Porphyrazines with annulated diazepine rings. 6. Synthesis and properties of the alkyl substituted derivative - MgII complex of tetrakis-2,3-(5,7-di-tert-butyl-6H-1,4-diazepino)porphyrazine

Novel MgII porphyrazine 3 bearing four appended seven-membered tert-butyl substituted 1,4-diazepine rings was prepared via Linstead macrocyclization of 5,7-di-tert-butyl-6[Formula: see text]-1,4-diazepine-2,3-dicarbonitrile 2, obtained by condensation of diaminomaleonitrile and 2,2,6,6-tetramethylheptanedione-3,5 (1) in anhydrous ethanol in the presence of P2O5. The structure of the dinitrile precursor 2 was established by single crystal X-ray work. 1H NMR study revealed that the 1,4-diazepine ring is present in the 6[Formula: see text] tautomeric form both in the dinitrile precursor 2 and the MgII complex 3. The inversion of the tert-butyl substituted diazepine ring occurs more easily than in the case of aryl and alkenyl substituted species. Although porphyrazine 3exhibit some tendency to aggregation in low-polar solvents the presence of bulky tert-butyl substituents stabilizes the monomeric form and hinders formation of H-bonded dimers characteristic for aryl and styryl substituted analogues.

Preparation, optical and electrochemical properties, and molecular orbital calculations of tetraazaporphyrinato ruthenium (II) bis(4-methylpyridine) fused with one to four diphenylthiophene units

2,5-Diphenyl-3,4-dicyanothiophene (1) and phthalonitrile (2) were mixed and treated with ruthenium (III) trichloride, 4-methylpyridine, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 2-ethoxyethanol at 135°C, to produce low-symmetrical tetraazaporphyrins (TAPs) (3), (4), (5), and (6) with one to three thiophene rings. Two thiophene-annelated tetraazaporphyrins were isolated as opposite and adjacent isomers 4 and 5. The structure of 3 was determined by X-ray crystallography, showing that the thiophene ring linked at the 3,4-positions on the tetraazaporphyrin scaffold deviates from the mean plane of the four central pyrrole nitrogen atoms (N1-N3-N5-N7). Optical and electrochemical properties of the products were examined by UV-vis and magnetic circular dichroism (MCD) spectroscopy, together with cyclic voltammetry. In the (1)H NMR spectra, the signals of 4-methylpyridine coordinating to the central ruthenium atom appeared at a higher magnetic field than those of uncoordinated 4-methylpyridine itself due to the shielding effect of the TAP ring. Increasing the number of fused thiophene rings resulted in 1) lower magnetic field shifts of the signals of axially coordinated 4-methylpyridine in the (1)H NMR spectra, 2) lower energy shifts of the Q band absorption in the UV-vis spectra, and 3) decreasing (cathodic shift) of the first oxidation potentials. The structures of simplified model compounds were optimized using the DFT method with the Gaussian 09 program at the B3LYP/LANL2DZ level for the Ru atom and the B3LYP/6-31G (d, p) level for the C, H, N, and S atoms. The optimized structures were utilized to calculate the NMR shielding constants, the HOMO and LUMO orbital energies, and the electronic absorption spectra.