Spectroscopic study on enantiomeric Ni(II) complexes of porphyrin-porphyrin Tröger's base and porphyrin-chlorin spiro-Tröger's base derivatives supported by DFT calculations.

The chiral properties of nickel(II) complexes of porphyrin-porphyrin Tröger's base and porphyrin-chlorin spiro-Tröger's base with phenyl or 3-methoxyphenyl substitutions in their meso-positions were studied. Enantioseparation of racemic mixtures was investigated via high-performance liquid chromatography (HPLC) on an analytical ReproSil Chiral-NR column. The optimal conditions were utilized for a multimilligram scale isolation with a semipreparative column. The purity of the isolated enantiomers was determined by HPLC and UV-Vis spectroscopy. The absolute configurations of the isolated enantiomers were determined by evaluating the Cotton effect in electronic circular dichroism spectra. The determination was supported by TDDFT calculations, in which good agreement was achieved between the experimental and simulated spectra. The maximum molar ellipticity values, [θ]λmax given in deg ∙ cm2 ∙ dmol-1, were [θ]435 = 1.73 ∙ 107 for phenyl spiroTB and [θ]436 = 1.24 ∙ 107 and [θ]436 = 2.15 ∙ 107 for 3-methoxyphenyl TB and spiroTB, respectively.

Experimental, Spectroscopic, and Computational Insights into the Reactivity of "Methanal" with 2-Naphthylamines.

The reactions of 2-naphthylamine and methyl 6-amino-2-naphthoate with formalin and paraformaldehyde were studied experimentally, spectrally, and by quantum chemical calculations. It was found that neither the corresponding aminals nor imines were formed under the described conditions but could be prepared and spectrally characterized at least in situ under modified conditions. Several of the previously undescribed intermediates and by-products were isolated or at least spectrally characterized. First principle density functional theory (DFT) calculations were performed to shed light on the key aspects of the thermochemistry of decomposition and further condensation of the corresponding aminals and imines. The calculations also revealed that the electrophilicity of methanal was significantly greater than that of ordinary oxo-compounds, except for perfluorinated ones. In summary, methanal was not behaving as the simplest aldehyde but as a very electron-deficient oxo-compound.

Preparation and Characterization of Metalloporphyrin Tröger's and Spiro-Tröger's Base Derivatives.

A series of metalloporphyrin dimers as Tröger's bases 1 or spiro-Tröger's bases 2 was prepared starting from five different C4-symmetry porphyrin derivatives substituted in meso-positions by Ph, 3-MeO-Ph, 4-MeO-Ph, 3,4-(MeO)2-Ph, or 3,5-(MeO)2-Ph. Free-base porphyrins were converted to metalloporphyrins, which were subsequently nitrated with nickel(II), copper(II), or zinc(II) nitrate to give ß-nitrometalloporphyrins. These were further reduced to ß-aminometalloporphyrins and treated with a methanal equivalent under acidic conditions to selectively obtain Tröger's base 1, spiro-Tröger's base 2, or a mixture of both, in yields up to 41% of 1 and 45% of 2 depending on the reaction conditions used. The ratio of 1 to 2 was influenced by the methanal equivalent used, the strength of the acid, and, above all, the solvent. The presence of a metal ion within the porphyrin core and the use of a chlorinated solvent were found to be essential for the formation of spiro-Tröger's base 2. The molecular structure of spiroTB 2a-Ni2 was proven by electron diffraction.