(I) complexes of N-allythioamides of pyrimidinyl (cyclohexenyl) carboxylic acids and products their proton- and iodocyclization

Ukrainian Chemistry Journal ◽

10.33609/0041-6045.85.3.2019.3-19 ◽

2019 ◽

Vol 85 (3) ◽

pp. 3-19

Author(s):

Polina Borovyk ◽

Mariia Litvinchuk ◽

Anton Bentya ◽

Svitlana Orysyk ◽

Yurii Zborovskiy ◽

...

Keyword(s):

Carboxylic Acids ◽

Metal Ion ◽

Polymer Chains ◽

Hydroxyl Group ◽

Hydroxyl Groups ◽

Polymer Complexes ◽

Vis Spectroscopy ◽

Polynuclear Coordination Compounds ◽

Complexation Reactions ◽

Oxygen Atoms

The possibility of using N-allylcarbothioamide derivatives as well as products of their iodine- and proton-initiated electrophilic heterocyclizations as chelating agents in complexation reactions with Zn(II) and Ag(I) ions is shown. Processing of the obtained experimental data showed that N-allythioamides of pyrimidinyl (cyclohexenyl) carboxylic acids H2L1 – H2L3 and their proton- and iodo-cyclization products HL4, HL5 containing four nucleophilic reaction centers (two oxygen atoms of the carbonyl and hydroxyl groups and N-, S-carbothioamide groups or N-atoms of the dihydrothiazole moiety) are polydentate ligands capable of coordinating with metal ions to form stable six-membered chelate metallocycles. A series of new chelating mono-, bi- and polynuclear complexes Zn(II) and Ag (I) of the composition [Zn2L1,32]n, [Zn2(HL1-3)2(CH3COO)2], [Ag2(HL1,3)2]n, [Zn(HL1-3)2], [Ag(H2L3)2NO3], [Zn(HL4,5)2], K[Ag(HL4,5)2] were synthesized and isolated in solid state. Their molecular structure was established by methods of elemental chemical analysis, NMR 1H, IR and UV-Vis spectroscopy. At a ratio of M:L 1:2, complexes were isolated in which two ligand molecules H2L1 − H2L3 are coordinated to the metal ion by the sulfur atoms of the carbothioamide group and the oxygen of the mono-deprotonated hydroxyl group. It was established that the products of the proton-/iodocyclization HL4, HL5 in the complex formation pass into the thione tautomeric form with coordination through the oxygen atoms of the deprotonated hydroxyl group and nitrogen atoms of the dihydrothiazole heterocycle. At M:L 1:1, binuclear or polynuclear coordination compounds are formed. It was shown that polymerisation in complexes [Zn2L1,32]n and [Ag2(HL1,3)2]n is due to the formation of Zn−(O2SN)−Zn and Ag−O−Ag polymer chains. Investigation of the solubility of the resulting complexes showed that the polymer complexes are weakly soluble or insoluble in DMSO, DMF, while the mononuclear are soluble in methanol, as well as in water.

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SYNTHESIS, SPECTRAL STUDIES, STRUCTURAL EVALUATION AND ANTIMICROBIAL ACTIVITY OF SOME NOVEL C R(III) COMPLEXES CONTAINING TETRADENTATE MACROCYCLIC LIGANDS

INDIAN DRUGS ◽

10.53879/id.54.06.10962 ◽

2017 ◽

Vol 54 (06) ◽

pp. 20-29

Author(s):

S Shukla ◽

◽

S. Gautam ◽

S Chandra ◽

A. Kumar

Keyword(s):

Metal Complexes ◽

Metal Ion ◽

Metal Salt ◽

Condensation Reaction ◽

Macrocyclic Ligand ◽

Agar Plate ◽

Macrocyclic Ligands ◽

Diffusion Method ◽

Spectral Studies ◽

Spectral Techniques

A string of novel coordination compounds of Cr(III) complexes have been derived and characterized from the macrocyclic ligands (L 1 -L 2 ) carried out by condensation reaction between ligands and the subsequent metal salt. The chemical composition of ligand was determined by analytical and spectral techniques i.e. elemental analysis, IR and Mass spectrocopy. Spectral techniques revealed tetradentate [N 4 ] the nature of ligand and its coordination mode to metal ion through nitrogen donor atoms. Metal complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic spectra, ePR studies. The geometry of these complexes was ascertained by molecular modelling study by using Gaussian 09 program. All metal complexes were found to exhibit octahedral geometry around the metal ion. The newly synthesized macrocyclic ligands and metal complexes were subjected for antimicrobial screening to determine the inhibition and control against tested microorganisms, bacteria ( S.lutea , S.aureus, S.albus and E.coli ) and fungi ( A.fulviceps, U . hordei, A. niger and P.catinus ) by using disc diffusion method and agar plate technique, respectively. The experimental results suggest that metal complexes exhibit enhanced inhibition zone than free macrocyclic ligand.

