Improved Synthesis and Detailed Characterization of a Hybrid Pyrazole‐TACN Dinucleating Ligand

Dalle, Kristian E.; Dechert, Sebastian; Meyer, Franc

doi:10.1002/zaac.201500563

Cited by 6 publications

(6 citation statements)

References 63 publications

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“…Line shape analysis of the CH 2 resonances H 10a /H 10b in the VT 1 H NMR spectra allowed to derive rate constants k for the prototropy at different temperatures, and activation parameters Δ H ‡ = 27.6 kJ · mol –1 and Δ S ‡ = –124.6 J · mol –1 · K –1 in [D 3 ]MeCN were derived from an Eyring plot (Figure S53 and Table S1, Supporting Information, and Table ). These values differ from those previously reported for a pyrazole derivative bearing 1,4,9‐triazacyclononane (tacn) arms attached to the CH 2 groups in 3‐ and 5‐positions of the central pyrazole (Δ H ‡ = 46.7 kJ · mol –1 and Δ S ‡ = –74 J · mol –1 · K –1 ; Table ), which likely reflects the effect of hydrogen bonding as the crystallographic structure analysis of the pyrazole/tacn hybrid had shown intramolecular N···H···N interactions between the tacn side arm and the pyrazole unit . The very similar 1 H NMR chemical shifts for H 2a/b and H 3a/b , even at low temperatures, suggest the absence of any significant C − H···N hydrogen bonding interactions between the pyrazole and the imidazolium‐2 H in [H 5 L 1 ](PF 6 ) 4 .…”

Section: Resultscontrasting

confidence: 90%

“…Values obtained for the two pyrazole‐N, viz. –176.1 ppm for NH pz and –75.3 ppm for N pz , are in the range reported previously for 15 N chemical shifts of pyrazole derivatives , , …”

Section: Resultssupporting

confidence: 85%

“…The 1 H NMR spectrum of [H 5 L 1 ](PF 6 ) 4 in dry [D 3 ]MeCN at 298 K and 500 MHz shows rather broad resonances for all protons of the imidazolium groups close to the pyrazole (H 2a/b , H 4a/b and H 6a/b ) and two closely spaced signals for the CH 2 groups attached to the 3‐ and 5‐positions of the pyrazole (H 10a /H 10b ; Figure ). These features are attributed to slow NH prototropy on the NMR time scale, which is well known for pyrazoles and pyrazole‐based ligands and was already described for some related ligand scaffolds in the literature . The H 10a/b protons are closest to the pyrazole unit and are most affected by the tautomerism.…”

Section: Resultsmentioning

confidence: 57%

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Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes

Resch

Dechert

Meyer

2019

Zeitschrift anorg allge chemie

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New hybrid ligands are reported that combine two types of popular donor groups within a single linear scaffold, viz., a central pyrazolate bridge and two appended bis(N-heterocyclic carbene) units; the ligand strands thus provide two potentially tridentate {NCC} compartments. The pyrazole/tetraimidazolium proligands, [H 5 L 1 ](PF 6 ) 4 and [H 5 L 2 ](PF 6 ) 4 , were synthesized via multi-step protocols, and the NH prototropy of [H 5 L 1 ](PF 6 ) 4 was examined by variable temperature (VT) NMR spectroscopy, giving solvent dependent activation parameters (ΔH ‡ = 27.6 kJ·mol -1 , ΔS ‡ = -125 J·mol -1 ·K -1 in [D 3 ]MeCN; 605ΔH ‡ = 40.4 kJ·mol -1 , ΔS ‡ = -86.9 J·mol -1 ·K -1 in [D 6 ]DMSO) that are in the range typical for pyrazoles. Reaction of the proligands with Ag 2 O gave hexametallic complexes [Ag 6 (L 1 ) 2 ](PF 6 ) 4 and [Ag 6 (L 2 ) 2 ](PF 6 ) 4 that involve all six potential donor atoms of the ligands, viz. the four C NHC and two N pz donors, in metal coordination. X-ray crystallography revealed a chair-like central {Ag 6 } deck in both complexes but different arrangements of the ligand strands, which goes along with significantly different Ag I ···Ag I distances that indicate more pronounced argentophilic interactions in case of [Ag 6 (L 1 ) 2 ] 4+ .

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Section: Resultscontrasting

confidence: 90%

“…Values obtained for the two pyrazole‐N, viz. –176.1 ppm for NH pz and –75.3 ppm for N pz , are in the range reported previously for 15 N chemical shifts of pyrazole derivatives , , …”

Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 57%

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Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes

Resch

Dechert

Meyer

2019

Zeitschrift anorg allge chemie

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“…The synthesis of the new proligand HL used in this work is schematically depicted in Scheme ; it is based on protocols reported previously for the derivative with peripheral isopropyl substituents , and the parent ligand devoid of any N-substituents, , with minor modifications. The commercially available synthon 3,5-pyrazole dicarboxylic acid monohydrate was converted into the more reactive acid chloride by treatment with thionyl chloride .…”

