Use of Pyrazole Hydrogen Bonding in Tripodal Complexes to Form Self Assembled Homochiral Dimers

Brewer, Greg; Butcher, Raymond J.; Zavalij, Peter Y.

doi:10.3390/ma13071595

Cited by 9 publications

(6 citation statements)

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“…We were curious if our revised mechanism was broadly applicable to cation radical accelerated nucleophilic aromatic substitution reactions with other nucleophiles and nucleofuges. Specifically, we were interested in probing whether the kinetic behavior of 2a is special due to the strong intermolecular hydrogen bonding exhibited by the pyrazole motif. , …”

Section: Resultsmentioning

confidence: 99%

“…Specifically, we were interested in probing whether the kinetic behavior of 2a is special due to the strong intermolecular hydrogen bonding exhibited by the pyrazole motif. 29,30 We again turned to VTNA to examine the kinetics of primary amine nucleophiles with fluoroarene electrophiles. An acridinium salt (Catalyst B) was used as the photoredox catalyst along with fluoroarene 1b, primary amine 2b, and TFE-d 3 in accordance with our previous work.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Mechanistic Investigations into Amination of Unactivated Arenes via Cation Radical Accelerated Nucleophilic Aromatic Substitution

2022

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A mechanistic investigation into the amination of electron-neutral and electron-rich arenes using organic photoredox catalysis is presented. Kinetic and computational data support rate-limiting nucleophilic addition into an arene cation radical using both azole and primary amine nucleophiles. This finding is consistent with both fluoride and alkoxide nucleofuges, supporting a unified mechanistic picture using cation radical accelerated nucleophilic aromatic substitution (CRA-SNAr). Electrochemistry and time-resolved fluorescence spectroscopy confirm the key role solvents play in enabling selective arene oxidation in the presence of amines. The synthetic limitations of xanthylium salts are elucidated via photophysical studies. An alternative catalyst scaffold with improved turnover numbers is presented.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Mechanistic Investigations into Amination of Unactivated Arenes via Cation Radical Accelerated Nucleophilic Aromatic Substitution

2022

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“…However, the calculated dipole moments of each pyrazole show a correlation to catemer or trimer formation with the former having a dipole moment greater than 2.5 and the latter less than 2.5. The dihedral angle between H-bonded 4-I-pzH planes of 41.85 (7)° is smaller than the dihedral angle of 59.74 (3)° reported for 4-F-pzH; the herringbone motifs of 4-F-pzH and 4-I-pzH, viewed along the c-axis, show that the kinks of the former are sharper (Figure 5). While there are C-H-π interactions with H…centroid distances of 2.72 (1) Å and 3.29 (1) Å, the structure of 4-I-pzH has no significant π-π interactions (Figure 6).…”

Section: Crystal Structure Descriptionmentioning

confidence: 62%

“…When N1 is protonated, pyrazole coordinates to metals through N2 as a monodentate ligand; however, N1 is readily deprotonated to form the pyrazolide ion, which can coordinate to metals in an exo-or endo-bidentate fashion in addition to monodentate coordination. The Lewis base tunability (via peripheral substitution) and structural rigidity of the pyrazole ligand led to its extensive applications in coordination chemistry [1][2][3], while the existence of both donor and acceptor sites in the same molecule enabled its role in supramolecular chemistry [4][5][6][7][8]. Pyrazoles can be substituted in the 3-, 4-, and 5-positions while maintaining the ability to form an N(H) .…”

Section: Introductionmentioning

confidence: 99%

Completion of Crystallographic Data for the Series of 4-Halogenated-1H-pyrazoles: Crystal Structure Determination of 4-Iodo-1H-pyrazole and Spectroscopic Comparison

et al. 2023

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Prior to 2021, 4-bromo-1H-pyrazole (published in 1999) was the only structurally characterized 4-halogenated-1H-pyrazole in the Cambridge Crystallographic Data Center (CCDC). The structures of 4-chloro-1H-pyrazole and 4-fluoro-1H-pyrazole were published in 2021 and 2023, respectively. Herein, we report the crystal structure for 4-iodo-1H-pyrazole, completing the crystallographic data for the series of 4-halogenated-1H-pyrazoles. The bromo and chloro analogs are isostructural, forming trimeric H-bonding motifs, whereas the fluoro and iodo analogs form non-isostructural catemers. We also compare the experimental and theoretical (by DFT calculations) IR and 1H NMR spectroscopic data of the four halogenated 4-X-pzH compounds and unsubstituted pyrazole (pzH). An explanation is offered for some counterintuitive structural, infrared, and 1H-NMR spectroscopic data.