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Alcohol-Initiated Dediazoniation of Aryldiazonium Ions to Aryl Radicals: A Simple and Efficient Route to Arylboronates

Journal of Chemical Research ◽

10.3184/174751918x15362432558247 ◽

2018 ◽

Vol 42 (9) ◽

pp. 481-485

Author(s):

Xiulian Zhang ◽

Zhicheng Zhang ◽

Yongbin Xie ◽

Yujie Jiang ◽

Ruibo Xu ◽

...

Keyword(s):

Electron Transfer ◽

Bond Formation ◽

Single Electron ◽

Single Electron Transfer ◽

Aryl Radical ◽

Radical Species ◽

Aryl Radicals ◽

Efficient Access ◽

Efficient Route ◽

Operational Simplicity

A simple and efficient access to arylboronates was achieved with methanol-initiated borylation of aryldiazonium salts. Reduction of aryldiazonium ions by single electron transfer from methanol affords aryl radical species, which undergo a subsequent C–B bond formation with bis(pinacolato)diboron. This highly practical borylation process, which can be carried out on the gram-scale, enjoys operational simplicity as well as mild and catalyst-free conditions.

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Copper (0) Mediated Single Electron Transfer-Living Radical Polymerization of Methyl Methacrylate: Functionalized Graphene as a Convenient Tool for Radical Initiator

Polymers ◽

10.3390/polym12040874 ◽

2020 ◽

Vol 12 (4) ◽

pp. 874 ◽

Cited By ~ 1

Author(s):

Adhigan Murali ◽

Srinivasan Sampath ◽

Boopathi Appukutti Achuthan ◽

Mohan Sakar ◽

Suryanarayanan Chandrasekaran ◽

...

Keyword(s):

Thermal Stability ◽

Electron Transfer ◽

Methyl Methacrylate ◽

Radical Polymerization ◽

Living Radical Polymerization ◽

Single Electron ◽

Single Electron Transfer ◽

Functionalized Graphene ◽

Radical Initiator ◽

Vis Spectroscopy

Polymer nanocomposites have been synthesized by the covalent addition of bromide-functionalized graphene (Graphene-Br) through the single electron transfer-living radical polymerization technique (SET-LRP). Graphite functionalized with bromide for the first time via an efficient route using mild reagents has been designed to develop a graphene based radical initiator. The efficiency of sacrificial initiator (ethyl α-bromoisobutyrate) has also been compared with a graphene based initiator towards monitoring their Cu(0) mediated controlled molecular weight and morphological structures through mass spectroscopy (MOLDI-TOF) and field emission scanning electron microscopy (FE-SEM) analysis, respectively. The enhancement in thermal stability is observed for graphene-grafted-poly(methyl methacrylate) (G-g-PMMA) at 392 °C, which may be due to the influence ofthe covalent addition of graphene, whereas the sacrificial initiator used to synthesize G-graft-PMMA (S) has low thermal stability as analyzed by TGA. A significant difference is noticed on their glass transition and melting temperatures by DSC. The controlled formation and structural features of the polymer-functionalized-graphene is characterized by Raman, FT-IR, UV-Vis spectroscopy, NMR, and zeta potential measurements. The wettability measurements of the novel G-graft-PMMA on leather surface were found to be better in hydrophobic nature with a water contact angle of 109 ± 1°.

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ChemInform Abstract: METAL ION CONTROLLED SYNTHESES OF NOVEL FIVE-COORDINATE ZINC AND CADMIUM COMPLEXES CONTAINING A HELICAL COORDINATION GEOMETRY AND THEIR TEMPLATE REACTION TO FORM COMPLEXES OF A PENTADENTATE MACROCYCLIC LIGAND

Chemischer Informationsdienst ◽

10.1002/chin.197450366 ◽

1974 ◽

Vol 5 (50) ◽

pp. no-no

Author(s):

L. F. LINDOY ◽

DARYLE H. BUSCH

Keyword(s):

Metal Ion ◽

Macrocyclic Ligand ◽

Coordination Geometry ◽

Cadmium Complexes ◽

Template Reaction

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