Section: Resultsmentioning

confidence: 99%

Reductive Transformations of a Pyrazolate-Based Bioinspired Diiron–Dinitrosyl Complex

et al. 2016

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Flavo-diiron nitric oxide reductases (FNORs) are a subclass of nonheme diiron proteins in pathogenic bacteria that reductively transform NO to NO, thereby abrogating the nitrosative stress exerted by macrophages as part of the immune response. Understanding the mechanism and intermediates in the NO detoxification process might be crucial for the development of a more efficient treatment against these bacteria. However, low molecular weight models are still rare, and only in a few cases have their reductive transformations been thoroughly investigated. Here, we report on the development of two complexes, based on a new dinucleating pyrazolate/triazacyclononane hybrid ligand L, which serve as model systems for nonheme diiron active sites. Their ferrous nitrile precursors [L{Fe(R'CN)}(μ-OOCR)](X) (1) can be readily converted into the corresponding nitrosyl adducts ([L{Fe(NO)}(μ-OOCR)](X), 2). Spectroscopic characterization shows close resemblance to nitrosylated nonheme diiron sites in proteins as well as previous low molecular weight analogues. Crystallographic characterization reveals an anti orientation of the two {Fe(NO)} (Enemark-Feltham notation) units. The nitrosyl adducts 2 can be (electro)chemically reduced by one electron, as shown by cyclic voltammetry and UV/vis spectroscopy, but without the formation of NO. Instead, various spectroscopic techniques including stopped-flow IR spectroscopy indicated the rapid formation, within few seconds, of two well-defined products upon reduction of 2a (R = Me, X = ClO). As shown by IR and Mössbauer spectroscopy as well as X-ray crystallographic characterization, the reduction products are a diiron tetranitrosyl complex ([L{Fe(NO)}](ClO), 3a') and a diacetato-bridged ferrous complex [LFe(μ-OAc)](ClO) (3a″). Especially 3a' parallels suggested products in the decay of nitrosylated methane monooxygenase hydroxylase (MMOH), for which NO release is much less efficient than for FNORs.

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“…In Cu 2 /O 2 chemistry, ( μ-η 2 :η 2 -peroxo)dicopper(II) complexes and their valence tautomeric bis(μ-oxo) forms as well as dicopper(II) complexes with a trans -μ-1,2-peroxo bridge ( T P ; Figure ) have been quite well studied. , Employing a compartmental pyrazolate/tacn hybrid ligand [L 1 ] − (tacn = 1,4,7-triazacyclononane), , a few years ago we contributed the first structural characterization of a cis -μ-1,2-peroxo dicopper( ii ) complex ( C P type) that was shown to strongly interact with Na + ions both in solution and in solid state ( B , Scheme ). Further elaboration via elongation of the ligand side arms in [L 2 ] − induced a shortening of the Cu···Cu distance and a Cu–O–O–Cu torsion angle close to 90° in the (peroxo)dicopper(II) complex C ; such near-orthogonal arrangement in between the C P and T P forms was shown to lead to ferromagnetic coupling and an unprecedented S = 1 ground state …”

Section: Introductionmentioning

confidence: 99%

Structurally Characterized μ-1,2-Peroxo/Superoxo Dicopper(II) Pair

et al. 2021

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Superoxo complexes of copper are primary adducts in several O2-activating Cu-containing metalloenzymes as well as in other Cu-mediated oxidation and oxygenation reactions. Because of their intrinsically high reactivity, however, isolation of Cu x (O2 •–) species is challenging. Recent work (J. Am. Chem. Soc. 2017, 139, 9831; 2019, 141, 12682) established fundamental thermochemical data for the H atom abstraction reactivity of dicopper(II) superoxo complexes, but structural characterization of these important intermediates was so far lacking. Here we report the first crystallographic structure determination of a superoxo dicopper(II) species (3) together with the structure of its 1e– reduced peroxo congener (2; a rare cis-μ-1,2-peroxo dicopper(II) complex). Interconversion of 2 and 3 occurs at low potential (−0.58 V vs Fc/Fc+) and is reversible both chemically and electrochemically. Comparison of metric parameters (d(O–O) = 1.441(2) Å for 2 vs 1.329(7) Å for 3) and of spectroscopic signatures (ν̃(16O–16O) = 793 cm–1 for 2 vs 1073 cm–1 for 3) reflects that the redox process occurs at the bridging O2-derived unit. The CuII–O2 •––CuII complex has an S = 1/2 spin ground state according to magnetic and EPR data, in agreement with density functional theory calculations. Computations further show that the potential associated with changes of the Cu–O–O–Cu dihedral angle is shallow for both 2 and 3. These findings provide a structural basis for the low reorganization energy of the kinetically facile 1e– interconversion of μ-1,2-superoxo/peroxo dicopper(II) couples, and they open the door for comprehensive studies of these key intermediates in Cu x /O2 chemistry.

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Improved Synthesis and Detailed Characterization of a Hybrid Pyrazole‐TACN Dinucleating Ligand

Cited by 6 publications

References 63 publications

Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes

Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes

Reductive Transformations of a Pyrazolate-Based Bioinspired Diiron–Dinitrosyl Complex

Structurally Characterized μ-1,2-Peroxo/Superoxo Dicopper(II) Pair

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