Assembly structures of 1:2 nickel(II) complex of 5-methylimidazol-4-yl-methylidene-l-phenylalanine and 1:2 nickel(II) complex of its racemic ligand

Shintoyo, Seira; Yamauchi, Satoshi; Oishi, Tomohiro; Matsumoto, Naohide; Fujinami, Takeshi

doi:10.1016/j.ica.2013.06.044

Cited by 2 publications

(3 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The structurally reported Schiff base complexes of an imidazole-4-carboxaldehyde with an amino acid give the anticipated aldimine product with copper(II) [36,37], nickel(II), [38], zinc(II) [39], and several lanthanide(III) ions [40,41]. The only example with an imidazole-2-carboxaldehyde gave the unexpected ketimine product [35].…”

Section: Choice Of Amino Acids and Imidazole Carboxaldehydesmentioning

confidence: 99%

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

Brewer,

Butcher

et al. 2023

Inorganics

View full text Add to dashboard Cite

The Schiff base reaction of imidazole-2-carboxaldehydes with the anion of alanine, leucine and phenylalanine in the presence of nickel(II) ion gives the neutral NiL2 complexes. The Schiff base ligand, L, binds through an imidazole nitrogen, NIm, the amino acid nitrogen, NAA, and a carboxylate oxygen, O, atom. The two N2O ligands bind to the nickel(II) in a meridional fashion with the NIm and O of each ligand in trans positions. These ligands can exist as the anticipated aldimine, Im − CH = NAA − CH(R) − CO2−, or the ketimine, Im − CH2NAA = C(R) − CO2−, tautomer. Tautomerization of the initially formed aldimine Schiff base results in movement of the hydrogen atom of the alpha carbon of the amino acid to the aldehyde carbon, CAld, atom of the imidazole carboxaldehyde with resultant relocation of the imine double bond in the reverse direction. Ten structures of the structurally unprecedented ketimine tautomer, prepared from imidazole-2-carboxaldehydes and a pyrazole-3-carboxaldehyde, were presented. The structural data supported the formation of the ketimines in each case, while the aldimine tautomer was observed with imidazole-4-carboxaldehydes. A rationale of this can be explained on the basis of charge distribution in the likely intermediate in the tautomerization.

show abstract

Section: Choice Of Amino Acids and Imidazole Carboxaldehydesmentioning

confidence: 99%

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

Brewer,

Butcher

et al. 2023

Inorganics

View full text Add to dashboard Cite

show abstract

“…In contrast, the six 4-substituted imidazole complexes prepared here, three as aldimines by method (a) and three as ketimines by method (b), were isolated as aldimines and ketimines, respectively, with no rearrangement observed. In addition to these, there are other structurally reported Schiff base complexes of an imidazole-4-carboxaldehyde condensed with an amino acid by method (a) that give the anticipated aldimine product with copper(II) [ 40 , 41 ], nickel(II) [ 42 ], zinc(II) [ 43 ], and several lanthanide(III) ions [ 44 , 45 ]. No tautomerization was observed in these reactions.…”

Section: Resultsmentioning

confidence: 99%

“…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

View full text Add to dashboard Cite

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.

show abstract

Assembly structures of 1:2 nickel(II) complex of 5-methylimidazol-4-yl-methylidene-l-phenylalanine and 1:2 nickel(II) complex of its racemic ligand

Cited by 2 publications

References 34 publications

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

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

Contact Info

Product

Resources

About