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“…Table 2 shows the chirality correlation data for nickel(II) aldimine complexes of the Schiff base condensate of an amino acid with an imidazole carboxaldehyde from this study and other available examples, Ni(F Ald -5Me4Im) 2 [ 42 ], Ni(F Ald -4Im) 2 [ 48 ], both enantiomers of Ni(V Ald -2Im) 2 [ 49 , 50 ] and Ni(L ket -NMe2Im)(L Ald -NMe2Im) [ 21 ]. The observation is that the ΔSS/ΛRR is the only enantiomeric pair observed indicating that it is the pair of lowest energy.…”

Section: Resultsmentioning

confidence: 99%

Selective Generation of Aldimine and Ketimine Tautomers of the Schiff Base Condensates of Amino Acids with Imidazole Aldehydes or of Imidazole Methanamines with Pyruvates—Isomeric Control with 2- vs. 4-Substituted Imidazoles

Brewer,

Butcher

et al. 2024

Molecules

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The Schiff base condensation of 5-methyl-4-imidazole carboxaldehyde, 5Me4ImCHO, and the anion of an amino acid, H2N-CH(R)CO2− (R = -CH3, -CH(CH3)2 and -CH2CH(CH3)2), gives the aldimine tautomer, Im-CH=N-CH(R)CO2−, while that of 5-methylimidazole-4-methanamine, 5MeIm-4-CH2NH2, with a 2-oxocarboxylate anion, R-C(O)-CO2−, gives the isomeric ketimine tautomer, Im-CH2-N=C(R)CO2−. All are isolated as the neutral nickel(II) complexes, NiL2, and are characterized by single crystal structure determination, IR, and positive ion ESI MS. In the cases of the 4 substituted imidazoles, either 5MeIm-4-CHO or 5MeIm-4-CH2NH2, both the aldimine and ketimine complexes are isolated cleanly with no evidence of an equilibrium between the two tautomers under the experimental conditions. The aldimines are blue while the tautomeric ketimines are green. In contrast, for the 2-substituted imidazoles, with either Im-2-CHO or Im-2-CH2NH2, the isolated product from the Schiff base condensation is the ketimine, which in the solid is green, as observed for the 4-isomer. These results suggest that for the 2-substituted imidazoles, there is a facile equilibrium between the aldimine and ketimine tautomers, and that the ketimine form is the thermodynamically favored tautomer. The aldimine tautomers of the 4-substituted imidazoles have three stereogenic centers, the nickel (Δ or Ʌ) and the two alpha carbon atoms (R or S). The observed pair of enantiomers is the ɅRR/ΔSS enantiomeric pair, suggesting that this pair is lower in energy than the others and that this is in general the preferred chiral correlation in these complexes.

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Use of Pyrazole Hydrogen Bonding in Tripodal Complexes to Form Self Assembled Homochiral Dimers

Cited by 9 publications

References 50 publications

Mechanistic Investigations into Amination of Unactivated Arenes via Cation Radical Accelerated Nucleophilic Aromatic Substitution

Mechanistic Investigations into Amination of Unactivated Arenes via Cation Radical Accelerated Nucleophilic Aromatic Substitution

Completion of Crystallographic Data for the Series of 4-Halogenated-1H-pyrazoles: Crystal Structure Determination of 4-Iodo-1H-pyrazole and Spectroscopic Comparison

Selective Generation of Aldimine and Ketimine Tautomers of the Schiff Base Condensates of Amino Acids with Imidazole Aldehydes or of Imidazole Methanamines with Pyruvates—Isomeric Control with 2- vs. 4-Substituted Imidazoles

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