Two new Ni(II) Schiff base complexes: X-ray absolute structure determination, synthesis of a 15N-labelled complex and full assignment of its 1H NMR and 13C NMR spectra

[2-((R)-{2-[(S)-1-Benzylpyrrolidin-2-ylcarbonylazanidyl]-phen-yl}(phen-yl)methyl-idene-amino)-4-hy-droxy-butano-ato-κN,N',N'',O]nickel(II) toluene disolvate

The central Ni atom in the title compound, [Ni(C(29)H(29)N(3)O(4))]·2C(7)H(8), is coordinated in a distorted square-planar environment by three N atoms [Ni-N = 1.942 (3), 1.843 (3) and 1.853 (3) Å] and one O atom [1.868 (3) Å] of the tetradentate ligand. The conformation of the hy-droxy-butano-ate side chain is controlled by an inter-molecular hydrogen bond.

Why is monoalkylation versus bis-alkylation of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and glycine so selective? MP2 modelling and topological QTAIM analysis of chiral metallocomplex synthons of α-amino acids used for the preparation of radiopharmaceuticals for positron emission tomography

Chiral Ni(II) complexes are used for the preparation of carbon-11 or fluorine-18 enantiomerically pure α-amino acids for positron emission tomography (PET). They enable the selective monoalkylation of a glycine synthon with high stereoselectivity and the preparation of enantiomerically pure α-amino acids with quarternary α-carbon. Molecular modelling of non-, mono- and di-substituted complexes using quantum theory of atoms-in-molecule (QTAIM) topological analysis of electron density allowed us to formulate a new theory explaining the reasons for highly selective monomethylation of the complexes. In the non-substituted complex (GK), the α-carbon atom exhibits a higher atomic volume and a more positive charge in comparison with mono- and di-substituted complexes. This unusual behaviour is accompanied by increasing the bond critical point (BCP) ellipticity of the iminic bond in GK explained by the higher mechanical strain. Both phenomena indicate the increased reactivity and probably originate in more compact core of GK where shorter distances in the internal coordination sphere result in the higher strain of its bonds.

Characterization of Ni(II) complexes of Schiff bases of amino acids and (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide using ion trap and QqTOF electrospray ionization tandem mass spectrometry

This work demonstrates the application of electrospray ionization mass spectrometry (ESI-MS) using two different mass analyzers, ion trap and hybrid quadrupole time-of-flight (QqTOF) mass analyzer, for the structural characterization of Ni(II) complexes of Schiff bases of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide with different amino acids. ESI enables the determination of molecular weight on the basis of rather simple positive-ion ESI mass spectra containing only protonated molecules and adducts with sodium or potassium ions. Fragmentation patterns are characterized by tandem mass spectrometric experiments, where both tandem mass analyzers provide complementary information. QqTOF data are used for the determination of elemental composition of individual ions due to mass accuracies always better than 3 ppm with the external calibration, while multistage tandem mass spectra obtained by the ion trap are suitable for studying the fragmentation paths. The novel aspect of our approach is the combination of mass accuracies and relative abundances of all isotopic peaks in isotopic clusters providing more powerful data for the structural characterization of organometallic compounds containing polyisotopic elements. The benefit of relative and absolute mean mass accuracies is demonstrated on the example of studied Ni(II) complexes.

{2-[(S)-({2-[(S)-1-Benzyl-pyrrolidine-2-carboxamido]phen-yl}(phen-yl)methyl-ene)amino]-4-hydroxy-butanoato-κN,N',N'',O}nickel(II)

The central Ni atom of the title compound, [Ni(C₂₉H₂₉N₃O₄)], is coordinated by three N atoms [Ni—N = 1.955 (2), 1.844 (2) and 1.872 (2) Å] and by one O atom [Ni—O = 1.862 (2) Å] in a pseudo-square-planar geometry. The conformation of the hydroxy­butanoate side chain is controlled by a strong intra­molecular hydrogen bond (H⋯O = 1.84 Å).