Remarkable isolation, structural characterisation and electrochemistry of unexpected scrambling analogues of 5-ferrocenyl-10,20-diphenylporphyrin

Selective condensation of 5-ferrocenyldipyrromethane, 1, and dipyrromethane, 2, with benzaldehyde, 3, led to 5-ferrocenyl-10,20-diphenylporphyrin, 5. During the condensation, an unusually large amount of scrambling was observed which led to the isolation of two further ferrocenylated porphyrin analogues 6 and 7. The structure of 6 was confirmed by a single-crystal X-ray study. A mechanism is proposed for this atypical scrambling which is likely to involve acid-catalysed reversion of the dipyrromethane synthesis. (1)H NMR further elucidated the structures of each complex and showed the existence of atropisomerism. An electrochemical study (cyclic voltammetry, Osteryoung square wave and linear sweep voltammetry) showed that there exists a linear relationship between the sum of the group electronegativities of meso substituents of the obtained porphyrins and the formal reduction potentials of the two observed ring-centred reduction processes, the meso substituent ferrocenyl-based oxidation process and the first ring-centred oxidation wave. These four relationships could be mathematically quantified. Due to the strong electron-withdrawing properties of the oxidised ferrocenium group, the second ring centred oxidation wave fell outside the potential window of dichloromethane as solvent.     

Octakis(dodecyl)phthalocyanines: Influence of Peripheral versus Non-Peripheral Substitution on Synthetic Routes,Spectroscopy and Electrochemical Behaviour

Non-peripherally octakis-substituted phthalocyanines (npPc’s), MPc(C₁₂H₂₅)₈ with M = 2H (3) or Zn (4), as well as peripherally octakis-substituted phthalocyanines (pPc’s) with M = Zn (6), Mg (7) and 2H (8), were synthesized by cyclotetramerization of 3,6- (2) or 4,5-bis(dodecyl)phthalonitrile (5), template cyclotetramerization of precursor phthalonitriles in the presence of Zn or Mg, metal insertion into metal-free phthalocyanines, and removal of Mg or Zn from the phthalocyaninato coordination cavity. The more effective synthetic route towards pPc 8 was demetalation of 7. npPc’s were more soluble than pPc’s. The Q-band λ_max of npPc’s was red-shifted with ca. 18 nm, compared to that of pPc’s. X-ray photoelectron spectroscopy (XPS) differentiated between N–H, N_meso and N_core nitrogen atoms for metal-free phthalocyanines. Binding energies were ca. 399.6, 398.2 and 397.7 eV respectively. X-ray photoelectron spectroscopy (XPS) also showed zinc phthalocyanines 4 and 6 have four equivalent N_meso and four equivalent N–Zn core nitrogens. In contrast, the Mg phthalocyanine 7 has two sets of core N atoms. One set involves two N_core atoms strongly coordinated to Mg, while the other encompasses the two remaining N_core atoms that are weakly associated with Mg. pPc’s 6, 7, and 8 have cyclic voltammetry features consistent with dimerization to form [Pc][Pc⁺] intermediates upon oxidation but npPc’s 3 and 4 do not. Metalation of metal-free pPc’s and npPc’s shifted all redox potentials to lower values.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.